Application Research Of Molecular Imprinting Technology In Improving Catalytic Selectivity

The removal of organic pollutants is a difficult problem in the field of environmental remediation.The advanced oxidation processes have been studied widely in recent years and are considered promising for organic wastewater treatment.The advanced oxidation processes based on sulfate radicals(SO4·-)exhibit superior performance compared to hydroxyl radicals(·OH)in the treatment of organic pollutants.For example,wide p H adaptation range,strong oxidizing ability and high stability.Iron oxide magnetic nanoparticles(Fe3O4 MNPs)have high catalytic activity,magnetic separation performance,non-toxicity,which are widely used in activated persulfate.However,the conventional PS advanced oxidation system is generally not selective for the degradation of the target pollutants,and the treatment effect is not satisfactory because the pollutants are high toxicity,low concentration and difficult to adsorb on the catalyst surface.Molecular imprinting technology is a technique for preparing polymers with specific selectivity for template molecules.The prepared polymers have wide adaptability,high stability and long service life.Therefore,this study combines advanced oxidation processes and molecular imprinting technology to achieve selective removal of target contaminants.Firstly,this study screens the catalysts and oxidants in the advanced oxidation system and evaluates the degradation p H adaptation range and degradation mechanism,laying the foundation for subsequent research.The sulfamethazine(SMT)selected as the model pollutant.Under the premise of other conditions,the Fe3O4 MNPs synthesized by the co-precipitation method had stronger catalytic activity,and the removal effect by Na2S2O8 was the best.Degradation experiments found that the Fe3O4 MNPs in the suspension state were more catalytically active.The Fe3O4 MNPs synthesized in this study can play a role in a wide p H range.The free radical quenching experiment proved that SO4·-and ·OH participate in the degradation process together.Secondly,the second part of the study is to combine the advanced oxidation system and molecular imprinting technology.The molecularly imprinted layer modified by in-situ polymerization on the surface of Fe3O4 MNPs to achieve the purpose of selective removal of MB,with pyrrole as monomer and methylene blue(MB)as template molecule.A complete removal of the added MB(20 mg/L)was achieved within 60 min with the addition of 7.2 m M Na2S2O8 and 4.8 m M imprinted composite under the conditions of p H 5.The adsorption kinetic data indicated that the material accorded with the pseudo second-order kinetic adsorption model,and the adsorption isotherm data accorded with the Langmiur adsorption model.When there were interferences such as methyl orange(MO)and rhodamine B(Rh B),the imprinted composite still presented the best removal effect to MB.After five times of repeated use,the imprinted composites maintained MB removal rate of more than 80% in 60 minutes,and the Fe2+ leaching amount(0.25 mg/L)during degradation was less than The Sanitary Standard of Drinking Water GB5749-2006(0.30 mg/L).It found that SO4·-and ·OH participate in the degradation process.Due to the universality of molecular imprinting techniques,this research can further extended to other contaminants that require specific removal.Finally,based on the research content of the second part,sodium dodecylbenzene-sulfonate(SDBS)is added during the preparation of the imprinted composite material,so the removal efficiency increase by more than 10 times.Synchronous and asynchronous comparisons of the degradation and adsorption processes indicated that MB could quickly reach the surface of the material to achieve adsorption equilibrium.The adsorption kinetic data indicated that the material prepared by adding SDBS also conformed to the Langmiur adsorption model,and the adsorption amount was 2.5-5.4 times than the material without SDBS,and the adsorption performance improved significantly.Finally,through the free radical quenching experiment,it was found that the contribution of the removal of the target is respectively the strong adsorption of the material > the oxidation of Na2S2O8 > the oxidation of SO4·-> the oxidation of ·OH.The material successfully applied in quartz crystal microbalance,which can quickly selectively adsorb and identify MB.