Effect of Alkali Metal Hydroxides on the Morphological Development

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RESEARCH ARTICLE DSpace@IZTECH Institutional Repository provided by DSpace@IZTECH Institutional 2 1 was ions 2 − 3 Journal of ions were − 3 Vol.10, 1–13, 2010 ∗ Li, Na, K). ions act as both capping = nanostructures was inves- Nanoscience and Nanotechnology 2 − 3 zmir, Turkey ˙ I It was claimed that the crys- 16 They reported that the synthesized 17 C, well-deﬁned nanocubes were reported the synthesis of cube-shaped CeO 15 , and Mustafa M. Demir ∗ studied by Li W–H et al. under hydrothermal conditions.When NO tallites synthesized in anlarger acidic and hydrothermal more medium monodisperse are a than neutral the or onesanions alkaline produced of medium.The cerium in source effect on CeO of the counter- present in the solution, the dissolution-recrystallizationcess pro- was largely improved.NO tigated by Hu et al. nanorods converted into cubes by addition of NO starting from cerium(III)temperatures nitrate over 24 and h.The[NaOH] NaOH authors on studied at the the different cubesticles effect and increased of found as thateffect the the of concentration size pH of was on the the increased.The par- crystallization of nanosized CeO ceria particles.As a wet-chemical technique, themal hydrother- process hasmorphology attracted can a readily be lot producedtrolling of at high attention parameters purity since by such con- perature, desired as concentration, reaction and time,Yang type et reaction of al. tem- reactant.Previously, 1533-4880/2010/10/001/013 doi:10.1166/jnn.2010.3608 8 7 9 , ceria) particles were produced via the hydrothermal treat- reverse- 2 11 10 as oxygen promoters and production from fuels. 6 2 and those involving homoge- 13 Under Hydrothermal Conditions Ceria, Crystal Growth, Growth Kinetics, Nanoparticles, Semiconductor. . The latter one is attributed to the trivalency of the cerium ion and appears to be 2 Therefore, synthetic methods have Özlem Kepenekçi, Mehtap Emirdag-Eanes have been used for the preparation of 1–3 14 Izmir Institute of Technology, Department of Chemistry, Gülbahçe köyü, Urla, 35430 Ceria has also received much attention in

sonochemical, 5 Experimental conditions suchParticle as morphology as [MOH], well reactiontal as conditions. size temperature, of While and crystallites rod-shaped was reaction particles precisely time were controlled obtained by were choice at studied. of 120 experimen- sensitive to alltemperature the reduce experimental the conditions intensityemission. studied. of the Both 370 extending nm reaction emission time and increase and the increasing intensity of the 400 nm Keywords: ment of cerium nitrate hexahydrate with various alkali metal hydroxides (MOH: M formed at higherkinetics, temperatures in regardless the ﬁnal of stagesferent of the mechanisms. crystallization, choice Grain showed that boundary of particlewith diffusion MOH. growth an controls rate Examination activation the is energy controlled particle ofenergy by of growth particle two 113.8 of in dif- kj/mol growth the 43.0–150.9 and presenceemissions kj/mol, surface of at diffusion respectively. NaOH 400 In for LiOH nm addition,gap ad and the of KOH 370 with particles CeO nm. the exhibit The activation strong former emission violet originates and from blue excitation of a wide band Nanocrystalline cerium(IV) oxide (CeO Copyright © 2010 AmericanAll Scientiﬁc rights Publishers reserved Printed in the United States of America 12

and as an oxygen pump due to its high oxygen ion 4 Effect of Alkali Metal Hydroxides on the Morphological Several techniques including hydrothermal, Authors to whom correspondence should be addressed. ∗ Development and Optical Properties of Ceria Nanocubes micellular, neous precipitation conductivity. in the area of catalysts for H been developed tocles tailor making the them morphology usefulticular, in of there practical these is applications.Incerium parti- par- oxide an (ceria) increasing that hasfields interest recently such been as in used an incells preparation oxygen various ion of conductor in solid-oxide fuel J. Nanosci. Nanotechnol. 2010, Vol. 10, No. xx Moreover, ceria hasment gained of ultraviolet much (UV) attention absorbentat material, about for its 400 develop- absorption nm being the strongest among all oxides. 1. INTRODUCTION Nanoscale semiconductor particles are ofto great interest their due uniquephysical morphology properties. dependent (size and shape) the area of three-way catalysts View metadata, citation and similar papers at core.ac.uk View metadata, citation RESEARCH ARTICLE .50 ) h opooyo h CeO the of morphology The Å). 