Visible-light-driven Photocatalytic Degradation And CO₂ Reduction Performance Of Bismuth Oxybromide-based Composite Nanomaterials

BiOBr has attracted attention in the field of photocatalysis due to its moderate band gap,unique lamellar crystal structure and excellent chemical stability.However,the application of BiOBr in visible-light catalysis area was limited due to the light absorption at the edge of visible light region.In this work,CdS/BiOBr,CuO/BiOBr and oxygen vacancy-rich BiOBr-OV/RGO composites were synthesized using BiOBr as basement.The details are summarized briefly as follows:（1）A novel CdS/BiOBr heterojunction comprised of CdS nanoparticles（NPs）decorating on BiOBr nanoflakes（NFs）was successfully synthesized by a facial microwave-assisted aqueous chemical synthesis technology,and the possible mechanism of crystal growth was proposed.The photocatalytic degradation performance of CdS/BiOBr heterojunction was investigated using malachite green（MG）as a simulated pollutant.The result showed that CdS/BiOBr sample prepared with0.06mmol cadmium acetate exhibited the best photocatalytic activity,the degradation rate was around 100%under the visible light for 40 min,of which the fastest pseudo-first-order kinetic rate constant reached 0.125 min^-1,having 22.6,4.4,and 3.2 times higher than that of pure CdS,BiOBr and the physical mixture,respectively.Meanwhile,the degradation experiments of congo red（CR）and methyl red（MR）were also carried out,the results showed that CdS/BiOBr heterojunction still had excellent photocatalytic performance for CR and MR,and the degradation rates were as high as 93.1%and93.3%,respectively.The capture experiment of active free radicals showed that the photocatalytic degradation MG process over CdS/BiOBr heterojunction was dominantly driven by the?O₂^-and h⁺active species.Combined with the analysis of energy band structure,the direct Z-scheme photocatalytic mechanism was proposed.（2）A novel CuO/BiOBr composite photocatalyst with p-n heterojunction were fabricated by a facile microwave-assisted aqueous chemical deposition strategy.The as-prepared CuO/BiOBr heterojunction was comprised of zero-dimensional（0D）CuO quantum dots（QDs）with average size of 4.1 nm uniformly grown on the 2D thin BiOBr nanoflakes（NFs）with{001}-facet exposure forming hierarchical structures,and the possible formation mechanism was proposed.Compared with pure BiOBr,CuO/BiOBr composite photocatalysis expands the absorption range of visible light and accelerates the spatial transfer and separation efficiency of photogenerated carriers.The CuO/BiOBr heterojunction exhibited greatly enhanced photocatalytic activity in the degradation of Congo red（CR）and Bisphenol A（BPA）under visible light irradiation.In which,the CuO/BiOBr composite photocatalyst prepared when the addition amount of copper acetate was 0.10 mmol had the highest degradation efficiency of CR and BPA of 96.8%and 90.3%,and the corresponding apparent kinetic rate constants were 4.92and 4.64 times that of pure BiOBr,respectively.Active free radical trapping experiments showed that·O₂^-and h⁺played a major driving role in the photocatalytic degradation of CR.Combined with the band structure analysis,the spatial charge-transfer mechanism of CuO/BiOBr p-n heterojunction was proposed.（3）BiOBr/RGO composite was prepared by one-step hydrothermal method,and then annealed at high temperature in vacuum to obtain oxygen vacancy-rich（OV）BiOBr-OV/RGO composite.Through ESR and XPS characterization analysis,it was proved that the oxygen vacancy was successfully constructed.In addition,visible light photocatalytic CO₂ reduction experiment showed that BiOBr-OV/RGO exhibited the best performance for CO₂ photoreduction.The evolution rate of main reduction product CO was up to 15.67μmol?g^-1?h^-1,which was about 4.5,2.4 and 1.4 times higher than that of BiOBr、BiOBr-OV and BiOBr/RGO,respectively.BiOBr-OV/RGO composite photocatalyst has excellent activity and stability of photocatalytic CO₂ reduction through four cycles of photocatalytic CO₂ reduction experiments.