molecules

Review In Situ Coupling of Ultrasound to Electro- and Photo-Deposition Methods for Materials Synthesis

Agnieszka Magdziarz * and Juan C. Colmenares * Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland * Correspondence: [email protected] (A.M.); [email protected] (J.C.C.); Tel.: +48-22-343-3215 (J.C.C.)

Academic Editor: Gregory Chatel Received: 20 December 2016; Accepted: 26 January 2017; Published: 31 January 2017

Abstract: This short review provides the current state-of-the-art of in situ coupling of ultrasound to chemical deposition methods. Synergetic action of ultrasound and light radiation or electrical fields may result in new powerful methodologies, which include sonophotodeposition and sonoelectrodeposition processes. The effect of ultrasound is explained on the basis of different physical mechanisms emerging from cavitation phenomenon. Some possible mechanisms of the interactions between ultrasound and photochemical and electrochemical processes are discussed here. The application of sonophotodeposition and sonoelectrodeposition as green energy sources in the syntheses of different nanomaterials is also reviewed.

Keywords: ultrasound; sonophotodeposition; sonoelectrodeposition; sonophotochemistry; sonoelectrochemistry; cavitation; current density

1. Introduction The fast development of sonochemistry started around a few decades ago when cheap ultrasonic equipment, such as the ultrasonic bath, started to be a common equipment in many chemical laboratories. This was also when the coupling of ultrasound with other chemical methods, such as electrochemistry or photochemistry began to be widely studied [1]. In his works Compton claimed that combination of two independent sources of energy often results in formation of new powerful methodologies [2,3]. In the mentioned processes, electrical and mechanical green energies are delivered to the reaction systems. In this way a high-energy microenvironment is created, that enables many chemical reactions to proceed thereby eliminating the necessity of the use of harmful and dangerous reagents and solvents [4]. Also, some operational variables (e.g., ultrasonic power and frequency, electric current) are available in these methods giving the possibility to control the kinetics of the process by their proper adjustment [4]. It is commonly known, that ultrasonic radiation (from 20 kHz to 1 GHz) is too weak for rupturing chemical bonds and that the acoustic filed cannot couple directly with molecular energy levels [5,6]. However, the extreme conditions (very high temperature and pressure), that are formed during the expansion of ultrasound in the liquid, are responsible for breaking the chemical bonds. This cavitation phenomenon together with other related mechanical phenomena such as acoustic streaming and microjetting, shockwaves, promotion of mass transport, as well as chemical effects can influence the electrochemical and photochemical processes [7]. The application of sonoelectrochemistry as well as sonophotochemistry is a very broad topic in chemistry. Therefore, in this short review we will focus on a very narrow combination of sonication with electrochemical deposition and sonication with photochemical deposition. Moreover, only their simultaneous use will be analyzed (in situ coupling). In the next part the interaction between ultrasound activation in the liquid environment and electrochemical and photochemical reactions will be explored. In the last part of this review some examples of the various materials

Molecules 2017, 22, 216; doi:10.3390/molecules22020216 www.mdpi.com/journal/molecules Molecules 2017, 22, 216 2 of 22 prepared by sonophoto-and sonoelectrodeposition methods are described paying particular attention to their morphological properties, chemical composition, and the influence of ultrasound during the synthesis procedure.

2. Mechanism of Sonoelectrodeposition and Sonophotodeposition Processes According to J. Klima there are four possible mechanisms of interaction between sonication and electrochemical processes equivalent to physical effects of ultrasound in liquids: (i) acoustic streaming, (ii) microstreaming and turbulence, (iii) microjets and (iv) shock waves [1]. Acoustic streaming is created when ultrasound passes through a liquid and a part of its energy is absorbed, which can be observed as a movement of the solution. It can enhance the mass transfer of the electroactive compounds, which is seen as an increase of electrochemical current and in the change of the shape of voltammetric curves [8,9]. Interestingly, an increase in current is not only observed in the place where ultrasonic energy is absorbed, but also can be seen if the working electrode is located outside of this region. This is caused by the radiation pressure, that can move the flow of liquid away from the absorption center. During turbulence, an increase of electrochemical current, similar to that obtained in acoustic streaming occurs, but only when the working electrode is placed in the region of turbulent motion. This effect results from the intense cavitation caused by mutual interaction of oscillating and collapsing bubbles. Microjets are formed as a consequence of the collapse of cavitational bubbles at or near the solid-liquid interface and are directed towards the electrode surface [10]. Their formation is a result of an intense transient cavitation in the vicinity of the electrode and can be seen as current pulses. Shock waves appear under some conditions after the violent bubble collapse and can erode the surface of the electrode. As a result, a new surface is formed, which is seen in the form of increased current pulses. This process occurs only with cavitation in close vicinity of the electrode surface. The main effect of physical activity of ultrasound on the electrochemical process is the enhanced mass transfer, which is manifested by an increase of electrolytic current. However, this increase of current depends on the applied mechanism; turbulence, microjets, and shock waves derived from cavitation taking place near the working electrode. Thus, under some conditions these three effects can appear together decreasing significantly the diffusion layer (far under 1µm), which is schematically presented in Figure1. In comparison, with the acoustic streaming the diffusion layer thickness can be reduced only to several micrometers, which means also a smaller increase of current. Among the mentioned mechanisms microjets are the most efficient in reduction of the diffusion layer and show the widest spectrum of use in electrochemistry. Apart from enhanced mass transfer of substrates and products to and from the electrode, they can also remove the absorbed material or even passivate the layer at the electrode [11–13]. This is enabled by the formation of very high pressure (several thousand bars) on the electrode surface at the moment of the jets of liquid reaching the surface [14]. On one hand, the activation of the electrode can occur, but on the other also its corrosion [15]. Therefore, cavitation can produce two opposite effects: mass transfer enhancement, which facilitates film formation, and reactivation of the electrode, which means destruction of the film layer. Apart from the influence of physical effects of ultrasound on the mechanism of electrodeposition, chemical effects also can play an important role. According to Garcias’ group the formation of OH• radicals in the process of sonolysis enhances the formation of nucleation centers by their adsorption on the electrode surface [16–18]. An interesting result of the study of nucleation mechanism in the sonoelectrodeposition process can be found in the work of Mallik et al. [19]. It reveals, that ultrasound is capable of breaking crystal bonds of the primary nuclei and on the defect-free crystal face induces secondary nucleation. Of course this process cannot occur infinitely long, due to increased adherence under sonication. The deposits obtained in this process consisted of reduced grain size in contrast to coarse grain deposits produced without sonication. Molecules 2017, 22, 216 3 of 22 Molecules 2017, 22, 216 3 of 23

Figure 1.1. Schematic representation of the diffusion andand boundaryboundary layerslayers atat thethe electrode-solutionelectrode-solution interfaceinterface as as applied applied in in the the diffusion diffusion layer layer model. model. Reprinted Reprinted from [20] from by [ 20permission] by permission of John Wiley of John & WileySons, Inc. & Sons, Inc.

IncreasedIncreased hardnesshardness ofof thethe deposit,deposit, enlargedenlarged filmfilm thickness,thickness, improvedimproved depositiondeposition ratesrates andand efficiencies,efficiencies, greater greater adhesion adhesion of of the the deposits deposits to toelectrode, electrode, and and brightness brightness enhancement enhancement are the are most the mostoften oftenmentioned mentioned benefits benefits of electrodeposition of electrodeposition of metals of metals assisted assisted with withultrasound ultrasound [21–23]. [21 –The23]. Thebrightness brightness of deposits of deposits depends depends on the oncurrent the current density density and it decreases and it decreases when current when density current increases density increasesabove a critical above avalue. critical The value. use of The ultrasound use of ultrasound increases increases the critical the current critical currentdensity densityand helps and to helps obtain to obtainelectrodeposits electrodeposits with increased with increased brightness. brightness. The ultras Theound ultrasound effects effects that influence that influence the brightness the brightness come comefrom shock from shockwaves waves followed followed by cavitation by cavitation erosion. erosion. As a result, As a result,films built films of built fine ofgrain fine size grain and size higher and highergrain-packing grain-packing density density are produced. are produced. The synergism between soundsound and light in sonoph sonophotochemicalotochemical processes is most often correlated withwith thethe enhancedenhanced massmass transfertransfer inducedinduced byby ultrasoundultrasound thatthat cancan affectaffect thethe photochemicalphotochemical reactionreaction ratesrates [[6].6]. However, thethe interactioninteraction betweenbetween sono-sono- andand photochemicalphotochemical irradiationirradiation strictlystrictly dependsdepends onon thethe typetype ofof ultrasound ultrasound effect effect produced produced in in the the liquid, liquid, which which is shown is shown in detail in detail in Figure in Figure2. It can2. It be can seen be thatseen this that enhanced this enhanced mass transfermass transfer can in consequencecan in consequence improve improve light absorption light absorption and modify and themodify reaction the pathway.reaction pathway. The energy The transfer energy to transfer molecules to molecule occurs onlys occurs when only cavitation when iscavitation produced. is Theproduced. transfer The of photoexcitedtransfer of photoexcited states in a purestates photochemical in a pure photoche systemmical is not system homogeneous is not homogeneous (see Figure (see3a), becauseFigure 3a), it dependsbecause it on depends how light on propagateshow light propagates through an through absorbing an absorbing medium and medium normally and itsnormally intensity its decreases intensity withdecreases a distance with [a24 distance]. It is also [24]. known, It is thatalso theknown, reaction that rate the in reaction photochemical rate in processphotochemical depends process on the concentrationdepends on the of theconcentration excited states. of the Figure excited3b predicts states. howFigure the 3b distribution predicts how of a the photoexcited distribution stated of a couldphotoexcited change whenstated sonication could change is added when to thesonicati system.on Anis added intense to mixing the system. provoked An by intense cavitation mixing and shockprovoked waves by shouldcavitation distribute and shock the excitedwaves should states indistribute the whole the reaction excited volume states in causing the whole the reactionreaction ratesvolume to causing be more the or reaction less the rates same to at be each more point or less of the the same solution. at each However, point of the not solution. only cavitation However, is thenot importantonly cavitation factor, is the but important also the relative factor, but formation also the rates, relative lifetimes, formation and rates, further lifetimes, decomposition and further of exciteddecomposition species. of Additionally, excited species. it was Additionally, suggested thatit was long-lived suggested excited that long-lived states could excited be quenched states could by cavitation.be quenched Another by cavitation. aspect ofAnother “sonophoto” aspect synergyof “sonophoto” can be foundsynergy in can some be worksfound wherein some it isworks said thatwhere the it combinedis said that effects the combined of ultrasound effects andof ul lighttrasound could and potentially light could generate potentially a new generate chemistry a new of photoexcitedchemistry of solutesphotoexcited under thesolutes extreme under conditions the extreme inside conditions cavitation inside microreactors cavitation [6 ].microreactors The Colmenares [6]. The Colmenares group performed an experiment comparing the deposition of iron on TiO2 group performed an experiment comparing the deposition of iron on TiO2 semiconductor, in order to obtainsemiconductor, iron oxide, in usingorder ultrasound,to obtain iron light, oxide, and using ultrasound ultrasound, coupled light, with and light ultrasound (results not coupled published). with Theylight (results compared not the published). morphology They and compared chemical the structure morphology of these and three chemical samples structure to find of out these if a three new samples to find out if a new chemistry occurred. They discovered that nanostructured hematite was the main form obtained in the sonophotodeposition as well as in the photodeposition process. In

