Removal Of Perchlorate Onto Biomass Carbon And Modified Material And Their Mechanisms

Perchlorate?ClO₄^-?is an emerging trace inorganic contaminant,the USEPA has listed ClO₄^-in the Contaminants Candidate List?CCL?.Nowadays,the pollution of ClO₄^-become more serious due to large amounts of ClO₄^-into water.In recent years,adsorption and reduction technology have been widely applied in treating perchlorate pollution,based on the status and short comings of adsorption and reduction technology.This work carried out research following several aspects.?1?The C.oleifera shell was pretreated by sodium hydroxide and zinc chloride,and the biomass carbon of C.oleifera shell was prepared by pyrolysis method.The structure and morphology of biomass carbon were characterized by SEM,XRD,XPS,BET and Zeta potentials.The mechanism of removal of perchlorate by biomass carbon was studied by adsorption experiment.The results show that pyrolysis temperature had a significant effect on the structure and morphology of biomass carbon.With the increasing of pyrolysis temperature,the specific surface area and total pore volume of biomass carbon were gradually increased,the condensed aromatic surface was enhanced,the surface hydrophobicity was gradually increased,-COH and-COOH content was gradually increased,the pHIEP value also increased,the higher pyrolysis temperature of biomass carbon and had higher perchlorate removal efficiency.The effects of pH,temperature,coexisting anion and initial concentration on the removal of perchlorate for biomass carbon were also investigated,the results show that pH and had coexistence of CO₃^2-a significantly effect on the removal of perchlorate.The adsorption of perchlorate on the biomass carbon was a spontaneous and exothermic process,and the maximum perchlorate adsorption capacity of biomass carbon was 25.99 mg/g.The mechanism for perchlorate removal by biomass carbon included two aspects:the oxygen-containing functional groups?-COH and-COOH?could adsorbed perchlorate by hydrogen bonding,and the nitrogen-containing functional groups?-N and-NH?adsorbed perchlorate by electrostatic force.The existing form of two types surface groups on biomass carbon were influenced by the solution pH value and leading to adsorption capacity variation.The perchlorate-saturated biomass carbon could be obtained by sodium hydroxide regeneration.The structural properties of biomass carbon were beneficial to the next step structure and surface modification treatment.?2?The biomass carbon was nitrogen-doped structure modified by ammoxidation.The structure and morphology of nitrogen-doped biomass carbon were characterized by SEM,XRD,XPS,BET and Zeta potentials,the electrochemistry properties were measured by electrochemical workstation,and the effect of nitrogen doping structure modification on the removal of perchlorate for biomass carbon was studied by adsorption experiment.The results show,ammoxidation temperature had a significant effect on the structure and morphology of nitrogen-doped biomass carbon.With increasing ammoxidation temperature,the surface area was remarkably decreased,the degree of graphitization was gradually decreased,oxygen-containing group was remarkably decreased and nitrogen-containing group was remarkably increased.The oxygen groups at the edges of graphene and defect sites react with the NH3,and the nitrogen atoms of NH3 displace oxygen groups into graphene of biomass carbon in low ammoxidation temperature?500-600 ??.When ammoxidation temperatures from 700 to 900? around 4 at.%carbon atoms and a part of the oxygen function groups at the edges of graphene and defect sites react with NH3 when the temperature rises to 800 ?and the nitrogen content reached the highest at 10.43 at.