0.15406 a ecin eecridota aiu temperatures various at out auto- carried 120 hydrother- from steel cerium were volume.The available stainless reactions of total teflon-lined of mal solution 50% mL to aqueous 23 up clave an a to inside nitrate added rapidly were M (MOH: feto laiMtlHdoie nteMrhlgclDvlpetadOtclProperties Optical and Development Morphological the on Hydroxides Metal Alkali of Effect 2 (Ce(NO hexahydrate the nitrate cerium from g produced 0.5 were of nanocrystals reaction oxide cerium The Method Experimental 2.1. PROCEDURE EXPERIMENTAL 2. CeO Br the as (such of anions formation other several the of during influence oxidizer cubes.The an and agent eepromdo ainCr cis Fluorescence Eclipse Cary Varian a on performed were measurements (PL) samples.Photoluminescence liquid for bandb rigtepeiiae t60 at cen- precipitates were by particles the separated min.The drying and 20 for by water rpm of obtained 6000 were mL at particles 15 trifugation resulting with temperature.The washed room to cool iedfrom1hto24h. 6H ePopwe ifatmtrwt uK Cu by with Philips-X- identified diffractometer a was on powder recorded products perPro (XRD the diffraction powder of X-ray structure crystal The Characterization 2.2. overnight. I ouiiyo egnst h eessfcetfrreactivity for sufficient time. the levels reasonable increase a the in and to oxides reagents metal of of alkalin- solubility of crystallization source the a for as used ity are mineralizers, as known also slc fifraino o fakl ae fetthe affect bases alkali CeO of of how morphology on and information there structure formed.However, of on particles lack the influence of direct is shape a and had size medium the hydrothermal the of ity swl srato ieadrato eprtr nthe on CeO temperature of growth reaction crystal and and time morphology reaction particle KOH) as NaOH, well (LiOH, base as alkali of concentration and type eaue n h rwhkntc a emdltdb the by modulated hydroxides. be metal tem- can of and kinetics type time growth of the particles combination and the a perature; of through shape controlled and be size can the characterization.We that for demonstrated utilized have were spectroscopy photoluminescence (PL) and microscopy spectroscopy, electron UV-vis transmission (HR-TEM), resolution high (SEM), microscopy electron scanning (XRD), diffractometry X-ray iswr esrdwt VVSsetoee (Var- spectrometer UV/VIS wit equipped a 50) with Cary ian measured proper- were optical ties microscope).The microscope F-20 electron Tecnai transmission and (TEM-FEI (SEM-Philips kv) 5 microscope FEG, electron XL-30S scanning by observed − n SO and , 2 )ada1%slto fakl ea hydroxide metal alkali of solution 10% a and O) 4 2 Cto240 = − a loivsiae hwn httebasic- the that showing investigated also was ) i a )Teauosakln solutions alkaline aqueous K).The Na, Li, 18 ihterato ie en var- being times reaction the with C ee eivsiaeteiflec of influence the investigate we Here, ahsse a hnalwdto allowed then was system Each ha1cm 2 atce.uhbases, particles.Such urzcvteholder cuvette quartz 2 aorsaswas nanocrystals aito of radiation 2 nair in C particles. 3 3 − 2 · , upne ndinzdwtrDet h o dispersibility low CeO the of to water.Due deionized particles in the suspended with absorbance done were nm.All measurements 290 fluorometry and at excitation under Spectrometer clyaiae o 0mnbfr measurement. before min 10 for agitated ically ..Srcua n opooia Characterization Morphological and Structural 3.1. DISCUSSION AND RESULT 3. yrtemltetetXRyDfrcinpten fCeO of patterns Diffraction treatment.X-Ray hydrothermal 1. Fig. ple hr h rcro shmgnul dissolved homogenously is reprecipitated. subsequently precursor and the where applied d LiOH. (d) n swl suratdCe(NO unreacted as well as and yteie t240 at synthesized ae rmamtlsl sn nakln ouina an as solution alkaline an using salt source. pre- a metal oxygen precursor on a from a based pared of is mechanism general, dissolution-precipitation in crystallization, Hydrothermal lie httepeusri mrhu,adta crys- that and amorphous, is CeO precursor talline the that claimed httepeusraraycnan h rsaln product crystalline the contains already precursor the that hr eetoso ohCe both of reflections sharp h eetosaewl nee o Ce NaOH. for of indexed well presence are the rep- reflections a in The hydrothermal of prepared to pattern precursor prior XRD mix- resentative RT the during at presents solutions 1(a) begins treatment.Figure reactant process the crystallization of ing amorphous the not is that precursor and the that demonstrated have we fCeO of 2 a -a ifato atr fpeusrpeiiae ro to prior precipitated precursor of pattern Diffraction X-Ray (a) Intensity/a.u aoatce nwtr h ape eeultrason- were samples the water, in nanoparticles 2 2 sotie hnahdohra rcs is process hydrothermal a when obtained is 04 060 50 40 30 particles 19 o 4hi h rsneo b O,()NaOH, (c) KOH, (b) of presence the in h 24 for C .Nnsi aoeho.1,1–13 10, Nanotechnol. Nanosci. J. ntepriua aeo CeO of case particular the In 2 2 O θ 3 n CeO and 15 3 3 oee,i hsstudy, this in However, Ce Ce(NO CeO 2 ♣ O 2 2 3 O Tepeec of presence .The 3 2 ) 3 . lal suggests clearly 6H eeeç tal. et Kepenekçi • 2 O CeO , 2 2 ,itwas (a) (b) (c) (d) powders , 2 2010 , RESEARCH ARTICLE 3 C for particles. The dis- 2 21 SEM images of cerium oxide nanocubes produced at 240 The edge length of the cubes was determined by sta- tributions of edgeexhibit Lorentzian length distributions which are isgrowth.The typical shown edge for length in crystal distributions Figureare with respect given 5.They to in time found Figure to S2.The be edges inwere the of used whereas nanoscale the they range fall particles whenNaOH into the were LiOH was submicron and employed. range KOH when 3.1.2. Concentration The change in concentrationcritical was conditions found for to be the one formation of of the CeO 24 h using LiOH, NaOH, and KOH. Fig. 2. tistical treatment ofand over TEM 100 images particles from using both Image SEM J software. 