Polythiophene Nanocomposites for Photodegradation Applications: Past, Present and Future

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provided by Elsevier - Publisher Connector Journal of Saudi Chemical Society (2015) 19, 494–504

King Saud University Journal of Saudi Chemical Society

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REVIEW ARTICLE Polythiophene nanocomposites for photodegradation applications: Past, present and future

Mohd Omaish Ansari a, Mohammad Mansoob Khan b,*, Sajid Ali Ansari a, Moo Hwan Cho a,*

a School of Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeongbuk 712-749, South Korea b Chemical Sciences, Faculty of Science, Universiti Brunei Darussalam, Jalan Tungku Link, BE 1410, Brunei Darussalam

Received 28 February 2015; revised 9 June 2015; accepted 15 June 2015 Available online 25 June 2015

KEYWORDS Abstract Polythiophene (PTh) has been the subject of considerable interest because of its good Polythiophene; environmental stability, unique redox electrical behavior, stability in doped or neutral states, ease Photocatalysis; of synthesis, and wide range of applications in many fields. Apart from its applications in the elec- Photodegradation; trical or electronic field, PTh has shown promising applications in photocatalytic degradation. The Visible light; fabrication of a catalyst, metal oxides with PTh, extends the absorption range of the modified com- UV irradiation; posite system, thereby enhancing the photocatalytic activity under UV or visible light irradiation. Polythiophene; Substituted PTh, such as alkyl substitution, modifies the electronic properties of the polymer, Nanocomposites thereby enlarging the potential for industrial applications. PTh or substituted PTh when combined with metal, metal oxide or a combination of both, can exhibit tailorable photocatalytic properties. This review focuses on the chemistry of the band gap engineering of PTh or PTh based systems and the mechanism of photocatalytic degradation. The major developments in the field of UV and visible light-assisted photocatalysis are discussed in terms of the parameters that affect the photocatalytic efficiency. On the other hand, some challenges still needs to be investigated experimentally, which are mentioned as the scope for future studies. For simplicity, the review has been classified

Abbreviations: VB, valence band; CB, conduction band; HOMO, highest occupied molecular orbital; LUMO, lowest unoccupied molecular orbital;

UV, ultraviolent; MO, methyl orange; RhB, rhodamine B; RhG, rhodamine 6G; DRS, diffuse reﬂectance spectroscopy; pHPZC, pH at point of zero charge; Pani, polyaniline; PPy, polypyrrole; PTh, polythiophene; PTh-Ac, poly(3-thiopheneacetic acid); POTh, poly(3-octylthiophene-2,5-diyl); P3Th, poly(3-hexylthiophene); PPTh, poly(3,4-propylenedioxythiophene); PFTh, poly(ﬂuorene-co-thiophene); PHTh, poly(3-hexylthiophene-2,5- diyl); PL, photoluminescence; BET, Brunauer–Emmett–Teller; LDHs, layered double hydroxide shells * Corresponding authors at: School of Chemical Engineering, Yeungnam University, Gyeongsan-si, Gyeongbuk 712-749, South Korea. Tel.: +82 53 810 2517; fax: +82 53 810 4631. E-mail addresses: [email protected] (M.M. Khan), [email protected] (M.H. Cho). Peer review under responsibility of King Saud University.

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http://dx.doi.org/10.1016/j.jscs.2015.06.004 1319-6103 ª 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Polythiophene nanocomposites for photodegradation applications 495

under a major subheading depending on the type of composite system used for photocatalysis. ª 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of King Saud University. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Contents

1. Introduction ...... 495 2. Polythiophene ...... 495 2.1. Chemical states and band gap of polythiophene ...... 496 2.2. Chemistry of the photocatalytic activity of polythiophene/metal–metal oxide composite and UV or visible light activity ...... 497 2.3. Polythiophene composite catalyst used in the field of photodegradation ...... 497 2.4. Substituted polythiophene composite photocatalyst used in the field of photodegradation...... 499 2.5. Multicomponent polythiophene composite catalyst used in the field of photodegradation ...... 500 2.6. Polythiophene based composite for the photocatalytic disinfection of microorganisms ...... 501 3. Summary, prospective and scope for future works ...... 501 4. Declaration of interest ...... 502 Acknowledgements ...... 502 References ...... 502

1. Introduction adsorption in the visible region. Accordingly, there has been considerable research on increasing the degradation rate of Owing to the rapid industrialization in recent decades, a huge pollutants by combining inorganic materials with PTh to amount of toxic effluent is being discharged into various water achieve synergetic and complementary behaviors between bodies on a daily basis. These ongoing processes pose a serious PTh and other organic or inorganic materials. problem for the availability of safe water for drinking, house- As a result, a large number of papers on PTh nanocompos- hold uses, agriculture, farming, etc. Therefore, there appears to ite based photocatalysts have been published within a short be an intimate shortage of clean water supply, which highlights span of time. The present review summarizes the systematic the urgent need for the purification of water, making waste progress in the development, mechanistic view and future water treatment an important issue of concern [1]. applications of PTh-based photocatalytic systems. For conve- A wide range of methods and technologies have been used nience, the discussion is divided into a several categories to remove organic or inorganic pollutants from water and depending on the type of the composite material and its waste-water to reduce their impact on the environment. chemistry. These methodologies involve adsorption on organic or inorganic materials [2], photocatalytic degradation, oxidation pro- 2. Polythiophene cesses, microbiological, or enzymatic decomposition [3].Of these, semiconductor photocatalysis has been widely applied Since the discovery of iodine-doped polyacetylene in 1977 [16], as a ‘‘green’’ technology for purification of air and the elimina- research in the field of conducting polymers has made consid- tion of organic contamination of water, and has become one of erable advances. On the other hand, only few conducting poly- the most important applied facets of heterogeneous catalysis mers have been found to be stable enough under normal [4]. processing conditions to be incorporated in practical applica- Semiconducting metal oxide nanoparticles have long been tions. Among them, the leading candidates are Pani, PPy explored as a photocatalytic material for the degradation of and PTh. Of these, Pani and PPy have been studied the most pollutants. TiO2 has attracted considerable attention since for many practical applications, such as sensors [17,18], photo- Fujishima and Honda [5] discovered its photocatalytic proper- catalytic activity [19], environment remediation [2] etc. Despite ties in their water splitting experiment. Similarly many other, being the least studied, PTh has shown many promising appli- metal oxide nanoparticles, such as ZnO [6,7], TiO2 [8–10], cations comparable to both Pani and PPy, such as electrical/ etc. [11,12], have been used to degrade non-biodegradable electrochemical applications, sensors and dye degradation pollutants via photocatalytic routes. [20]. Recently, PTh, just like other conjugated polymers, has On the other hand, the wide band gap of metal oxides (Eg been applied in the photocatalytic area to sensitize metal 3.2 eV or greater) limits their ability to absorb visible light oxides and develop high performance PTh/metal oxide photo- (k > 380 nm), which limits their widespread use. Therefore, catalytic materials [21]. intense research has been conducted to lower their band gap, In addition to pure PTh, functionalized PTh has also such as with metals or nonmetal doping [13,14], composite attracted considerable interest owing to their interesting elec- synthesis with polymers [15] etc. Among these processes, fabri- trical, electrochemical and optical properties. The introduction cation with conducting polymers, such as PTh, has been shown of flexible pendant chains onto the backbone improves the to effectively lower the band gap by allowing greater solubility and processability allowing more complete 496 M.O. Ansari et al.

