Preparation And Photocatalytic Properties Of A Novel Modified BiOBr Photocatslyst

BiOX(X=Cl,Br,I), as an indirect band-gap semiconductor, is a layer-structured semiconductor of square matlockite-type (PbFCl) that alternately consists of tetragonal [Bi2O2] layer and two halogen atom-layers. It has attracted extensive concern of researchers owing to their good photocatalytic activity. However, due to wide bandgap of BiOCl, it can only be activated by ultraviolet sunlight, which is less than4%in the sunlight spectra; and although BiOI is able to activitated by visible light, its poor stability is incapable to fulfill the practical environment pollution application. BiOBr, as a potential candidate photocatalyst with bandgap between2.64-2.91eV, is able to absorb the sunlight in near UV and visible light region, so it is meaningful to improve its photocatalytic performance by strengthening its sunlight utilization. This issue has increasingly attracted the interests of researchers.In this thesis, based on simple hydrolysis method, we prepared the catalyst of Ag/BiOBr and Ag/BiOBr0.5C]0.5by a photoreduction method and citric acid, assited modified photoreduction method. The prepared Ag/BiOBr and Ag/BiOBr0.5Cl0.5powders were investigated with the X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Transmission electron microscope (TEM) and ultraviolet-visible diffuse reflectance spectra (DRS). Then, simulated sunlight and visible light were used as light source to illuminate photocatalyst particles, the MO, RhB and phenol in water were chosen as objective organic pollutant in the study of photocatalysis. Results show that:(1) The as-prepared Ag/BiOBr nano particles were the tetragonal primitive crystal structure with good crystallinity and high purity, and composed of homogeneous plates with a diameter of about20nm. The Ag nano particles the surface of BiOBr, existed in the form of metallic Ag species; although the Ag deposition has not changed the samples’morphologies, the visible light absorption intensity was enhanced, and appeared an obvious surface plasma resonance (SPR) absorption of metallic Ag nanoparticles around480nm. Besides, the samples prepared by citric acid assisted modified photoreduction method showed higher visible light absorption intensity.(2) The appropriate Ag/BiOBr-2preparation condition was:2wt%silver loadtion,45min photoreduction, the pH value of photoreduction solution at3; the prepared Ag/BiOBr-2in this condition exhibited high photocatalytic activity and stability. Furthermore, the reactive active species were h+and·O2(3) We prepared Ag/BiOBr0.5Clo.5composite photocatalyst with good crystallinity and high purity, and composed of Bi、O、Br、Cl、Ag five elements, and the surface silver existed in the form of metallic Ag species. Although the Ag deposition has not changed the samples’morphologies, the visible light absorption intensity was enhanced, and appeared an obvious surface plasma resonance (SPR) absorption of metallic Ag nanoparticles around500nm. Besides, the samples prepared by citric acid assisted modified photoreduction method showed higher visible light absorption intensity.(4) The as-prepared lwt%Ag/BiOBr0.5Cl0.5exhibited high visible light photocatalytic degradation efficiency on MO, RhB, and high simulated sunlight photocatalytic degradation efficiency on phenol, and good stability, the results further indicated that this photocatalysts didn’t show obvious selectivity. Furthermore, the reactive active species were h+and·O2(5) Based on the above results, we speculated the photocatalytic mechanism:the schottky barrier formed between the metallic Ag and the surface of semiconductor (BiOBr, BiOBr0.5Cl0.5), can restrain the combination of photo generated carriers; and metallic Ag nano particles can trap photo induced electrons as an electron conductor, and accelerate the separation efficiency of photogenerated e--h+pairs. Moreover, the SPR improved the incident utilization and enhanced photocatalytic activity.The above findings indicated that the formed hetro junction between noble Ag and BiOBr, BiOBr0.5Cl0.5was able to improve the light absorbance capacity and enchance simulated sunlight utilization, so this modified route could advance the photocatalytic performance of BiOBr and BiOBr0.5Cl0.5.