Preparation And Properties Of Magnetically Recoverable Multilayer Nanocatalyst

Semiconductor photocatalysis is a novel technology that uses mild photochemical reactions to store and utilize solar energy.In recent years,it has been widely used in dye wastewater treatment because of its green,pollution-free and sustainable development strategy.In this paper,the magnetic core-shell material with Fe₃O₄ as the core and polydopamine（PDA）as the shell can be an excellent carrier for photocatalysts because of its high stability and modifiability.Firstly,Fe₃O₄ was synthesized by solvothermal method,and the core-shell structure Fe₃O₄@PDA was formed by coating Fe₃O₄ with the characteristic of self-polymerization under the weakly alkaline condition of dopamine,then,butyl titanate was hydrolyzed to wrap a layer of Ti O₂ on it to form the first photocatalyst Fe₃O₄@PDA@Ti O₂.Using the coordination ability of bis（2-hydroxypropionic acid）diammonium dihydroxide（Ti-BALDH）and dopamine（DA）,combined with the self-polymerization of DA,a coordination polymerization layer was formed on Fe₃O₄@PDA to obtain Fe₃O₄@Ti-PDA composite.In addition,in order to broaden the light absorption range of magnetic core-shell photocatalyst,CuS was compounded on Fe₃O₄@PDA to form Fe₃O₄@PDA/CuS in this paper.In this paper,CuS was compounded on Fe₃O₄@PDA to form Fe₃O₄@PDA/CuS.Similarly,Cu²⁺was coordinated with phenolic hydroxyl group on PDA and then reduced with Na₂S to form CuS in situ on PDA surface to obtain the third photocatalyst Fe₃O₄@PDA/CuS.The above photocatalysts were characterized by FT-IR,SEM,XRD,XPS,TGA,Nitrogen adsorption and desorption,VSM and other methods to characterize the structure,morphology and stability.Using Fe₃O₄@Ti-PDA as photocatalyst and Fe₃O₄@PDA@Ti O₂ as control group,the photocatalytic experiment of model pollutant methylene blue under visible light irradiation was carried out without adding H₂O₂ as cocatalyst.It was found that the degradation rate of methylene blue could reach 92.4%after 120min,which was significantly higher than that of Fe₃O₄@PDA@Ti O₂（32.5%）in the control group.The degradation efficiency of Fe₃O₄@Ti-PDA on methylene blue remained at 86.47%after three cycles,showing good cycling stability.The catalytic mechanism was studied through the trapping experiment.Isopropanol was selected as the trapping agent of·OH,p-benzoquinone as the trapping agent of·O^2-,disodium ethylenediamine tetraacetate as the trapping agent of h⁺,and 1,3-diphenyliso-benzofuran as the trapping agent of ¹O₂.It was clear that h⁺was the main active substance in the photocatalytic process.Similarly,Fe₃O₄@PDA/CuS was used as catalyst,methylene blue was used as model pollutant,and no H₂O₂ was added as cocatalyst.The photocatalytic experiment was conducted under visible light irradiation.The results showed that the degradation rate of methylene blue was 91.6%after exposed to visible light for 180min.After three cycles,the degradation efficiency of methylene blue can still maintain 83.95%,indicating that it has excellent cycling stability.The active substances produced by Fe₃O₄@PDA/CuS in the photocatalytic process were determined by the same method as the first system,and it was found that h⁺and·OH were the main substances.The above results show that the photocatalyst designed in this paper shows high catalytic activity for organic dye methylene blue,providing a new potential solution for the treatment of dye sewage.At the same time,the introduction of magnetic material Fe₃O₄ realizes the separation and recycling of photocatalyst,which provides strong support for the practical application of photocatalytic degradation technology.