Study On Bisphenol A Degradation And Algae Removal Of Carbon Quantum Dots Modified BiOBr Composite Photocatalyst

With the development of modern industry,persistent refractory organic pollutants and algal blooms have become common pollution sources in polluted water.Among them,endocrine disruptors and algae are increasingly polluting the water body.Photocatalytic technology has gradually become an effective method to solve this environmental problem.In this study,carbon quantum dots（CQDs）surface modification and oxygen vacancy（O_V）embedding were used to modify the BiOBr semiconductor catalyst,and CQDs-Bi O_1-xBr composite nano photocatalyst was constructed.Using bisphenol A（BPA）and Microcystis aeruginosa as target pollutants,supplemented by persulfate（PS）as cooxidant,the removal law of pollutants by CQDs-Bi O_1-xBr/PS visible-light photocatalytic system under different reaction conditions was systematically studied.The microstructure,morphology and photocatalytic properties of the samples were studied by a variety of physical,chemical and optical characterization methods.The results show that CQDs are successfully bonded to the surface of Bi O_1-xBr,the light absorption boundary of the composite is significantly widened to the visible region,and has excellent visible-light response.Based on the electron transfer characteristics of CQDs and the successful doping of O_V,the structure and physicochemical properties of the composite photocatalytic materials have been greatly improved.The photocatalytic experiment showed that when the concentration of catalyst was 0.5 g/L,the concentration of BPA was 10 mg/L and the addition of PS was 2 m M,the degradation effect of 2%CQDs-Bi O_1-xBr/PS system was the best,BPA could be completely degraded and removed within 20 min,and the salinity could reach 43.8%;When the catalyst concentration was 1 g/L,the algae density of Microcystis aeruginosa was 2.7×10⁶ cells/m L and PS dosage was 2 m M,the algae removal effect of 2%CQDs-Bi O_1-xBr/PS system was the best,and Microcystis aeruginosa could be completely removed within 5 h.Through free radical quenching experiment,indirect detection means and EPR direct detection means,it is proved that the main active oxidants of visible light catalytic system are·OH,·SO₄^-,·O₂^-and h⁺,in which h⁺and·O₂^-play a leading role.Time of flight mass spectrometer（TOF-MS）was used to identify the main intermediates produced in the degradation of BPA,and its degradation pathway was analyzed.On this basis,we applied the system to the removal experiment of Microcystis aeruginosa,and studied the algae removal of the photocatalytic system.The excellent algae removal performance was characterized by the number of algae cells,chlorophyll a concentration,organic matter inside and outside cells,electrical conductivity and photosynthetic ability.The effects of different reaction conditions on algae removal experiment were explored.Finally,combined with the catalyst characterization data and the degradation law of pollutants,the degradation reaction mechanism of CQDs-Bi O_1-xBr/PS visible light photocatalytic system was proposed respectively.