Polythiophene

* * S n

R Poly(3-alkylthiophene)

O O Poly(3,4-ethylene dixoxythiophene)

OH Poly(hydroxymethyl-3,4-

ethylenedioxythiophene)

O O

Poly-(fluorene-co-thiophene)

1-n S n

Figure 1 Structures of PTh and its derivatives. characterization of the materials. Poly(3-alkylthiophene)s with comparative visible and UV light transition possibilities of large alkyl groups, such as butyl, can be readily melt-or PTh along with those of metal oxides. solution-processed into films, which, after oxidation, can exhi- The substitution of PTh with either electron withdrawing or bit exceptionally high electrical conductivity [22]. Moreover, electron releasing groups can be an alternative way for band such introduction modifies the electronic properties of the gap engineering. This tunes the HOMO and LUMO of the polymer, thereby increasing the possibilities for industrial conjugated polymer system, thereby altering the band gap. applications. Fig. 1 shows the basic structures of PTh and The introduction of electron withdrawing groups, such as nitro some of its derivatives. or cyano in PTh system, has been reported to increase the oxidation potential, and affect the band gap. Lambert et al. [24] 2.1. Chemical states and band gap of polythiophene reported that poly(cyclopentadithiophene)s bearing electron withdrawing keto or dicyano groups at the bridging carbon PTh exhibits a large range and ‘‘well-behaved’’ chemical prop- has a band gap of 1.20 eV and 0.80 eV, respectively. erties, making it suitable for selective and efficient modification This low band gap has been explained due to the increased at the molecular level that can be used to tailor its physical, quinoid character of PTh or its derivatives [25]. Another optical and electronic properties. This backbone of PTh can assumption is that the systems can also be viewed as alternant be modified by the incorporation of different monomer build- donor acceptor systems, where the thiophene ring acts as a ing blocks, such as fused ring systems, and substitution by donor. Therefore, the introduction of electron withdrawing alkyl chains into PTh. This alters the chemical behavior, which groups may lower the band gap of the PTh system, but have in turn affects the band gap, an important parameter in the a serious impact on the solubility, which ultimately decreases field of photocatalysis [23]. The band gap of PTh is in the their processability and limits their practical applications [26]. range of 2.0 eV and varies according to the type of doping. The electron donating group increases the HOMO level of This band gap is sufficiently small compared to metal oxides, the conjugated system which reduces the band gap. Alkyl groups, as in the case of butyl or pentyl substituted PTh, such as TiO2, ZnO etc. Owing to this sufficiently small band gap, it is possible to excite an electron from the VB to the decrease the oxidation potential of the thiophene ring due to CB using both UV and visible light. Fig. 2 shows the the inductive effect [27]. On the other hand, linear alkyl chains Polythiophene nanocomposites for photodegradation applications 497

Figure 2 Different transition possibilities in UV and visible light for (a) metal oxides and (b) PTh. of sufficient length (typically 6–9 carbons) contribute indirectly with ease due to the polymer-mediated process. Electrons from to reducing the energy gap by enhancing the long-range order the CB of PTh are transferred directly to the CB of metal oxi- in the polymer through lipophilic interactions between the des making the composite active in visible light (Fig. 3). In the alkyl chains, which leads to a decrease in the band gap [27]. case of UV irradiation, the transfer of electrons occurs at a Compared to electron withdrawing groups, electron donating much higher rate due to the activity of the metal oxide, which groups, such as the long alkyl chains, opens up the structure increases the catalytic activity considerably. The excited-state of the alkyl group substituted PTh or their derivatives, which electrons readily injected into the CB of metal oxides are sub- increases their solubility, processability and thus finds a variety sequently transferred to the surface and reacts with adsorbed of practical applications. water and oxygen to yield hydroxyl and superoxide radicals. These oxidative radicals are responsible for the photocatalytic 2.2. Chemistry of the photocatalytic activity of polythiophene/ activity of the composite of PTh with metal oxides [29]. metal–metal oxide composite and UV or visible light activity 2.3. Polythiophene composite catalyst used in the field of PTh like other conducting polymers under visible light irradi- photodegradation ation, absorbs light to induce a p fi p* transition, transporting the excited-state electrons to the p orbital, which is also The major drawback of any metal oxide-mediated photocatal- referred to as the VB to CB or HOMO to LUMO transition ysis process is the high rate of electron and hole recombina- [28]. UV and visible irradiation is sufficient in energy for this tion, which decreases the overall photocatalysis efficiency. transition because of the low band gap of PTh. Therefore, Dye sensitized photocatalytic materials show high efficiency due to the ease of the electron transition, PTh can act easily in the degradation of pollutants, where the dye acts as a sensi- as a sensitizer to metal oxides where the transition of the elec- tizer and facilitates electron transfer to the CB of TiO2. The Å tron to the CB is not possible under visible light because of its electron is captured to produce active radicals, such as O2 , wide band gap. In the case of metal oxide composites with ÅOOH and ÅOH, which are responsible for the photodegrada- PTh, the transition of an electron to the CB of TiO2 occurs tion process [30,31]. On the other hand, the loose attachment

∗ CB LUMO π

Visible ∼ Visible no excitation Eg 2.5 eV excitation E ∼ 3.2 eV light light g HOMO π VB h+ Pure metal oxide PTh nanostructure

O2 ∗ LUMO π CB O2

Visible E ∼ 2.5 eV light g Visible light HOMO π VB PTh Pure metal oxide nanostructure

