Polyaniline/zinc oxide (PANI/ZnO) composite photocatalysts were prepared from neutral media by in situ chemical oxidation of aniline (ANI) in the presence of different amounts of diethylene glycol (DEG). The PANI/ZnO composite photocatalysts were synthesized to efficiently remove organic dye (acid blue, AB25) from model wastewater. The PANI/ZnO composite photocatalysts were studied with the intention of efficient removal of organic dye (acid blue, AB25) from wastewater to obtain low-cost heterogeneous catalysts that offer high catalytic activity and stability. The conductive PANI polymer, which absorbs Vis irradiation, was used in this work as ZnO absorbs only ultraviolet (UV) irradiation; thus, the composite photocatalysts’ activity was broadened into the Vis region. Characterization of the composite photocatalysts was done by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, electric conductivity, UV-Vis spectroscopy, and by specific surface area (SBET) measurements. The composites’ photocatalytic activity under solar irradiation was validated by monitoring degradation of the AB25 dye. This study presented that it was possible both to prepare PANI and to prevent ZnO dissolution if in situ polymerization starts from neutral media with the addition of DEG. Additionally, efficient removal of AB25 dye, about 90% in 60 min, was achieved. The first-order rate constants of the photodegradation of AB25 by PANI/ZnO 0.02/0.024/0.04 DEG (and pure ZnO)) were computed to be 0.0272/0.0281/0.0325 (and 0.0062) min⁻¹, indicating that the morphology and surface of the photocatalysts have significantly influenced the catalytic activity.

The polyaniline/TiO₂ (PANI/TiO₂) composite photocatalysts were prepared by the in situ chemical oxidation of aniline (An) in the presence of TiO₂ particles. For this purpose, photocatalysts with different amounts of PANI polymer were prepared and analysed. Fourier-transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis indicated successful synthesis of the PANI polymer and its conductivity was also determined. The micrographs of field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) were used to explain the impact of the aniline amount on the aggregation process during the synthesis of the composites. The smallest size of aggregates was obtained for the photocatalysts with 15% of PANI (15PANI/TiO₂) due to the formation of homogenous PANI. The photocatalytic activity of studied PANI/TiO₂ photocatalysts was validated by monitoring the discoloration and mineralization of Reactive Red azo dye (RR45) in wastewater. The 15PANI/TiO₂ sample presented the highest photocatalytic efficiency under ultraviolet A (UVA) irradiation, in comparison to pure TiO₂. This was explained by the formation of uniformly dispersed PANI on the TiO₂ particles, which was responsible for the synergistic PANI-TiO₂ effect.

The waste fly ash (FA) material was subjected to chemical treatment with HCl at elevated temperature for a different time to modify its porosity. Modified FA particles with highest surface area and pore volume were further used as a support for TiO ₂ catalyst during FA/TiO ₂ nanocomposite preparation. The nanocomposite photocatalysts were obtained by in situ sol–gel synthesis of titanium dioxide in the presence of FA particles. To perform accurate characterization of modified FA and FA/TiO ₂ nanocomposite photocatalysts, gas adsorption-desorption analysis, X-ray diffraction, scanning electron microscopy, UV/Vis and Infrared spectroscopy were used. Efficiency evaluation of the synthesized FA/TiO ₂ nanocomposites was performed by following the removal of Reactive Red 45 (RR45) azo dye during photocatalytic treatment under the UV-A irradiation. Photocatalysis has been carried out up to five cycles with the same catalysts to investigate their stability and the possible reuse. The FA/TiO ₂ photocatalyst showed very good photocatalytic activity and stability even after the fifth cycles. The obtained results show that successfully modified waste fly ash can be used as very good TiO ₂ support.