Molecules 2017, 22, 216 4 of 22 chemistry occurred. They discovered that nanostructured hematite was the main form obtained in the sonophotodeposition as well as in the photodeposition process. In contrast, different iron oxide Molecules 2017, 22, 216 4 of 23 forms were registered after sonodeposition. This could be interpreted in that the same mechanism, Molecules 2017, 22, 216 4 of 23 mainlycontrast, photocatalytically-induced different iron oxide forms electrons were registered is responsible after sonodeposition. for the reduction This of could the iron be interpreted precursor after compilationincontrast, that the ofdifferent “sono”same mechanism,iron with oxide “photo”. forms mainly Onwere thephotocatalyt registered other hand, ically-inducedafter a sonodeposition. clear physical electrons effectThis is couldresponsible of ultrasound be interpreted for wasthe seen in a betterreductionin that dispersion the of samethe iron mechanism, of precursor Fe2O3, which aftermainly compilation was photocatalyt localized of “sono”ically-induced not only with on“photo”. theelectrons surface, On theis responsible butother also hand, in fora the clear the bulk of the material.physicalreduction effect An of the important of iron ultrasound precursor issue was inafter thisseen compilation experimentin a better ofdispersion is“sono” the reaction with of Fe “photo”.2O solution3, which On consistingwasthe otherlocalized hand, of not 30% a clearonly of water and 70%onphysical the of surface, acetonitrile. effect of but ultrasound also In such in the was environment bulk seen of in the a better thematerial. reductive dispersion An important power of Fe2 ofO 3issue, sonication which in wasthiswas localizedexperiment probably not is only reduced,the reaction solution consisting of 30% of water and 70% of acetonitrile. In such environment the becauseon the only surface, a low but amount also in of the H •bulkradicals of the with material. high An reductive important power issue could in this be experiment formed. Asis the a result, reductivereaction solution power of consisting sonication of was 30% probably of water reduced, and 70% because of acetonitrile. only a low amountIn such of environment H• radicals with the a mechanical role of sonication and a chemical role of light were found in the sonophotodeposition highreductive reductive power power of sonication could be was formed. probably As areduced, result, a because mechanical only rolea low of amount sonication of H and• radicals a chemical with processrolehigh in of reductive thislight particular were power found case.could in the be sonophotodeposition formed. As a result, processa mechanical in this roleparticular of sonication case. and a chemical role of light were found in the sonophotodeposition process in this particular case.

Figure 2. Interaction of ultrasound effect with photochemical reactions. Reprinted from [6] with Figure 2. Interaction of ultrasound effect with photochemical reactions. Reprinted from [6] with permissionFigure 2. Interaction of Springer. of ultrasound effect with photochemical reactions. Reprinted from [6] with permission of Springer. permission of Springer.

Figure 3. Distribution of excited states in the photochemical process (a) and after addition of sonication,Figure 3. Distribution (b). (Dots represent of excited the densitystates in of theactivated photochemical species). Adaptedprocess from(a) and [24] after with additionpermission of Figure 3. Distribution of excited states in the photochemical process (a) and after addition of fromsonication, Elsevier. (b). (Dots represent the density of activated species). Adapted from [24] with permission sonication (b). (Dots represent the density of activated species). Adapted from [24] with permission from Elsevier. 3.from Materials Elsevier. Obtained by the Sonoelectrodeposition and Sonophotodeposition Processes 3. Materials Obtained by the Sonoelectrodeposition and Sonophotodeposition Processes In this part we discuss the examples of the materials prepared by using sonoelectro- and 3. Materials Obtained by the Sonoelectrodeposition and Sonophotodeposition Processes sonophotodepositionIn this part we methods,discuss the see examples also Table of 1. Ththee sonoelectrodepositionmaterials prepared by has using already sonoelectro- been used and for preparationsonophotodepositionIn this part of wevast discussnumber methods, of the materials. see examples also Table Herein, of 1. Th thewee describesonoelectrodeposition materials several prepared examples has by showingalready using been sonoelectro-the diversity used for and sonophotodepositionofpreparation the materials of vast that methods,number can be ofobtained seematerials. also by Table Herein,using1. th The weis method. describe sonoelectrodeposition Sonoelectrodeposseveral examples has itionshowing already of lead the been diversityoxide used on for of the materials that can be obtained by using this method. Sonoelectrodeposition of lead oxide on

Molecules 2017, 22, 216 5 of 22 preparation of vast number of materials. Herein, we describe several examples showing the diversity of the materials that can be obtained by using this method. Sonoelectrodeposition of lead oxide on glassy carbon and platinum electrodes was studied by Garcia et al. [16] (Table1, Entry 1). In this experiment a commercial ultrasonic bath (30 kHz, 100 W) together with a platinum electrode and a glassy carbon rod as working electrodes were used. The authors observed that the behavior of these electrodes under action of ultrasound was different. The response of the platinum electrode was unchangedMolecules in comparison 2017, 22, 216 with silent conditions. In contrast, activation of the glassy carbon5 of 23 electrode during electrodeposition of lead dioxide was observed when the ultrasound was applied. Interestingly, glassy carbon and platinum electrodes was studied by Garcia et al. [16] (Table 1, Entry 1). In this no changes were observed in the surface topography of the electrode. Therefore the activation of experiment a commercial ultrasonic bath (30 kHz, 100 W) together with a platinum electrode and a the electrodeglassy was carbon directly rod as working correlated electrodes with were the used formation. The authors of some observed surface that the functional behavior of these groups in the reaction ofelectrodes OH• radicals, under action formed of ultrasound in the aqueous was differe sonolysis,nt. The response with of the the carbon platinum surface. electrode Thesewas groups play the roleunchanged of intermediates in comparison inwith the silent mechanism conditions. In of contrast, lead oxide activation deposition of the glassy and carbon are electrode consumed as the during electrodeposition of lead dioxide was observed when the ultrasound was applied. reaction progresses. The influence of ultrasound power and frequency on sonoelectrodeposition of Interestingly, no changes were observed in the surface topography of the electrode. Therefore the PbO2 on aactivation glassy carbonof the electrode electrode was wasdirectly studied correlate ind thewith subsequentthe formation worksof some ofsurface Garcia’s functional group [17,18] (Table1, Entrygroups 2). in The the sonoelectrochemicalreaction of OH• radicals, reactor formed in consisting the aqueous of so anolysis, jacketed with Sonoreactor the carbon surface. (20 kHz, 100 W max. power)These was groups used play in the these role of studies. intermediates The authorsin the mechanism found thatof lead the oxide increase deposition of power and are as well as consumed as the reaction progresses. The influence of ultrasound power and frequency on frequency of ultrasound had an influence on the kinetics of the electrodeposition process, increasing sonoelectrodeposition of PbO2 on a glassy carbon electrode was studied in the subsequent works of the nucleationGarcia’s constant group [17,18] and (Table decreasing 1, Entry the 2). inductionThe sonoelectrochemical time. This reactor was correlatedconsisting of with a jacketed the enhanced generationSonoreactor of OH• radicals, (20 kHz, which 100 W canmax. be power) adsorbed was used on the in these electrode studies. surface The authors and therefore found that the the number of nucleationincrease centers of should power beas well increased. as frequency A formed of ultr nucleusasound had favors an influence the lead on oxide the kinetics deposition. of the However, electrodeposition process, increasing the nucleation constant and decreasing the induction time. This the potential of the electrode also influences the electrodeposition, therefore these experiments were was correlated with the enhanced generation of OH• radicals, which can be adsorbed on the electrode performedsurface under and conditions therefore the wherenumber theof nucleation electrodeposition centers should process be increased. was A notformed favored. nucleus favors Glassy carbon was also usedthe lead as a substrateoxide deposition. in the nextHowever, experiment the pote withntial depositionof the electrode of lead also oxide influences film performedthe by Saez et al.electrodeposition, [25] (Table1, Entry therefore 3). They these used experiments two experimental were performed setups, under one conditions consisted where of a the sonoreactor electrodeposition process was not favored. Glassy carbon was also used as a substrate in the next (20 kHz) andexperiment plates with of deposition graphite of as lead substrate oxide film electrodes performed by and Saez in et al. the [25] other (Table one 1, Entry an ultrasound3). They bath (40 kHz, 100used W) two with experimental larger plates setups, ofone graphite consisted orof titaniuma sonoreactor as electrodes(20 kHz) and wereplates appliedof graphite (see as Figure4). The obtainedsubstrate results electrodes were compared and in the other with one the an mechanical ultrasound bath agitation (40 kHz, procedure. 100 W) with The larger authors plates of discovered that only thegraphite ultrasound or titanium field as electrodes enhanced were the applied electrodeposition (see Figure 4). The of obtained lead oxide results providing were compared a finer grain, with the mechanical agitation procedure. The authors discovered that only the ultrasound field more homogeneous,enhanced the stress-freeelectrodeposition and of nodule-free lead oxide prov filmiding deposit a finer grain, on both moresubstrates. homogeneous, Acoustic stress-freestreaming and microjetsand nodule-free were mainly film responsibledeposit on both for substrates. the good Acoustic adherence streaming of the and film microjets on the were coarse mainly and rough surface ofresponsible the electrode for the substrate. good adherence The only of the drawback film on the was coarse a random and rough presence surface ofof pores.the electrode To avoid them, the specificsubstrate. pretreatment The only of drawback the electrode was a surface random was pres suggestedence of pores. as To well avoid as study them, ofthe the specific application of pretreatment of the electrode surface was suggested as well as study of the application of high-frequencyhigh-frequency ultrasound ultrasound fields. fields.

Figure 4. (A) 20 kHz sonoreactor adapted as a sonoelectrochemical device: (1) lead dioxide electrode, Figure 4. ((2)A) copper 20 kHz counter-electrode sonoreactor adapted(foam geometry), as a sonoelectrochemical (3) working solution, (4) device: cooling jacket, (1) lead (5) glass dioxide cell, electrode, (2) copper(6) counter-electrode Teflon holder, (7) ultrasonic (foam geometry),transducer. (B (3)) 40 workingkHz ultrasound solution, bath: (1) (4) lead cooling dioxide jacket, electrode, (5) glass cell, (6) Teflon(2) holder, copper (7) counter-electrode, ultrasonic transducer. (3) working (solution,B) 40 kHz (4) ultrasonic ultrasound bath, bath: (5) ultrasonic (1) lead transducers. dioxide electrode, Reprinted from [25] with permission from Elsevier. (2) copper counter-electrode, (3) working solution, (4) ultrasonic bath, (5) ultrasonic transducers. Reprinted from [25] with permission from Elsevier.