3 2 20 3 , the particles 2 nanocubes phase was .At 0 .This lends 2 2 to 56 nanocube is single- particles obtained by 2 2 Effect of Alkali Metal Hydroxides on the Morphological Development and Optical Properties 2010 particles was examined.It was 2 C for 24 h the signals of Ce(NO C for 24 h separately with the alkali bases disappeared and the pure CeO 3 O 2 particles prepared in the presence of LiOH, NaOH, phase as reported in the work of Tsunekawa et al. 2 2 Microscopy images, in principal, provide two- at different tilt angles in the range of 0 were influenced significantlyThe by spectra the (in type Fig.1)CeO of labeled MOH as b, used. c, and d refer to the crystalline.The crystalline nature of the resultant CeO detected, regardless of thephology alkali (size base and used.Particleand shape) mor- concentration can of betemperature. MOH, controlled reaction by time, the type and reaction 3.1.1. Type of Alkali Base The effect of alkaliof metal the hydroxides precipitated on CeO the morphology found that the formation and growth of CeO heating at 240 LiOH, NaOH, and KOH.Theuniform particles cubic all shape appearing with to have different on edge theclearly lengths counter-cation observed depend- employed.The for the cubicin relatively shape large the particles is presence produced ofof the NaOH.Figure high 3 resolution presentsarea TEM an images electron as overview diffraction well (SAED)precipitated as patterns the in selected of the theto particles presence the of onesby 8 LiOH precipitated M and byshow KOH MOH.In clear NaOH, have view contrast of sharp the latticeof corners.HRTEM fringes cubes with images 0.22 interplanar prepared nm, spacings revealing that the CeO much support inhas showing a that uniform this cubic representative shape. particle image presents abeam two-dimensional is view.As tilted, theappear.A the electron uniform other cubic shape edges appears of at the 48 structure begin to J. Nanosci. Nanotechnol. 10, 1–13, dimensional views of the specimen.Therefore,ance the of appear- square facesshapes in other TEM than imagesprisms.To cubes may overcome such originate as from thisparticle square was uncertainty, selected plates and a the orrespect electron to square beam representative the was plane tiltedlocated.The upon with which idea the was specimen tocube particle obtain to was be a confident side-view ofshows image the TEM of shape images of the the of particles.Figure the 4 representative CeO cubes was also verifiedtaken by over their SAED an patternbasically area which a of was ring 21similarly and nm XRD can in pattern. be diameter.The pattern indexed to is fluorite structure, Figure 2 shows SEM images of CeO and Ce Kepenekçi et al. (Supplementary Fig.S1).When hydrothermalis treatment applied at 240 and KOH, respectively.All reflectionsbe in indexed the to spectra a81-0792) can face-centered with cubic a structure latticeis parameter (JCPDS slightly of no larger 5.412CeO than Å. the This value value of 5.410 Å for the pure RESEARCH ARTICLE feto laiMtlHdoie nteMrhlgclDvlpetadOtclProperties Optical and Development Morphological the on Hydroxides Metal Alkali of Effect h sdbs a a iH b aH c O.nesso HRTEM show KOH.Insets (c) patterns. NaOH, SAED (b) LiOH, and (a) images was base used The eprtr n ecintm a xda 240 at fixed while was performed time was reaction and concentration temperature MOH of Variation 3. Fig. tr n ihrcnetaindet h sadripening Oswald the to process. due temper- concentration higher higher at and formed be ature of could chemistry cubes larger the used, of MOH aggre- form.Independent powder more the be in to low gated appeared at and small obtained were particles concentrations uniform-shaped.The were and nrae rm01Mt ,CeO M, 8 to M was 0.1 concentration dif- from the of increased MOH.As presence SEM of the shows concentrations in precipitated ferent information) particles the (supporting of images S3 h.Figure 24 4 E mgso CeO of images TEM 22 2 aoue yteie t240 at synthesized nanocubes 2 atce o larger got particles o 4h. 24 for C and C srdsae t120 at out rod-shaped crystals.Starting grad- as cubic-shaped crystals into rod-shaped transformed increased, ually was temperature the h otitnesga 11 sn h cerrequation Scherrer the using (111) (Eq.