Study On The Preparation Of Bi, Zn-based Photocatalysts And Its Visible-light-responsive Photocatalytic Performance Fororganic Wastewater

Photocatalytic oxidation technique is an effective route towards reducing non-biodegradable contamination in the 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 etc., greatly retarding its practical application and industrial usage. In this regard, seeking and developing visible-light-responsive photocatalysts with excellent performance is hence of significant importance in the field of water treatment and environmental remediation.Zinc and bismuth-based semiconductor materials possess favourable visible-light photocatalytic performance, as well as reduced graphene-oxide(RGO) has excellent adsorptive capacity and high optical transparency. In view of the above-mentioned aspects, the preparation of zinc, bismuth based photocatalyst with efficient visible-light-responsive photocatalytic activity, namely BiVO4, BiOF/Bi2O3/RGO and ZnO, were described in detail in this thesis by virtue of hydrothermal synthetic method and chemical hydrolysis approach, with optimizing the calcination temperatures, SDBS content and RGO content. The crystallinity, morphology, adsorption property, band structure, chemical construction, photochemistry property, and electron transfer feature of the obtained photocatalysts were well characterized with the aid of X-ray diffraction analysis(XRD), scanning electron microscope( S E M), high resolution transmission electron microscope(HRTEM), N2 adsorption, Fourier transform infrared spectroscopy(FT-IR), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy(UV-vis DR), photoluminescence spectroscopy(PL), and cyclic voltammetry(CV) etc. The photocatalytic activities were evaluated by the degradation of simulated wastewater containing rhodamine B(RhB), orange IV(OG-IV), and metronidazole(MNZ) under visible light or natural sunlight irradiation, thus provided fundamental understanding towards the preparation and application of zinc, bismuth based visible-light-responsive photocatalyst. This thesis mainly encompasses the following sections:(1) Study on the preparation and visible-light-responsive performance of rod-like BiVO4 photocatalyst: a novel BiVO4 photocatalyst was prepared with hydrothermal method by using Bi(NO3)3·5H2O and NH4VO3 as raw materials. The results indicated that calcination temperature had important effects on both the performance and photocatalytic activity of BiVO4 photocatalyst, the sample calcinated at 300 °C(BiV-3) performed a superior photocatalytic activity; BiV-3 showed a rod-like shape and belonged to monoclinic scheelite, with a visible light absorption edge, band-gap, and surface area were 540 nm, 2.44 eV, and 3.4652 m2/g, respectively; the photocatalytic activity of BiV-3 was evaluated by the degradation of 10 mg/L RhB and 7.5 mg/L OG-IV simulated wastewater under natural sunlight irradiation, the results indicated that the degradation of RhB and OG-IV in the presence of 1.0 g/L and 0.5 g/L catalyst dosage achieved 99% and 75%, respectively, which was higher than that of sample without calcination(54% and 26%); Both the photocatalytic degradation of RhB and OG-IV are well-suited with the first-order kinetics model, and the reaction rate constant of photocatalytic degradation of RhB and OG-IV is 0.852 h-1 and 0.142 h-1, respectively; Bi V-3 had excellent repeatability and stability.(2) BiOF/Bi2O3/RGO composite photocatalysts with stable and efficient natural sunlight photocatalytic activity were prepared by hydrolysis method: BiOF/Bi2O3 nanostructures were prepared with hydrolysis method by using Bi(NO3)3·5H2O and NaF as raw materials, where the as-prepared BiOF/Bi2O3 was subsequently incorporated with reduced graphene oxide(RGO) sheets to form BiOF/Bi2O3/RGO composites by water bath reduction method. The results indicated that calcination temperature had important effects on the photocatalytic activity of BiOF/Bi2O3 photocatalyst, the sample calcinated at 300 °C(BF-3) performed a superior photocatalytic activity; as well as the RGO content, the highest photocatalytic performance can be achieved for the BiOF/Bi2O3/RGO composite photocatalysts with 1 wt% RGO(BG-1). The photocatalytic activity of BG-1 was evaluated by the degradation of 15 mg/L RhB simulated wastewater in the presence of 0.5 g/L catalyst dosage under natural sunlight irradiation, the degradation of RhB achieved 99%, which was about 48% higher than that of sample without RGO(BF-3), and the BG-1 exhibited excellent stability and repeatability.(3) The effect of surfactant content on the hydrothermal synthesis of ZnO photocatalyst: Zn(CH3COO)2·2H2O and NaWO4·2H2O were chosen as the starting materials, the addition of sodium dodecyl benzene sulfonate(SDBS) as a decorating agent for the preparation of ZnO photocatalyst. The results indicated that the highest photocatalytic performance can be achieved for the ZnO photocatalysts with 0.75 g SDBS(ZO-0.75); the property of ZnO, such as the morphology, and band gap, etc. was greatly changed in the presence of SDBS. ZO-0.75 was rod-like shape and its band gap was 3.17 eV. The results of the hydroxyl radical trapping experiment indicated that the main active ingredient in this system was ·OH; the degradation of MNZ achieved 72% in the presence of ZO-0.75 under simulated visible light irradiation, which was about 56% higher than that of ZnO without SDBS.