Molecules 2017, 22, 216 6 of 22 Molecules 2017, 22, 216 6 of 23

TheThe first first trial trial of of sonoelectrodeposition sonoelectrodeposition of of platinum platinum on on a a glassy glassy carbon carbon electrode electrode was was reported reported by by PolletPollet et al.al. [26[26]] (Table (Table1, Entry1, Entry 4). For4). For this, this, a special a special jacketed jacketed cooling cooling electrochemical electrochemical cell with cell a 20with kHz a 20ultrasonic kHz ultrasonic probe was probe designed. was designed. It was confirmed It was confir bymed the authors by the authors that for thethat formation for the formation of Pt deposits of Pt depositsa substantial a substantial overpotential overpotential is required is and required that the and whole that process the whole is irreversible. process is In irreversible. the process drivenIn the processunder sonication driven under the positivesonication shift the in positive potentials shift provoked in potentials a decrease provoked in concentration a decrease in and concentration nucleation andoverpotentials nucleation overpotentials thus facilitating thus the facilitating electrodeposition the electrodeposition of platinum. Theyof platinum. also observed They also a significant observed adifference significant between difference morphology between morphology of the Pt deposits of the obtainedPt deposits under obtained silent under conditions silent in conditions comparison in comparisonwith forced convectionwith forced conditions, convection like rotationconditions, and sonication.like rotation Individual and sonication. Pt nanoparticles Individual deposits Pt nanoparticleswere produced deposits with no agitationwere prod whereasuced agglomerateswith no agitation of larger whereas Pt nanoparticles agglomerates were formedof larger under Pt nanoparticlessonication and were rotation. formed In thisunder work, sonication the use and of continuousrotation. In ultrasound this work, had the ause detrimental of continuous effect ultrasoundon the electrocatalytic had a detrimental performance effect on of the the electrocat fuel cell inalytic comparison performance with of the the pulsed fuel cell ultrasound in comparison used within galvanostatic the pulsed ultrasound deposition used reported in galvanostatic earlier by the deposition same author reported [27]. earlier Later by on, the more same sophisticated author [27]. Laterplatinum on, more structures sophisticated were obtained platinum by structures using sonoelectrodeposition. were obtained by using Heli sonoelectrodeposition. et al. [28] reported Heli the etsynthesis al. [28] reported of platinum the synthesis hierarchical of platinum nanoflowers, hierarchical whereas nanoflowers, fractal nanoplatinum whereas fractal structures nanoplatinum were structuressynthesized were by Taguchisynthesized et al. by [29 ].Taguchi More information et al. [29]. More on these information materials on is collected these materials in Table is1, collected Entries 5 inand Table 6, respectively. 1, Entries 5 and 6, respectively. BiomedicalBiomedical materials materials were were synthesized synthesized using using sono sonoelectrochemicalelectrochemical deposition deposition by by Han Han et et al. al. [30] [30] (Table(Table 11,, EntryEntry 7).7). CalciumCalcium phosphatephosphate (CaP)(CaP) coatingscoatings werewere depositeddeposited onon carboncarbon fibersfibers creatingcreating bioceramicbioceramic composites composites which which could could be be used to reconstruct bone defects. For For this this purpose, highly highly irregularirregular objects objects often often need need to to be be coated coated and and the the electrodeposition electrodeposition method method makes makes this this task task easier easier in comparisonin comparison with with other other available available methods. methods. The The synthesis synthesis setup setup consisted consisted of of an an ultrasonic ultrasonic bath 2 (40(40 kHz, kHz, 2.16 2.16 W/cm W/cm2),), carbon carbon fabric fabric as as the the working working electrode electrode and and the the whole whole procedure procedure was was performed performed 2 underunder a constant current density (20 mA/cmmA/cm2).). The The authors authors observed observed that that the the action action of of ultrasound significantlysignificantly influences influences morphologymorphology asas wellwell asas thethe chemicalchemical composition composition of of the the CaP CaP coatings. coatings. Figure Figure5 5compares compares the morphologythe morphology of the coatings of the electrodeposited coatings electrodeposited under silent mode under vs. sonoelectrodeposited. silent mode vs. sonoelectrodeposited.It is clearly seen that It application is clearly seen of silent that application mode resulted of silent in the mode formation resulted of in a porousthe formation layer withof a porousplate-like layer crystals with (~1plate-likeµm) or smallcrystals spheres. (~1 µm) In contrast,or small veryspheres. uniform In contrast, coatings, very with uniform small needle-like coatings, withcrystals small (<0.1 needle-likeµm) and acrystals good adhesive (<0.1 µm) strength and werea good obtained adhesive under strength sonication were mode. obtained Regarding under sonicationthe chemical mode. structure Regarding it was the discovered chemical thatstructure application it was discovered of ultrasound that promoted application the of formation ultrasound of 3− 2− promotedPO4 instead the formation of HPO4 of. PO Concluding,43− instead theof HPO CaP4 coatings2−. Concluding, obtained the with CaP thecoatings use of obtained ultrasound with were the usemore of acceptedultrasound by were the osteoblast more accepted cells. by the osteoblast cells.

(1) (2)

FigureFigure 5. Morphologies and and composition composition of of CaP CaP obtained by: by: (1) (1) electrodeposition electrodeposition in in the the absence absence of of sonicationsonication vs. vs. (2) (2) sonoelectrodeposition. sonoelectrodeposition. Reprin Reprintedted from from [30] [30] with with permission permission from from Elsevier.

TheThe influence influence of different current densitiesdensities (5, 8, 13,13, 20,20, andand 3434 mA/cmmA/cm2)) on on morphologies morphologies and and structuresstructures of of CaP CaP coatings coatings on on carbon carbon surfaces surfaces prepared prepared by sonoelectrodeposition by sonoelectrodeposition was wasstudied studied by Han by etHan al. etin al.the innext the work next [31] work (Table [31] 1, (Table Entry1, 8). Entry It was 8). observed It was observed that morphology that morphology of the CaP of thedeposits CaP changeddeposits changedwith increasing with increasing current currentdensity density(see Figure (see Figure6). The6). plate-like The plate-like crystals crystals were were formed formed at the at lowest current density 5 mA/cm2, a mixture of spherical and needle-like structures appeared at 8 mA/cm2. The further increase of the value of current density resulted in the formation of needle-like

Molecules 2017, 22, 216 7 of 22 the lowest current density 5 mA/cm2, a mixture of spherical and needle-like structures appeared at 2 8 mA/cmMolecules. The 2017 further, 22, 216 increase of the value of current density resulted in the formation of7 of needle-like 23 morphology with more uniform structures and smaller crystal sizes as the current density grew. It was concludedmorphology that at thewith lower more currentuniform structures density an and insufficient smaller crystal concentration sizes as the current of OH density− ions grew. was theIt cause of formationwas concluded of octacalcium that at the phosphate. lower current Ondensity the an other insufficient hand, concentration the higher currentof OH− ions densities was the and the cause of formation of octacalcium phosphate. On the other hand, the higher current densities and the needle-like morphology confirmed the formation of the apatite form of calcium phosphate. needle-like morphology confirmed the formation of the apatite form of calcium phosphate.

Figure 6. Scanning electron microscopy (SEM) micrographs of the samples prepared by Figuresonoelectrodeposition 6. Scanning electron under different microscopy current (SEM)densities. micrographs (a) 5 mA/cm2; (b of) 8 mA/cm the samples2; (c) 13 mA/cm prepared2; by sonoelectrodeposition(d) 20 mA/cm2; and under (e) 34 different mA/cm2. Reprinted current densities. from [31] with (a) 5 permission mA/cm2 ;(of bSpringer.) 8 mA/cm 2;(c) 13 mA/cm2; (d) 20 mA/cm2; and (e) 34 mA/cm2. Reprinted from [31] with permission of Springer. Another work in this field was dedicated to the formation of hydroxyapatite/porous carbon composite scaffolds and reported by Liu et al. [32] (Table 1, Entry 9). The obtained material was Anotherhomogeneously work in coated this fieldwith the was needle- dedicated or sheet-sha to theped formation crystals of ofhydroxyapatite hydroxyapatite/porous such as on the carbon compositeexternal scaffolds and internal and reported surface of by the Liu scaffold. et al. [32This] (Tableuniform1, Entrycoating 9). ensured The obtainedan adequate material was homogeneouslymicroenvironment coated and promoted with the the needle- adhesion or and sheet-shaped proliferation ofcrystals osteoblast of cells, hydroxyapatite no matter of thesuch as on thelocation external on and the porous internal carbon surface scaffold. of theThe scaffold.biomedical application This uniform of CaP coating coatings ensured makes them an an adequate interesting topic for many research groups and therefore, there are many works available in the microenvironment and promoted the adhesion and proliferation of osteoblast cells, no matter of the literature. Also Zhao et al. obtained a nano/micro-sized CaP coating prepared on carbon/carbon locationcomposites on the porous [33] (Table carbon 1, Entry scaffold. 10). The Theobtained biomedical coating consisted application of hydroxyapatite of CaP coatings and brushite. makes them an interestingThe authors topic observed for many that researchat different groups deposition and voltages therefore, the morphology there are many of the workscrystals availablechanged. in the literature.In the Also most Zhao homogenous et al. obtained coating (voltage a nano/micro-sized of deposition 2.4 V) CaP the nano-sized coating prepared and needle-like on carbon/carbon crystals compositesof hydroxyapatite [33] (Table1 ,were Entry embedded 10). The in obtained a micro-size coatingd and consisted plate-like ofstructure hydroxyapatite of brushite. and This brushite. The authorshomogeneous observed structure that at resulted different in an deposition enhanced adhesive voltages and the cohesive morphology strength of of the the coating. crystals changed. An intriguing work was performed by Wang et al., who filled in TiO2 nanotubes with CdS In the most homogenous coating (voltage of deposition 2.4 V) the nano-sized and needle-like nanoparticles through a single-step sonoelectrodeposition method [34] (Table 1, Entry 11). In this crystalsexperiment of hydroxyapatite TiO2NTs as werea working embedded electrode, in and a micro-sized an ultrasonic andbath plate-like(40 kHz, 2.4 structure kW/m2) under of brushite. This homogeneousconstant current structure density resulted(5 mA/cm in2) anwere enhanced used. Deposition adhesive of andCdS cohesivenanoparticles strength inside ofthe the TiO coating.2 Annanotubes intriguing was work facilitated was by performed the action byof ultrasou Wang etnd, al., which who is filledshown inin TiOFigure2 nanotubes 7. First of all, with CdS nanoparticlesultrasound through promoted a single-step dissolution of sonoelectrodeposition elemental sulfur. Next, it methodenhanced [expelling34] (Table of 1the, Entry air from 11). the In this nanotubes, which was a process that enabled the ions to enter inside the tube. Finally, ultrasound2 experiment TiO2NTs as a working electrode, and an ultrasonic bath (40 kHz, 2.4 kW/m ) under helped to obtain smaller and uniformly2 sized CdS nanoparticles. A real effect of this process is constantpresented current below density in the (5 transmission mA/cm ) wereelectron used. microscopy Deposition (TEM) ofimage CdS (Figure nanoparticles 7, on the right). inside An the TiO2 nanotubesordered was tubular facilitated structure by of the TiO action2 with CdS of nanoparticles ultrasound, deposited which isinto shown the channels in Figure is clearly7. Firstseen. of all, ultrasoundThis result promoted also confirms dissolution that ultrasound of elemental did not sulfur. damage Next, the ordered it enhanced structure expelling of the TiO of2NTs the during air from the nanotubes,sonoelectrodeposition which was a process of CdS nanoparticles. that enabled Such the obtained ions to CdS-TiO enter inside2NTs electrodes the tube. gave Finally, a stronger ultrasound helpedphotocurrent to obtain smaller and an extended and uniformly photoresponse sized under CdS visible nanoparticles. light (up to 480 A realnm) in effect comparison of this with process is the CdS-TiO2NTs electrodes prepared using electrodeposition without sonication. presented below in the transmission electron microscopy (TEM) image (Figure7, on the right). An ordered tubular structure of TiO2 with CdS nanoparticles deposited into the channels is clearly seen. This result also confirms that ultrasound did not damage the ordered structure of the TiO2NTs during sonoelectrodeposition of CdS nanoparticles. Such obtained CdS-TiO2NTs electrodes gave a stronger photocurrent and an extended photoresponse under visible light (up to 480 nm) in comparison with the CdS-TiO2NTs electrodes prepared using electrodeposition without sonication. Molecules 2017, 22, 216 8 of 22 Molecules 2017, 22, 216 8 of 23

