Study On The Degradation Of Organic Pollutants By Persulfate Activation With Polyelectrolyte Functionalized Carbon Nanotube Membrane Electrode

Advanced oxidation technology based on persulfate activation is widely used for the removal of organic pollutants due to its strong oxidation capacity,wide application range of pH and fast reaction speed.The transition metal-based heterogeneous catalyst can effectively activate persulfate,but the poor stability of the catalyst and the leaching of metal ions greatly limit its practical application.Using nonmetallic carbon materials to activate persulfate can effectively avoid the above problems,but the problems of difficult dispersion of original carbon materials,few active sites and low activation efficiency still need to be solved.For this reason,this paper intends to build polyelectrolyte functionalized carbon nanotube（CNT）membrane electrode,improve the persulfate activation efficiency by virtue of the interaction between polyelectrolyte molecules and CNT,and efficiently degrade pollutant through non-radical pathway.In this paper,the coupling mechanism between polyimide（PEI）,poly（diallyl dimethyl ammonium chloride）（PDDA）and CNT was investigated,the structure-activity relationship between the operation process parameters and the degradation efficiency of target pollutants was clarified,the dominant active substance types in the two systems were investigated,and the stability and degradation universality of two reaction systems were evaluated.The main research contents are as follows:（1）Based on van der Waals force,CNT was effectively dispersed in PEI aqueous solution.PEI-CNT composite membranes were prepared by interfacial polymerization,and the PEI-CNT composite membrane activated persulfate（PDS）system was constructed.In the single flow mode of the penetrating reactor,levofloxacin（LFX）was used as the target pollutant for the degradation experiment.The results showed that under the optimal reaction conditions of 0.75 mM PEI concentration,1.5 mM PDS initial concentration,1 mL/min flow rate,and 7.0±0.5 initial pH,the degradation efficiency of LFX（2 mg/L）could reach 100%within 5 minutes.PEI-CNT/PDS system can achieve rapid and efficient removal of low concentration LFX.The analysis of active substances showed that non-radical pathway mediated by singlet oxygen（¹O₂）and electron transfer played a key role in the process of PDS activation.The unique electron donating ability of PEI is used to adjust the surface electronic structure of CNT,which enables efficient activation of PDS and efficient degradation of the target pollutant.（2）Based on the good dispersibility of CNT in PDDA aqueous solution,the PDDA-CNT composite electroactive membrane was prepared by interfacial polymerization,and the PDDA-CNT activated persulfate（PMS）system was constructed.In the circulating flow mode of the penetrating reactor,Congo red（CR）was used as the target pollutant for the degradation experiment.The results showed that when the mass ratio of PDDA to CNT was 10:90,the initial concentration of PMS was 1.5 mM,the applied voltage was-1 V,and the flow rate was 5 mL/min,CR（10 mg/L）was completely degraded within 40 min.The analysis of active species showed that¹O₂and non-radical pathway mediated by direct electron transfer played a major role in PDDA-CNT/PMS system.Due to the unique electron absorption characteristics of polyelectrolyte PDDA,the electronic structure of CNT surface is adjusted.At the same time,the enhanced convection mass transfer effect of the penetrating reactor and the synergistic enhancement of the auxiliary electric field jointly promote the efficient degradation of CR.Based on the interface charge transfer doping strategy,a polyelectrolyte-CNT activated persulfate system was constructed,which provides a feasible scheme and design idea for heterogeneous metal free catalyst in persulfate activation.