(1)). signal ceria intense of most analysis of the (FWHM) from full-width-at-half-maximum profiles.Aver- the estimated measuring was XRD by size their by crystallite of evaluated age as broadening size to line crystallite determi- order observing kinetics, particles.For in growth of studied of evolution nation was the growth understand particle fully of kinetics The Kinetics Growth Particle 3.2. only confirmed. not is is a superposition crystals time–temperature temperature-dependent.Thus, of clear morphology also it the but that here, time-dependent say influences given to results that safe the parameter is on effective morphology.Based most particle the is particles the of temperature the 240 fixing moni- at by to reaction process out evolving the carried tor were experiments Time-dependent Time Reaction 3.1.3. ecintmeauei yrtemlsnhsso CeO of synthesis hydrothermal in temperature reaction eaeamxueo o-ieadcbcparticles.Extend- t cubic time product reaction and the hydrothermal rod-like ing the of mixture h, a 1 became after 6.Initially, Figure in lspeae yNO,a 240 parti- at to NaOH, contrast by KOH.In was prepared and experiments cles LiOH both time-dependent for of cubic performed to set converted same were ones.The particles rod-like whereby sition angle. asaepeoiatycb-hpdadfial t240 at finally and cube-shaped predominantly are tals nevl ewe n 4hTeeouino repre- of evolution h.The 24 CeO and sentative 1 between intervals ev glmrto t160 at agglomeration heavy banda 120 at obtained epc oices ntmeaueuigLO sarep- a as LiOH CeO with using size case.Rod-shaped temperature and in resentative morphology increase in to change respect the shows 7 Figure Temperature Reaction shorter 3.1.4. of min 30 at even time. rod-like realized reaction while never KOH and were LiOH particles of presence the in obtained rsn eeaei gemn ihterslsrpre by reported results the we al. with et results agreement Yang in formed.The are are here present cubes uniform well-shaped rg eko h 2 the on the peak of Bragg (FWHM) full-width-at-half-maximum the as defined where stewvlnt fradiation, of wavelength the is 23 15 h uhr eosrtdta oto fthe of control that demonstrated authors The 2 atce rcpttdb aHi shown is NaOH by precipitated particles ih8MNO laibs o time for base alkali NaOH M 8 with C .Nnsi aoeho.1,1–13 10, Nanotechnol. Nanosci. J. o h l he laibases.As alkali three all the for C

o2hfav cl i ain)and radians) (in scale D ,tecytl eoecbcwith cubic become crystals the C, = B 0 cos .hna 200 at C.Then rdtemrhlgcltran- morphological the ored 9

B ,nnszdcbsare cubes nanosized C, 2 aoatce were nanoparticles B stepa width peak the is

eeeç tal. et Kepenekçi B steBragg the is h crys- the C , 2010 (1) C 2 RESEARCH ARTICLE 2 5 (3) (4) (2) .In , the is the T is the t can be K Q n is the average n o for a given D t ; t t is the gas constant and Q Q for a given time R remains the same.Thus, Kt .The value of RT RT − − ° For the thermally activated = Q 38 /T n 24 o versus In D exp is the grain exponent; exp o o Q/nR n − D K K n − can be found from the slope of the 0; D = = versus 1 n = n , these equations can be simplified as; K t D D o is the pre-exponential constant; 100 nm o ° K 56 D>D is the grain size at time, n D By plotting In The grain-growth dependency on time was evaluated via is the absolute temperature. 100 nm the grain exponent ( grain size at time, rate constant; T and processes ( where slope will beobtained equal to by plottinga In constant temperature range, activation energy of grain growth; hydrothermal synthesis results inbility an of increase precursors and inreactive enhances species the to/from the solu- the diffusion particleing process surface in of thereby larger result- crystals as well. the following equations: ° 29 100 nm ° 48 synthesized using LiOH from different angles proving three dimensional cubic structure of the CeO 2 Effect of Alkali Metal Hydroxides on the Morphological Development and Optical Properties cubes prepared in the pres- 2010 2 100 nm ° 0 C for 24 h. particles.Increasing the temperature of the 2 100 nm Edge length distributions of CeO Representative TEM images of CeO The progressive increase of the crystallite size of cubic ence of MOH at 240 Fig. 5. J. Nanosci. Nanotechnol. 10, 1–13, Fig. 4. nanocrystals. ceria with concentration,mineralizer time, is and temperature shownalkali for in base each Figure in 8.Therole the concentration in reaction of medium theWhen the played ultimate base an concentration sizewith important is high of high enough, chemical the nanocrystals to potential resulting larger can CeO be nanocrystals. synthesized, leading Kepenekçi et al. RESEARCH ARTICLE iHadKHgv mle atce ihhigh with particles smaller gave using KOH synthesized and when LiOH nanoparticles oxide cerium tions, feto laiMtlHdoie nteMrhlgclDvlpetadOtclProperties Optical and Development Morphological the on Hydroxides Metal Alkali of Effect d ,()1 ,()2 .h etn eprtr a 240 was temperature heating h.The 24 (f) h, 16 (e) h, 8 (d) inepoe isbten1–5,wihvre with varies which 6 10–25%, reac- between hydrothermal lies the are of employed yield yield product tion I.The and Table energy, in activation presented rate, growth cle of values low with particles gave large NaOH rather with synthesized nanoparticles ues.However, ln of plot 6. Fig. iesos(delnt n rsalt ie,parti- size), crystallite and length (edge Dimensions eisSMiae fmrhlg vlto fcbcCeO cubic of evolution morphology of images SEM Series D essln versus t Fg9.ae nteecalcula- these on (Fig.9).Based n . .h aeue ooti CeO obtain to used base C.The n val- 2 aoatce ihtesews rlne ecintm a ,()2h c h, 4 (c) h, 2 (b) h, 1 (a) time reaction prolonged stepwise the with nanoparticles fKHNtsrrsnl,Qi ihs o hs particles these presence for the highest is in Q produced surprisingly, particles KOH.Not the of at for yields achieved lowest obtained the is