Construction Of BiOBr-Based Composite Photocatalyst And Their Photocatalytic Degradation Performance Of Organic Pollutants

Photocatalytic oxidation is a new environmentally friendly technology,which has a very broad application prospect in the field of coping with global environmental and energy crisis.In particular,the development of visible light responsive photocatalysts is a hot topic in recent years.BiOBr is a visible light driven catalyst,which has a strong absorption of visible light with a wavelength of less than 440 nm,and the photogenerated holes of BiOBr have strong oxidation ability.However,as a single-component photocatalyst,BiOBr still has a gap between photocatalytic performance and the actual applicationis.In order to improve the photocatalytic performance of BiOBr photocatalyst,the Z scheme WO₃/BiOBr composite photocatalyst,BiOBr@RGO/DT composite photocatalyst,BiOBr nanosheet array electrodes and BiOBr/WO₃ nanorods array electrodes were prepared.In addition,a variety of analysis methods such as X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),Energy-dispersive X-ray spectroscopy(EDS),Scanning electron microscope(SEM),Transmission Electron Microscopy(TEM),Ultraviolet–visible spectroscopy(UV–Vis),Photoluminescence(PL)spectrum and photoelectric test,etc.were employed to determine the physicochemical properties of the catalysts including crystal structure,morphology characteristics,light absorption,fluorescence properties and optical performance,etc.At the same time,the catalytic degradation of ciprofloxacin(CIP),gaseous formaldehyde and bisphenol A(BPA)were studied and the catalytic degradation mechanism was also investigated.The main research results are as follows:(1)A visible light-driven 3D hierarchical photocatalyst WO₃/BiOBr(WB)was prepared by solvothermal method,through which 2D BiOBr ultra-thin nanosheets grew on 1D WO₃ nanotube bundles.The as-prepared WB-0.5 (i.e.W:Bi with a mole ratio of0.5:1) had the highest photocatalytic degradation efficiency of 94.7% for ciprofloxacin hydrochloride under visible light irradiation(??400 nm)within 120 min;such efficiency was about 5.2 and 1.6 times higher than that of individual WO₃and BiOBr,respectively.Its removal rate of total organic carbon was 41.2%.Moreover,WB-0.5 showed high reusability and photostability,and its photocatalytic activity did not show any obvious decrease even after five cycles.The characterisation of WB-0.5's crystal structure,morphology,and surface elemental state confirmed its 3D hierarchical structure and formation of heterojunction.Its direct Z-scheme system was tested by analysing the active species,photocurrent characteristics,Mott–Schottky plots,UV-Vis diffuse reflection spectroscopy and in situ irradiation XPS.The 3D hierarchical structure may provide increased active sites and enhance light absorption efficiency.The direct Z-scheme configuration is particularly beneficial for improving photocatalytic activity.Therefore,this work may provide a feasible strategy for designing a Z-scheme 3D hierarchical photocatalyst.(2)A visible light-driven composite photocatalyst BiOBr@RGO/DT was prepared by solvothermal method.The additive of RGO is fixed 1% (relative to BiOBr).When the optimized mass ratio of diatomite to BiOBr is 1.5,the photocatalytic degradation rate of gaseous formaldehyde by composite photocatalyst was the highest,reaching 89.6% within 3 hours,1.6 times that of BiOBr alone.The optimum relative humidity for degradation of gaseous formaldehyde is 45%.After four cycles of photocatalytic reactions,the decrease of catalytic performance of BiOBr@RGO/DT-1.5 keep almost unchanged,indicating good stability of this catalyst.The high catalytic performance of composite photocatalyst BiOBr@RGO/DT is attributed to the adsorption and enrichment of gaseous formaldehyde by diatomite,and thus increases the formaldehyde degradation efficiency of BiOBr.(3)Bismuth oxybromide(BiOBr)nanosheet arrays(NSAs)were successfully prepared on the surface of indium tin oxide glass(hydrophilic pretreated)by solvothermal method using[C₁₆mim]Br ionic liquid as bromine source and template.The effects of different reaction temperatures on array synthesis were investigated.BiOBr NSA-160(NSAs prepared at 160°C for 8 h)had the best photoelectrocatalytic(PEC)activity.The removal rate of ciprofloxacin hydrochloride by BiOBr NSA-160 was 91.4%by applying a bias voltage of 0.9 V and irradiating under visible light for 180 min.Results of the analyses of the morphology,photoelectric properties,energy band structure,and degradation active species show that BiOBr NSA-160 is a p-type photocatalyst with a thickness of approximately 500 nm,a light response range of less than 440 nm,and photocurrent density of 69?A/cm² at the optimal bias voltage is 0.9 V.The high PEC activity of BiOBr NSA-160 was deduced from two aspects:one is that the bias potential effectively improves the separation efficiency of photogenerated carrier,and the other is that the structure of the nanoarray increases light absorption and active sites.BiOBr NSAs are promising PEC material for application in pollutant removal.(4)BiOBr/WO₃ composite nanorod array photoelectrode was prepared by a two-step reaction.WO₃ nanorod array was first prepared on the surface of FTO glass substrate,and then BiOBr thin nanosheets were grown on WO₃ nanorods by solvent thermal method.The surface morphology and XPS characterization showed that BiOBr nanosheets were tightly combined on WO₃ nanorods and have a strong binding force.The photoelectrocatalytic degradation efficiency of BPA by BiOBr/WO₃ photoelectrode reached 95.7% within 3 hours,and 2.8 times that of photodegradation alone,and the total organic carbon(TOC)removal rate reached 37.2%.The high photoelectrocatalytic performance of BiOBr/WO₃ is due to the fact that its heterojunction can effectively separate photo-generated carriers and quickly migrate to the external circuit under bias voltage,thus improving the separation efficiency of photo-generated carriers.Meanwhile,the three-dimensional structure of the catalyst also increases the absorption and utilization efficiency of light and provides more active sites.