Figure 3 PTh mediated electron transfer to the CB of metal oxides under visible light irradiation. 498 M.O. Ansari et al. of dyes with the metal oxide is a major drawback, which results then reacts with O2 adsorbed on the TiO2 surface to produce in poor stability for long term applications [32]. Conducting oxidative radicals responsible for the photodegradation polymers, such as PTh in the place of dyes, is an efficient process. method of resolving these problems because the polymer can In addition to the conventional in situ polymerization tech- be coated on the surface of metal oxides, and the resulting niques used for the preparation of PTh based photocatalysts, composite would exhibit strong interactions as well as high other techniques, such as microemulsion route and the electro- absorption in the UV and visible region of the solar spectrum. chemical or photoinduced polymerization of PTh, also pro- In situ polymerization techniques have mostly been used for duced interesting results due to the different morphological the fabrication of metal oxides. Zhu et al. [33] exploited the features that give them different properties [37]. The properties of the high electron mobility of PTh to fabricate a microemulsion phase acts as an inert medium which prevents PTh/TiO2 nanocomposite for the photocatalytic degradation the coalescence of nanoparticles. Degradation studies using of MO dye under UV light irradiation. A self-designed UV- PTh nanoparticles for commonly used textile dyes, such as irradiation instrument with 10 W germicidal lamps with a Orange II and MO, under UV irradiation indicated higher cat- maximum wavelength of 253.7 nm was used for the catalysis alytic activity due to the low band gap of the PTh nanoparti- process. The change in the MO concentration was measured cles. Under UV irradiation, PTh nanoparticles exhibited by a UV–vis spectrophotometer and was related to the degra- higher degradation rates than normal PTh because of the lar- dation of MO. Morphological analysis showed that during in- ger specific surface areas. The photocatalytic degradation reac- situ polymerization, PTh is coated on the TiO2 nanoparticles tion simply followed pseudo first-order reaction kinetics. The and the overall composite absorbs in the wavelength range rate constants of the normal PTh nanoparticles were relatively of 200–800 nm compared to TiO2, which absorbs only in the low compared to TiO2 and the degradation rate of the PTh 400 nm region. This suggests that the PTh/TiO2 nanocompos- nanoparticles was much higher than TiO2. One explanation ite can be excited by solar light. In addition to the photodegra- is that the energy of the photo-induced radicals coming from dation phenomenon, the PTh/TiO2 nanocomposite also allows the narrower bang gap (2.0 eV) of PTh nanoparticles is much surface adsorption of the dye, which changes with the PTh to lower than that from TiO2 (3.2 eV) [38]. TiO2 weight ratio. With the increase in PTh ratio, the adsorp- The electropolymerization of thiophene on TiO2 films leads tion capacity of the PTh/TiO2 nanocomposites increases first to a slow and intact coating of PTh on TiO2. Liang et al. [39] and decreases afterward, which is related to the structural fea- used the electropolymerization technique for the surface coat- tures of the nanocomposite system. When tested under UV ing of PTh on TiO2. They reported that the low potential light illumination, the pure PTh used as a catalyst did not show avoids degradation of the polymer as well as any side reactions any appreciable degradation of MO (<5.0%). Pure TiO2 between the electrolytes and electrodes. The thickness of the showed 48.5% MO degradation, whereas PTh/TiO2 showed PTh layer on TiO2 can be controlled easily by the concentra- 56.6% degradation. The rate of degradation initially starts at tions of thiophene monomers in the electrolyte solution. In a high pace after which it becomes stable due to the adsorption the absorption spectra, the PTh/TiO2 composites revealed a of dye on the active sites of the catalyst. PTh/TiO2 with a broad absorption band in the range, 400–600 nm, with a main higher PTh content exhibited limited catalytic activity, which shoulder at 540 nm. This confirmed the interaction of PTh is because PTh adsorbed on the surface of TiO2 occupied most with TiO2 as the composite processed all the absorption of the surface active sites of TiO2, thereby preventing the MO regions of TiO2 and PTh. Owing to the high absorption in molecule from reaching the active sites of TiO2 for the UV and visible light region, the electropolymerized degradation. PTh/TiO2 composites showed high photocatalytic degradation The surface property is an important factor for the photo- of 2,3-dichlorophenols when tested under UV and visible light. catalytic properties and is closely related to the PTh to TiO2 The enhanced effect was explained by the high rate of charge weight ratio. In another development reported previously, it transfer from the sulfur site of PTh to TiO2, as evident from was shown that with increasing PTh content from 0% to XPS analysis. 2%, the adsorption capacity of the PTh/TiO2 composites A similar interaction of the sulfur site with TiO2 was also toward MO increases [34]. Zeta potential studies showed that achieved in other controlled polymerization conditions. in the dispersion, the surface of the TiO2 is negatively charged Under normal conditions, PTh is simply deposited on the sur- while the surface of the PTh/TiO2 composites is positively face of TiO2; hence, the interface between the polymer and charged. Therefore, due to coulombic repulsion, MO is barely TiO2 is not stabilized for the formation of a heterojunction, adsorbed on the TiO2 surface. On the other hand, the posi- which favors the rate of charge injection when stimulated by tively charged surface of the PTh/TiO2 composites can adsorb light excitation. Photoinduced polymerization is another tech- MO strongly, which would contribute to the high photodegra- nique of composite preparation by utilizing photoexcited TiO2 dation efficiency because it facilitates efficient interfacial nanoparticles and achieving the free radical polymerization of charge transfer. The adsorbed MO molecules are also helpful alkenes. This technique leads to good adhesion between the in preventing the recombination of photoelectrons and holes polymeric materials and inorganic materials because the poly- [35]. Therefore, the strong adsorption properties of the merization reaction is initiated locally by charge transfer PTh/TiO2 composites could increase the photocatalytic across the inorganic semiconductor-monomer interface degradation rate of MO [36]. The PTh/TiO2 nanocomposite, [40,41]. The PTh/TiO2 nanocomposite prepared using the pho- when studied for its visible light activity, also showed toinduced polymerization technique showed a strong interac- substantial visible light photocatalytic activity. TiO2 is excited tion between the sulfur sites of the PTh backbone and the by UV light only; hence PTh acts as a sensitizer. PTh because TiO2 particles, which can explain the highly efficient photocat- of its strong absorbance in the visible light region upon excita- alytic degradation of RhB under UV irradiation or visible light tion transfers the electron to the CB of TiO2. The CB electron irradiation [42]. Polythiophene nanocomposites for photodegradation applications 499

