Efficiency And Mechanism Of Persulfate Activation By Polyaniline-derived Carbon Materials For Chlorophenols Degradation In Water

The extensive use of chlorophenols（CPs）in agriculture and industry made them ubiquitous in all types of environmental mediums globally.Higher toxicity and bioaccumulation of the excessive presence of CPs pose a serious threat to wildlife,aquatic animals and human beings,which urgently need to be removed.Persulfate advanced oxidation processes（PS-AOPs）based on carbon materials are effective technologies for removing CPs from water bodies.However,most of the carbon materials currently face shortcomings such as harsh preparation conditions,complicated processes,difficult for large-scale production and high fabrication costs for environmental applications,and their performances still need to be further improved.Activated carbon and biochar,which have low cost and abundant sources,are usually unsatisfied in terms of catalytic activity,stability and separability.This limits the further applications of carbon materials.Therefore,it is necessary to develop efficient and novel PS carbon catalysts that are easy to produce on a large scale and have stable performance.Conducting polymers,mainly polyaniline（PANI）,are characterized by inexpensive raw materials and mature fabrication procedures,which endow their derived carbon materials have the advantages of low preparation cost and large-scale production.Meanwhile,the N atoms bonded by covalent bonds on PANI can be doped efficiently during carbonization,and the surface properties of its derived carbon materials are easy to adjust.The above-mentioned traits make PANI-derived carbon materials have great potential to become economical and efficient PS carbon catalysts.However,as far as we know,there are few studies on the application of PANI-derived carbon materials to the removal of pollutants in water by PS activation.The application potentials and the corresponding mechanism have not been fully verified and developed.Based on this,this thesis prepared a series of novel PS carbon-based catalysts with PANI as the main carbonization precursor and deeply explored their efficiencies and mechanisms of activating PS to degrade CPs.The main research content and results are as follows:（1）Preparation of PANI-derived nitrogen-doped carbon nanotubes（CPNT-T）and the exploration of corresponding catalytic performances and mechanismsPANI nanotubes were synthesized by oxidative polymerization,and nitrogen-doped carbon nanotubes were simply prepared by carbonization.The performance and mechanism of activated peroxydisulfate（PDS）for 2,4-dicholophenol（2,4-DCP）degradation by nitrogen-doped carbon nanotubes prepared at different carbonization temperatures were investigated.The results showed that higher carbonization temperatures were favorable for the improvement of catalytic activities.CPNT-10obtained by carbonization at 1000°C showed optimal catalytic activity,and 95.66%of2,4-DCP（100 mg/L）could be removed within 60 min by the addition of CPNT-10（300mg/L）.The CPNT-10/PDS system exhibited a high PDS utilization efficiency and a wide p H adaptation range.Moreover,the single oxygen（¹O₂）was the main active species and limited free radicals played an auxiliary role,while direct electron transfer was negligible.The vacancy,graphitic sp² C,C=N,and pyridine-N-O were all involved in PDS activation.Among them,the vacancy was the decisive factor.（2）Preparation of copolymer-derived carbon materials（CPAn Py X）and the factors affecting non-free radical pathwaysThe nitrogen-doped carbon material with higher specific surface area（CPAn Py X:114.25 m²/g.CPNT-10:79.4 m²/g）was obtained by carbonization of PANI-PPy copolymer,and the performance and mechanism of activated PDS for 2,4-DCP degradation were comparatively explored using the carbon materials derived from the mono-polymer（CPAn X and CPPy X）as controls.The results evidenced that the copolymerization approach can effectively increase the specific surface area and pore volume of the materials,thus enhancing the PDS adsorption capacity and leading to a significant improvement in the catalytic performance.The rate constant for the CPAn Py X/PDS system was approximately 7.32 and 10.83 times better than that in the CPAn X/PDS and CPPy X/PDS systems,respectively.Nearly 100%of 2,4-DCP（100mg/L）could be removed within 60 min by the addition of 200 mg/L of CPAn Py X.The CPAn Py X/PDS system,with good catalytic activity in the p H=3.00–8.00,showed strong resistance to Cl^-and NO₃^-,and exhibited significant selectivity for electron-rich organic pollutants.The ¹O₂ pathway and the electron transfer pathway were the main reaction routes for 2,4-DCP removal.For mono-polymer-derived carbon materials,the reaction system of CPAn X with a higher degree of defects was more favorable for the occurrence of the ¹O₂ pathway,while the reaction system of CPPy X with a higher degree of graphitization was favorable for the occurrence of the electron transfer pathway.The copolymer-derived carbon materials inherited and promoted the catalytic pathways of each polymer-derived carbon material.The structure-effective relationship suggests that the C=O group was the main active site affecting the contribution of the¹O₂ pathway,while the electron transfer capacity of the reaction system and the potential of the complex formed by catalyst and PDS determined the ability of the electron transfer pathway for pollutants removals.