Preparation And Modification Of Carbon-based Nanomaterials For Catalytic Degradation Application

Peroxymonosulfate（PMS）-based advanced oxidation processes（AOPs）are receiving great attention in water treatment due to their advantages such as high oxidation capacity,operational simplicity,and flexible activation pathways.So far,many studies on PMS activators have focused on metal-based catalysts,and although these catalysts have demonstrated promising catalytic efficiencies,the risk of metallic leaching limits their widespread application.And the carbon-based catalyst is expected to be the ideal PMS activator due to its environmental and cost effectiveness.To realize the practical application of carbon-based catalysts for PMS activation,there are still some urgent issues to be solved.（1）The catalytic activity of pristine carbon-based catalysts is low,which makes it difficult to satisfy practical necessities.（2）The relationship between catalyst structure and catalytic activity is not clear.In particular,the role of the edge sites is often neglected.（3）Treatment of high salinity wastewater is difficult due to the quenching effect of free radicals.（4）The conversion of mechanical energy or solar energy into chemical energy to activate PMS has not been sufficiently researched and developed,while the piezoelectric catalysis or piezoelectric photocatalysis process is usually accompanied by the generation of H2O2,which is expected to further reduce the dosage of PMS.Therefore,it is of theoretical and practical significance to develop advanced carbon-based catalysts,especially piezoelectric or piezo-photocatalysts,for efficient activation of PMS.In this dissertation,the following research work was carried out using non-metallic heteroatom doping and defect engineering as strategies for carbon-based catalyst modification.（1）The treatment of wastewater with high salinity is still a challenge because of the quenching effect of various anions on radical processes.The nonradical process may be a more promising pathway.Herein,a 3D structured nitrogen-doped graphene nanosheet anchored with carbon nanotubes（N-GS-CNTs）was prepared by direct pyrolysis of K3Fe（CN）6.The as-prepared catalyst can effectively activate peroxymonosulfate（PMS）for mineralization of tetracycline（TC）over a wide p H range（from 3 to 11）and even in high saline water（500 m M Cl^-,HCO3^-,etc.）.The degradation mechanism was elucidated by both experimental characterizations and DFT calculations.The high catalytic efficiency was attributed to accelerated electron transfer from donor（TC）to acceptor（PMS）in the presence of the catalyst,which acts as electron shuttle mediators to promote a nonradical process.At the same time,the catalyst also enhances the production of singlet oxygen（¹O2）,hence further increasing the degradation rate.This study not only provides a simple method for synthesizing N-GS-CNT catalysts but also provides new insights into the electron transfer pathway for the removal of organic pollutants under high salinity conditions.（2）A controllable synthetic route of carbon nanosheets co-doped with phosphorus and nitrogen was developed by pyrolysis of a supermolecular aggregate of self-assembled melamine,phytic acid,and carbon sheet.The as-prepared catalyst has shown a substantially increased efficiency for peroxymonosulfate（PMS）activation in the degradation of tetracycline（TC）.The roles of dopants and edge sites were systematically investigated by both experimental characterizations and theoretical simulations.Compared with the undoped catalyst,the P/N co-doped catalyst has substantially enhanced the adsorption of PMS/TC and the subsequent electron transfer process,which is recognized as the dominant nonradical mechanism.Consequently,an efficient catalytic activity was obtained for the degradation of TC as well as other pollutants even under high salinity（500 m M）and high concentration wastewater（500ppm）.This work not only presents a non-metallic carbocatalyst with high catalytic activity for extensive environmental remediation,but also provides new insights into the edge P/N co-doping effects on the electron-transfer dominated nonradical activation of PMS.（3）An effective piezocatalytic semiconductor（C3N5-x-O）was prepared with a two-step thermal polymerization/etching method.Experimental characterizations and structural simulations revealed that the dual-defects of O doping and N vacancy in C3N5 not only increases the asymmetry and the exposure of triangular pores,but also optimizes the band structure and charge distribution of the thin-layered C3N5-x-O,endowing it with an enhanced piezoelectricity and increased active surfaces.Piezocatalysis-mediated pollutant degradation and H2O2production were achieved with substantially improved efficiencies over the pristine carbon nitrides.Under ultrasound-assisted piezocatalysis,tetracycline was degraded with a kinetic rate of 0.0356 min^-1 and this figure was further increased to 0.0561 min^-1 in piezocatalytic-Fenton.A yield of 0.615 m M/g/h for piezocatalytic production of H2O2 was achieved in pure water.The synergistic effect of the defect sites revealed in present work could facilitate the more rational design of nitrogen-rich carbon nitrides for environmental remediation and the production of value-added chemicals.Particularly,to provide ideas for the development of high-performance piezoelectric-based PMS activators.（4）An efficient piezo-photocatalyst（C3N5-x-CN）with enhanced piezo-photocatalytic performance was successfully fabricated by introducing cyano groups（-CN）and N vacancies into the semiconductor C3N5 through a two-step thermal polymerization/etching procedure.As-prepared C3N5-x-CN exhibits a synergistic enhancement of piezoelectricity and photoelectricity in ultrasound-assisted photocatalytic system.Experimental characterization and computer simulations confirmed that the introduction of dual-defect sites in C3N5 creates an active catalytic surface,which not only increases the piezoelectricity,but also promotes the carrier separation,thus achieving an overall improved piezo-photocatalytic performance.The piezo-photocatalytic system enables efficient removal of tetracycline with a kinetic constant of 0.0342min^-1 and this figure is increased to 0.0492 min^-1 in the presence of PMS.Furthermore,a yield of 1359μM/g/h of H2O2 was produced under piezo-photocatalytic treatment of pure water.The synergistic mechanism and relative activity of dual-defect sites unraveled in this work could facilitate the construction of a multifunctional platform for carbon-nitride based piezo-photocatalysis.In particular,the effectiveness of piezo-photocatalytic activation of PMS was increased,as was our knowledge of the mechanism behind this process.