Preparation Of Visible Light-responsive Ni-BiOCl And Study On Photomagneto-Coupled Algae Removal Efficiency And Mechanism

Eutrophication of the water body brings outburst growth of algae,and algae cells release a large amount of harmful substances into the water environment,severely degrade water quality,and pose severe challenges for drinking water safety.Photocatalytic technology has attracted widespread attention due to its high efficiency,low consumption,and environmental protection.However,most of the catalysts have weak or no response to visible light,which limits its widespread application.In order to broaden the photoresponse range of the catalyst and improve the utilization efficiency of visible light,this paper prepares a new visible light response catalyst Ni-BiOCl,and combining photocatalysis technology with magnetic treatment technology to propose a photo-magnetic coupling algae removal technology.The subject took the common dominant algae species,Microcystis aeruginosa,which caused cyanobacteria blooms as the treatment object,and prepared nickel（Ni）doped modified nickel-bismuth oxychloride（Ni-BiOCl）and then characterized the prepared catalyst.Experiments on photocatalysis and photomagnetic coupling of algae were carried out,the main factors affecting the algae removal process were explored,and the mechanism of algae removal was analyzed.The main research results include the following aspects.（1）A simple one-step hydrothermal synthesis method was used to prepare a novel Ni-BiOCl visible light-responsive catalyst,and the surface morphology,structural characteristics,and electrochemical performance of the prepared BiOCl and Ni-BiOCl were characterized.The results showed that the prepared BiOCl and Ni-BiOCl were in the form of nanosheets.Ni was successfully doped into the BiOCl lattice without changing the main lattice structure.The doping of Ni effectively reduced the band gap energy of BiOCl and widened its light absorption range,which made it able to respond to visible light;ESR characterization showed that the main active material produced by the catalyst after excitation is O₂^-.Rhodamine B and bisphenol A tests showed that Ni-BiOCl has higher photocatalytic performance than pure BiOCl,and 9%Ni-BiOCl showed the best photocatalytic performance under visible light.（2）The effects of the amount of Ni doped,the amount of catalyst added,the light intensity,the speed of rotation and the initial concentration of algae liquid on the photocatalytic algae removal effect were investigated.The experiments showed that the optimal catalyst doping amount was 9%,the optimal catalyst dosage was 0.05 g,the optimal light intensity was 65 klux,and the optimal magnetic stirrer speed was 500 r/min.And at a concentration of 2.6×10⁶cells/mL,the algae inhibition rate was as high as 93.04%after 60 minutes of photocatalytic reaction under these conditions.Combined with the capture agent experiments and EEM analysis,this paper explored the mechanism of photocatalytic algae inhibition under visible light,and it was found that Ni-BiOCl was excited under visible light to generate photogenerated electron-hole pairs（e^--h⁺）,and e^-migrated from the valence band to the conduction band,then it reacted with O₂to generate free radicals（·O₂^-）.Generally,·O₂^-and h⁺first destroy the cell wall of Microcystis aeruginosa,deactivate the active fluorescent substances in the cell,and then catalyze the leakage of intracellular oxidation.Materials such as chlorophyll and phycocyanin are inorganic.（3）The effects of magnetic field strength,magnetic field pretreatment time,and algae concentration on the photo-magnetic coupling of algae removal were investigated.The experimental results showed that with the magnetic field strength increases,the algae removal efficiency becomes larger,however the magnetic field pretreatment time has no significant effect on the photocatalytic algae removal.It is interesting that compared with photocatalytic high concentration algae removal alone（3.6×10⁶cells/mL,4.6×10⁶cells/mL,5.6×10⁶cells/mL,6.6×10⁶cells/mL）,the efficiency of photo-magnetic was improved by31.29%,57.68%,55.39%,49.19%.Sacrificial agent experiment showed that magnetic field can promote the generation of the oxidative substances,therefore the efficiency of light-optical-magnetic coupling algae removal were improved.