Figure 7. On the left: a schematic diagram of the possible sonoelectrochemical deposition interaction. Figure 7. On the left: a schematic diagram of the possible sonoelectrochemical deposition On the right: a transmission electron microscopy (TEM) image of CdS-TiO2NTs after CdS interaction. On the right: a transmission electron microscopy (TEM) image of CdS-TiO NTs after sonoelectrochemical deposition with the inset energy dispersive X-ray (EDX) spectrum. Reprinted2 CdS sonoelectrochemicalfrom [34]. © IOP Publishing. deposition Reproduced with the with inset permission. energy dispersive All rights reserved. X-ray (EDX) spectrum. Reprinted from [34]. © IOP Publishing. Reproduced with permission. All rights reserved. The impact of deposition temperature on the residual stress of Cu films sonoelectrodeposited on Thethe graphite impact substrate of deposition was investigated temperature by Mallik on the et residualal. [35] (Table stress 1, Entry of Cu 12). films The sonoelectrodepositedexperiments were on thecarried graphite out substrateon a graphite was electrode investigated usingby an Mallikultrasonic et al. probe [35] (Table(20 kHz,1, Entry20% output) 12). The at experimentsdifferent temperatures: 25, 20, 15, 10, and 5 °C. It was observed that the type of residual stress in the Cu films were carried out on a graphite electrode using an ultrasonic probe (20 kHz, 20% output) at different was only compressive, which◦ means that films “want” to expand, at each applied deposition temperatures:temperature. 25, 20,The 15, maximum 10, and 5valueC. It of was compressive observedthat residual the type stress of residualwas registered stress inat the the Cu lowest films was onlydeposition compressive, temperature, which means 5 °C. thatThe filmsmechanical “want” proper to expand,ties of the at eachfilms appliedare strongly deposition related with temperature. the The maximumresidual stress. value Therefore, of compressive the maximum residual values stress of was hardness, registered elasticity, at the and lowest surface deposition adhesion temperature, at the 5 ◦C.grain The mechanicalsurface were properties also obtained of the at films5 °C. areThis strongly could be related correlated with with the residualthe effects stress. of residual Therefore, the maximumcompressive values stresses of on hardness, suppressing elasticity, crack propagation. and surface Interestingly, adhesion at an the opposite grain surfacetendency were was also obtainedobserved at 5 for◦C. adhesion This could at begrain correlated boundaries, with wh theich effectsdecreased of residualtogether compressivewith the deposition stresses on suppressingtemperature. crack Such propagation. behavior was Interestingly, ascribed to anchanges opposite in energy tendency of the was grains observed on the surface for adhesion and at the at grain boundaries,boundaries which as well decreased as to some together interfacial with tension the depositionoccurring during temperature. the atomic Such force behaviormicroscopy was (AFM) ascribed measurement. Ultrasound was reported to have a significant enhanced effect on the magnitude of to changes in energy of the grains on the surface and at the boundaries as well as to some interfacial the compressive stress by increasing the adatom mobility and attachment of the islands with a tensionsubstrate. occurring Also during the impact the of atomic low deposition force microscopy temperature (AFM) on the measurement. morphology of Ultrasoundthe copper deposition was reported to havewas a studied significant by Mallik enhanced et al. [36] effect (Table on 1, the Entry magnitude 13). Temperatures of the compressive selected for this stress experiment by increasing were the adatomas following: mobility 25, and 19.5, attachment −1 and −3 °C, of and the an islands ultrasonic with bath a substrate. (30 kHz, 60 Also W) was the the impact source of of lowsonication. deposition temperatureDifferent onresults the morphologybetween sonicated of the and copper silent deposition conditions wasas well studied as between by Mallik ambient et al. and [36] low (Table 1, Entrytemperatures 13). Temperatures are clearly selected seen in forFigure this 8. experiment Inhomogeneous were morphology as following: consisted 25, 19.5, of near−1 andgranular−3 ◦ asC, and an ultrasonicwell as highly bath distorted (30 kHz, areas 60 W) with was some the perforated source of grains sonication. obtained Different at 25 °C under results sonication between (Figure sonicated and silent8a (i)). conditions This distortion as well was as betweenexplained ambientby the ab andlating low effect temperatures of microstream are clearly jetting. seen At inlower Figure 8. temperature 19.5 °C and under sonication (Figure 8b (i)) bimodal faceted Cu structures with bigger Inhomogeneous morphology consisted of near granular as well as highly distorted areas with some and smaller grains were deposited. Enhanced mass transport by ultrasound, improved bulk perforated grains obtained at 25 ◦C under sonication (Figure8a (i)). This distortion was explained deposition, simultaneous nucleation, and grain growth were some of the factors◦ responsible for this by theresult ablating according effect to ofthe microstream authors. The corresponding jetting. At lower samples temperature at silent conditions 19.5 C (Figures and under 8a (ii) sonication and (Figure8b8 (ii))b (i)) presented bimodal dendritic faceted Cu structures. structures Totally with biggerdifferent and morphology smaller grains of Cu were films deposited. was obtained Enhanced at mass− transport1 °C temperature by ultrasound, with sonication. improved In bulkFigure deposition, 8c (i) a uniform simultaneous copper covered nucleation, surface and with grain well growth wereagglomerated some of the factors spheroids responsible is seen. forThe this low result temperat accordingure, favoring to the authors. the form Theation corresponding of small nuclei, samples at silentimproved conditions the rate (Figure of mass8a (ii) transfer, and Figure creating8b(ii)) enhanced presented nucleation, dendritic as structures.well as degassing Totally of different the morphologyelectrode of surface Cu films by ultrasound, was obtained giving at − adherent1 ◦C temperature and bright withdeposits, sonication. which were In Figure favorable8c (i) for a uniformthe copperobtained covered morphology. surface with Similarly, well agglomerated the deposit formed spheroids at −3 °C is presented seen. The a uniform low temperature, and fully coalesced favoring the fine grained Cu coating (Figure 8d (i)). Conversely, the deposits obtained at silent mode (Figures 8c formation of small nuclei, improved the rate of mass transfer, creating enhanced nucleation, as well as (ii) and 8d (ii)) showed branched, not dense structures. degassing of the electrode surface by ultrasound, giving adherent and bright deposits, which were favorable for the obtained morphology. Similarly, the deposit formed at −3 ◦C presented a uniform and fully coalesced fine grained Cu coating (Figure8d (i)). Conversely, the deposits obtained at silent mode (Figure8c (ii) and Figure8d (ii)) showed branched, not dense structures. Molecules 2017, 22, 216 9 of 22

Molecules 2017, 22, 216 9 of 23

Figure 8. SEM images of copper deposits with (i) and without (ii) sonication at (a) 25, (b) 19.5, (c) −1 Figure 8.andSEM (d) − images3 °C. Reprinted of copper from deposits [36] with withpermission (i) and from without Elsevier. (ii) sonication at (a) 25, (b) 19.5, (c) −1 and (d) −3 ◦C. Reprinted from [36] with permission from Elsevier. The effect of ultrasound amplitude on the formation of poly(pyrrole) PPy/Prussian blue (PB) and poly(pyrrole) Ppy/dodecylbenzenosulphonate (DBS) nanocomposites was investigated by The effect of ultrasound amplitude on the formation of poly(pyrrole) PPy/Prussian blue Hostert et al. [37,38] (Table 1, Entries 14 and 15). The following amplitudes of ultrasonic horn (PB) and(20 poly(pyrrole) kHz, 130 W) were Ppy/dodecylbenzenosulphonate checked at: 20%, 40%, and 60%. It was (DBS) found nanocomposites that by changing was the amplitude investigated by Hostertof et ultrasound al. [37,38] the (Table morphology1, Entries and 14 distribution and 15). The of nanoparticles following amplitudes on the electrode of ultrasonic can be tuned. horn The (20 kHz, 130 W) wereinfluence checked of different at: 20%, US 40%,amplitude and 60%.on the It ITO was electrode foundthat modified by changing by PPy/Fe(CN) the amplitude64− and PPy/PB of ultrasoundnano the morphologyis presented and in Figure distribution 9 [37]. A similar of nanoparticles globular morp onhology the electrode is clearly seen can under be tuned. silent as The well influence as at of each US amplitude for the control electrode non-modified with Prussian4− blue. In contrast, on the different US amplitude on the ITO electrode modified by PPy/Fe(CN)6 and PPy/PBnano is presented surface of PPy/PBnano electrode the globules with inorganic structures are only seen at 20% amplitude in Figureconditions.9[ 37]. AAt similar the higher globular amplitudes morphology (40% and is 60%) clearly rather seen smooth under surfaces silent aswith well very as small at each US amplitudeaggregates for the are control seen, which electrode can originate non-modified both orga withnically Prussian and inorganically. blue. In This contrast, enhanced on thesurface surface of PPy/PBmorphologynano electrode was the explained globules by withbetter inorganic inclusion of structures small PBnano are nanoparticles only seen at within 20%amplitude PPy film under conditions. At the higher amplitudes (40% and 60%) rather smooth surfaces with very small aggregates are seen, which can originate both organically and inorganically. This enhanced surface morphology was explained by better inclusion of small PBnano nanoparticles within PPy film under increased sonication. The PPy/PBnano electrode presented enhanced electrochemical features such as good stability over continuous cycling and sensitivity towards reduction of H2O2. Similarly, a smoother film deposit with Molecules 2017, 22, 216 10 of 23 Molecules 2017, 22, 216 10 of 22

increased sonication. The PPy/PBnano electrode presented enhanced electrochemical features such as good stability over continuous cycling and sensitivity towards reduction of H2O2. Similarly, a a distinct voltammetric behavior was obtained in the case of Ppy/DBS electrodes under sonochemical smoother film deposit with a distinct voltammetric behavior was obtained in the case of Ppy/DBS conditions [38]. It was also observed that the use of ultrasound facilitated the charge-transfer process electrodes under sonochemical conditions [38]. It was also observed that the use of ultrasound at thefacilitated Ppy/electrolyte the charge-transfer interface process and resulted at the Ppy/elec in differenttrolyte charge interface distribution, and resulted explained in different by charge different amountsdistribution, of intercalated explained DBS by anions.different amounts of intercalated DBS anions.

