Preparation And Photocatalytic Activities Of Pt-modified Bi_xO_y Br_z?BiOBr,Bi₄O₅Br₂? Photocatalysts

BiOBr semiconductor,with[Bi₂O₂]²⁺slabs interlaced by double Br^-ion slabs that greatly improves the separation efficiency of photo-generated electrons and holes,has attracted much attentions owing to its excellent photocatalytic activity and stability under visible light?400 nm<?<420 nm?irradiation.Due to the low conduction band position of BiOBr,the photoelectron reduction ability is not high,resulting in limited photocatalytic efficiency.The preparation of non-stoichiometric Bi-O-Br photocatalysts as a method to achieve the regulation of the energy band structure by changing the intrinsic elemental content of the material,not only does not require the introduction of external ions or molecules,but also through this method can be effective improve the energy band structure of the material,and thus the effective utilization of sunlight,thereby reducing the recombination rate of photogenerated carriers and enhancing the redox ability of photogenerated hole-electron pairs,has attracted the interest of researchers.However,its utilization of solar energy is still not high.Therefore,how to modify Bi_xO_y Br_z photocatalytic materials to improve the photoelectron reduction ability has become a key problem to be solved.Many studies have shown that the loading of noble metal Pt can improve the photocatalytic performance of Bi_xO_yBr_z catalytic materials.In this paper,pure BiOBr and Bi₄O₅Br₂ were prepared by hydrolyzation method.Then the as-prepared Bi_x O_yBr_z photocatalysts decorated with smaller amount?0.02 to 0.5wt.%?ofPtnanoparticlesweresuccessfullypreparedvianew electrostatic-adsorption assisted light-reduction route.The as-prepared samples were characterized by XRD,SEM,HRTEM,EDS,XPS,UV-vis DRS,PL and Photocurrent measurements.The photocatalytic activities were tested through the photocatalytic degradation of Bisphenol A?BPA?under simulated sunlight,UV light and visible light irradiation.The active species and dynamic behaviors of photocatalytic charge carriers,as well as the possible degradation mechanism were investigated and discussed.The main findings of the paper are as follows:?1?3D BiOBr flower-microspheres decorated with small amount?0.02 to0.5wt.%?ofPtnanoparticlesweresuccessfullypreparedvia electrostatic-adsorption assisted light-reduction method.The as-synthesized method exhibits a smaller amount of Pt metal NPs on the photocatalyst surface with the higher dispersion.Pt loading did not change the structural morphologies,crystallinity and crystalline of BiOBr crystal,but play a vital role in acting as electron capturer to reduce the recombination efficiency of photoinduced e^-and h⁺pairs,and also provide a plasma resonance effect for extending the light-response range,greatly achieving the highly-efficient photocatalytic activity of BiOBr under simulated sunlight irradiation.0.2 wt.%Pt/BiOBr sample reveals the highest photocatalytic activity for the degradation on BPA with almost 92%under 10 min,much better than pure Bi OBr and?P25?TiO₂.The main active species are h⁺and·OH in this photocatalysis process,relative to the presence of synergistic effect Pt⁴⁺and Pt⁰ and the photocurrent effect to certain extent.?2?A series of Pt/Bi₄O₅Br₂ photocatalysts were prepared by strong electrostatic adsorption assisted photo-reduction method.The influence of Pt loading on the photocatalytic activity of Bi₄O₅Br₂ was studied.From the experimental results,the optimal loading of Pt/Bi₄O₅Br₂ is 0.2 wt%.The XRD results show that the Bi₄O₅Br₂ corresponds to the standard card?JCPDS No.97-041-2591?,which indicates that the obtained Bi₄O₅Br₂ sample has a monoclinic crystal structure.SEM results show that Pt/Bi₄O₅Br₂ material is composed of many irregular nanosheets;absorption spectra show that Bi₄O₅Br₂undergoes a slight red shift after Pt loading,which is favorable for the absorption of visible light.The 0.2 wt%Pt/Bi₄O₅Br₂ sample showed the highest photocatalytic activity.The degradation efficiency of BPA was 96%when the degradation time was 30 minutes under the visible light irradiation,which was much higher than other photocatalysts.?3?The results suggest that the mechanism of the increase in photocatalytic activity of Pt/Bi_xO_yBr_z is:the existence of Pt NPs on the photocatalysts surface could not only provide a plasma resonance effect for extending the light-response range to enhance the photocatalytic performance,but also act as electron capturer to reduce the recombination efficiency of photoinduced e^-and h⁺pairs,and consequently,achieving the enhanced photocatalytic activity and stability of Pt/Bi_xO_yBr_z photocatalyst.The capture agent experiments show that the reactive species of the noble metal-supported Bi_xO_yBr_z catalyst in the photocatalytic process are the result of the interaction of multiple active species.