Apart from TiO2, other materials, such as ZnO and of the solar spectrum. Muktha et al. [47] from their PL results, metal–organic frameworks, (MIL-101(Cr) and Bi25FeO40), in reported a quenching phenomenon as the content of TiO2 in combination with PTh have also shown promising catalytic the composites was increased, which was attributed to the properties. ZnO absorbs a larger fraction of the UV spectrum presence and distribution of TiO2 in the P3Th matrix because than TiO2 but has limited applications because of the charge transfer occurs from P3Th to TiO2. They explained that occurrence of photocorrosion and the susceptibility to facile upon UV excitation, the electron from the CB of TiO2 may be dissolution at extreme pH [43]. Khatamian et al. [44] reported excited to the empty states in P3Th owing to the lower band that the surface modification of ZnO with PTh can improve gap of P3Th compared to that of TiO2. The process enhances the absorption characteristics of ZnO to produce a highly vis- the oxidative property of TiO2 and stabilizes the VB hole of ible light active photocatalyst. The optical properties of the TiO2. On the other hand, P3Th may also absorb UV radiation prepared PTh/ZnO by DRS showed a broad peak in the visible allowing energy transfer to the TiO2 nanoparticles followed by region. The pHPZC changes with the addition of PTh to ZnO the creation of a VB hole and CB electron. This electron- due to a change in the surface property of the composite. mediated mechanism leads to the formation of ÅOH radicals This was also evident from morphological studies because responsible for the degradation process. ZnO nanoparticles are surrounded by PTh, which reduces Similar studies have been carried out by various authors to the agglomeration of ZnO nanoparticles in the PTh/ZnO sys- examine the absorption and visible light activity of P3Th/TiO2 tem. The BET results showed that the surface area of nanocomposites. In a study by Wang et al. [48], DRS PTh/ZnO is higher than that of ZnO and the obtained surface spectroscopy showed that P3Th/TiO2 possesses a much lower 2 1 areas of PTh/ZnO and ZnO were 199.74 and 9.9 m g , band gap than TiO2 and can be easily excited to produce more respectively. A study of pHPZC suggests that the surface of electron–hole pairs under visible light irradiation. They the composite is positively charged, which is in contrast to reported that the optimal P3Th to TiO2 ratio gave the highest ZnO, and MO being negatively charged can be adsorbed easily photocatalytic efficiency. The catalytic degradation rate of the on the surface, which is beneficial for the photodegradation MO dye increased initially and later decreased with increasing properties. The photocatalytic mechanism has been explained P3Th/TiO2 molar ratio from 30:1 to 125:1, reaching a maxi- in a similar manner to the case of PTh/TiO2 as discussed ear- mum of 88.5% in 10 h when the molar ratio of P3Th/TiO2 lier, i.e. the transfer of an electron to the CB of TiO2. On the was 75:1. The photocatalytic mechanism was found to be sim- other hand, the authors concluded that a specific threshold of ilar, via electron transfer from P3Th to the CB of TiO2. The PTh is necessary to prevent recombination, and PTh in very electron in the CB of TiO2 reacts with oxygen to yield a super- Å small amounts resulted in poor efficiency. This might be due oxide radical, O2 . This leads to the formation of a positively to the inability of a small amount of PTh to transfer sufficient charged hole (h+) due to electron migration from the VB of electrons to the CB of ZnO, which is further responsible for the TiO2 to the p orbital of P3Th, which then reacts with OH Å Å degradation process. Similar characteristics, as in the case of or H2O to generate OH. The super-oxide radical ion O2 Å PTh/ZnO have been observed for the PTh/Bi25FeO40/MIL- and hydroxyl radical ( OH) are responsible for the degradation 101(Cr) composite [45]. The visible light absorption increased of the organic compounds. due to the high absorption of MIL-101(Cr). Therefore, the In another development, Zhu et al. [49], who used catalysis of RhB was achieved efficiently under visible light P3Th/TiO2 for the degradation of MO dye, reported that irradiation. The photocatalytic mechanism is believed to occur the catalytic reactions occurred via different reactive path- via a polymer mediated process, i.e. transfer and separation of ways under UV and visible light irradiation. The azo bond photogenerated charge carriers through the PTh-connected of the MO molecule was dominantly cleaved under UV light interface between MIL-101 and Bi25FeO40. irradiation, while under visible irradiation, apart from the cleavage of the azo bond, intermediates with chromophoric 2.4. Substituted polythiophene composite photocatalyst used in groups formed. Further studies on the degree of P3Th oxida- the field of photodegradation tion showed that the excessive oxidation of P3Th decreases the photocatalytic activity of the P3Th/TiO2 composites. Derivatives of PTh, such as alkyl substitution, improve the From the degradation results of MO using P3Th/TiO2 with processability of the polymer and may extend their applica- different degrees of P3Th oxidation, it was concluded that tions to various fields. Among the different substituted PTh, as the side chains of P3Th became oxidized, they had a the alkyl substituted P3Th has been applied widely in the field stronger interaction with TiO2, leading to an increase in the of photocatalytic degradation. The alkyl group acts as an elec- polarity of P3Th [50]. This reduces the separation ability of tron donor, which is helpful in increasing the effective conjuga- P3Th to oxygen, and the photoinduced electrons can be tion length of thiophene ring backbone and enhancing the transferred easily from P3Th to TiO2 particles, making the electron mobility. P3Th has strong absorption in visible region P3Th/TiO2 composite photocatalytic active. Under extensive (band gap of 1.9–2.0 eV), higher charge carrier mobility, good oxidation, however, the backbone of the polymer was solubility, processability, long-term stability [46]. Therefore, it destroyed, leading to a decrease in the degree of p-p conjugation of the polymer. This decreases the efficiency of the can be considered a good candidate as a sensitizer of TiO2 and may be a possible replacement for PTh due to the higher pro- photo-excitation of electrons from the valence bond to the cessability of the former. antibonding polaron state under visible light irradiation. P3Th can be synthesized using 3-hexylthiophene as a mono- Therefore, fewer electrons are excited by visible light irradia- mer by a simple in situ oxidative polymerization technique tion and transferred to the conducting band of TiO2 to generate oxidative species. Thus, the photocatalytic activity of similar as in the case of PTh. The composite of P3Th/TiO2 exhibits broad absorption, both in the UV and visible regions the P3Th/TiO2 composites decreases when P3Th is oxidized excessively. 500 M.O. Ansari et al.