con- here, were presented yield successfully experiments high the is Q.In a low species product.Similarly, reactant to only prod- of high, verted to fraction is Q small reactant when convert a theory, collision to acti- to chemical required the ucts.According in (Q) to proportional yield energy inversely used.Particle vation is base general, in alkali reactions, of type the 2 a NaOH. was .Nnsi aoeho.1,1–13 10, Nanotechnol. Nanosci. J. eeeç tal. et Kepenekçi , 2010 RESEARCH ARTICLE 2 7 At high C for 24 h. 27 Particles 2 C and (d) 240 C, (c) 200 crystals with well-defined shapes 2 C, (b) 160 and MOH.Generally speaking, the growth of 3 3 monomer concentrations, crystalsone direction, grow yielding in rod-shaped particles.The preferentially elongated Submicron-sized CeO nanocubes exposed predominantly thewith truncation {200} of cubic the facets corners exposing the {111} facets. 3.3. Discussion on Formation of CeO (rod-like or cubic)a have been regular carefully(CeNO hydrothermal prepared through reaction taking place between crystals is a non-equilibrium phenomenon.Differentnal exter- conditions may change theand course of effecting the particle crystalgested growth morphology.Previously, Peng that sug- the concentrationgrowth solution of plays existing a monomerevolution key of in role the the in shapes the of determination the resulting and crystals. the change innals the of the intensityrelationship (200) ratio of and of (100) crystallite(200)/(111) the planes.Figure size at 10 diffraction with different shows sig- the totalratio the reaction intensity of times.The ratio (200)/(111) intensity of decreasesKOH when and going NaOH.The fromfaster growth than LiOH rate that to of ofThe the the (100) ratio (200) plane of in planeresulting this the is in reaction nanocubes (200)/(111) process. with plane sharperNaOH (possessing corners.In is the the smallest highest (200)/(111) case ratio), of the for CeO LiOH, 28 27 Effect of Alkali Metal Hydroxides on the Morphological Development and Optical Properties 2010 synthesized using LiOH and the heating temperature was (a) 120 2 submicron particles.The change in curvature 2 SEM images of CeO All the crystallites do not grow to the same size because of the corners of the cubes (Fig.3) can be followed by J. Nanosci. Nanotechnol. 10, 1–13, Measurement of FWHM peak widthof allows the the calculation separationresults distance in between the crystallite ability totallite.The faces.This model intensity ratio the of actual reflections shape(111) from of planes the the were (200) crys- changed and shape with reaction of time ceria causinggrowth to the of the change (111) from planelower occurs polyhedron than because to its that free of cube.The The energy the crystal is changes (200) its planeto shape during hexagon and crystal (truncated chemistry octahedron) from growth. cubic and rod-like finally CeO to truncated as estimated from Eq.(4).However,the using LiOH highest permits yieldlowest) Q. due to its comparablythe lower internal (in crystallites fact neighboring are crystallites.They restricted grow to by fillOn all the the vacant presence voids. other of hand,thus leaving surface them crystallites free have toface grow and less reach away restraint the from maximum the sizeof particle achievable reaction sur- for conditions.The a given growth set be of observed different planes by can comparingreflections in the the intensity X-ray diffractograms.Here, ofcrystallites the corresponding growth is of not symmetrical,two because prominent growth planes, rate {200} of and the {111} are not equal. Fig. 7. Kepenekçi et al. RESEARCH ARTICLE feto laiMtlHdoie nteMrhlgclDvlpetadOtclProperties Optical and Development Morphological the on Hydroxides Metal Alkali of Effect etaino ooe stehgetdrn h course the during Ce(OH) highest con- precipitation.Anisotropic the the particle is sug- reaction, of monomer this the of of with beginning centration consistent the lowered.The were model.At if obtained is gested have shapes solution we spherical in results more concentration into monomer transformed the be can shape 8. Fig. omdoc h Ce the once formed tion.NO 8 rsalt ie ae n()cnetain b ecintm,ad()rato temperature. reaction (c) and time, reaction (b) concentration, (a) on based sizes Crystallite 3 − oscnpsil xdz eim(I)in in ions (III) cerium oxidize possibly can ions 3 + osaemxdwt h O solu- MOH the with mixed are ions 3 uliare nuclei h ytmt CeO to system the icn ntblt odsouin hstedsouinmight dissolution the sig- thus impart dissolution, to rods instability the nificant of this points triggers end medium process.The alkali equilibrium an of character strong ated.The setrtoo bu 0wr banda 120 at obtained were 10 about of ratio aspect rwho h osA ihrrato eprtr t 160– and (to temperature nucleation reaction 240 higher by rods.At depleted the of is growth monomer of concentration ) h islto/ersalzto rcs siniti- is process dissolution/recrystallization the C), .Nnsi aoeho.1,1–13 10, Nanotechnol. Nanosci. J. 2 species. 17 o-ieprilswt an with particles Rod-like eeeç tal. et Kepenekçi C.The , 2010 RESEARCH ARTICLE 9 , quite small compared for KOH and LiOH are 48 n crystals.These are aggre- − 2 10 So, the dissolution of parti- × 2 Reaction time 16 . = 10 − 4 10 × 8 1 NaOH LiOH KOH (Ce(OH) = sp K Intensity ratio of (200)/(100) of the powders prepared in the 01020

