Synthesis And Photocatalytic Performance Study Of BiOBr Modified Materials With Wide Spectral Response

At present,semiconductor photocatalyst,a new type of green and sustainable energy material,has great application prospects in wastewater and waste gas treatment,CO₂ reduction,hydrolysis hydrogen,nitrogen fixation and solar energy conversion.Therefore,it has been extensively researched due to the strong oxidizing ability,simple and easy control of the reaction process,and broad application prospects in solar energy utilization.The photocatalysis mechanism of semiconductors is that the photocatalyst is excited to produce photogenerated electron and hole pairs.At this time,some photogenerated electrons and holes can migrate to the catalyst surface and react with contaminants to achieve degradation.BiOBr,as a hot point of visible-light response semiconductor photocatalysis,possess some excellent characteristics,such as unique open layer structure,indirect transition mode and admirable photocatalytic activity.However,its photocatalytic activity is still restricted by a series of factors such as low solar light responsiveness,high recombination rate of photoelectron-hole pair and weak reduction ability of photogenerated electron.Based on this,we carefully designed a CQDs/BiOBr composite by a two-step hydrothermal method in order to make use of the CQDs can drive BiOBr into broader-spectrum-response.The paper reveals it can improve spectral response of BiOBr by up-conversion luminescence of CQDs.In addition,the photosensitization of CQDs could improve the reduction ability of photogenerated electrons of BiOBr,and the strong conductivity of CQDs can improve the separation efficiency of photogenerated electron and hole pairs of BiOBr.In this paper,the photocatalytic activity of CQDs/BiOBr composites was investigated by the degradation of bisphenol A?BPA?in water.Compared with pure BiOBr?20%?,the photocatalytic activity of 4-CQDs/BiOBr was increased to 66%.However,the photocatalytic activity of the CQDs/BiOBr composite is not very satisfactory and needs to be further improved.Therefore,this paper also introduces fluoride ion on the CQDs/BiOBr binary composite material to form a fluoride ion modified CQDs/BiOBr?CQDs/BiOBr/F?composite photocatalyst.The degradation of BPA and RhB showed that the photocatalytic activity of the ternary composite photocatalyst was much higher than that of binary CQDs/BiOBr?photocatalytic activity was 45%?,up to 70%?degradation time:24 min?.For research why the photocatalytic activity is improved,we do various characterizations to study the role of fluoride ion in CQDs/BiOBr/F composite photocatalyst.The result demonstrates that fluoride ion adsorbs on the surface of BiOBr,which to modify the BiOBr with CQDs,thereby facilitating the BiOBr easy to absorb cationic pollutants on the surface and broadening their visible light response.The range to further enhance its photocatalytic degradation activity.The main contents are as follows:1.We design a novel assembly of nanosized CQDs particles supported on BiOBr becoming CQDs/BiOBr by a mild two-step hydrothermal method.The as-prepared hybrid photocatalysts exhibiting much more optimum photocatalytic activity than pristine BiOBr,which could be attributed to the fact that CQDs could drive BiOBr into broader-spectrum-response.It is found that CQDs can effectively broaden the spectral response range of BiOBr through the degradation experiments under monochrome light conditions.Secondly,CQDs can be found to have up-conversion luminescence through the up-conversion fluorescence spectra of CQDs and photodegradation experiments.Through the analysis of transient photocurrent and fluorescence intensity,CQDs have super conducting electron capability.Radical trapping experiment and ESR characterization under monochromatic light irradiation showed that CQDs also had photosensitization roles,thus improving photocatalytic degradation activity.2.In order to further improve the visible light photocatalytic activity of CQDs/BiOBr complex,we design CQDs/BiOBr/F composite by adding an appropriate amount of sodium fluoride in the process of preparing CQDs/BiOBr.It was found that fluoride ion modification can effectively improve the visible light photocatalytic activity through the photocatalytic degradation of BPA and RhB under visible light irradiation.The study of transient photocurrent and fluorescence intensity shows that fluoride ion is beneficial to the separation of photogenerated electrons and holes pair.It also found that the modification of the fluoride ion is conducive to broadening the absorption of visible light,thereby further improving the photocatalytic degradation activity of visible light through the analysis of the ultraviolet-visible absorption spectrum.