Another derivative of PTh, PFTh, in combination with a strong interaction between the interface of PTh and TiO2– TiO2 also showed enhanced catalytic degradation properties Cu. The TiO2–Cu composite showed absorption in the region, [51]. DRS studies revealed a broad absorption for 450–500 nm. On the other hand, extension of the absorption PFTh/TiO2 in the region from 360 to 500 nm compared to regions in the PTh/TiO2–Cu composite also indicates strong pure TiO2, where no absorption was observed after 400 nm. interactions between PTh and TiO2–Cu, which is expected to The PL results indicated that the electrons on the CB of accelerate photo-induced charge transfer from the PTh to PFTh were transferred to the CB of TiO2. Owing to the lower TiO2–Cu, and subsequent enhancement of the photocatalytic reductive potential of PFTh (1.35 V) than TiO2 (0.65 V), it efficiency of the catalyst. When tested for the degradation of became thermodynamically possible for electrons to be RhB, as the PTh content in TiO2–Cu was increased from 0.5 injected from the CB of the polymer to the CB of TiO2, which to 2.0 wt.%, the rate of RhB degradation increased, reaching plays an important role in photocatalytic degradation. Similar a maximum at polymer loading of 1.0 wt.%, and decreases results have been reported for the photocatalytic degradation with further increase in polymer loading to 2.0 wt.%. This of phenol, RhB and MO by PFTh/ZnO under visible light irra- shows that there is some specific threshold for PTh to exhibit diation [52]. For the PPTh/ZnO composite, it was shown that the optimal catalytic properties in the composite system. The the amount of ZnO in the polymer has a great effect on the experiment also showed that the concentration of PTh in conjugation length and degree of oxidation of the composite TiO2–Cu played a significant role in enhancing the photocat- [53]. Among 3%, 5% and 7% ZnO loadings in the polymer, alytic activity. The change in pH alters the charge on the cat- FTIR and UV–visible spectral analysis showed that a 5% alyst, which affects the adsorption and desorption of the dyes loading had the longest conjugation length compared to other on the catalyst surface. For PTh/TiO2–Cu, the photocatalytic weight percentages. This can be explained in that when ZnO is rate also increased with increasing pH. This is due to the effect excited by radiation capable of electron transfer from the VB of pH on the ionization rate on the surface according to the to the CB, the electron–hole pairs react with hydroxyl ions following reactions: to produce reactive radicals, such as ÅO and ÅOH [54]. These 2 TiOH þ Hþ! TiOHþ ð1Þ strong oxidants in stepwise reactions can enhance the conjuga- 2 tion length of the polymer. On the other hand, ZnO at higher TiOH þ OH!TiO þ H O ð2Þ weight percentages will also lead to the separation of oxidants 2 to some extent due to other possible reactions; hence, a higher The pH study showed that the dispersion of PTh/TiO2–Cu weight percentage may lead to a decrease in the conjugation is positively charged under acidic conditions, which is in con- length [55]. The photocatalytic activity is explained by the syn- trast to negatively charged TiO2–Cu. Therefore, the adsorption ergistic effect of PPTh and ZnO. The 5% ZnO loading gave of positively charged RhB becomes impossible under acidic the highest photocatalytic efficiency under UV irradiation for conditions due to electrostatic repulsion; however, in alkaline the dye. The higher conjugation and oxidation degree leads pH, the charge on the catalyst is reversed and the condition to good electron mobility and is believed to be an important becomes favorable for photocatalytic activity. Another expla- Å factor for enhancing the photocatalytic activity. nation is that the OH radicals are easier to generate by oxidiz- Little work has also been done on the photocatalytic activ- ing more hydroxide ions on the TiO2 surface; thus, the ity of carbon-based materials with a PTh composite. GO has a efficiency of the photocatalytic process is enhanced in alkaline functional oxygen group capable of interacting with PTh or its media. derivative via a p–p interaction between the nonpolar regions The photodegradation mechanism proceeds normally via a of GO and the molecular layers of PTh. The composite polymer mediated process; however the important difference is PHTh/GO sheets, when studied for their photophysical that upon excitation, the electrons from the VB of TiO2 are 2+ 2+ properties, such as UV–visible absorption, photothermal trapped by Cu to form an unstable TiO2–Cu complex. 2+ desorption spectroscopy, and steady-state PL studies, showed The trapped TiO2–Cu electrons are moved immediately to enhanced optical absorption, charge transfer and photocat- the HOMO of PTh, which eliminates their electron–hole alytic properties [56]. The formation of a charge-transfer recombination process. Owing to the lower reduction potential complex between GO and PHTh was proposed, which creates of PTh than TiO2–Cu, the electrons are transferred easily to additional sub-band gap states that result in absorption at the CB of TiO2 and a further degradation reaction occurs sim- lower energies than the band gap. PHTh/GO hybrids when ilarly, as discussed earlier. Fig. 4 shows a schematic diagram of studied for the oxidative Mannich reaction under ambient the photocatalytic degradation mechanism. solar light showed promising results. Therefore, owing to its In another major development, PTh/TiO2–montmorillonite ability to be excited by sunlight, PHTh/GO hybrids have was evaluated for the sonophotocatalytic degradation of RhG potential applications as an efficient photocatalyst in organic [59]. When sonication is added to the photocatalytic system, synthesis. the transformation of organic products occurs through reactions with ÅOH radicals generated from the collapsing bubbles. In addition, the concentration of the organic material 2.5. Multicomponent polythiophene composite catalyst used in decreases as hydroxylation progresses. The enhanced effects the field of photodegradation by photocatalysis and sonocatalysis can be attributed to the following reasons: the increased amounts of the oxidative spe- Multicomponent systems consisting of PTh/metal oxides and cies generated, and an increase in the mass transport of chem- metal particles have also attracted attention to further extend ical species between the solution phase and the photocatalyst the absorption limit of the composite system and enhance surface and vice versa [60]. PTh/TiO2–Montmorillonite, when the catalytic activity [57]. Chandra et al. [58] reported that a assessed for catalytic reactions, showed a higher sonocatalytic PTh/TiO2–Cu composite prepared by a sol–gel process showed degradation rate of RhG compared to the photocatalytic Polythiophene nanocomposites for photodegradation applications 501

O2 ∗ LUMO π CB O2

Visible E ∼ 2.5 eV light g Visible Cu2+ π HO• light HOMO VB h+ PTh Pure metal oxide nanostructure

Figure 4 Metal mediated electron transfer to PTh and metal oxide.

