Electro-Catalytic Degradation Of Organic Arsenic Based On Fe₃C Loaded Carbon Nanofibers

In recent years,the widespread use of herbicides in the field of agriculture caused serious environmental problems of organic arsenic,which brought new challenges for the safety of drinking water quality.As the typical organic arsenic,methylarsonic acid?MMA?and dimethylarsinic acid?DMA?pose a threat to human health once they enter human body,resulting the damage of DNA.Due to the contribution of Methyl substituting effect on the stability of DMA,the removal of DMA from water is usually difficult by the traditional water treatment stategies,such as adsorption and oxidation.Therefore,the possibility of utilizing heterogeneous Electric-Fenton for the removal of DMA was investigated in this work.The efficiency and underlying mechanism of DMA degradation over carbon fiber-based electrocatalysts were studied.In the research,the influence of current intensity,initial pH and oxygen flow rate on the H2O2 production over carbon fibers?ACF?electrodes was evaluated.In was indicated that the highest yield of H2O2 could be achieved for the pH between 3 and 4.The production of H2O2 increased with the current intensity rised,however polarization response was occured that reduced the current efficiency once the current excessed reach 0.2 A.The further increase of current density resulted in the deterioration of current efficiency,due to the occurance of polarization.Furthermore,the production of H2O2 increased with the increase of oxygen flow rate,till reached the maxium with the gas flow of 50 m L/min.For the heterogeneous electo-catalysis,novel Fe₃C loaded carbon nanofibers were fabricated through the calcination of templates prepared by electrospinning.Based on the cahracterizations,composite catalysts with the legnth in the range of several micrometers and tens of micrometers were obtained.The diameter of porous rod-like products was about 400 to 500 nm.The BET surface area of catalysts was determined to be 343 m2/g,with the pore size of 0.5 nm.Graphite layer coated Fe₃C nanoparticles were successfully deposited onto the surface of carbon fiber matrix.The influence of experimental factors on the heterogeneous Electric-Catalysis removal of DMA was investigated,including initial pH,initial concentration,current density and catalyst dosage.Results showed that the highest removal efficiency of 96 % could be achieved under the initial pH of 3,initial concentration of 5 mg/L,current density of 0.15 A and catalyst dosage of 500 mg/L.As-synthesized catalysts exhibited superior activity for the degradation of DMA,due to the promoted charge transfer during electro-catalysis processes.As a result,the formation of oxidation active species could be significantly enhanced.In addition,the large specific surface of composites also contributed to the abundant adsorptive sites for the adsorption of oxidation products,based on the quasi monolayer or monolayer reversible adsorption.The intermediate products was further studied by the digestion of catalyst,which indicated the maintainance of total arsenic balance.The removal processes of DMA during Electric-Fenton reaction was revealed.DMA was firstly oxidized into MMA,which could be adsorpted by the accummulated catalysts at the cathode.The subsequent As?V?oxidated by MMA which adsorpted at the cathode assured the concentration of the effluent As?V?below the detection limit.The mechanism of DMA degradation was proposed,which was beneficial for the removal of organic arsenic by Electric-Fenton reaction.