4− Figure 9. Representative FEG-SEM images taken from ITO electrodes modified by PPy/Fe(CN)6 and 4− Figure 9. Representative FEG-SEM images taken from ITO electrodes modified by PPy/Fe(CN)6 PPy/PBnano employing different US amplitude. All electrodes were modified by the same PPy and PPy/PB employing different US amplitude. All electrodes were modified by the same PPy depositionnano charge 160 mC/cm2. Reprinted from [37] with permission from Elsevier. deposition charge 160 mC/cm2. Reprinted from [37] with permission from Elsevier. A series of work regarding formation of bimetallic nanoparticles by using sonoelectrodeposition Amethod series was of work reported regarding by Luong formation et al. [39–41]. of bimetallic Co-Pt nanoparticles nanoparticles were by so usingnoelectrodeposited sonoelectrodeposition and methodthen was thermally reported treated by Luongunder CO et al.to become [39–41]. encapsul Co-Pt nanoparticlesated within carbon were cages sonoelectrodeposited [39] (Table 1, Entry and 16). For this aim an ultrasonic horn was used in a dual role: as a cathode and ultrasound emitter then thermally treated under CO to become encapsulated within carbon cages [39] (Table1, Entry 16). working in a pulse mode. The authors observed the formation of a heterogeneous CoPt film with For this aim an ultrasonic horn was used in a dual role: as a cathode and ultrasound emitter working separate population of Pt-rich and Co-rich particles after the sonoelectrodeposition process. This was in a pulseexplained mode. by different The authors deposition observed rates of the these formation elements, of because a heterogeneous of the differences CoPt in film their with standard separate populationelectrode of Pt-richpotentials. and Annealing Co-rich particles in the CO after resulted the sonoelectrodepositionin the creation of many core-shell process. Thisstructures was explainedwith by differentmetallic depositioncores and carbon-onion rates of these shells elements, (see Figure because 10). of Also the differencesa hard magnetic in their Co-Pt standard phase electrodewas potentials. Annealing in the CO resulted in the creation of many core-shell structures with metallic cores and carbon-onion shells (see Figure 10). Also a hard magnetic Co-Pt phase was registered. A similar reaction setup was used for the preparation of FePt nanoparticles [41] (Table1, Entry 17), although the annealing step was performed under H2. Similarly to the previous example the sonoelectrodeposition Molecules 2017, 22, 216 11 of 23 Molecules 2017, 22, 216 11 of 22 registered. A similar reaction setup was used for the preparation of FePt nanoparticles [41] (Table 1, Entry 17), although the annealing step was performed under H2. Similarly to the previous example of Fethe and sonoelectrodeposition Pt led to formation of of Fe small and Pt domains led to format of pureion of Fe small and Pt.domains Again, of pure a large Fe and difference Pt. Again, between a 2+ 4+ the standardlarge difference electrode between potential the standard of Fe and electrode Pt was potential given of as Fe a2+reason and Pt4+ for was the given lack as of a alloy reason formation. for Afterthe annealing, lack of alloy when formation. diffusion After processes annealing, occur, when the diffusion ordered processes L10 face-centered occur, the ordered tetragonal L10 face- (fct) FePt phasecentered was registered. tetragonal Also, (fct) theFePt saturation phase was magnetization registered. Also, and the the saturation coercivity magnetization of the nanoparticles and the were improvedcoercivity after of the the annealing nanoparticles process. were Similar improved results after were the annealing obtained process. in the recent Similar work results of thiswere group reportingobtained the in synthesis the recent of work FePd of nanoparticlesthis group reporting [40] (Tablethe synthesis1, Entry of 18).FePd The nanoparticles annealing [40] process (Table under1, Entry 18). The annealing process under (Ar + 5% H2) atmosphere also resulted in the formation of an (Ar + 5% H2) atmosphere also resulted in the formation of an ordered L10 fct FePd structure with hard ordered L10 fct FePd structure with hard magnetic properties. In the electrodeposition of metallic magnetic properties. In the electrodeposition of metallic nanoparticles ultrasound helped to remove nanoparticles ultrasound helped to remove the nanoparticles which were growing on the cathode the nanoparticles which were growing on the cathode surface. surface.

Figure 10. HRTEM images of typical encapsulated nanoparticles, with (inset) the central portions of Figure 10. their respectiveHRTEM Fourier images transforms of typical to encapsulated indicate the good nanoparticles, crystallinity withof both (inset) core (sharp the central spots/streaks portions of their respectivein the Fourier Fourier transform) transforms and the to well-defined indicate the ring good that crystallinity arises from ofthe both carbon core shell. (sharp Reprinted spots/streaks from in the Fourier[39] © IOP transform) Publishing. and Reproduced the well-defined with permission. ring that arisesAll rights from reserved. the carbon shell. Reprinted from [39] © IOP Publishing. Reproduced with permission. All rights reserved. It is worth mentioning other researchers and their contribution to sonoelectrodeposition studies, however we will not discuss them in detail here. Chang et al. reported preparation of Ni-Co/Al2O3 It is worth mentioning other researchers and their contribution to sonoelectrodeposition composite coating with improved properties due to the use of ultrasound [42] (Table 1, Entry 19). studies, however we will not discuss them in detail here. Chang et al. reported preparation Better properties of Zn-Ni-Al2O3 coating electrodeposited in ultrasound assistance, especially of Ni-Co/Alcorrosion2 Oresistance3 composite and hardness, coating we withre also improved found in the properties works done due by toZheng the et use al. (Table of ultrasound 1, Entries [42] (Table201, Entryand 21) 19). [43,44]. Better propertiesNoble metals of Zn-Ni-Al Ag and 2OAu3 coatingstructures electrodeposited were also synthesized in ultrasound by assistance,using especiallysonoelectrodeposition. corrosion resistance Cheng andet al. hardness,reported the were formation also foundof differentially in the works shaped done Ag nanoparticles by Zheng et al. (Table[45]1, Entries(Table 1, 20Entry and 22), 21) Tuan [ 43 et,44 al.]. obtained Noble Ag metals NPs loaded Ag and on Auactive structures carbon [46] were (Table also 1, Entry synthesized 23) by usingwhereas sonoelectrodeposition. the synthesis of gold nanorods Cheng et was al. proposed reported by the Rahi formation et al. [47] of (Table differentially 1, Entry 24). shaped An Ag nanoparticlesinteresting [45 combination] (Table1, Entry of sonoelectrodeposition 22), Tuan et al. obtained with galvanic Ag NPs replacement loaded on was active proposed carbon by [ 46Rousse] (Table 1, Entryet 23) al. whereas [48] (Table the synthesis1, Entry of25) gold for nanorods the synthesis was proposedof copper-silver by Rahi bimetallic et al. [47] (Tablenanopowders.1, Entry 24). Sonoelectrodeposition was used for the preparation of the inner copper core whereas the galvanic An interesting combination of sonoelectrodeposition with galvanic replacement was proposed by reaction allowed the replacement of surface copper atoms by silver atoms forming an outer shell. The Rousse et al. [48] (Table1, Entry 25) for the synthesis of copper-silver bimetallic nanopowders. synthesis of iron-chromium alloy nanoparticles employing pulsed sonoelectrodeposition was Sonoelectrodepositionperformed by Zin et wasal. [49] used (Table for 1, the Entry preparation 26). The effects of the of innerdifferent copper synthesis core parameters, whereas the such galvanic as reactionbath allowed temperature, the replacementpH, and electrolyte of surface composition, copper on atoms process by efficiency silver atoms and nanoparticles forming an features outer shell. The synthesiswere studied. of iron-chromiumThe effect of sonication alloy nanoparticleson electroplating employing of iridium was pulsed investigated sonoelectrodeposition by Ohsaka et al. was performed[50] (Table by Zin 1, Entry et al. 27). [49 A] very (Table interesting1, Entry work 26). The comparing effects direct of different current synthesis electrodeposition parameters, and pulse such as bath temperature,electrodeposition pH, with and electrolytesono-assisted composition, direct current on processelectrodeposition efficiency and and sono-assisted nanoparticles pulse features wereelectrodeposition studied. The effect in the of sonication synthesis of on the electroplating NiZnS electrode of iridium was done was by investigatedSeetharaman byet al. Ohsaka [51] (Table et al. [50] (Table1,1 ,Entry Entry 28). 27). Pulse A electrodeposit very interestingion enabled work higher comparing cathodic direct current current density electrodepositionto be applied at the and electrode interface and to control surface properties of the composite coatings. Sonication added to pulse electrodeposition with sono-assisted direct current electrodeposition and sono-assisted pulse this method increased surface smoothness and decreased the residual stresses of the electrode. The electrodeposition in the synthesis of the NiZnS electrode was done by Seetharaman et al. [51] (Table1, best performance in the oxygen evolution studies showed an electrode prepared by the sono-assisted Entry 28). Pulse electrodeposition enabled higher cathodic current density to be applied at the electrode interface and to control surface properties of the composite coatings. Sonication added to this method increased surface smoothness and decreased the residual stresses of the electrode. The best performance in the oxygen evolution studies showed an electrode prepared by the sono-assisted pulse Molecules 2017, 22, 216 12 of 22

Molecules 2017, 22, 216 12 of 23 electrodeposition method. A simplified scheme reflecting the key of sonoelectrodeposition is presented pulse electrodeposition method. A simplified scheme reflecting the key of sonoelectrodeposition is in Figurepresented 11. in Figure 11.

