In recent years, there has been an increasing interest in the development of polymer/inorganic nanohybrid materials [1–3]. Inorganic semiconductors such as ZnO, TiO2, MnO2, and ZrO2 have been extensively investigated as hybrids with polymers having synergetic or complementary properties and behavior for the fabrication of a variety of devices. Among these semiconductors, ZnO has promising applications in electrical engineering, catalysis, ultraviolet absorption, photodegradation of microorganisms, and optical and optoelectronic devices [4–8]. Although ZnO exhibits many advantages, there are still some disadvantages such as the lack of visible light response, low quantum yield, and lower photocatalytic activity. Also, it is important to shift the photoactivation region of ZnO particles toward visible wavelengths. Previous studies demonstrated that conducting polymers incorporated with ZnO could display reasonable catalytic activity under light illumination [9–12], and the delocalized conjugated structures of conductive polymers have been proven to arouse a rapid photoinduced charge separation and decrease the charge recombination rate in electron transfer processes [13, 14].
However, ZnO is an amphoteric oxide, and it can react with acid or base to form a water-soluble salt. Therefore, a successful incorporation of ZnO into a conducting polymer matrix is the main research topic. Up to now, there are many reports on the preparation methods of conducting polymer/ZnO composites [15–17], and the methods are mainly electrochemical polymerization  and mechanical mixing . Since ZnO has the possibility of forming a soluble salt, the common chemical oxidative polymerization method is difficult to apply for preparing conducting polymer/ZnO composites. Although electrochemical polymerization can be an effective method for obtaining conducting polymer/ZnO composites, the composites are just the layer-by-layer hybrid films of conducting polymers and ZnO, which is the main factor in limiting the use of the composites. In mechanical mixing method, the composites were just the physical mixture of inorganic particles and polymer, and the polymer should be prepared before the mechanochemical mixing [20, 21]. The uniform distribution of inorganic particles in the polymer matrix is considered to be difficult in the case of mechanical mixing method.
Among conducting polymers, polyaniline and polythiophene are widely used for the fabrication of conducting polymer/ZnO hybrid materials [22, 23]. Although there are many reports about polythiophene-type conducting polymer/ZnO nanohybrid materials, the main aspect of these studies is on the investigation of hybrid bulk heterojunction solar cells based on the blend of polythiophene-type conducting polymers and ZnO nanoparticles [24–26]. As a derivative of polythiophene, poly(3,4-ethylenedioxythiophene) (PEDOT) has been utilized as a charge storage material because of its many favorable properties, including reduced bandgap, low oxidation potential for conversion to the conducting state, and high stability in the conducting form, as well as its larger electroactive potential window and higher cycling stability than polyaniline [27–29]. Sharma et al. reported that PEDOT/ZnO nanocomposite films displayed improved I-V characteristics, indicating that the heterojunction of nano-ZnO and PEDOT can enhance their photovoltaic properties . Zhang et al. fabricated a self-powered UV photodetector on the basis of the property of the PEDOT:PSS/ZnO heterojunction, which may offer theoretical support in future optoelectronic device fabrication and modification . However, up to now, there is no report for the application of PEDOT/ZnO for dye ultraviolet-visible (UV-vis) photodegradation.
According to the previous report, PEDOT can be prepared by in situ sublimation/polymerization of 2,5-dibromo-EDOT . This may bring some possibility of the preparation of a PEDOT/ZnO nanohybrid material by the same method. Herein, we report the exploration of synthesizing PEDOT/ZnO nanocomposites in powder form by in situ solid-state heating method, and the content of nano-ZnO in the reaction system was varied from 10 to 20 wt%. The structural and morphological properties of the composites were investigated by Fourier transform infrared (FTIR) spectroscopy, UV-vis absorption spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). Furthermore, the comparative photocatalytic activity of the PEDOT/ZnO nanocomposites, nano-ZnO, as well as PEDOT under different light sources for the degradation of methylene blue (MB) was investigated.