process. This was attributed to the advantageous properties of film, when studied for the visible light-induced catalytic degra- sonication favoring the ease of generation of charged species as dation of iprobenfos fungicide using bubbling gases with vary- well as to the effect of PTh, which promoted electron transfer ing oxygen partial pressures, showed a high rate of fungicide from the excited PTh polymer to the CB of TiO2. These two degradation [66,67]. The rate of fungicide degradation effects in combination gave high photocatalytic efficiency for increased with increasing oxygen partial pressure, and the film the degradation of RhG. showed remarkable stability, even after 10 h of irradiation (>380 nm), with no peeling of the films. To find out the active 2.6. Polythiophene based composite for the photocatalytic species responsible for the degradation process, the fluores- disinfection of microorganisms cence quenching constant (kq) was determined from the slope of the Stern–Volmer plots. The estimated kq value was 3 1 Å 3.6 · 10 kPa , which is related to the formation of O2 by Matsunaga et al. [61] reported that the TiO2 photocatalyst may cause the death of bacterial cells in aqueous media under illu- electron transfer from an excited POTh film to molecular oxy- Å mination. Since then, extensive studies have been carried out gen. This formation of O2 suggests that the photocatalytic Å on the photocatalytic disinfection of microorganisms using process involves a series of oxidative radicals, such as O2 , HOÅ ,HO , and ÅOH, which is similar to the case when TiO TiO2 as a photocatalyst under UV light irradiation [62]. The 2 2 2 2 was used as a photocatalyst [68]. inability of TiO2 to absorb the visible light, however, has lim- Compared to TiO2 particles in aqueous suspensions, the ited its applications. Doping TiO2 with PTh may extend the POTh film showed a low quantum yield, hence, the photocat- absorption region of TiO2 and then enhance the photocatalytic disinfection phenomenon [63]. The photocatalytic activity is alytic activity of the polymer film was inferior to that of TiO2 Å due to the OH generated during the photocatalytic process, particles [66,67]. On the other hand, the application of TiO2 which is supposed to be the major lethal species responsible particles to the degradation of wastewater treatments is gener- for photocatalytic disinfection [64]. ally difficult because of their difficult filtration and settling. Shang et al. [65] in their study of PTh-Ac coated The low activity of the polymer film can be attributed mainly to the low redox potential compared to that of TiO2 as well as Fe3O4@LDHs magnetic nanospheres as a photocatalyst for the photocatalytic disinfection of pathogenic bacteria under to the low surface area. Therefore, the combined effect of TiO2 solar light irradiation, and showed that PTh-Ac plays a key with the POTh film is believed to give enhanced disinfection role in the disinfection process. The ÅOH radicals that are properties and may also solve the problems of the settling of responsible for photocatalytic disinfection can be generated TiO2 nanoparticles. Å 1 easily from superoxide radicals ( O2 ) or singlet oxygen ( O2) on the surface of PTh-Ac. Therefore, it was assumed that the 3. Summary, prospective and scope for future works photocatalytic disinfection mechanism of this study was due Å to the creation of OH, which is generated from the surface Many studies of photodegradation under UV and visible light Å of Fe3O4@PTh-Ac-LDHs. The generated OH could cause sig- irradiation using composites based on PTh or its derivatives nificant disorder in the permeability of bacterial cells, DNA have been reported. Compared to other conducting polymers, damage and decomposition of the cell walls. Experiments per- such as Pani or PPy, PTh has attracted less attention and the formed on Escherichia coli confirmed that the cell structure research on the photocatalytic properties of PTh can be con- was distorted, and the ruptured cell wall could be observed sidered to be in its infancy at this stage. clearly by TEM analysis. The cell was no longer intact and Among the metal oxides examined thus far, TiO2 and ZnO the outer membrane of the cell was damaged, leading to leak- have attracted attention in this area, whereas there are very few age of the interior component. This highlights the substantial reports on other metal oxides. Composites of PTh or its Å disorder in membrane permeability by OH in the disinfection derivatives can be prepared with different metal oxides to process, followed by the free efflux of intracellular con- assess their photocatalytic properties under UV and visible stituents, which leads to cell death. Derivatives of PTh in film light irradiation. Carbon-based materials, such as graphene, form when studied for the disinfection of fungicide also CNT or GO also have exciting future prospects owing to their showed promising applications under visible light. The POTh conductive nature, and may give high charge mobility in 502 M.O. Ansari et al. composites, which is beneficial for the catalytic properties. [10] M.M. Khan, S.A. Ansari, D. Pradhan, M.O. Ansari, D.H. Han, Owing to the much broader absorption in the visible region J. Lee, M.H. Cho, Band gap engineered TiO2 nanoparticles for of PTh and carbon based materials, more research will be visible light induced photoelectrochemical and photocatalytic needed in the field of visible light photocatalysis, which might studies, J. Mater. Chem. A 2 (2014) 637–644. provide a green photocatalytic methodology for future [11] S.A. Ansari, M.M. Khan, M.O. Ansari, S. Kalathil, J. Lee, M.H. Cho, Band gap engineering of CeO nanostructure using applications. 2 an electrochemically active biofilm for visible light applications, PTh films can be used for the immobilization of metal oxi- RSC Adv. 4 (2014) 16782–16791. des, which can solve the problems of separation and isolation [12] S.A. Ansari, M.M. Khan, M.O. Ansari, J. Lee, M.H. Cho, of the catalyst and greatly improve the reproducibility of the Visible light-driven photocatalytic and photoelectrochemical composite photocatalyst. In addition, there appears to be fur- studies of Ag–SnO2 nanocomposites synthesized using an ther scope for the synthesis of PTh based photocatalysts with electrochemically active biofilm, RSC Adv. 4 (2014) 26013– different morphologies, such as core shell, wire, network struc- 26021. ture etc. using simple chemical or electrochemical routes. [13] Y. Wang, R. Zhang, J. Li, L. Li, S. Lin, First-principles study on Green synthetic methods, such as catalyst synthesis via electro- transition metal-doped anatase TiO2, Nanoscale Res. Lett. 9 chemically active biofilms have attracted considerable interest (2014) 46–53. [14] B. Ahmmad, Y. Kusumoto, M.S. Islam, One-step and large scale these days, and it might be the most common possible method- synthesis of non-metal doped TiO2 submicrospheres and their ology for the synthesis of PTh or its derivative-based photocat- photocatalytic activity, Adv. Powder Technol. 21 (2010) 292–297. alysts in the near future. [15] D. Mukherjee, S. Barghi, A.K. Ray, Preparation and

characterization of the TiO2 immobilized polymeric 4. Declaration of interest photocatalyst for degradation of aspirin under UV and solar light, Processes 2 (2014) 12–23. [16] H. Shirakawa, E.J. Louis, A.G. MacDiarmid, C.K. Chiang, A.J. The authors alone are responsible for the content and writing Heeger, Synthesis of electrically conducting organic polymers: of the paper. halogen derivatives of polyacetylene, (CH)x, J. Chem. Soc., Chem. Commun. 16 (1977) 578–580. Acknowledgements [17] M.O. Ansari, F. Mohammad, Thermal stability, electrical conductivity and ammonia sensing studies on p-toluenesulfonic This study was supported by Priority Research Centers acid doped polyaniline:titanium dioxide (pTSA/Pani:TiO2) Program through the National Research Foundation of nanocomposites, Sens. Actuators B 157 (2011) 122–129. Korea (NRF) funded by the Ministry of Education [18] T. Patois, J.B. Sanchez, F. Berger, J.Y. Rauch, P. Fievet, B. Lakard, Ammonia gas sensors based on polypyrrole films: (2014R1A6A1031189). influence of electrodeposition parameters, Sens. Actuators B 171–172 (2012) 431–439. References [19] M.O. Ansari, M.M. Khan, S.A. Ansari, K. Raju, J. Lee, M.H. Cho, Enhanced thermal stability under DC electrical [1] P.K. Shih, W.L. Chang, The effect of water purification by conductivity retention and visible light activity of Ag/ oyster shell contact bed, Ecol. Eng. 77 (2015) 382–390. TiO2@Polyaniline nanocomposite film, ACS Appl. Mater. [2] R. Kumar, M.O. Ansari, M.A. Barakat, DBSA doped Interfaces 6 (2014) 8124–8133. polyaniline/multi-walled carbon nanotubes composite for high [20] V.C. Gonçalves, D.T. Balogh, Optical chemical sensors using efficiency removal of Cr(VI) from aqueous solution, Chem. Eng. polythiophene derivatives as active layer for detection of volatile J. 228 (2013) 748–755. organic compounds, Sens. Actuators B 162 (2012) 307–312. [3] S. Pricelius, C. Held, S. Sollner, S. Deller, M. Murkovic, R. [21] R. Qiu, D. Zhang, Z. Diao, X. Huang, C. He, J.L. Morel, Y. Ullrich, M. Hofrichter, A. Cavaco-Paulo, P. Macheroux, G.M. Xiong, Visible light induced photocatalytic reduction of Cr(VI) Guebitz, Enzymatic reduction and oxidation of fibre-bound azo- over polymer-sensitized TiO2 and its synergism with phenol dyes, Enzyme Microb. Technol. 40 (2007) 1732–1738. oxidation, Water Res. 46 (2012) 2299–2306. [4] F. Cao, P. Yin, X. Liu, C. Liu, R. Qu, Mercury adsorption from [22] R.D. McCullough, The chemistry of conducting fuel ethanol onto phosphonated silica gel prepared by polythiophenes, Adv. Mater. 10 (1998) 93–116. heterogenous method, Renewable Energy 71 (2014) 61–68. [23] R.A. Kru¨ger, T.J. Gordon, T.C. Sutherland, T. Baumgartner, [5] A. Fujishima, K. Honda, Electrochemical photolysis of water at Band-gap engineering of polythiophenes, J. Polym. Sci. Pol. a semiconductor electrode, Nature 238 (1972) 37–38. Chem. 49 (2011) 1201–1209. [6] M.M. Rashad, A.A. Ismail, I. Osama, I.A. Ibrahim, A.T. [24] T.M. Lambert, J.P. Ferraris, Narrow band gap polymers: Kandil, Photocatalytic decomposition of dyes using ZnO doped polycyclopenta[2,1-b;3,4-b0]dithiophen-4-one, J. Chem. Soc.