FigureFigure 11. A11. schematicA schematic representation representation of the the synt synthesishesis of ofthe thematerials materials by means by meansof the of the sonoelectrodeposition method. sonoelectrodeposition method. On the other hand, not many examples concerning materials obtained by the Onsonophotodeposition the other hand, not method many examplescould be concerningfound in the materials literature.obtained For example, by the this sonophotodeposition method was methodimplemented could be found and studied in the literature.by Colmenares For example,group. Forthis the methodlast two wasyears implemented they have reported and studied by Colmenarespreparation group. of several For thetitania-based last two photocatalytic years they have systems. reported We will preparation briefly overview of several these works. titania-based The first trial of sonophotodeposition of metal nanoparticles on the surface of a semiconductor photocatalytic systems. We will briefly overview these works. The first trial of sonophotodeposition of concerned palladium on the commercial TiO2 P90 photocatalyst [52] (Table 1, Entry 29). The reaction metal nanoparticlessetup consisted on of the an ultrasonic surface of bath a semiconductor and a 6W Hg lamp concerned (λmax = 254 palladium nm), which on is presented the commercial in Figure TiO 2 P90 photocatalyst12a. In all [52 photocatalyst] (Table1, Entry (0.5 wt%, 29). 1 Thewt%, reaction and 2 wt% setup Pd) palladium consisted was of totally an ultrasonic reduced to bath the metallic and a 6W Hg lamp (λmaxform= although 254 nm), the which air calcination is presented step in was Figure the 12lasta. in In the all photocatalystsynthesis procedure. (0.5 wt%, These 1 results wt%, andof 2 wt% Pd) palladiumsonophotodeposition was totally reducedwere compared to the metallicwith the formtraditional although photodeposition the air calcination where the step palladium was the last in oxide was the only detected form on the surface. Therefore, the crucial role in formation of Pd° was the synthesis procedure. These results of sonophotodeposition were compared with the traditional ascribed in the sonophotodeposition method to sonochemically formed radicals. The authors claimed photodepositionthat these radicals where could the palladium additionally oxide remove was the the oxygen only atoms detected from formthe organometallic on the surface. structure Therefore, of the ◦ crucial rolethe palladium in formation precursor. of Pd As awas result, ascribed the residual in the carbon sonophotodeposition combined with the oxygen method from to the sonochemically air flow formedand radicals. palladium The was authors not oxidized. claimed The that same these semiconductor, radicals could TiO additionally2 P90, and the remove same reaction the oxygen setup atoms from thewere organometallic then used in structurethe synthesis of theof bimetallic palladium samples precursor. Pd-Au/TiO As a2 result,and Pd-Cu/TiO the residual2 reported carbon in the combined next two articles [53,54]. The simultaneous sonophotodeposition of palladium and gold resulted in with the oxygen from the air flow and palladium was not oxidized. The same semiconductor, TiO2 the complete reduction of gold whereas palladium was partially reduced to the metallic form as well P90, andasthe the samePdO form reaction being setupalso detected were then[53] (Table used 1, in Entry the synthesis30). The authors of bimetallic observed samplesthe formation Pd-Au/TiO of 2 and Pd-Cu/TiOrandom alloys2 reported between in the the Pd-Au next nanoparticles two articles as [well53,54 as]. a Thestrong simultaneous metal-support interaction sonophotodeposition effect of palladium(SMSI) andbetween gold these resulted nanoparticles in the and complete TiO2. According reduction to the of goldauthors whereas the formation palladium of SMSI was effect partially reducedcould to the be metallica result of form the asshock well waves as the and PdO interparticle form being collisions also produced detected by [53 cavitation.] (Table1 ,It Entry is 30). The authorsimportant observed to mention the that formation this effect of was random observed alloys only in between the case of the one Pd-Auphotocatalyst nanoparticles with a specific as well as composition of metals (1 wt% Pd50-Au50/TiO2 P90), which means that the amount of the introduced a strong metal-support interaction effect (SMSI) between these nanoparticles and TiO . According metals must be optimized. The SMSI effect had a strong influence on the photocatalytic results,2 in to the authorsterms of thegas formationphase conversion of SMSI of effectmethanol could and beselectivity a result to of methyl the shock formate. waves In contrast, and interparticle the collisionsmonometallic produced 1 bywt% cavitation. Pd/TiO2 P90 Itphotocatalyst is important was to not mention active in the that selective this effect photoreaction was observed towards only in the casemethyl of one formate. photocatalyst Similarly, in with the sonophotodeposit a specific compositionion of palladium of metals and copper, (1 wt% metallic Pd50-Au50/TiO copper and 2 P90), which meanspalladium that as thewell amountas palladium of theoxide introduced were obtained metals [54] (Table must 1, beEntry optimized. 31). The partial The reduction SMSI effect of had a strongpalladium influence was on explained the photocatalytic by the presence results, of copper in termsand the ofretarding gas phase effect conversionthat it could have of methanol on the and total reduction process of Pd. Also the SMSI effect was observed for 1 wt% Pd-Cu(1-1)/TiO2 P90 selectivity to methyl formate. In contrast, the monometallic 1 wt% Pd/TiO P90 photocatalyst was not photocatalyst, which at the same time was the best performing material in the2 gas phase oxidation of active inmethanol. the selective Concluding, photoreaction the addition towards of a second methyl metal, formate. gold or Similarly, copper, to in palladium the sonophotodeposition significantly of palladiumchanged and copper,the reaction metallic route. copper Generally and palladiumworse results as in well this as reaction palladium were oxide obtained were for obtained the [54] (Table1,photocatalysts Entry 31). Theprepared partial by reductionthe photodeposition of palladium method. was In the explained next work by iron the and presence noble metal of copper and the(Pt-Fe retarding and Pd-Fe effect pairs) that were it sonophotodeposited could have on the on the total self-prepared reduction TiO process2/zeolite ofY semiconducting Pd. Also the SMSI material [55] (Table 1, Entry 32). Different forms of deposited metals were determined by their effect was observed for 1 wt% Pd-Cu(1-1)/TiO2 P90 photocatalyst, which at the same time was reduction potentials. Platinum has the largest positive reduction potential among these metals. the best performing material in the gas phase oxidation of methanol. Concluding, the addition of a second metal, gold or copper, to palladium significantly changed the reaction route. Generally worse results in this reaction were obtained for the photocatalysts prepared by the photodeposition method. In the next work iron and noble metal (Pt-Fe and Pd-Fe pairs) were sonophotodeposited on the self-prepared TiO2/zeolite Y semiconducting material [55] (Table1, Entry 32). Different forms of deposited metals were determined by their reduction potentials. Platinum has the largest positive Molecules 2017, 22, 216 13 of 22 reduction potential among these metals. Therefore, Pt2+ was easily reduced to the metallic form in comparisonMolecules 2017 with, 22,Fe 2163+ , which is a stronger reducer and undergoes an easy oxidation during13 of 23 the air calcination step. As a result, mainly Pt◦ and Fe3+ forms were obtained in the Pt-Fe/TiO /zeolite Y Therefore, Pt2+ was easily reduced to the metallic form in comparison with Fe3+, which is a stronger2 2+ photocatalyst.reducer and In undergoes the case ofan theeasy Pd-Fe/TiO oxidation during2/zeolite the air Y photocatalystcalcination step. Pd As aform result, dominated mainly Pt° and over the ◦ Molecules 2017, 223+, 216 13 of 23 Pd andFe3+ alsoforms the were Fe formobtained of iron in wasthe detected.Pt-Fe/TiO2 Palladium/zeolite Y hasphotocatalyst. smaller positive In the reduction case of potentialthe 2+ 3+ thanPd-Fe/TiO platinumTherefore,2/zeolite therefore Pt2+ was Y photocatalysteasily it could reduced be Pd moreto the form metall easily dominatedic oxidizedform in overcomparison during the Pd° thewith and air Fealso3+ calcination., whichthe Fe is forma stronger A of very iron good dispersionwasreducer detected. of platinum and Palladium undergoes nanoparticles hasan easy smaller oxidation withpositive theduring reductio average the airn potentialsizecalcination between than step. platinum 2 As and a result, 3 nmtherefore mainly was obtainedit Pt° could and be using the sonophotodepositionmoreFe3+ easily forms oxidized were obtainedduring method. the in air Thesethe calcination. Pt-Fe/TiO good morphologicalA2/zeolite very good Y photocatalyst. dispersion properties of platinumIn as the well case nanoparticles as theof the formation with the average size between◦ 2 and 32+ nm was obtained using the sonophotodeposition3+ method. of SchottkyPd-Fe/TiO barrier2/zeolite between Y photocatalyst Pt and Pd TiO 2formresulted dominated in better over the activity Pd° and of also this the photocatalyst Fe form of iron in liquid phaseThese phenolwas good detected. degradation. morphological Palladium Thehas properties smaller authors positive as also well observed reductioas the formationn potential that the of than particlesSchottky platinum barrier of therefore deposited between it could metals Pt° be and are in TiOmore2 resulted easily in oxidized better activity during ofthe this air photocatalystcalcination. A veryin liquid good phase dispersion phenol of degradation.platinum nanoparticles The authors close vicinity to TiO2 particles, however formation of any specific structure (e.g., alloys, core-shell) alsowith observed the average that thesize particles between of 2 anddepos 3 itednm wasmetals obtained are in usingclose thevicinity sonophotodeposition to TiO2 particles, method. however was notformationThese confirmed good of any morphological by specific other structure techniques. properties (e.g. asalloys, A well different asco re-shell)the formation reaction was notof setup, Schottky confirmed consisted barrier by other between of an techniques. ultrasonic Pt° and A horn and adifferent sun-imitatingTiO2 resulted reaction in Xenon setup,better activityconsisted lamp (see of thisof Figure an photocatalyst ultrasonic 12b) was horn in liquid checked and phasea sun-imitating in phenol the sonophotodeposition degradation. Xenon lamp The (see authors Figure of iron on the self-prepared12b)also was observed checked TiO that in2/zeolite the the sonophotodeposition particles Y material of deposited [56] ofmetals (Table iron onare1, the Entryin closeself-prepared 33). vicinity Iron to TiO was TiO2/zeolite2 sonophotodeposited particles, Y material however [56] as the Fe(Table3+formationform 1, Entry and of 33). wasany Ironspecific mostly wa sstructure sonophotodeposited located (e.g. in thealloys, bulk co re-shell)as of the the Fe photocatalyst.was3+ form not andconfirmed was Inmostly by contrast, other located techniques. Fe in3+ theiron bulkA surface enrichmentof thedifferent photocatalyst. was reaction observed setup, In whencontrast, consisted an Fe ultrasound-assistedof3+ aniron ultrasonic surface hornenrichment and wet a sun-imitating impregnation was observed Xenon when method lamp an (see wasultrasound- Figure applied for 12b) was checked in the sonophotodeposition of iron on the self-prepared TiO2/zeolite Y material [56] the synthesisassisted wet of impregnation similar Fe/TiO method/zeolite was applied Y system. for the The synthesis authors of similar were lookingFe/TiO2/zeolite for the Y explanationsystem. (Table 1, Entry 33). Iron was sonophotodeposited2 as the Fe3+ form and was mostly located in the bulk The authors were looking for the explanation of this behavior in different ultrasound-operating of this behaviorof the photocatalyst. in different In contrast, ultrasound-operating Fe3+ iron surface zones,enrichment from was inside observed in the when reactor an ultrasound- sonication horn zones, from inside in the reactor sonication horn applied in the sonophotodeposition method, and appliedassisted in the wet sonophotodeposition impregnation method method,was applied and for fromthe synthesis outside of ofsimilar the reactorFe/TiO2/zeolite in the Y ultrasonic system. bath from outside of the reactor in the ultrasonic bath used in the ultrasound-assisted wet impregnation used inThe the authors ultrasound-assisted were looking for wet the impregnation explanation of method.this behavior The in amount different of ultrasound-operating iron on the surface of the method. The amount of iron on the surface of the photocatalyst was directly correlated with the photocatalystzones, from was inside directly in the correlated reactor sonication with the horn results applied of selectivein the sonophotodeposition photo-oxidation method, of benzyl and alcohol resultsfrom of outside selective of the photo-oxidation reactor in the ultrasonic of benzyl bath alcohol used into in the benzaldehyde, ultrasound-assisted which wet were impregnation better for the into benzaldehyde, which were better for the photocatalyst prepared by the sonophotodeposition photocatalystmethod. The prepared amount byof ironthe sonophotodeposition on the surface of the method.photocatalyst A simplified was directly scheme correlated reflecting with the the key method.of sonophotodepositionresults A simplified of selective scheme photo-oxidation is presented reflecting inof theFigurebenzyl key alcohol13. of sonophotodeposition into benzaldehyde, which is presented were better in for Figure the 13. photocatalyst prepared by the sonophotodeposition method. A simplified scheme reflecting the key of sonophotodeposition is presented in Figure 13.