(AgCl)

0.9 0.8 0.7 0.6 0.5 0.4 (200)/(111) intensity ratio intensity (200)/(111) Kinetics of particle growth was systematically studied sp to frequently observed precipitatedK products, for example gation and Ostwald ripening.In theber former, of a growing certain particles num- randomlylarge adhere particle together aggregates to form scope with images nonuniform of shape.Micro- shape; particles thus the clearly mechanism of showlatter, aggregation is Ostwald uniform ruled out.The ripening, particle namically can driven spontaneous be process definedticles in dissolve, as which reduce small in a par- sizefrom thermody- and small disappear.Atoms detach particlescles and causing diffuse large particles to toparticles.From grow attach examination at to of the expense the largeproduct, of formed parti- small information particles can in be the to obtained morphology, by but only notticles.Therefore, with about it regard the development is of hardnism the of to par- particles elucidate from aHowever, only a growth the comparision mecha- final offrom shape physical microscopy and dimensions structure. and obtained may line give a broadening hinttallite in dimension about XRD was the comparable patterns cles growth to mechanism.The observed the in crys- size microscopyLiOH of and for the KOH.The the parti- values ones13.1 of and prepared 8.4, using respectively,surface and diffusion.This associated mechanism with involvessmall growth dissolution particles.The by of solubility product ofitate the is, initial precip- cles, and therefore,the the particles rate remain smaller.Inobtained of contrast, in growth for the will thecles presence be particles of observed low NaOH, by and three the microscopy size times showed of larger themindicate.The the than to particles parti- the be grew results nearly by from lattice line or grain-boundary broadening Fig. 10. presence of MOH. for each MOH.Different growth kineticsmechanisms as well were as found.There growth aredescribing two the possible growth ways of of CeO e No 28 Yield, % particles 2 d rods were con- particles. 2 2 C within 24 h of reac- Q (kJ/mol) c Effect of Alkali Metal Hydroxides on the Morphological Development and Optical Properties 2010 for CeO t polyhedron particles with value) 2 n ( Eventually, CeO b 17 (nm) particles in terms of size and shape. as a function of In 2 D a Generally, the face with the higher density 28 Mean of Average Dimensions of particles obtained at 240 Plot of In According to classical theories of crystallization, the Derived from Eq.(4). From TEM images. Line broadening of XRD signals as calculated via Eq.(1). Derived from Eq.(2). Gravimetry. additional surfactant was used intion our mixture case; contains rather, the onlyhydrothermal reac- reactants method.Consequently, required this for reactionreally a offers convenient a simple and suitable pathwell-defined for CeO mass production of shape-controlled growth ofrelative crystals specific is surface determinedthe energy by of crystal. the each face or facets of with {200} facets.The entirebased on morphological the development results obtaineddiffraction from microscopy was and summarized detailed graphically as in Scheme 1. verted into well-defined CeO Type of edgealkali length crystallitebase distribution Particle size (nm) growth rate {200} and {111} facets.The growthto rate of be {200} appeared higherwith than respect that to {111} of led {111}.Enlargement to of cube-shaped {200} CeO d e J. Nanosci. Nanotechnol. 10, 1–13, LiOHNaOHKOH 41a 158b 56c 22 54 36 8.6 3.7 13.1 43.0 113.8 150.9 10.2 24.7 9.3 Table I. Fig. 9. occur at both end points. Kepenekçi et al. of surface atoms ising blocked the by crystal a growth ofalong surfactant colloidal adsorbed this crystals, dur- and facet the is growth therefore considerably restricted. tion time in theenergy, and presence yield of of 8 hydrothermal M synthesis. MOH, particle growth rate, activation RESEARCH ARTICLE 9 m()Ro eprtr ursec pcr fteCeO the of spectra fluorescence temperature Room nm.(d) 290 feto laiMtlHdoie nteMrhlgclDvlpetadOtclProperties Optical and Development Morphological the on Hydroxides Metal Alkali of Effect 10 11. Fig. 1. Scheme c 160 (c) fLO,NO n O.h ocnrto fdsesos1 dispersions of concentration KOH.The and NaOH LiOH, of pcr fteCeO the of spectra ne stebn-a ausfrbss()Ro eprtr ursec pcr fteCeO the of spectra fluorescence temperature Room bases.(b) for values band-gap the is Inset ,()120 (d) C, a h VVSasrac pcrmo CeO of spectrum absorbance UV-VIS The (a) rpia btatt xantedvlpetpril opooydrn yrtemlsnhsso CeO of synthesis hydrothermal during morphology particle development the expain to abstract Graphical 2 aoatce iprin ihdfeetrato ie a 4h b 6h c ,()4h e ,()1hEctto wavelength h.Excitation 1 (f) h, 2 (e) h, 4 (d) h, 8 (c) h, 16 (b) h, 24 (a) times reaction different with dispersions nanoparticles .xiainwvlnt 9 nm. 290 wavelength C.Excitation 2 aoatce banda 240 at obtained nanoparticles 2 05 aoatce iprin ihdfeetrato eprtrs()240 (a) temperatures reaction different with dispersions nanoparticles × 10 − 3 n h xie aeegh20n.c omtmeauefluorescence temperature Room nm.