SnO2 nanoparticles prepared by solvothermal method, Arabian Chem. Commun. 11 (1991) 752–754. J. Chem. 7 (2014) 71–77. [25] J.M. Toussaint, J.L. Bre´das, Novel low bandgap polymers: [7] S.A. Ansari, M.M. Khan, S. Kalathil, A. Nisar, J. Lee, M.H. polydicyanomethylene – cyclopentadithiophene and -dipyrrole, Cho, Oxygen vacancy induced band gap narrowing of ZnO Synth. Met. 23 (1993) 103–106. nanostructures by an electrochemically active bioﬁlm, [26] J. Roncali, Molecular engineering of the band gap of p- Nanoscale 5 (2013) 9238–9246. conjugated systems: facing technological applications, [8] S. Kalathil, M.M. Khan, S.A. Ansari, J. Lee, M.H. Cho, Band Macromol. Rapid Commun. 28 (2007) 1761–1775.

gap narrowing of titanium dioxide (TiO2) nanocrystals by [27] J. Roncali, R. Garreau, A. Yassar, P. Marque, F. Garnier, M. electrochemically active bioﬁlms and their visible light activity, Lemaire, Effects of steric factors on the electrosynthesis and Nanoscale 5 (2013) 6323–6326. properties of conducting poly(3-alkyithiophenes), J. Phys. [9] M.M. Khan, S.A. Ansari, M.I. Amal, J. Lee, M.H. Cho, Highly Chem. 91 (1987) 6706–6714.

visible light active Ag@TiO2 nanocomposites synthesized using [28] L. Zhai, R.D. McCullough, Regioregular polythiophene/gold an electrochemically active bioﬁlm: a novel biogenic approach, nanoparticle hybrid materials, J. Mater. Chem. 14 (2004) Nanoscale 5 (2013) 4427–4435. 141–143. Polythiophene nanocomposites for photodegradation applications 503

[29] K. Sivakumar, V.S. Kumar, J.J. Shim, H. Yuvaraj, [47] B. Muktha, D. Mahanta, S. Patil, G. Madras, Synthesis and

Photocatalytic and antimicrobial activities of poly(aniline- photocatalytic activity of poly(3-hexylthiophene)/TiO2 co-o-anisidine)/zinc oxide nanocomposite, Asian J. Chem. 26 composites, J. Solid State Chem. 180 (2007) 2986–2989. (2014) 600–606. [48] D. Wang, J. Zhang, Q. Luo, X. Li, Y. Duan, J. An, [30] T. Wu, G. Liu, J. Zhao, H. Hidaka, N. Serpone, Photoassisted Characterization and photocatalytic activity of poly(3-

degradation of dye pollutants. V. self-photosensitized oxidative hexylthiophene)-modiﬁed TiO2 for degradation of methyl transformation of Rhodamine B under visible light irradiation orange under visible light, J. Hazard. Mater. 169 (2009) 546–550.

in aqueous TiO2 dispersions, J. Phys. Chem. B 102 (1998) [49] Y. Zhu, Y. Dan, Photocatalytic activity of poly(3- 5845–5851. hexylthiophene)/titanium dioxide composites for degrading [31] X. Zhang, D.D. Sun, G. Li, Y. Wanga, Investigation of the roles methyl orange, Sol. Energy Mater. Sol. Cells 94 (2010) 1658–1664. of active oxygen species in photodegradation of azo dye AO7 in [50] S. Xu, L. Gu, K. Wu, H. Yang, Y. Song, L. Jiang, Y. Dan, The

TiO2 photocatalysis illuminated by microwave electrodeless influence of the oxidation degree of poly(3-hexylthiophene) on lamp, J. Photochem. Photobiol. A 199 (2008) 311–315. the photocatalytic activity of poly(3-hexylthiophene)/TiO2 [32] P. Wang, S.M. Zakeeruddin, J.E. Moser, M.K. Nazeeruddin, T. composites, Sol. Energy Mater. Sol. Cells 96 (2012) 286–291. Sekiguchi, M. Gra¨tzel, A stable quasi-solid-state dye-sensitized [51] L. Song, R. Qiu, Y. Mo, D. Zhang, H. Wei, Y. Xiong, solar cell with an amphiphilic ruthenium sensitizer and polymer Photodegradation of phenol in a polymer-modified TiO2 gel electrolyte, Nat. Mater. 2 (2003) 402–407. semiconductor particulate system under the irradiation of [33] Y. Zhu, S. Xu, L. Jiang, K. Pan, Y. Dan, Synthesis and visible light, Catal. Commun. 8 (2007) 429–433. characterization of polythiophene/titanium dioxide composites, [52] R. Qiu, D. Zhang, Y. Mo, L. Song, E. Brewer, X. Huang, Y. React. Funct. Polym. 68 (2008) 1492–1498. Xiong, Photocatalytic activity of polymer-modified ZnO under [34] Y. Li, A. Lu, C. Wang, X. Wu, Characterization of natural visible light irradiation, J. Hazard. Mater. 156 (2008) 80–85. sphalerite as a novel visible light-driven photocatalyst, Sol. [53] A. Ali, R. Jamal, W. Shao, A. Rahman, Y. Osman, T. Energy Mater. Sol. Cells 92 (2008) 953–959. Abdiryim, Structure and properties of solid-state synthesized [35] S. Xu, Y. Zhu, L. Jiang, Y. Dan, Visible light induced poly(3,4-propylenedioxythiophene)/nano-ZnO composite, Prog. photocatalytic degradation of methyl orange by Nat. Sci. Mater. Int. 23 (2013) 524–531.

