Electrochemical Oxidation Of Perfluorooctanoic Acid And CO₂ Reduction By B/N Doped Diamond

The pollution of toxic and refractory organic pollutants in water and the massive emission of carbon dioxide（CO₂）pose a serious threat to the ecological environment and human health.Electrochemical degradation of organic pollutants and CO ₂ conversion has the advantages of mild conditions,simple operation,environmental friendliness and no need to add additional chemical reagents.The electrocatalytic oxidation can completely mineralize organic pollutants,which is a promising advanced water treatment technology.However,the low catalytic activity of electrode leads to slow degradation rate and high energy consump tion of refractory organic pollutants.The conversion of CO₂ into valuable compounds by electrocatalytic reduction can slow down the emission of greenhouse gas CO₂ and make resource utilization.The main problems are the low activity of electrocatalyst and the difficulty of C-C coupling reaction,resulting in low generation efficiency and poor selectivity of multi-carbon products.To overcome the above problems,we designed highly active B/N doped diamond（BND）electrode,and studied the controllable preparation of BND with different compositions,as well as the regulation effect of B/N doping content and sp²-C on the electrocatalytic performance of BND electrodes.Their performance for electrocatalytic oxidation of refractory organic pollutants and electrocatalytic reduction of CO ₂,were further investigated.The main research achievements are as follows:（1）BND electrodes with different B and N doping concentrations were prepared by hot wire chemical vapor deposition.The morphology,crystal structure s and dopant contents of the prepared BNDs were characterized.The effect of B and N contents on the performance for electrochemical oxidation of perfluorooctanoic acid（PFOA）by BND was studied.The results show that the BND electrode is a complete and continuous film composed of 40～160 nm nanoparticles.BN D is cubic diamond with good quality.In sodium sulfate electrolyte,the degradation rate of PFOA on BND increased with the appropriately increase of B and N content.Under the low current of 4m A cm^-2,the degradation rate of BND with B content of1.10 at%and N content of 0.71 at%is the fastest,with kinetic rate of 0.030 min^-1,and its total organic carbon removal rate is 92.3%,which is among the best valuesreported in the literatures.Free radical identification experiments showed that BND electrochemically activated sulfate solution to produce SO₄^·-and·OH,with strong oxidation capability,overcoming the limitation that most electrode materials could not activate sulfate to produce SO₄^·-.The degradation experiments with the addition of free radical quenchers showed that PFOA was mainly degraded by SO₄^·-and·OH.（2）The strategy of introducing sp²-C into BND was proposed to promote CO₂electroreduction towards multi-carbon products at low overpotential.B/N and sp²-C doped hybrid carbon（BNHC）was prepared by high temperature calcination of diamond powder,and the effects of B/N doping and sp²-C on the performance of CO₂ reduction were studied.The results show that the prepared BNHC is consisted of 4.7±0.6 nm core-shell nanoparticles with a cubic diamond core（sp³-C）and a graphite carbon shell（sp²-C）.When N content is 5.2at%and B content is 6.2 at%,BNHC can selectively produce ethanol by electroreduction of CO₂ at low overpotential.At the voltage of-0.5～-0.6 V（vs.RHE）,the Faradaic efficiency of multicarbon product is 58.8%～69.1%,among which the efficiency of ethanol production is51.6%～56.0%.The high efficiency of ethanol production on BNHC is mainly attributed to the synergistic effect of sp²-C and sp³-C and B/N doping,in which the B/N doped sp³-C is favorable to the formation of multicarbon products,and the sp²-C significantly reduces the overpotential of ethanol production.