Preparation Of Magnetic Bismuth-based Photocatalysts Towards Representative Analgesics Photodegradation In Aqueous

Analgesics left in water bodies can be chronic toxic to aquatic organisms and humans,while semiconductor photocatalysts which are able to degrade organic pollutants have attracted great interest in recent years.Bismuth-based photocatalysts have also attracted much attention due to the advantages of good visible-light response,narrow band gap and good stability.However,the pure bismuth-based photocatalysts limit the practical application due to the drawbacks of the recombination of photogenerated charge,the agglomeration of nanoparticles,the deficiency of photocatalytic activity and the difficulty of recycling.Therefore,according to the above problems,we have prepared three kinds of magnetic bismuth-based photocatalysts with excellent recyclability and high catalytic activity in this paper.The representative analgesics carbamazepine,diclofenac and ibuprofen（initial concentration:10 mg/L）in water were used as target pollutants.This paper has analyzed the photocatalytic activities of as-prepared magnetic bismuth-based photocatalysts and pure photocatalysts comparatively,explored the effects of common anions and co-existed substances on catalytic performance,clarified the analgesics degradation mechanism and the products degradation path using photocatalysts,and verified the good regeneration ability of as-prepared magnetic bismuth-based photocatalysts to provide the theoretical data and technical support for removal of residual analgesics in water and application of bismuth-based photocatalysts.The research key points and results of this thesis are generalized as follows:1.The magnetic biochar-based bismuth-based photocatalyst Fe₃O₄/BiOBr/BC was prepared via modified one-step hydrolysis method.The addition of vessel-like reed straw biochar（BC）effectively solved the problem of easy agglomeration of BiOBr nanoparticle and improved the separation of photogenerated charge.Under 3hours（h）energy-saving LED visible light irradiation,the removal rate of carbamazepine（CBZ）by Fe₃O₄/BiOBr/BC could reach 95.51%.The effect of pH on CBZ photodegradation by Fe₃O₄/BiOBr/BC was insignificant indicating the wider practical application.The common anions(Cl^-,NO₃^-,SO₄^2-)and dissolved organic matter（DOM）in water showed beneficial or detrimental effects to some extent.The free radical trapping experimental results showed that the high catalytic activity of Fe₃O₄/BiOBr/BC on CBZ was attributed to the contribution of·O₂^-and·OH.Combined with high-resolution mass spectrometer（HRMS）analysis,15 main intermediates and 2 ring-rupturing products were detected.The results of five rounds of reuse experiments further demonstrated photocatalyst Fe₃O₄/BiOBr/BC had good recycling performance.2.The magnetic biomass carbon quantum dots-based bismuth-based photocatalyst Fe₃O₄/BiOBr/CQDs was prepared via hydrothermal and photodeposition methods.Corncob biomass carbon quantum dots（CQDs）with diameters of 5-7 nm and spherical Fe₃O₄ particles were successfully loaded onto the surface of the plate-like BiOBr.Due to the excellent light absorption and electron transfer ability of CQDs,the catalytic activity of Fe₃O₄/BiOBr/CQDs was significantly improved,which further improved the removal efficiency of the analgesic drug CBZ.Under 2 h energy-saving LED visible light irradiation,the CBZ removal rate by Fe₃O₄/BiOBr/CQDs with the addition of 4 mL CQDs（FeBrCQDs-4）could reach 99.52%.FeBrCQDs-4 had high photocatalytic activity on CBZ degradation in weakly acidic,neutral and alkaline environments.Cl^-,SO₄^2-and DOM all inhibited the photodegradation of CBZ to some extent,while the effect of NO₃^-on CBZ photodegradation could be ignored.·O₂^-and h⁺were the main active species in the reaction system,leading to three possible degradation pathways of CBZ.Fe₃O₄/BiOBr/CQDs had strong stability and could be reused to remove CBZ.3.Novel nanosphere/nanorod/nanosheet-like magnetic heterojunction photocatalyst Fe₃O₄/Bi₂S₃/BiOBr was prepared via solvethermal method.（0 0 1）and（1 1 0）crystal surfaces of BiOBr with higher surface energy were favorable for the improvement of catalytic activity of photocatalyst Fe₃O₄/Bi₂S₃/BiOBr.Under 40minutes（min）and 30 min visible LED light irradiation,the removal rates of diclofenac（DCF）and ibuprofen（IBU）were up to 93.81%and 96.78%,respectively.The original DCF solution without any pH regulation was beneficial to the photocatalytic degradation process,and the removal efficiency of IBU in acidic and neutral environments was significantly higher than that in alkaline environment.Cl^-,NO₃^-,SO₄^2-and DOM commonly found in water bodies promoted or inhibited the degradation of DCF and IBU to some extent.h⁺and e^-were the most active species in the degradation of DCF and IBU,respectively.During the degradation process,12and 9 main intermediates were detected in DCF and IBU solutions respectively.The good reusability indicated that the photocatalyst Fe₃O₄/Bi₂S₃/BiOBr had certain application value in the removal of analgesics in water.