polythiophene/TiO2 composite particles, Water Air Soil Pollut. [54] D. Fu, G. Han, Y. Chang, J. Dong, The synthesis and properties 213 (2010) 151–159. of ZnO–graphene nano hybrid for photodegradation of [36] Y. Zhu, S. Xu, D. Yi, Photocatalytic degradation of methyl organic pollutant in water, Mater. Chem. Phys. 132 (2012) orange using polythiophene/titanium dioxide, React. Funct. 673–681. Polym. 70 (2010) 282–287. [55] T. Abdiryim, A. Ubul, R. Jamal, Y. Tian, T. Awut, I. Nurulla, [37] J. Wang, D. Zhang, One-dimensional nanostructured Solid-state synthesis and characterization of polyaniline/nano-

polyaniline: syntheses, morphology controlling, formation TiO2 composite, J. Appl. Polym. Sci. 126 (2012) 697–705. mechanisms, new features, and applications, Adv. Polym. [56] S. Wang, C.T. Nai, X.F. Jiang, Y. Pan, C.H. Tan, M. Nesladek, Technol. 32 (2013) 323–368. Q.H. Xu, K.P. Loh, Graphene oxide–polythiophene hybrid with [38] Y. Cheng, J. Wang, Y.C. Bao, Y.L. Ma, G.H. Wang, Synthesis broad-band absorption and photocatalytic properties, J. Phys. of polythiophene nanoparticles by microemulsion Chem. Lett. 3 (2012) 2332–2336. polymerization for photocatalysis, Adv. Mater. Res. 399–401 [57] Y. Wang, W. Chu, S. Wang, Z. Li, Y. Zeng, S. Yan, Y. Sun, (2012) 1312–1319. Simple synthesis and photoelectrochemical characterizations of

[39] H.C. Liang, X.Z. Li, Visible-induced photocatalytic reactivity of polythiophene/Pd/TiO2 composite microspheres, ACS Appl. polymer–sensitized titania nanotube ﬁlms, Appl. Catal. B 86 Mater. Interface 6 (2014) 20197–20204. (2009) 8–17. [58] M.R. Chandra, T.S. Rao, S.V.N. Pammi, B. Sreedhar, An [40] N.C. Strandwitz, Y. Nonoguchi, S.W. Boettcher, G.D. Stucky, enhanced visible light active rutile titania-copper/polythiophene

In situ photopolymerization of pyrrole in mesoporous TiO2, nanohybrid material for the degradation of rhodamine B dye, Langmuir 26 (2010) 5319–5322. Mater. Sci. Semicond. Process. 30 (2015) 672–681. [41] Z. Weng, X. Ni, Oxidative polymerization of pyrrole [59] N.K. Boutoumi, H. Boutoumi, H. Khalaf, B. David, Synthesis and

photocatalyzed by TiO2 nanoparticles and interactions in the characterization of TiO2-montmorillonite/polythiophene-SDS composites, J. Appl. Polym. Sci. 110 (2008) 109–116. nanocomposites: application in the sonophotocatalytic [42] S. Xu, L. Jiang, H. Yang, Y. Song, Y. Dan, Structure and degradation of rhodamine 6G, Appl. Clay Sci. 80–81 (2013) 56–62.

photocatalytic activity of polythiophene/TiO2 composite [60] M.M.C. Pirola, E. Selli, Degradation of organic water particles prepared by photoinduced polymerization, Chin. J. pollutants through sonophotocatalysis in the presence of TiO2, Catal. 32 (2011) 536–545. Ultrason. Sonochem. 10 (2003) 247–254. [43] H. Fu, T. Xu, S. Zhu, Y. Zhu, Photocorrosion inhibition and [61] T. Matsunaga, R. Tomoda, T. Nakajima, H. Wake, enhancement of photocatalytic activity for ZnO via Photochemical sterilization of microbial cells by

hybridization with C60, Environ. Sci. Technol. 42 (2008) semiconductor powders, FEMS Microbiol. Lett. 29 (2006) 8064–8069. 211–214. [44] M. Khatamian, M. Fazayeli, B. Divband, Preparation, [62] O. Akhavan, E. Ghaderi, Photocatalytic reduction of graphene

characterization and photocatalytic properties of oxide nanosheets on TiO2 thin film for photoinactivation of polythiophene-sensitized zinc oxide hybrid nanocomposites, bacteria in solar light irradiation, J. Phys. Chem. C 113 (2009) Mater. Sci. Semicond. Process. 26 (2014) 540–547. 20214–20220. [45] M. Lv, H. Yang, Y. Xu, Q. Chen, X. Liu, F. Wei, Improving the [63] G. Cˇı´k, S. Priesolova´, H. Bujda´kova´,F.Sˇersˇenˇ, T. Potheoöva´,J. + visible light photocatalytic activities of Bi25FeO40/MIL-101/ Krisˇtıń, Inactivation of bacteria G -S. aureus and G -E. coli by PTH via polythiophene wrapping, J. Environ. Chem. Eng. 3 (2) phototoxic polythiophene incorporated in ZSM-5 zeolite, (2015) 1003–1008. Chemosphere 63 (2006) 1419–1426. [46] D.E. Motaung, G.F. Malgas, C.J. Arendse, S.E. Mavundla, C.J. [64] K. Shang, S. Ai, Q. Ma, T. Tang, H. Yin, H. Han, Effective Oliphant, D. Knoesen, Thermal-induced changes on the photocatalytic disinfection of E. coli and S. aureus using

properties of spin-coated P3HT:C60 thin ﬁlms for solar cell polythiophene/MnO2 nanocomposite photocatalyst under solar applications, Sol. Energy Mater. Sol. Cells 93 (2009) 1674–1680. light irradiation, Desalination 278 (2011) 173–178. 504 M.O. Ansari et al.

[65] K. Shang, B. Sun, J. Sun, J. Li, S. Ai, Poly-(3-thiopheneacetic [67] C. Wen, K. Hasegawa, T. Kanbara, S. Kagaya, T. Yamamoto,

acid) coated Fe3O4@LDHs magnetic nanospheres as a Visible light-induced catalytic degradation of iprobenfos photocatalyst for the efficient photocatalytic disinfection of fungicide by poly(3-octylthiophene-2,5-diyl) film, J. pathogenic bacteria under solar light irradiation, New J. Chem. Photochem. Photobiol. A 133 (2000) 59–66. 37 (2013) 2509–2514. [68] M.R. Hoffmann, S.T. Martin, W. Choi, D.W. Bahnemann, [66] C. Wen, K. Hasegawa, T. Kanbara, S. Kagaya, T. Yamamoto, Environmental applications of semiconductor photocatalysis, Photocatalytic properties of poly(3-octylthiophene-2,5-diyl) film Chem. Rev. 95 (1995) 69–96. blended with sensitizer for the degradation of iprobenfos fungicide, J. Photochem. Photobiol. A 137 (2000) 45–51.