Degradation Of Typical PPCPs By CeO₂-doped Carbon Nanotube Electrocatalytic Microfiltration Membranes

The use of pharmaceuticals and personal care products（PPCPs）,which are characterized by pseudo-persistence and intrinsic biological activity,is increasing as people’s living standards improve,and they can accumulate in living organisms,posing a potential threat to human health.However,most PPCPs cannot be effectively removed by conventional water treatment processes,so there is an urgent need to develop targeted treatment technologies.Carbon nanotube electrochemical membranes（ECM）have the advantage of simultaneous membrane separation and electrocatalytic oxidation for efficient removal of hard-to-degrade pollutants from water bodies.Metal or metal oxide-loaded ECMs have stronger electrocatalytic oxidation ability and can achieve efficient removal of PPCPs from water.Based on this,CeO₂-loaded ECM（CeO₂@CNT electrocatalytic membrane）was prepared in this dissertation,and a flow-through electrocatalytic system was constructed in combination with Na ClO,based on characterizing the exposed crystal surfaces and crystal defects of CeO₂particles,the pathway of activation of Na ClO by CeO₂@CNT electrocatalytic membrane was investigated,The effectiveness of the system in treating a variety of representative PPCPs was explored,and the mechanism of the degradation of PPCPs by CeO₂@CNT electrocatalytic membrane was revealed.The main findings are as follows:（1）The physical-chemical and electrochemical properties of CeO₂@CNT electrocatalytic membranes were analyzed and characterized using various instrumentation,and the effects of exposed crystalline surfaces and crystal defects of CeO₂particles on the physical-chemical properties and electrochemical performance of CeO₂@CNT electrocatalytic membranes were investigated.The results show that CeO₂can be uniformly loaded onto the CNT surface,and CeO₂and CNT interleave with each other to form a porous film surface attachment layer.Compared with ECM,CeO₂@CNT electrocatalytic membrane has more oxygen vacancies（O_v）,higher hydrogen precipitation potential,smaller equivalent polarization resistance and faster electron transfer rate.The greater exposure of CeO₂{110}crystalline surfaces with O_vand Ce³⁺enables higher electrochemical activity and faster electron transfer rate of CeO₂@CNT electrocatalytic membranes compared to{111}crystalline surfaces.（2）EPR spectroscopy was used to detect the activation of Na ClO by CeO₂@CNT electrocatalytic membrane to generate ROS and RCS,to explore the role of CeO₂loading on activated oxygen（ROS）and activated chlorine（RCS）generation,and to reveal the pathways of ROS and RCS generation.The results showed that the activation of Na ClO by CeO₂@CNT electrocatalytic membrane mainly produced·OH,ClO·,·O₂^-and ¹O₂,among which the accumulated concentrations of·OH and ClO·were comparatively high.The presence of CeO₂substantially increased the cumulative concentration of ROS and RCS with O_vand Ce³⁺being the main active sites.The oxygen reduction reaction（ORR）is the main reason for the production of·OH,·O₂^-and ¹O₂,and the activation of ClO·at the Ce³⁺site is the main reason for the production of ClO·and ¹O₂.In addition,the conversion of Olat to Ov on CeO₂is one of the reasons for the generation of ¹O₂.（3）The degradation of PPCPs by CeO₂@CNT electrocatalytic membrane was carried out to explore the effect of system operating conditions on the degradation efficiency and to elucidate the degradation mechanism of PPCPs.The results showed that the removal efficiency of CeO₂@CNT electrocatalytic membrane reached 91.2%,91.3%,94.4%,99.3%and 89.4%for diclofenac,sulfamethoxazole,ciprofloxacin,tetracycline and carbamazepine,respectively.The apparent reaction rate constant（k）of the CeO₂@CNT electrocatalytic membrane was increased by a factor of 2.9compared with that of ECM.In the activation of Na ClO to produce ROS and RCS,both·OH and ¹O₂were able to cause degradation of PPCPs.In the-OH degradation pathway,PPCPs undergo substitution reaction,decarboxylation reaction,dechlorination reaction and cleavage reaction successively.In contrast,in the ¹O₂degradation pathway,PPCPs will be directly attacked,followed by cleavage,hydroxylation and decarboxylation.The ¹O₂degradation produces simpler intermediates compared to the·OH degradation pathway.In addition,CeO₂@CNT electrocatalytic membrane has more ideal stability and can maintain better treatment effect in the presence of various anions and natural organic matter,and the degradation efficiency did not decrease significantly after nine consecutive cycles of experiments.The activation of Na ClO by CeO₂@CNT electrocatalytic membrane also substantially reduced the generation of disinfection by-products（DBPs）.The research results of this dissertation provide a new material and technology for the efficient removal of PPCPs,which is conducive to enhancing the water treatment capacity of China and providing technical and theoretical support for safeguarding people’s health and ecological safety.