View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Journal of Saudi Chemical Society (2015) 19, 494–504 King Saud University Journal of Saudi Chemical Society www.ksu.edu.sa www.sciencedirect.com 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 vis- ible light-assisted photocatalysis are discussed in terms of the parameters that affect the photocat- alytic 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. Production and hosting by Elsevier 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 inor- ganic 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) S O O Poly(3,4-ethylene dixoxythiophene) S OH Poly(hydroxymethyl-3,4- ethylenedioxythiophene) O O S 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.