Preparation Of Layered Double Hydroxides-Based Composites For PMS Activation To Purify Organic Pollutants

With the rapid development of economy and the rapid rise of industry and agriculture,a large number of organic pollutants are discharged into the water body,resulting in increasingly serious water pollution problems,and even being harmful to human health.However,traditional water treatment methods including adsorption,flocculation and biological treatment fail to completely degrade organic pollutants.Therefore,how to efficiently treat organic pollutants has become the focus of current research.Advanced oxidation processes（AOPs）based on peroxymonosulfate（PMS）have attracted extensive attention due to their strong oxidation capacity and fast treatment efficiency.Iron-based heterogeneous catalysts have become ideal choices for activating PMS to degrade organic pollutants due to their high oxidation efficiency,environmental friendliness and low cost.Layered double hydroxides（LDHs）,as a layered two-dimensional materials,have excellent chemical stability and high mechanical strength.LDHs have attracted wide attention as iron-based catalysts due to the adjustability of metal ions in the host layers.Also,the atomic-scale distribution of metal ions in the host layers provide the possibility to prepare heterogeneous catalysts with highly dispersed catalytic active sites.At the same time,the exchangeability of interlayer anions provides convenience for the subsequent intercalation and delamination.After delamination,the catalytic active sites of LDHs can be fully exposed and the reaction rate can be improved.Therefore,in this paper,LDHs are used as the precursors and the composite catalyst（CLCN-550）used with LDH and carbon-nitrogen material（CN）is prepared by calcination.Moreover,the LDH/Mo S₂composite catalytic membrane through electrostatic self-assembly of LDH and Mo S₂nanosheets is prepared by delamination and vacuum filtration.The main details are as follows:First,Mg Fe Al-LDH was prepared by homogeneous precipitation method,and citrate intercalated-LDH（CA-LDH）was prepared by using the exchangeability of LDH interlayer anions,and then calcined with urea to obtain LDH/CN composite catalyst（CLCN-550）.CA,as a structure-directing agent,was conducive to adjusting the interface of the two components and preparing a layered heterostructure.The morphology and composition of the catalyst were characterized by TEM,XRD and XPS,and the performance of CLCN-550/PMS system for removing BPA was investigated.The results showed that CLCN-550 catalyst could effectively activate PMS to remove BPA,and the removal rate reached nearly 100%within 10 minutes.The mechanism study found that its superior performance was mainly attributed to the synergistic effect between LDH and CN,which had effective interface electron transfer,promoting the rapid generation of O₂^·-,and thus effectively removing organic pollutants.In addition,CLCN-550 catalyst had good anti-interference ability in actual wastewater.To further overcome the recovery of catalysts from batch systems and improve the utilization rate of free radicals,the membrane-based nanoconfinement catalysis was proposed.LDH nanosheets with positive charge were prepared by delamination method.LDH/Mo S₂composite catalytic membrane was prepared by electrostatic self-assembly between negatively charged Mo S₂nanosheets and LDH nanosheets.The catalytic membrane was characterized by SEM,TEM,AFM,XRD and XPS,and the performance of the catalytic membrane for removing BPA was investigated.The results showed that when the catalytic membrane catalyst loading was 0.6 mg/cm²,the removal rate of BPA reached nearly 100%,and the system had a high permeation flux(417.33 L·m^-2·h^-1·bar^-1).Compared with the conventional heterogeneous AOPs system,the interlayer nano-channel of the catalytic membrane was conducive to promoting mass transfer,and the generated free radical species could quickly contact with the pollutants,and could completely degrade the pollutants within 25 ms.Moreover,under the cross-flow filtration operation mode for a long time（8 h）,it still maintained high removal rate and stability.The mechanism study showed that^·OH and SO₄^·-were the main free radical species in LDH/Mo S₂catalytic membrane/PMS system,and maintained a high free radical strength for a long time.Therefore,the LDH/Mo S₂catalytic membrane with nanoconfinement effect could effectively treat organic pollutants and avoid subsequent recovery problems,which had great potential in water treatment.