Figure 12. Different reaction setups for the sonophotodeposition synthesis: (a) US bath-UV lamp Figure 12. Different reaction setups for the sonophotodeposition synthesis: (a) US bath-UV lamp setup: setup: (1) batch photoreactor, (2) argon line, (3) 6 W UV lamp, (4) ultrasonic bath, (5) reflux condenser (1) batchFigure photoreactor, 12. Different (2) argonreaction line, setups (3) 6for W the UV sonophotodeposition lamp, (4) ultrasonic synthesis: bath, (5) (a reflux) US bath-UV condenser lamp (6) lamp (6) setup:lamp (1)cooling batch photoreactor, system; (b) (2) US argon horn-Xe line, (3) lamp 6 W UVsetup: lamp, (1) (4) photoreactor,ultrasonic bath, (2) (5) reflux150 W condenser Xe lamp, cooling system; (b) US horn-Xe lamp setup: (1) photoreactor, (2) 150 W Xe lamp, (3) ultrasonic horn, (3) (6)ultrasonic lamp cooling horn, (4) system; magnetic (b) stirrerUS horn-Xe and (5) lampcooling setup: system. (1) photoreactor, (2) 150 W Xe lamp, (4) magnetic(3) ultrasonic stirrer horn, and (5)(4) magnetic cooling system.stirrer and (5) cooling system.

Figure 13. A schematic representation of the synthesis of the materials by means of the Figure 13. A schematic representation of the synthesis of the materials by means of the Figuresonophotodeposition 13. A schematic method. representation of the synthesis of the materials by means of the sonophotodeposition method. sonophotodeposition method.

Molecules 2017, 22, 216 14 of 22

Table 1. Examples of different materials prepared by sonoelectrodeposition and sonophotodeposition methods.

Entry Type of Material Synthesis Setup Characteristics of the Material Application/Test Reaction Ref. Sonoelectrodeposition The activation of glassy carbon electrode in Potential application of PbO as Ultrasonic bath (30 kHz, 100 W), contrast to platinum electrode. This activation 2 PbO /glassy carbon electrode an anode in: electrochemical 1. 2 glassy carbon rod and polyoriented was explained by the formation of surface [16] PbO /Pt electrode degradation, synthesis, batteries, 2 platinum as the working electrodes functional groups, because no change in sensors, but not tested by authors topography of the electrode surface was seen Sonoreactor (20 kHz, 100 W), The influence of ultrasound frequency on the Potential application of PbO as glassy carbon rod as the working kinetics of electrodeposition process of lead 2 an anode in: electrochemical 2. PbO /glassy carbon electrode electrode, platinum wire as the dioxide was registered. The explanation of this [17,18] 2 degradation, synthesis, batteries, counter electrode, calomel phenomenon was found in the increase of sensors, but not tested by authors electrode as the reference OH• generation Ultrasonic horn (20 kHz), or Homogeneous, free from stress and nodules. ultrasonic bath (40 kHz, 100 W), PbO film was obtained on both electrodes. Sonoelectrochemical degradation of PbO /glassy carbon electrode 2 3. 2 plates of graphite or titanium as the A strong improvement in the quality of these perchloroethylene (PCE) in sulfate [25] PbO /Ti electrode 2 working electrodes, copper as the deposits, a lower corrosion rate in the media; electrochemical recovery of zinc counter electrode accelerated test reactions The electrodeposition of Pt was facilitated by Ultrasonic probe (20 kHz), glass Pt/glassy carbon electrode (GC) a decrease in nucleation overpotentials. Potentially as electrodes for PEMFCs and 4. carbon (or carbon gas diffusion [26] Pt/gas diffusion layer (GDL) Formation of larger nanoparticles and their DMFCs, but not tested by the authors layer) as the working electrode agglomerates were observed Ultrasonic bath (45 W), Pt working Platinum layer built of irregular and electrode, glassy carbon counter fragmentized nanoparticles, gathered in Non-enzymatic sensor of 5. Platinum nanoflowers [28] electrode, Ag reference electrode, self-affined larger structures, finally forming hydrogen peroxide constant potential 50 mV hierarchical nanoflowers The nanoplatinum displayed: fractal features, Ultrasonic bath, Pt/Ir electrodes as homogeneous size distribution and very high Non-enzymatic and enzymatic sensors the working electrode, Pt wire as electroactive surface. Formation of stable 6. Nanoplatinum fractal structures for measuring hydrogen peroxide [29] the counter electrode, constant nanostructures were promoted by a high duty and glucose overpotential 10 V cycle (900 mHz) and reduction of amorphous structure due to cavitation effect Ultrasonic bath (40 kHz, Better morphology: a uniform coating with Biomedical application: bioceramic 2.16 W/cm2), carbon fabric as the small crystals and good adhesive strength, 7. CaP/carbon fibers composites used for the reconstruction of [30] working electrode, constant current was obtained under this condition in bone defects density (20 mA/cm2) comparison with a silent mode Molecules 2017, 22, 216 15 of 22

Table 1. Cont.

Entry Type of Material Synthesis Setup Characteristics of the Material Application/Test Reaction Ref. Ultrasonic bath (40 kHz, 2.16 W/cm2), carbon fabric as the Different morphology of the CaP coatings working electrode, platinum plate depends on the current density. More uniform 8. CaP/carbon fibers Biomedical application [31] as the counter electrode, different structures with smaller crystal sizes were current densities: 5, 8, 13, 20, and obtained at higher values of current density 34 mA/cm2 A homogeneous coating with HA crystals Hydroxyapatite (HA)/porous carbon Ultrasonic stirring, porous carbon, Biomedical application: in vitro 3D 9. across external as well as internal surfaces of [32] composite scaffolds constant voltage 3 V culture of osteoblasts the porous carbon scaffold was obtained The most homogeneous coating was obtained Ultrasonic device (25 kHz, 100 W), at 2.4 V and formed an interlocking structure C/C electrode as the cathode, along the depth direction of the coating Biomedical application, especially as 10. CaP-coated C/C composites graphite as the anode, different [33] without any defects or uncovered areas. dental and medical implant materials voltages: 2.0, 2.4, 2.7, and 3.0 V, This resulted in improved adhesive and controlled temp. 50 ± 3 ◦C cohesive strength of the coating

Ultrasonic bath (40 kHz, TiO2 nanotubes were successfully filled with 2.4 kW/m2), TiO NT as the CdS small-sized nanoparticles with more 2 Potential application in photocatalytic working electrode, Pt foil as the homogeneous distribution. A stronger 11. CdS/TiO NT reactions, but not performed by [34] 2 counter electrode, constant current photocurrent and extended photoresponse to the authors density (5 mA/cm2), constant the visible light were observed for temperature 50 ◦C such composites Ultrasonic probe (20 kHz, 20% A maximum value of compressive residual output), graphite electrode as the stress in the Cu films was registered at 5 ◦C. cathode, Pt electrode as the anode, This result has a direct influence on the Potential application in electronic 12. Cu/Graphite Ag electrode as the reference [35] mechanical properties of the film, as the industry, but not tested by the authors electrode, different set of maximum hardness and elasticity occurred temperatures: 25, 20, 15, 10, also at the lowest deposition temperature and 5 ◦C Ultrasonic bath (30 kHz, 60 W); Cleaner nanorange deposits of copper were graphite electrode as the cathode, obtained under sonication. Different copper electrode as the anode, morphology of Cu films was registered at Potential application in electronic 13. Cu/Graphite calomel electrode as the reference; different deposition temperatures: from [36] industry, but not tested by the authors temperatures selected for this inhomogeneously deposited distorted grains experiment were as following: 25, at 25 ◦C to uniform coatings with fine grains 19.5, −1 and −3 ◦C at −3 ◦C Molecules 2017, 22, 216 16 of 22

Table 1. Cont.

Entry Type of Material Synthesis Setup Characteristics of the Material Application/Test Reaction Ref. With the increasing ultrasound amplitude the Ultrasonic horn (20 kHz, 130 W) Electrocatalytic reduction of H O . Poly(pyrrole)/Prussian blue morphology of the film changed from large 2 2 14. with different amplitudes: 20%, Potential application in electrocatalysis [37] (PB) nanocomposite aggregates to small particles homogeneously 40%, and 60%; ITO electrodes (sensors/biosensors) distributed over the electrode surface Different morphology of the films obtained Ultrasonic horn (20 kHz, 130 W) under silent and sonochemical conditions Potential application as electrochemical Poly(pyrrole)/dodecylbenzenesulphonate 15. with different amplitudes: 20%, reflected in a distinct voltammetric behavior of based devices: sensors, biosensors [38] (DBS) film 40%, and 60%; platinum electrode electrodes. Diminished the charge-transfer and supercapacitors resistance of the films An ordering of Co-Pt phase, hard magnetic Pulse mode operating ultrasonic properties and formation of metallic Potential magnetic application horn acted as the cathode and 16. Co-Pt NPs core-carbon onion shell structure after (e.g., ultrahigh-density magnetic storage [39] ultrasound emitter, platinum plate sonoelectrodeposition with annealing in media), but not tested by the authors as the counter electrode CO atmosphere Pulse mode operating ultrasonic Improvement of magnetic properties and Potential magnetic application horn acted as the cathode and ordering of crystal structure of FePt were 17. FePt NPs (e.g., ultrahigh-density magnetic storage [41] ultrasound emitter, platinum plate obtained when sonoelectrodeposition was media), but not tested by the authors as the counter electrode followed by annealing at high temp Pulse mode operating ultrasonic Sonoelectrodeposition with the following Potential magnetic application horn acted as the cathode and annealing at high temp. resulted in formation 18. FePd NPs (e.g., ultrahigh-density magnetic storage [40] ultrasound emitter, platinum plate of the ordered L1 crystal structure and hard 0 media), but not tested by the authors as the counter electrode magnetic properties of FePd NPs Ultrasonic power (0–160 W), nickel Potential application in plate as anode, polished mild steel Uniform, compact coating with a fine grains 19. Ni-Co/Al O automobile/aerospace industry, but not [42] 2 3 sheet as cathode, under pulse and enhanced mechanical properties tested by the authors reverse current Uniform dispersion of nano-alumina in the Ultrasonic horn (20 kHz, 150 W) Zn-Ni matrix. Different composition of the with ultrasonic power applied 0.7 Potential application as 20. Zn-Ni-Al O composite layers: the outermost layer consists [43] 2 3 W/cm2, Zn plate as the anode, Cu anti-corrosion coatings of Al O and Zn(OH) while transitional layer as the cathode 2 3 2 contains Al2O3, ZnO, Zn, and Ni Increased content and more uniform Ultrasonic horn (20 kHz, 150 W) dispersion of nano-alumina particles resulted different ultrasonic power applied Potential application as 21. Zn-Ni-Al O in improved anticorrosion property and [44] 2 3 (from 0 W/cm2 to 1.2 W/cm2), anti-corrosion coatings hardness of the composite coating Zn plate as the anode (0.7 W/cm2) Molecules 2017, 22, 216 17 of 22

Table 1. Cont.

