| Photocatalysis, one of the most promising remediation technologies, has received extensive attention in past decades. Monoclinic scheelite-type BiVO4 exhibits a better photocatalytic activity under visible light irradiation since it can decompose organic pollutant as H2O and CO2, which is an environmental friendly photocatalyst with non-toxic and high-stability. However, BiVO4 is difficult to be removed from the solution, which will generate secondary pollution in the process of photocatalysis degradation. Besides, BiVO4 photocatalyst has a small surface area and low absorbability with organic pollutants, which is not beneficial for the photocatalysis. Therefore, immobilization of BiVO4 onto one carrier material can enrich the organic substances by adsorption and enhance the photocatalytic performance. Moreover, this composite catalyst can be easily recovered from aqueous suspensions for reuse.For the above reasons, this research used bentonite that possess rich reserves, layered structures, large surface areas and high absorbability of organic substances as a carrier material. A series of loading visible photocatalyst BiVO4/bentonite calcined at different temperatures were prepared by solution combustion synthesis method. The crystal type, surface topography, particle size, light absorption range, constituent elements of BiVO4/bentonite photocatalyst were characterized by X-ray diffraction(XRD), field emission-scanning electron microscope(FE-SEM), Transmission Electron Microscope(TEM), specific surface area(BET), UV-vis diffuse reflectance spectra(UV-vis DRS), Energy Spectrum Analysis(EDS). The adsorption kinetics of C.I.Reactive Blue 19 onto BiVO4/bentonite was investigated. The influences of factors including the dye initial concentrations, the dye initial pH value and type of light on the photocatalysis were discussed. The main research papers were summarized in the following statements:(1) Among the three photocatalysts prepared at different calcined temperature, BiVO4/bentonite crystallite was a monoclinic structure with diameter of about 30nm, and showed strong absorption in visible light region 400～500nm when it was calcined at 300℃.(2) The experimental data fitted very well the pseudo-second-order kinetic model as the initial concentration was between 15～45mg/L and the experimental temperature was 298-318K. The activation energy of the sorption was calculated using the pseudo-second-order rate constant, and it was found to be 28.75 KJ/mol, which meant that the adsorption process was due to the combined control of chemical adsorption and physicial adsorption.(3) Through the visible photocatalytic degradation simulation experiments, it was found that the photocatalysis of BiVO4/bentonite calcined at 300℃was the best. It was found that using 50mg photocatalyst, when pH=5.5, the C.I.Reactive Blue 19 solution was degraded by 93.9% from the initial concentration of 25mg/L within 120min under 400W metal halide lamp irradiation. It can maintain almost the same activity after being repeatedly used for 5 times.(4) The relation between ln(C/C0) and irradiation time t presented a well linearity in all factors. The reactions followed the Langumuir-Hinshelwood first-order reaction kinetics very well. |
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