Preparation And Photocatalytic Properties Of Novel Typed Bismuth Vanadate/Reduced Graphene Oxide And Tin-doped Zinc Oxide Semiconductor

This thesis deals with the controlled fabrication, thorough characterization, as well as detailedinvestigations of photocatalytic properties of BiVO4, BiVO4/RGO composites and Sn-doped ZnO (Sn-ZnO)photocatalysts. The dumbbell-shaped BiVO4, BiVO4/RGO composites and Sn-ZnO nanospheres weresynthesized by hydrothermal, thermal reduction and solvothermal routes. The crystallographic,morphological, physicochemical, and photo-chemical properties of as-prepared photocatalysts were wellcharacterized by a variety of techniques, such as X-ray diffraction (XRD), Fourier transform infrared(FT-IR) analyzer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Nitrogenadsorption-desorption isotherm (BET), ultraviolet-visible diffuse reflectance (UV-vis DR) spectroscopy,and photoluminescence (PL) spectrophotometer. The natural-sunlight-driven photocatalytic performancesof obtained photocatalysts were then investigated in detail, therefore providing theoretical basis for thein-batch synthesis of novel photocatalysts as well as for the usage of these photocatalysts into realapplication sectors with regard to the efficient degradation of refractory wastewaters. The main contentsand concluding remarks of this thesis encompass the following aspects:1. Study on the synthesis and relevant photocatalytic activities of dumbbell-shaped BiVO4/RGOcomposites: This section reports the controllable synthesis of uniform dumbbell-shaped BiVO4hierarchicalstructures at a large scale through a facile low-temperature hydrothermal approach, where there was noinvolvement of any surfactant in the whole process. The as-produced BiVO4was of pure monoclinic phasewith uniform dumbbell-shapes, the average length and width of which was at3μm and2μm, respectively.The surface area of the prepared BiVO4was4.6003m2/g and the average pore diameter of the BiVO4wasof48nm. The value of the band gap was measured to be2.44eV, giving rise to the visible-light response ofthe as-synthesized BiVO4product. Regarding the investigation of the natural sunlight photocatalyticperformance, Rhodamine B (RhB) has been selected as the target pollutant. The effects of catalyst dosageand initial concentration of RhB on the photocatalytic degradation efficiency were probed, where theoptimum dosage of dumbbell-shaped BiVO4was set to be0.15g and the optimum initial RhBconcentration was7.5mg/L. In this study, the decolorization efficiency of RhB in the presence of BiVO4 reached96%after10h sunlight irradiation, revealing that the as-synthesized dumbbell-shaped BiVO4possessed good natural-sunlight-driven photocatalytic activity. On this basis, the as-synthesizeddumbbell-shaped BiVO4products were then incorporated with prepared reduced grapheneoxide (RGO) sheets to form BiVO4/RGO composites, and the obtained composites were usedto investigate the effect of photocatalytic performances of dumbbell-shaped BiVO4by couplingwith RGO. A noticeable augmentation in the natural-sunlight-driven decolorization efficiency(approx.26%increase compared with that of pure BiVO4) of RhB could be achieved bycoupling with RGO under experimentally optimum conditions.2. Study on the synthesis and relevant photocatalytic activities of Sn-ZnO nanosphere photocatalyst:This section deals with the fabrication of Sn-ZnO and ZnO nanosphere photocatalysts with the involvementof ZnCl2and glucose via a solvothermal method. Both the obtained Sn-ZnO and ZnO were of highcrystallinity. The Sn-ZnO possessed uniform size and shape distributions, whereas the ZnO photocatalystwas prone to aggregation. Regarding the investigation of the natural sunlight photocatalytic performance,the p-nitrophenol solution has been selected as the target pollutant. Comparison investigation of thenatural-sunlight-driven photocatalytic activities between the Sn-ZnO and ZnO nanosphere photocatalystsrevealed that a noticeable augmentation in the natural-sunlight-driven degradation efficiency ofp-nitrophenol, the removal rate of COD, and the removal rate of TOC (approx.27%,19%, and12%increase compared to that of pure ZnO, respectively) could be achieved after10h sunlight irradiation withthe presence of Sn dosage. These results indicated that Sn-ZnO had higher photocatalytic activity and Sndoping greatly augmented the photocatalytic activity of ZnO. In addition, the cycle-stabilizedphotocatalytic performances of Sn-ZnO photocatalysts have been probed, where it was observed thedegradation efficiency still reached72%even after five cycling runs (compared to81%at its first usage),revealing that the prepared Sn-ZnO photocatalysts possessed great photocatalytic repeatability and stabilityover prolonged irradiation time.