%.The results of adsorption experiment showed that the nitrogen-doped structure modification of biomass carbon was not conducive to the removal of perchlorate,the structure would leading to the biomass carbon to unfavorable perchlorate removal after nitrogen-doped structure modification,the surface oxygen-containing functional groups decreased leading to the perchlorate removal efficiency remarkably decreased.The electrochemical properties of biomass carbon after nitrogen-doped structure modification could be effectively improved,which had higher capacitance and lower internal impedance,perchlorate-saturated nitrogen-doped biomass carbon could be regeneration by electrochemical method.?3?Based on ammoxidation treatment C.oleifera shell biomass carbon material and leading to perchlorate adsorption capacity was remarkably decreased,using the surfactant of benzalkonium chloride to modified treatment for biomass carbon.The structure and morphology of benzalkonium chloride modified biomass carbon were characterized by SEM,XRD.XPS.BET and Zeta potentials.The mechanism of removal of perchlorate by benzalkonium chloride modified biomass carbon was studied by adsorption experiment.The experiment results shown benzalkonium chloride modified biomass carbon material?BAC-CAC?had broader pH scope of application?2.0-10.0?,the removal efficiency insensitive to temperature variation,coexistence of CO₃^2-had a little effect on the removal of perchlorate,the other four coexisting ions not had effect on the removal of perchlorate.The adsorption mechanism of benzalkonium chloride modified biomass carbon was studied by XPS,Zeta potential and Raman.The results show that the surface zeta potential of biomass carbon was effectively improved after modified by benzalkonium chloride.The perchlorate was adsorbed onto the surface of benzalkonium chloride modified biomass carbon by ion exchange,the oxygen-containing groups?-COH and-COOH?on the surface could adsorption perchlorate by hydrogen bonding,and the maximum adsorption capacity was 82.29 mg/g.The perchlorate-saturated BAC-CAC could be regenerated by high concentration of sodium chloride solution.The benzalkonium chloride modified biomass carbon had higher perchlorate removal efficiency than nitrogen-doped biomass carbon.?4?Based on the studies and results obtained,the benzalkonium chloride modified biomass carbon was used as the carrier for metal palladium?Pd?and rhenium?Re?,and synthesis adsorption/reduction bifunctional biomass carbon.And the structure and morphology of bifunctional biomass carbon were characterized by various means.The results show that,Re and Pd atoms could be availably doped on the carrier,but leading to surface area and prove volume significantly decreased.The perchlorate was absorbed quickly onto the carrier of benzalkonium chloride biomass carbon.Then,the adsorbed perchlorate could be reduced to chloride by Re-Pd/BC under hydrogen activation.The effects of pH,temperature,coexisting anion on the reduction of perchlorate and Re-Pd cluster transformation for Re-Pd/BC were also investigated,the results show that the efficiency of perchlorate reduction was markedly influenced by solution pH,improved temperature of reduction solution was beneficial to perchlorate reduction,coexistence anions could be decreased the perchlorate reduction rate constant.The transformation of Re-Pd cluster was remarkably influenced by the solution pH.With pH increasing Re-Pd bimetallic cluster was generally dissociated,when pH reached to 12.0 the bimetallic cluster was absolutely dissociated on the surface of Re-Pd/BC,and leading to Re-Pd/BC catalyst absolute deactivation.?5?The perhlorate could be effectively reduced in the solution under extraneous hydrogen activation.In order to explore the perchlorate reduction performance of Re-Pd/BC under endogenesis hydrogen activation,the three-dimensional electrochemical reactor was used to reduce perchlorate by titanium cathode electrode endogenesis production hydrogen.The effects of pH,temperature,coexisting anion on the electrochemical reduction of perchlorate for Re-Pd/BC were also investigated,the results show that perchlorate could be effectively reduced in a three-dimensional electrochemical reactor and Re-Pd/BC used as particle electrodes under optimized conditions?introduced nitrogen,solution pH 3.0,current density 20 mA?.Excessive oxygen in the solution lead to Re-Pd/BC deactivation,increasing the current density could increase the perchorate electrochemical reduction,the perchlorate reduction did not influence when the current density was higher than 20 mA,coexisting nitrate ion could lead to perchlorate reduction rate constant decreased significantly,tributyl alcohol could bind to H*atoms in the solution and lead to perchlorate reduction efficiency significantly decreased,the efficiency of perchlorate reduction was markedly influenced by solution pH,with pH increasing Re-Pd bimetallic cluster was generally dissociated and leading to the efficiency of perchlorate electrochemical reduction significantly decreased.