Insights Into The Efficiency And Mechanism Of Activation Of Persulfate Via Modified Carbon-based Materials For Removal Of Bisphenol A

Endocrine disrupting chemicals（EDCs）are a kind of pollution substances which are widely found in environmental water body,which have the characteristics of strong ecotoxicity and difficult biodegradation.They can pose a serious threat to human health by interfering with neuro-endocrine-reproductive networks.Advanced oxidation process（AOPs）are a kind of water treatment technology which are widely used to degrade organic pollutants such as EDCs in water due to their strong environment adaptability,hige degree of mineralization,long duration of oxidation and high oxidation efficiency.Carbon-based materials,as a cheap,green and efficient catalyst,can overcome the problems of poor stability and metal precipitation in advanced catalytic oxidation technology of metal materials.And they have shown great application potential in advanced persulfate oxidation technology（PS-AOPS）.In this paper,based on the preparation of modified carbon-based materials,four activated persulfate oxidation systems of modified carbon-based materials were constructed.And the effect of the activation of peroxydisulfate（PS）on the removal efficiency of bisphenol A（BPA）by four modified carbon-based materials were studied,and the mechanism were analyzed.These thesis consists of four parts as follows:（1）In the third chapter,carbon nitride（g-C₃N₄）modified carbon materials（Cs/g-C₃N₄）were synthesized by one-step calcination using coffee grounds and melamine as precursors.It was found that Cs/g-C₃N₄ could effectively activate PS to remove BPA.Adding 0.2 m M PS and 0.5 g/L Cs/g-C₃N₄ at neutral p H condition,the removal rate of BPA was 100%（30 min）.The mechanism analysis of radical quenching,EPR technology,and electrochemical techniques（CV,LSV,EIS,and the open circuit voltage）show that in the reaction process of Cs/g-C₃N₄/PS system,the unstable unpaired electrons of Cs/g-C₃N₄ can be captured by PS,the oxidized carbon-based material（[Cs/g-C₃N₄]*）with two electrons lost has a higher oxidation potential,the vacancies can be further filled by capturing electrons of BPA,resulting in oxidative degradation of BPA.The activation energy for Cs/g-C₃N₄/PS system was obtained as 16.93 k J/mol on basis of the Arrhenius equation.The results showed that the removal efficiency of BPA improved with PS concentration and Cs/g-C₃N₄ dosage increasing,BPA concentration decreasing.And Cs/g-C₃N₄/PS system can adapt to a wide p H range（p H 3.0-9.0）.Finally,LC-MS technology was used to analyze the main intermediate products in the process of BPA degradation,and the degradation paths of BPA were proposed.（2）In the fourth chapter,S-doped modified porous carbon（SCs）with high specific surface area were synthesized by calcination using coffee grounds as raw material,sodium bicarbonate as pore-forming agent and 2,5-thiophene dicarboxylic acid as sulfur source.It was found that SCs could activate PS to effectively remove BPA.The results of mechanism analysis show that S doped on carbon materials can effectively improve the adsorption performanc e of carbon based materials,and can activate PS degradation of BPA through the nonradical pathways.The excellent oxidative effectiveness of the SCs/PS system originated from singlet oxygen（¹O₂）and electron transfer.The structural defects and C=O on the surface of carbon materials are the main catalytic active sites.And[SCs]*could despoil electrons from oxygen atoms in H₂O molecules or OH^-anions to form ¹O₂and it’s supposed that S doping can effectively create C=O groups,which were determined to be the main active sites contributing to the direct electron transfer.What’s more,the effects of common anions（Cl^-and HCO₃^-,1 m M and 5 m M）and humic acid（1 mg/L and 5 mg/L）on the removal of BPA were studied.The results showed that Cl^-had little effect on the removal of BPA,while HCO₃^-and humic acid had slight effect on the removal of BPA.And SCs/PS system can also adapt to a wide p H range（p H 4.0-10.0）.（3）In the fifth chapter,boron modified porous carbon（BCs）with low cost and environment friendly was prepared by using coffee grounds as raw material,sodium bicarbonate as pore-forming agent and boric acid is the boron source.Compared with B-free porous carbon（Cs）,BCs has higher adsorption and catalytic performance.It can adsorb BPA and activate PS to degrade BPA efficiently.The removal rate constant（kobs）of BPA was proportional to the adsorption capacity（q_e）of BPA（R²=0.999）.Electron paramagnetic resonance and radical quenching indicated that different from the radical-based oxidation,nonradical pathways were demonstrated to dominate the oxidation processes in BCs/PS system.The results of mechanism analysis showed that PS could activate BCs to form metastable intermediate[BCs]*complex with a high oxidation potential,which are the main active oxidizer for BPA degradation in BCs/PS system.The experimental results of subsequent mechanism discussion and electrochemical analysis（CV,Tafel corrosion analysis and the open circuit voltages）show that BCs can not only improve the efficiency of PS consumption,but also elevated potential of derived nonradical[BCs]*complexes,and then accelerated BPA removal efficiency via electron transfer process.The effect of the dosage of carbon-based material on the removal of BPA was studied,the adsorption and oxidation of BPA on Cs and BCs can be evaluated theoretically using the Langmuir-Hinshelwood（L-H）kinetic model（R²>0.99）,which showed that BCs can promote the efficiency of the reaction.（4）Based on the excellent performance of BCs synthesis and its activation of PS,in chapter six,Na BH₄ was used to reduce Fe SO₄ to synthesize nano zero-valent iron（n ZVI）and attach it to the surface of BCs to prepare n ZVI@BCs composite material.The n ZVI@BCs/PS system with both radical oxidation and nonradical oxidation were constructed.Compared with n ZVI@Cs/PS and BCs/PS,n ZVI@BCs/PS system could greatly promote the degradation and mineralization of BPA.Further analysis demonstrated that n ZVI@BCs/PS system can remove and degrade BPA in two ways:radical pathway and nonradical pathway.On the one hand,electron spin resonance and radical quenching studies showed that^·OH,SO₄^·-and O₂^·-were mainly produced in the n ZVI@BCs/PS system,which are responsible for the degradation of BPA.On the other hand,the open circuit voltages of n ZVI@BCs and n ZVI@Cs in different systems indicated that nonradical pathway still exist in our system.PS could grab the unstable unpaired electron on n ZVI@BCs to form a carbon materials surface-confined complex（[n ZVI@BCs]*）with a high redox potential,then accelerate BPA removal efficiency via electron transfer.Furthermore,it was found that in the n ZVI@BCs/PS system,the degradation of BPA was mainly limited by the concentration of th e PS and the dosage of the carbon-based material,while the reaction p H had little effect on it.The common anion Cl^-can promote the degradation of BPA,mainly because excessive negatively charged Cl^-can provide electrons to PS,and can also produce excessive active chlorine and sulfate to participate in the degradation process of BPA;HCO₃^-could quench^·OH and SO₄^·-in the reaction system,resulting in a lower BPA removal rate.In this paper,the advanced oxidation system of PS activated by four modified carbon-based materials developed based on coffee grounds showed strong oxidation performance on endocrine disruptor BPA.This study provides a new insight for development of high-performance carbocatalysts toward environmental remediation.