(c) 290 wavelength excited the and M o 4hTecnetaino iprin 1 dispersions of concentration h.The 24 for C 2 aoatce iprin ihdfeetakl bases alkali different with dispersions nanoparticles .Nnsi aoeho.1,1–13 10, Nanotechnol. Nanosci. J. 2 cubes. eeeç tal. et Kepenekçi ,()200 (b) C, 05 × 10 , 2010 − 3 M. C, RESEARCH ARTICLE 11 C forces the particles C, the particles have a rod-like SEM images of cerium oxide nanocubes produced prior to particles.At 120 2 to take on aprocess.Edge cubic length shape via is a highlyprecision dissolution-recrystallization tailorable through with choice remarkable reaction of time, alkali reaction baseMOH.In temperature, and general, and by all concentration adjusting similar of alkali behavior metals in employedlogical terms here development of show and theirdiffer optical in influence their features.However, affect on they onnism particle morpho- underlying growth kinetics; this the growth mecha- seemsThe to be particles cation-dependent. grow throughKOH and surface LiOH diffusion whereas whenboundary they using or follow lattice-diffusion growth processpresence via when of a formed grain- NaOH.A inalkali- more the and as detailed well studyticle as alkaline-earth morphology including bases and all that growth control kinetics par- is underway. morphology.Increasing the temperaturemedium of to between the 160 reaction and 240 SUPPLEMENTARY FIGURES Fig. S1. hydrothermal treatment at room temperature. 4. CONCLUSION We have reported hydrothermal synthesisCeO of monodisperse phase.Increasing temperature favors thetal structure hexagonal over the crys- face-centered cubicthe structure although latter isthe thermodynamically tendency towards more thehigher stable.Therefore, temperature face-centered subsequently cubic leads structurenumber to a at of decrease defect inresult the sites is at obtained higherreaction from temperatures.A the times similar particles whenAs obtained the the at reaction temperature different time wasnal is at held extended, the 370 constant. intensitytion nm temperature of and diminishes this extending reaction gradually.By sig- timeprocess increasing the nucleation is reac- improved,crystal leading growth and thus to allowing the greaterfavorable particles lattice to completeness find (i.e. a of the more qualityimproved).Therefore, of this the result resultant suggests370 crystals that nm is emission can at be a result of existence of Ce(III). n C in + 3 nano- 2 33 32 . 30 + 3. 4 31 = particles precipitated Effect of Alkali Metal Hydroxides on the Morphological Development and Optical Properties n 2 2010 Zhang et al.found the Nanoparticles 2 29 2. = n O.The particle suspensions were grain-growth, obtained by homo- 2 2 nanoparticles as measured at an excitation wave- 2 Figure 11 presents normalized emission of the particles The chemical nature of mineralizers influences the for 24 h.The concentration of1.05 the mM. dispersive A solutions well-defined was 315 clear nm absorption peak was locatedeach observed at of for these the bases.Thefrom bandgap particles energies precipitated the were from estimated cut-offwhere the wavelength tangent as crossedabsorption the peaks measured wavelength were axis.Measured 307 atresponding nm, the to 314 nm, bandgaps point and offor 327 3.38 LiOH, nm, eV, NaOH, cor- 3.17 eV, andvalues and KOH, are 2.98 respectively.These consistent eV bandgap with the literature. the crystal structure of the matrix of Ce in the presence oftimes, MOH and at various concentrations temperatures,sion were of reaction the recorded particles for in H the suspen- particles synthesized in the presence of MOH at 240 Figure 11 shows the absorption spectra of CeO geneous precipitation, as grain-growth of nanoparticles, astional prepared mixed-oxide by method the to conven- have length of 290at nm 400 (4.28 nm eV), (3.10nal eV) show can and two be 370 attributed emission to nmwhereas the signals (3.27 the band-edge eV). origin exciton The annihilation, of firstOne the sig- of second the signal common istion approaches open of to for this debate. the signal possible is explana- ascribed to the presence of Ce stable for the timetionally, independent required measurements for the ofshowed measurements.Addi- comparable solid-state results spectra andour confirmed experimental the method.The validityCeO of emission spectra of the J. Nanosci. Nanotechnol. 10, 1–13, precipitated from thereaction hydrothermal precursor times at(Fig.11(d)).For different (Fig.11(c)) all and samples,at the different 400 intensity temperatures of nmture emissions increases.However, and the relative 370ond intensity emission nm of with the respect isfrom sec- to excitation enhanced the annihilation emission asCe(III) which is defect resulted the states remarkably are tempera- considered reduced.The to be hexagonal crystal structural arrangementConsiderable of research atoms hascence during been properties crystallization. focused ofmay on nanomaterials reveal the the because fluores- from presence the fluorescence synthesis of process.Incence crystalline this emission context, defects spectra photolumines- of resulting pure CeO value of growth rate isics 3.7. in Studies on theChen grain-growth literature kinet- found point pure CeO out similar results.Chen and 3.4. Optical Properties of CeO Kepenekçi et al. diffusion of three (3)found individual to be growing larger nuclei comparedand and to NaOH the were ones under prepared identical by LiOH preparation conditions.The RESEARCH ARTICLE feto laiMtlHdoie nteMrhlgclDvlpetadOtclProperties Optical and Development Morphological the on Hydroxides Metal Alkali of Effect 12 S3. Fig. S2. Fig. E mgso eimoienncbspoue t240 at produced nanocubes oxide cerium of images SEM CeO of distribution size Particle 0.1 MLiOH 0.1 MNaOH 0.1 MKOH

