Study On The Preparation And Photocatalytic Performances Of Zinc, Bismuth Based/Graphene Visible-Light-Responsive Photocatalysts

Photocatalytic oxidation technique is an effective route towards reducing non-biodegradable contamination in the industrial organic wastewater, which possesses huge potential in the prospect of sustainable development. However, photocatalytic oxidation technique has its certain drawbacks at the current stage, such as low quantum efficiency, poor visible light utilization efficiency, poor photostability etc., greatly retarding its practical application and industrial usage. In this regard, seeking and developing visible-light-responsive photocatalysts with advanced activity, high photostability, as well as good recycling performance is hence of significant importance in the field of water treatment and environmental remediation.In this thesis, ZnO, ZnSnO3, ZnMoOx, BiVO4 and BiOCl were loaded on graphene(along with reduced graphene-oxide(RGO)) possessed unique electronic properties, large specific surface area,excellent adsorptive capacity, and high optical transparency, for the preparation of zinc, bismuth based/graphene composite photocatalyst with efficient visible-light-responsive photocatalytic activity. The crystallinity, morphology, adsorption property, band structure, chemical construction, photochemistry property, and electron transfer feature of the as-synthesized composite photocatalysts were well characterized with the aid of X-ray diffraction analysis(XRD), scanning electron microscope(SEM), high resolution transmission electron microscope(HRTEM), energy dispersive X-ray spectroscopy(EDX), N2absorption-adsorption spectrometer(BET), UV-Vis absorption spectroscopy(UV-Vis), Fourier transform infrared spectroscopy(FT-IR), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy(DRS),photoluminescence spectroscopy(PL), cyclic voltammetry(CV), and electrochemical impedance spectroscopy(EIS). The photocatalytic activities were evaluated by the degradation of simulated wastewater containing metronidazole(MZ), rhodamine B(Rh B), and sulfanilamide(SN) under visible light or natural sunlight irradiation. The formation process of specific shaped photocatalyst, the mechanism of the enhancement in the visible-light-driven composite photocatalytic performances, and the degradation mechanism of the contaminants have been systematic probed to(i) reveal the relationship between themorphology, property, and photocatalytic performance of certain composite,(ii) explore new route for controllable fabrication of visible-light-responsive catalytic materials with advanced performance, and(iii)provide fundamental understanding towards the preparation and application of zinc, bismuth based/graphene visible-light-responsive composite photocatalyst. This thesis mainly encompasses the following four sections:(1) Zn O columns and ZnSnO3 hollow nanospheres were prepared by carbon template-assisted approach, which were further decorated by graphene to form novel ZnO/RGO and ZnSnO3/RGO nanocomposite photocatalysts by hydrothermal method, respectively. The results indicated that the functional groups on the surface of carbon nanospheres attracted large amounts of Zn2+ ions through coordination or electrostatic interactions, and the removal of the carbon nanospheres by calcination treatment afterwards could lead to the formation of specific morphology; both ZnO/RGO and ZnSnO3/RGO possessed excellent visible-light catalytic activity, the degradation efficiency of MZ in the presence of catalysts were both enhanced about 30%; the enhanced photocatalytic activity of novel composite photocatalyst was speculated to stem from the improved light utilization, higher adsorptive property, and enhanced quantum yield by the introduction of RGO.(2) Novel rhombus-shaped ZnMoOx/RGO composite photocatalysts were prepared in a controllable manner by an in-situ, ultrasonic-assisted growth strategy. The results indicated that ZnMoOx was a mixture phase of ZnMoO4 and ZnMoO3, the in-situ growth process started from the “seeds” formed by the oxygen-containing groups on the GO surface contacting with Zn2+; the degradation efficiency of RhB by the ZnMoOx/RGO composites with 3 wt% RGO was best, which was 3.4 times larger than that of pure ZnMoOx sample(28.4%), the investigation also indicated that the composites possessed excellent photostability; the enhanced photocatalytic activity of ZnMoOx/RGO photocatalyst might be attributed to the improved light absorption, band gap narrowing, and efficient separation of photo-generated electron/hole pair. In addition, the ZnMoOx/RGO also exhibited good electrical performance as the supercapacitor electrode and noticeably antibacterial activity.(3) A new low-temperature hydrothermal method for the controlled synthesis of diverse BiVO4 architectures was developed. The results indicated that the morphological structure was affected by the portions of either NH3·H2O or NaOH, the morphology of BiVO4 at different pH value depended upon thecompetition between the nucleation and growth rates during the crystal formation; a typical hydrothermal ripening process known as Ostwald ripening can be applied to describe the formation of dumbbell-shaped BiVO4 hierarchical architectures; the photogenerated holes were the dominant oxidative species in the BiVO4 photo-degradation system; the shape-controlled BiVO4 exhibited preferably natural sunlight-responsive photocatalytic activity. The enhanced photocatalytic performances were neither related to the surface area values nor the aspect ratios of the fabricated photocatalysts, but associated with the unique shaped configurations produced under specific low temperature hydrothermal conditions. The novel three-dimensional acicular sheaf shaped BiVO4/RGO composite photocatalysts were prepared by water bath reduction method, The results indicated that the highest photocatalytic performance can be achieved for the BiVO4/RGO composite photocatalysts with 1 wt% RGO, the degradation efficiency of RhB was98.5% and about 65% higher than that of BiVO4, which also possessed excellent photostability; The improvement photocatalytic activity of BiVO4/RGO was not related to the specific surface area, but associated with the enhanced light harvesting efficiency and reduced charge recombination rate of the composites.(4) A novel BiOCl/RGO composite photocatalysts was prepared by a chemical hydrolysis reaction-water bath reduction method. The results indicated that the composite photocatalyst contained 1wt% RGO exhibited superior photocatalytic response, where the degradation rate of SN at 82.7% stayed30% higher than that of pure BiOCl; The enhanced photocatalytic performances of BiOCl/RGO composites were neither related to the surface area values nor the bandgap of the fabricated photocatalysts, but associated with the enhanced visible light absorption and advanced electron transfer ability. On a basis of the analysis on the SN intermediate products by HPLC, IC, FT-IR, 1H NMR, 13 C NMR and MS, the degradation pathway of SN was speculated, where it was confirmed that the main degradation product of SN was sulfanilic acid.