Study On Degradation Of Methylene Blue With Zinc Based Layered Double Hydroxides

With the rapid development of textile dyes industry, the variety and quantity of the dyes is increasing, pay more and more people pay attention to its’contaminative problem. And it is necessary to decolorate and degradate of methylene blue (a high conjugate cationic dye, short for MB), which is a typical organic pollutants in wastewater. The traditional photocatalysts such as TiO2, ZnO and CdS has the photocatalytic activity for organic water, but the solar energy utilization rate is low. Therefore, the development of high quantum yield, can be efficient semiconductor photocatalyst stimulate the solar spectrum in the visible light, is the current hot and difficult to solve in the photocatalytic technology. The layered double hydroxides (LDHs) with large surface area, pore volume, special layered structure,"memory effect" of calcined products, interlayer anionic exchangeability, and narrow band gap, improving the utilization rate of sunlight greatly, so that it is gradually valued in the photocatalytic field. The main results of this dissertation are as follows:(1) LDHs-based intercalated and assembly catalytic materialszinc based layered double hydroxides with different trivalent metal cations (Al3+, Fe3+, Cr3+) were synthesized by coprecipitation method, and the kinetics and thermodynamics for Methylene Blue (MB) degradation were studied. The results show that all of the catalysis samples of ZnAl-LDHs, ZnFe-LDHs, ZnCr-LDHs have good photocatalytic activity under visible light. The tenthalpy and entropy values appear the tendency of increase, and the reaction rate constants of three catalysts increased with increasing temperature. Moreover, ZnAl-LDHs show the largest reaction rate constant and highest catalytic activity at the same temperature. The photocatalysts are characterized by PXRD, FT-IR and UV-Vis DRS. In addition, the possible mechanisms for photocatalytic degradation on Methylene blue with ZnAl-LDHs were also discussed in details.ZnAl Layered double hydroxides with different intercalated anions (NO3-, Cl-and CO32-) are synthesized by a coprecipitation method, and photocatalytic degradation properties of Methylene Blue (MB) are tested. The results show that intercalated anions influence the photocatalytic degradation process of methylene blue and ZnAl LDHs intercalated with carbonate exhibits the highest catalytic activity. With180min irradiation of visible lamp, the absorption peaks of methylene blue solution disappear with a degradation rate of95%. The photocatalysts are characterized by XRD, FT-IR, TG-MS and UV-Vis DRS. In addition, the kinetic of the process and degradation mechanism are described by Origin8.1Linear Fitting and Gaussian software simulation. It is found that the degradation kinetics are best fitted with the first-order kinetic model and MB is degradated into colorless small organic molecules.(2) LDHs-based modified catalytic materialsThree different composites, including FeOOH/ZnAl-LDHs calcined composites (CFL), ZnAl-LDHs calcined product (ZnAl-LDO) and ZnFeAl-LDO calcined product (ZnFeAl-LDO), were synthesized by sol-gel method, and their activity for photocatalytic degradation of methylene blue(MB) under visible light were studied. Composites were analyzed by PXRD, SEM, and BET characterization, confirming the formation of good crystal structure. The degradation performance of MB degradation is following the order:CFL (95%)> ZnFeAl-LDO (60%)> ZnAl-LDO (23%)> CF (10%). In addition, a possible mechanism for photocatalytic degradation on MB has also been presumed. Moreover, Frontier electron densities on atoms of MB were also calculated, which in satisfactory agreement with the possible mechanism.