The Preparation And Photocatalytic Activity Investigation Of Zinc Oxide And Bismuth Oxide

Semiconductor photocatalysis which utilizes clean and renewable solar energy to activate the photodegradation of contaminations and without secondary pollution is an efficiency and sustainable environment-friendly technology to provide solution for environmental issue, especially for dye wastewater treatment. It has become a hot issue in laboratories and industrial applications. ZnO, one kind of wide band gap semiconductor, which band-gap energy gets close to TiO2 but get larger exciton binding energy, more economical, more powerful response to UV light and can be excited by UV light to produce reactive oxygen substances to photodegrade pollutants, has become a hot semiconductor photocatalyst. However, wide band gap limits the absorption of visible light. Recently, with the studies and development of photocatalysts in response to visible light, narrow band gap semiconductor Bi2O3 and its modifications have become very popular and promising photocatalysts. Bi2O3, which can motivated by visible light to generate electron transition and produce reactive oxygen species to degradate organic pollutants. As a non-stoichiometric phase of bismuth oxide, the physical and chemical properties of Bi2O2.33 have been studied, but its light-absorbing properties and photocatalytic activity are not clear yet. Based on the above discussion, the main work of this paper are as follows:(1) ZnO nanoparticles have been preparared by Super (sub) critical hydro thermal synthesis. The influences of parameters like reaction temperature, pressure, the concentration and the type of alkali to the size and morphology of ZnO were studied. The growth mechanism of ZnO crystals was discussed. Five different morphologies of ZnO nanoparticls were as the photocatalyst photodegraded rhodamine B under UV light, to investigate the photocatalytic activity of ZnO nanoparticles. The impacts of process parameters on the photodegradation rate of Rhodamine B were also studied. It showed that ZnO nanoparticles with the narrowest band gap and the maximum specific surface area and pore volume, could get a photodegradation rate of 99.67% after 6 h and the kinetic constant is 24 times higher than that of direct photolysis.(2) Bi2O3 particles were prepared by mild co-precipitation method. Different morphologies of Bi2O3 particles were prepared by adding different surfactants. Modified Bi2O3 was prepared by doping Ag with different amount. The photocatalytic activity of all as-prepared samples was investigated by the photodegradation of rhodamine B under simulated sunlight. The results showed that with the minimum band-gap energy, spherical-like Bi2O3 with SDS as surfactant behavied the highest photocatalytic activity of photodegradation rate of 85.60% after 150 min, the kinetic constant of which is 14.45 times to the direct photolysis. Modified Bi2O3 with 3% Ag doped got a photodegradation rate of 95.02% after 120 min, the kinetic constant of which is 48.77 times higher than that of direct photolysis and 2.78 times higher than that of pure Bi2O3. Ag doping can reduce the combination of photo-generated carriers, broad the visible light response range and improve the photocatalytic activity of semiconductor photocatalyst.(3) Bi2O2.33 and Ag-doped Bi2O2.33 were successfully synthesized via a facile and chemical strategy, the photocatalytic activity of which was investigated by the photodegradation of rhodamine B under simulated sunlight. The Ag-6% sample yielded the highest RhB removal ratio of 93.54%, the kinetic constant of which is 26.5 times higher than that of direct photolysis and 2.7 times higher than that of pure Bi2O2.33. The reactive oxygen species of O2 and ·OH were detected by EPR during the photoreaction. As such, the prepared Ag-doped Bi2O2.33 seems a promising photocatalyst with high photocatalytic activity and stability, showing a great potential in the field of environmental remediation.