（3）Preparation of copolymer-derived carbon materials encapsulating Fe-based nanoparticles（Fe@CPAn Py X）and the acceleration effect of Fe core on the non-free radical pathway and its mechanismTo enhance the performance of the non-radical pathway of CPAn Py X and give full paly to the advantages of the non-radical pathway,CPAn Py X encapsulated with Fe-based nanoparticles（Fe@CPAn Py X）were prepared by adjusting the oxidant.Their performances and mechanisms of activated PMS for 2,4-DCP degradation were comparatively investigated.The results showed that the presence of Fe-based nanoparticles significantly enhanced the catalytic activity of the catalyst for PMS,and nearly 97.24%of 2,4-DCP（100 mg/L）could be removed within 6 min with the addition of 200 mg/L of Fe@CPAn Py X,and the degradation efficiency reached 17.2 times higher than that of the CPAn Py X/PMS system.It showed significant advantages compared with various reported similar systems.The presence of Fe ions during carbonization is one of the reasons for improved catalytic performances because it can significantly increase the specific surface area,graphitization and defect/disorder levels of the catalysts during the carbonization processes.After encapsulating Fe-based nanoparticles,the material still degraded 2,4-DCP via a non-radical pathway,in which the electron transfer pathway played a dominant role and ¹O₂ played an auxiliary role.In the catalytic process,the external N-doped carbon material,rich in defects and graphitic-N,was the main component involved in the reaction,while the internal Fe core mainly acts as“electron supply stations”of the outer carbon shell to facilitate the non-radical pathway.The identification of the intermediates and toxicity analysis showed that the toxicity of the pollutants significantly reduced after the reaction.Benefiting from the enhanced non-radical pathway,the Fe@CPAn Py X/PMS system exhibited extremely high potential for applications with wide p H applicability（p H=3.00–11.00）,strong resistance to water matrixes,significant electron-rich pollutants selectivity and good reusability.（4）Construction of Fe@CPAn Py X/PVDF catalytic membrane and evaluation of its pollutant degradation performanceGiven that the activation of PMS by Fe@CPAn Py X is dominated by the electron transfer pathway,the lower mass transfer efficiency of the heterogeneous system will greatly limit its performance.Afterwards,Fe@CPAn Py X was loaded onto polyvinylidene fluoride（PVDF）membranes to construct Fe@CPAn Py X/PVDF catalytic membranes and its performance in PMS activation for the 2,4-DCP degradation was explored by a continuous flow mode.The results showed that the Fe@CPAn Py X/PVDF/PMS catalytic membrane system exhibited an extremely high degradation efficiency,which could achieve 99.74%removal of 2,4-DCP within a residence time of 0.867 s.The corresponding degradation efficiency was nearly 840-fold higher than that of the heterogeneous Fe@CPAn Py X/PMS system.Besides,the apparent kinetic constants were generally improved by 2 to 5 folds of magnitude compared with the previously reported 2,4-DCP degradation systems.The system achieves strong resistance to interference with all water matrices through p H adjustment and maintains stable efficiency in various actual water samples.The single-layer Fe@CPAn Py X/PVDF catalytic membrane with loading of 1.5 mg/cm² could maintain the complete removal of high-concentration 2,4-DCP contaminated water（100 mg/L）at a high flux of 306 LMH for 2 h and retained more than 80%of the removal rate after4 h of continuous operation.In addition,increasing the number of catalytic membranes and decreasing the initial concentration of pollutants are both effective methods for extending the life span.In addition,the system exhibits good removal efficiency for all pollutants that do not contain strong electron-absorbing groups.In summary,this thesis proposes a simple and effective route and strategy for the preparation of high-performance PS carbon catalysts and establishes several catalytic degradation systems for the efficient degradation of CPs.The research results deepen the insights into the mechanisms of PS activation by carbon materials and provide the materials,theoretical,and technological support for the treatment of CPs wastewater by PS-AOPs based on carbon materials.