Construction Of Novel Nanocomposites For Catalytic Degradation Of Organophosphorus Pesticides In Water

Various kinds of organophosphorus pesticides（OPPs）,which are widely used in agriculture and horticulture,are introduced into water resources from agricultural runoffs,industrial sewage and chemical spills.OPPs not only directly pollute water environment,but also inhibit acetylcholinesterase and damage the nervous system,thereby threatening human health.Therefore,it is urgently needed to develop effective methods to eliminate OPPs contamination.Recently,much attention has been focused on activation of peroxymonosulfate（PMS）by heterogeneous catalysts for micropollutants removal from water.However,reactive oxygen species（ROS）produced during catalytic oxidation can transform the organic phosphorus into inorganic form,and the generated phosphate is troublesome problem since discharge of phosphorus into aqueous solution can cause water eutrophication.Based on this,this paper focused on the development of a series of magnetic nanomaterials with adsorption and catalytic capabilities by simple and facile synthesis methods,and an efficient PMS activation system was constructed to achieve organophosphorus degradation and in-situ phosphate adsorption.The removal behaviors and reaction mechanisms of various OPPs in water were systematically explored.The main research contents of this subject are as follows:（1）Zr-doped Fe₃O₄ magnetic nanoparticles were prepared via a facile solvothermal method and employed to activate PMS for degrading diazinon.The experiment results revealed that Zr_（0.3）Fe₃O₄composite played a dual role as both adsorbent and heterogeneous catalyst for removal of diazinon.Attractively,the introduction of Zr into the cubic spinel structure of Fe₃O₄ endowed the nanoparticles with prominent adsorption capacity for released phosphate during the oxidation reaction,thereby alleviating secondary pollution.Combined with electron paramagnetic resonance（EPR）spectra and quenching studies,Zr_（0.3）Fe₃O₄ effectively catalyzed PMS to produce four kinds of reactive oxygen species（ROS）,and ¹O₂ and·O₂^-were dominantly responsible for diazinon degradation.Furthermore,the possible degradation pathways of diazinon in Zr_（0.3）Fe₃O₄/PMS system were discussed based on liquid chromatography mass spectrometry（LC-MS）analysis.（2）To further enhance the catalytic activity,Co-doped Fe₃O₄magnetic particles encapsulated by zirconium-based metal-organic frameworks（Co-Fe₃O₄@Ui O-66）were prepared.The catalyst exhibited efficient catalytic performance,achieving 94.4%removal of fenitrothion（FNT）in the presence of PMS（1 m M）within 60?min.Moreover,the produced phosphate during the degradation process was also completely adsorbed onto the catalyst.Both sulfate and hydroxyl radicals were responsible for the degradation of FNT,and the mechanism was proposed based on the analyses of XPS and FTIR.It was found that the synergistic effect between Fe and Co effectively improved the catalytic performance,and phosphate was in-situ adsorbed on the catalyst through the inner-sphere complexation.The degradation products of FNT in the system were identified and the possible pathways were proposed.This study provided a promising and adoptable strategy to develop core-shell catalysts derived from MOFs with high catalytic performance and stability.（3）Based on the fact that Co-based MOF（ZIF-67）has excellent catalytic activity for PMS,a magnetic composite（MZU）having a double-layer of two kinds of MOFs（ZIF-67 and Ui O-66）was prepared with Fe₃O₄ as the core.Due to the abundant Zr-OH group on the surface of MZU,the enrichment of phenylphosphonic acid（PPOA）at the active sites can be conducive to the oxidation reaction by activating PMS,and the removal rate of PPOA is 95.3%within 30 min.Ui O-66 shell can restrain the leaching of Co ions under intricate reaction conditions,and effectively adsorb the released inorganic phosphorus.The mechanism study suggested that SO₄·^–,·OH and ¹O₂ played a key role in the degradation of PPOA in MZU/PMS system.Furthermore,the acceleration of electron transfer between Fe₃O₄ and cobalt active sites of ZIF-67 could induce the redox cycling of Co（II）and Co（III）,thereby enhancing the catalytic activity.The stability of the catalyst was confirmed by XPS and XRD analysis,which ensured that the MZU/PMS system still had high activity after 5 consecutive cycles.（4）To present the selective removal of OPPs by MZU/PMS,PPOA was selected as the target pollutant,and five representative OPPs commonly found in water environment were studied for adsorption and degradation experiments.MZU exhibited different adsorption abilities on different types of organophosphorus compounds.In single solution,the mineralization degree of OPPs by the MZU/PMS system for 30 min basically followed to the corresponding pseudo-first-order kinetic rate constant(k_obs).In the mixed solution,the degradation efficiency of PPOA was the highest,and the value of k_obs was 0.153 min^–1.Depends on the strong interaction between the target pollutant and the catalyst through P–O–Zr bond,PPOA has the highest enrichment property on the surface of MZU,and can be preferentially oxidized by ROS.To better reveal the factors influencing the removal rate of OPPs during the heterogeneous catalytic reaction process,a quantitative-structure–activity-relationship（QSAR）model was developed using the multiple linear regression（MLR）method.This study illustrates the synergistic effect of adsorption and ROS-dominated catalytic reaction through experiment and model.The reported results provide new insights into a highly selective and efficient heterogeneous PMS activation system for targeted contaminant removal.