Counts 20 40 0 53 45 30 15 Particle size(nm) 0 m500nm 500 nm 2 200 nm aoatce npeec f()LO,()NO,()KOH. (c) NaOH, (b) LiOH, (a) of presence in nanoparticles

Counts 10 20 30 0 5 MLiOH 5 MNaOH 5 MKOH 04 06 70 60 50 40 30 24 h:40,5nm 16 h:39nm 8 h:36,5nm 4 h:32,4nm 2 h:30,5nm 1 h:28,3nm Particle size/nm o 4hTecnetain n oto h ae r ie nteimages. the in given are bases the of sort and concentrations h.The 24 for C

Counts 10 20 0 0 0 300 200 100 0 200 nm 24 h:56nm 16 h:43,1nm 8 h:42nm 4 h:39,5nm 2 h:37,8nm 1 h:34,9nm Particle size/nm .Nnsi aoeho.1,1–13 10, Nanotechnol. Nanosci. J. 8 MLiOH 8 MKOH 8 MNaOH 24 h:158nm 16 h:133,5nm 8 h:88,7nm 4 h:83,1nm 2 h:73,7nm 1 h:64,8nm eeeç tal. et Kepenekçi , 2010 RESEARCH ARTICLE . . . . 13 . . . (2002) (1997) (2007) (2006) 74, 598 38, 439 22, 247 J. Power . J. Colloid (1996) Nanotech- (2003) 45, 2 Catal. Today Semiconduc- (2006) Chem. Mater. Chem. Mater. . 57, 507 53, 117 93, 309 (1995) J. Phys. Chem. C Appl. Phys. Lett. J. Am. Ceram. Soc. 79, 1793 . . (2004) 289, 351 . 107, 13563 J. Rare Earths . 30, 2171 (2002) Mater. Lett. (2005) . J. Am. Ceram. Soc. (2005) 58, 390 (1997) . . Solid State Ionics Angew. Chem. Int. Ed. (1999) 4, 3794 . 16, 1960 (2003) . . J. Mater. Sci. (2007) J. Am. Ceram. Soc. J. Cryst. Growth 80, 2649 109, 24380 J. Phys. Chem. B Mater. Lett. . (2000) . (2002) (2003) 15, 459 . (2007) . Progr. Cryst. Growth Char. Mater. 90, 62510 (1998) 85, 3440 . . . . Catalysis Reviews-Science and Engineering (2001) Nanotechnology 246, 78 77, 407 (2008) . (2003) (2002) (2002) Adv. Mater. 71, 271 (1997) J. Phys. Chem. B 18, 185606 J. Am. Ceram. Soc. Phys. Chem. Chem. Phys. . . . . Received: 14 June 2010.Accepted: 15 June 2010. 35, 1378 (1999) L.Yin, Y.Wang, G.Pang, Y.Koltypin, and A.Gedanken, Z.F.Ma, G.C.Liang, and J.S.Liang, 9, 2197 Interface Sci. (2004) T.Masui, K.Fujiwara, K.Machida, and G.Adachi, P.L.Chen and I.W.Chen, T.Zhang, P.Hing, H.Huang, and J.Kilner, Z.L.Wang and X.Feng, X.Peng, 15, 2289 M.-S. Tsai and X.-Z. Xiao, M.V.M.Boaro, C.de Leitenburg, G.Dolcetti,Catal. and Today A.Trovarelli, A.Trovarelli, (1996) A.Trovarelli, C.Leitenburg, M.Boaro, and G.Dolcetti, 353 N.Imanaka, M.Masui, H.Hirai, and G.Adachi, K.A.T.Byrappa, H.Mai, L.Sun, Y.Zhang, R.Si,C.Yan, W.Feng, H.Zhang, H.Liu, and S.Sathyamurthy, K.J.Leonard,Paranthaman, R.T.Dabestani, and M.P. E.R.Leite, M.A.L.Nobre, M.Cerqueira,Varela E.Longo, and J.A. H.Wang, J.J.Zhu, J.M.Zhu, X.H.Liao, S.Xu,Chen, T.Ding, and H.Y. 80, 3814 nology N.-C. Wu, E.-W. Shi, Y.-Q. Zheng,85, and 2462 W.-J. Li, S.Tsunekawa, K.Ishikawa, Z.Q.Li, Y.Kawazoe, andPhys. Rev. A.Kasuya, Lett. Public domain software to(National be downloaded Institute from of http://rsb.info.gov/ij Health). R.D.Vengrenovich, Y.V.Gudyma, and S.V.Yarema, tors H.P.Klug and L.E.Alexander, X-rayCrystaline Diffraction Procedures: and For Amorphous(1974) Materials, Wiley & Sons, New York N.B.Kirk and J.V.Wood, X.D.Zhou, W.Huebner, and H.U.Anderson, Z.Yang, K.Zhou, X.Liu, Q.Tian, D.Lu, and S.Yang, Q.Z.F.Wu, P.Xiao, H.Tao, X.Wang, and Z.Hu, G.Philip and W.L.Jessop, Chemical SynthesisFluids, Using Wiley-Vch Verlag Supercritical GmbH J.-S. Lee and S.-C. Choi, 112, 17076 T.K.K.Alston, M.Palin, M.Prica, and P.Windibank, Sources T.U.K.Hibino and Y.Kuwahara, M.B.Fernando and G.P.W Marques, B.Vodungbo, Y.Zheng, F.Vidal, D.Demaille,Appl. and Phys. V.H.Etgens, Lett. (2005) .WJn J.-S.Choi,and J.Cheon, T.-W.Jun, 6. 7. 8. 9. 4. 5. 2. 3. 1. 32. 33. 31. 29. 30. 28. 27. 26. 10. 11. 12. 24. 13. 16. 20. 21. 22. 23. 25. 14. 15. 17. 18. 19. References and Notes was was 2 2 Effect of Alkali Metal Hydroxides on the Morphological Development and Optical Properties 2010 nanoparticles with the stepwise pro- nanoparticles with the stepwise pro- C.The base used to obtain CeO C.The base used to obtain CeO 2 2 This work was supported by XRD patterns of CeO XRD patterns of CeO NaOH. LiOH. longed reaction time (a)The 1 heating h, temperature (b) was 2 240 h, (c) 4 h, (d) 8 h, (e) 16 h, (f) 24 h. longed reaction time (a)The 1 heating h, temperature (b) was 2 240 h, (c) 4 h, (d) 8 h, (e) 16 h, (f) 24 h. J. Nanosci. Nanotechnol. 10, 1–13, the ScientiﬁcTurkey and (grant Technologicaltute no: Research of Council TBAGDr.I.Lieberwirth Technology 108T664) of (2009IYTE26).The of andDr.R.C.Eanes authors MPIP Izmir thank for for Insti- ing his suggestions TEMmanuscript. scientiﬁc during images the and and preparation proofread- of the written Acknowledgments: Fig. S5. Fig. S4. Kepenekçi et al.