Preparation of some novel photocatalysts active under visible light using TiO₂ for remoral of various pollutants

Research Aim: At the recent years existence of various organic pollutants in the aqueuos sources has received increasing attention on environmental issue, which caused by discharges of industrial, hospital wastewater and household activities. These contaminants can cause severe adverse effects in human and wildlife. Thus, the aims of this thesis are fabrication of the novel nanocomposites based on TiO2 by creating oxygen vacancies and Ti3+ states and also coupling it with narrow band gap semiconductors to increase the harvesting of visible light and boost the separation of charge carriers, that due to efficient heterojunction formations between counterparts of nanocomposites with unique properties and investigation photocatalytic performance of the as-fabricated nanocomposites for elimination of various pollutants in water. Research method: At first, the background of the work was probed by investigating different scientific sources. afterwards, the electronical and optical properties of materials was studied and based on the band potentials of the photocatalysts components, the possible photocatalytic mechanisms of the photocatalysts for boosting their photocatalytic performance are also ascertained in detail. Findings: The investigation of the photoability for the as-fabricated nanocomposites in the elimination of different organic pollutants demonstrated that increasing the absorption of visible light due to the existence of narrow band gap semiconductors, high capability to generation and separation rate of the charge pairs at the interface of the semiconductors, and the enhanced specific surface area are the main cases for the boosted photocatalytic performance of the optimally prepared nanocomposites compared to the counterpatrs. Conclusion: This thesis focuses on the simple fabrication of four types of novel photocatalysts with activity under visible light by hydrothermal and ultrasonication methods. The structural, morphological, chemical, optical, and textural properties of the samples were characterized by XRD, EDX, SEM, TEM, HRTEM, XPS, FT-IR, UV–vis DRS, PL and BET techniques. Photocatalytic ability of the nanocomposites was studied by degradations of different cationic and anionic organic pollutants such as rhodamine B, methylene blue, methyl orange, and fuchsine under visible-light illumination. The degradation rate constants of pollutants over the optimal nanocomposites were higher than those of the pristine counterpatrs. In order to evaluate the role of photogenerated reactive species on the degradation of pollutants over the nanocomposites, different scavengers such as benzoquinone, ammonium oxalate, and 2-PrOH were added to the reaction system. Finally, the potential application of the prepared photocatalysts and their reuseabilities were investigated. It was shown that there is no significant loss in photocatalytic ability after successive cycles, which implied that the nanocomposites are highly stable in the photocatalytic processes.