Entry Type of Material Synthesis Setup Characteristics of the Material Application/Test Reaction Ref. Shaped silver NPs were obtained: spheres Ultrasonic bath (20 kHz, 100 W), with a diameter about 30 nm, wires with Potential application in microelectronics, stainless steel as a the cathode, 22. Ag NPs a diameter 30 nm and length 200–900 nm and optical, electronics, magnetic devices, [45] Ru-Ti alloy as a the counter dendrites, formed with increasing but not tested by the authors electrode, controlled-current 60 mA concentration of silver solution Ag NPs with the size of 4–30 nm dispersed in Sonicator working in a pulse mode, a non-toxic solution due to the use of silver Antibacterial activity against 23. Ag NPs loaded on active carbon silver plate used as the cathode, plate as a source of silver ions. In the next step [46] Escherichia coli platinum plate as the anode Ag NPs were loaded on the surface of active carbon Special size, shape and structure of nanorods Au nanorods deposited on gold surface Ultrasonic bath (45 W) and 24. were obtained: a width of 80–120 nm, a length Nitrofurazone sensor [47] (Au-Au NR) working Au electrode of 140–370 nm, and an aspect ratio of 1.6–3.5 Ultrasonic horn with titanium probe used as the working Cu core-Ag shell structure (7 nm diameter Bactericidal properties against electrode working in a pulse mode; of NPs) obtained by combination of 25. Cu-Ag NPs Staphylococus aureus and [48] copper rod as the counter electrode, sonoelectrodeposition for the inner core and Escherichia coli bacteria saturated mercury sulfate as the galvanic replacement reaction for outer shell reference electrode Process efficiency decreases with increasing Ultrasonic horn with titanium temperature of the electrolyte. Structural and Potential technological application probe used as the working morphological features of the NPs are not (good mechanical, anti-corrosive and 26. Fe-Cr alloy NPs electrode working in a pulse mode [49] influenced by the synthesis temperature. The water-resistant properties), but not tested (20 kHz); platinum net used as the crystalline structure of NPs depends on the by the authors counter electrode electrolyte’s composition Ultrasonic homogenizer (20 kHz), Reduced defects, including cracks in the Potential industrial and chemical 27. Iridium NPs on a copper plate copper plate as the cathode, iridium deposits. Accelerated rate of application (as an inert material), but not [50] platinum plate as the anode iridium deposition tested by the authors The smallest size of deposit particles (17 nm), Ultrasound irradiation of 20 kHz uniform coatings in fine-grained structures of at different current densities, pulse the alloy, better surface morphology, the Oxygen evolution reaction (OER) in 28. NiZnS alloy electrodeposition at various duty highest surface area, the highest exchange [51] alkaline media cycles at 10 Hz; nickel current density (8.25 × 10−3 A/cm2) and high mesh electrode current density (0.42 A/cm2) were achieved in pulse sonoelectrodeposited electrodes Molecules 2017, 22, 216 18 of 22

Table 1. Cont.

Entry Type of Material Synthesis Setup Characteristics of the Material Application/Test Reaction Ref. Sonophotodeposition Total reduction of palladium, despite the air calcination step. In contrast, surface PdO Ultrasonic bath and 6 W Hg lamp Gas phase photocatalytic degradation of 29. Pd/TiO P90 forms were detected in the material prepared [52] 2 (λ = 254 nm) methanol max by pure photodeposition. This confirmed the role of sonication in the reduction process Formation of random alloys between Pd-Au Ultrasonic bath and 6 W Hg lamp NPs and SMSI effect between NPs and TiO2 Gas phase selective photocatalytic 30. Pd-Au/TiO2P90 [53] (λmax = 254 nm) for one specified composition of metals: 1 wt% oxidation of methanol to methyl formate. Pd50-Au50/TiO2 P90

SMSI effect between Pd-Cu NPs and TiO2 for Ultrasonic bath and 6 W Hg lamp one specified composition of metals: 1 wt% Gas phase selective photocatalytic 31. Pd-Cu/TiO2P90 [54] (λmax = 254 nm) Pd-Cu(1-1)/TiO2 P90. Retarding effect of Cu oxidation of methanol to methyl formate on total reduction of Pd ◦ 3+ Mainly Pt and Fe in Pt-Fe/TiO2/Ze and Pd2+ and Fe3+ in Pd-Fe/TiO /Ze were formed Pd-Fe/TiO /Zeolite Ultrasonic bath and 6 W Hg lamp 2 Liquid-phase photocatalytic oxidation of 32. 2 (reduction potentials dependency). A very [55] YPt-Fe/TiO /Zeolite Y (λ = 254 nm) phenol under UV lamp 2 max good dispersion and control over the particle size in the case of Pt nanoparticles Ultrasonic horn (20 kHz, 700 W, Liquid-phase selective photocatalytic 4–5 nm sized Fe3+ NPs mainly located in the 25% of amplitude) and oxidation of benzyl alcohol into 33. Fe/TiO /Zeolite Y bulk of the material due to the physical effect [56] 2 sun-imitating Xenon lamp benzaldehyde in acetonitrile under of ultrasound (240–2000 nm) UV-Vis irradiation Molecules 2017, 22, 216 19 of 22 Molecules 2017, 22, 216 20 of 23

4. Final Remarks 4. Final Remarks A comparisonA comparison between between the mechanism the mechanism of sonoelectro- of sonoelectro- and sonophotodeposition and sonophotodeposition is schematically is presentedschematically in Figure presented 14. The in chemistryFigure 14. ofThe these chemistry processes of these is totallyprocesses different is totally (electrochemical different reactions(electrochemical vs. photoexcitation), reactions vs. howeverphotoexcitation), their synergism however their with synergism ultrasound with ultrasound is mainly basedis mainly on the cavitationbased processon the andcavitation within process that the and enhanced within massthat transfer.the enhanced In the mass case oftransfer. sonoelectrodeposition In the case of the enhancedsonoelectrodeposition mass transfer is the usually enhanced seen mass as the transfer increase is usually of electrochemical seen as the increase current of electrochemical or as the increased currentcurrent pulses, or as depending the increased on current the type pulses, of physical depending effect. on Suchthe type activation of physical of effect. electrodes Such resultsactivation mainly in betterof electrodes mechanical results properties mainly ofin thebetter deposits mechanical and electrocatalyticproperties of the performance. deposits and Onelectrocatalytic the other hand, performance. On the other hand, in sonophotodeposition it influences mainly the transfer of in sonophotodeposition it influences mainly the transfer of photoexcited states. This is mostly reflected photoexcited states. This is mostly reflected in the enhanced photochemical reaction rates, but can in the enhanced photochemical reaction rates, but can also end in a modified reaction pathway. also end in a modified reaction pathway.

FigureFigure 14. 14. SchematicSchematic representationrepresentation summarizing summarizing both both (1) (1)sonoelectrodeposition sonoelectrodeposition and and (2) sonophotodeposition processes. (2) sonophotodeposition processes. The variety of the materials obtained by sonolectrodeposition and sonophotodeposition Themethods variety is collected of the materials in Table obtained1. The cited by examples sonolectrodeposition prove that theand combination sonophotodeposition of sonication with methods is collectedelectrodeposition in Table has1. already The citedbrought examples a new strategy prove for thatthe synthesis the combination of nanomaterials. of sonication On the other with electrodepositionhand, not many has examples already of combination brought a new between strategy sonication for the and synthesisphotodeposition of nanomaterials. leave a free space On the otherfor hand, future not research many examplesin this area. of As combination has been mentioned between in sonication the introductory and photodeposition part, this short leavereview a free spacecovers for future a very research specific in topic this and area. discusses As has beenthe syne mentionedrgy of “sonophoto in the introductory and sonoelectro” part, this only short in the review field of the synthesis of materials. However, there are different applications of such synergy described covers a very specific topic and discusses the synergy of “sonophoto and sonoelectro” only in the field in the literature. For instance, the combination of ultrasound and light in homogeneous and of theheterogeneous synthesis of materials.liquid systems, However, the influence there are of ultr differentasound applications on photocatalytic of such decomposition synergy described reactions in the literature.or excitation For instance, of solutes the by combination sonoluminescence of ultrasound can be found and in light the works in homogeneous of Rosenthal andet al. heterogeneous [6], Toma liquidet systems,al. [24] or Gogate the influence [57]. A wide of ultrasound range of application on photocatalytic of sonoelectrochemistry decomposition was reviewed reactions by or Garcia excitation of soluteset al. by[7] sonoluminescenceand references therein. can For be foundinstance, in sonoelectroanalysis the works of Rosenthal [20,58,59], et al. sonoelectrochemical [6], Toma et al. [24 ] or Gogateenvironmental [57]. A wide remediation range of application [57,60], or sonoelectroche of sonoelectrochemistrymistry in the wassynthesis reviewed of nanomaterials by Garcia et[61] al. are [7] and referencescurrently therein. very active For instance, research areas. sonoelectroanalysis [20,58,59], sonoelectrochemical environmental remediationAcknowledgments: [57,60], or J.C. sonoelectrochemistry Colmenares is very grateful in thefor the synthesis support from of nanomaterials the National Science [61 ]Centre are currently in Poland very activewithin research Sonata areas. Bis Project No. 2015/18/E/ST5/00306. Agnieszka Magdziarz wants to thank the National Science Centre (NCN) in Poland for the support within the research project DEC-2013/11/N/ST5/01923.

Acknowledgments:Conflicts of Interest:J.C. ColmenaresThe authors declare is very no grateful conflict forof interest. the support The founding from the sponsors National had Science no role in Centre the design in Poland withinof Sonata the study; Bis Projectin the collection, No. 2015/18/E/ST5/00306. analyses, or interpretation Agnieszka of data; Magdziarz in the writing wants of the to thankmanuscript, the National and in the Science Centre (NCN) in Poland for the support within the research project DEC-2013/11/N/ST5/01923. decision to publish the results. Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results. Molecules 2017, 22, 216 20 of 22

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