Preparation And Photocatalytic Properties Of CuO/AgBr And Ag/g-C₃N₄/AgBr Photocatalyst Composites

With global energy shortage developed, the efficient use and development of energy has become the general trend of human development. Semiconductor photocatalytic technology as a new clean technology has been rised in response to the proper time and condition, with the development and research in recent years, photocatalytic technology was widely used in the treatment of pollutants,catalytic hydrogen production, photocatalytic sterilization and other fields.AgBr as a new type of semiconductor photocatalyst owned about 2.46 eV band gap. The e--h+pairs separated under visible light irradiation andthe seperation showed good photocatalytic activity. However, Ag Br was easy to produce elemental silver(Ag0) under light irradiation, which was called light resistance. The AgBr industrial application process has been restricted by its stability. Scientists have attempted a series of modified ways to improve the photocatalytic activity and stability of AgBr.In this paper, we regarded AgBr as research object. We respectively adopted the precipitation method and the hydrothermal synthesis method to synthesize CuO/AgBr and Ag/g-C3N4/AgBr improving the photocatalytic activity and stability. The as-prepared samples were tested by X-ray diffraction(XRD), UV-Vis diffuse reflectance spectroscopy(UV-Vis), Field emission scanning electron microscopy(FESEM), X-ray photoelectron spectroscopy(XPS), Photoluminescence(PL), Electron spin resonance(ESR) techniques and Fourier transform infrared spectra(FTIR).Besides, the photocatalytic activity and stability of CuO/AgBr and Ag/g-C3N4/AgBr hybrid were evaluated by photocatalytic degradation undervisible light irradiation. The conclusions were as followd:1.We adopted the precipitation method to synthesized the CuO-modifed sliver bromide photocatalyst(CuO/Ag Br):1) As can be seen from XRD spectra, the particle size of Cu O/AgBr was less than that of pure AgBr. Thereby, the absorption spectrum of Cu O/AgBr became blue shift, which was benefit for the as-prepared sample dispersed in the degradation solution improving the photocatalytic activity. At the same time the SEM spectra could also demonstrate the fact that particle size decreased.2) By comparing the degradation of methyl orange with different photocatalysts under visible light irradiation, the results showed that the degradation of methyl orange(C0=15 mg?L-1) over Cu O/AgBr was maintained at92%, which was much higher than pure Ag Br and CuO under the same condition. After three cycle tests, the degradation of MO with re-Cu O/AgBr composite could maintain above 90%, which showed good photocatlytic activity and stability.3) According to the XPS, PL and ESR spectra, we could see that the oxygen vacancies were produced on the surface of CuO/AgBr composite. The oxygen vacancies could facilitate the separation of electron-hole for accelerating the transfer of electrons. The electrons combined with adsorbed O2 to generate superoxide radicals(·O2-) for improving the photocatalytic activity under visible light.4) In addition, the use of bromine water regeneration method could significantly restore photocatalytic activity.2.We adopted the hydrothermal synthesis method for the preparation of Ag/g-C3N4/AgBr composite photocatalyst:1) We have synthesized spherical Ag/g-C3N4/AgBr composite by hydrothermal method, which exhibited good crystallinity. Amount of Ag0 generated on the surface of composites catalyst. Besides, Ag0 had absorbency tovisible light due to the surface plasmon resonance effect. This results showed that a small amount of loading Ag0 could improve the visible light absoption for photocatalyst.2) By examining the Ag/g-C3N4/AgBr composite photocatalyst degradation of methyl orange under visible light, we could see that the degradation rate of Ag/g-C3N4/AgBr(the molar ratio of g-C3N4:AgBr is 1:50) was 0.303 min-1which was 21.8 times and 1.6 times than that of pure g-C3N4 and pure AgBr under the same condition, respectively. After three cycle tests, the degradation rate of Ag/g-C3N4/AgBr maintained above 90%, which showed good photocatalytic activity and stability.3) By exploring the influences of different active species of Ag/g-C3N4/AgBr in capture agent experiment, we could see that the superoxide radicals(·O2-) and the holes(h+) were the main active species. Amount of Ag0 could be excited from Ag+ with light irradiation. Electrons transferred to the conduction band of AgBr so that the electrons could react with O2 to generate ·O2- which accelerated the degradation of methyl orange.