Study On The Degradation Of Phenol In Water By The Cathode Of Biomass Carbon-based Microbial Fuel Cell

Phenol is a kind of refractory organic pollutant commonly found in industrial wastewater.Its high toxicity seriously endangers human health and aquatic life.The traditional phenol-containing wastewater treatment technology has disadvantages such as high energy consumption and easy to emerge secondary pollution.Microbial fuel cells(MFCs)can not only treat wastewater,but also generate electricity.It is a new wastewater treatment process which belongs to bioelectrochemical system and has the advantages of low energy consumption and high efficiency.The ORR activity of cathode catalyst is the key factor limiting the performance of MFC.At present,Pt/C and activated carbon(AC)widely used in MFC cathode have disadvantages such as high price and poor durability,which are difficult to meet the long-term wastewater treatment requirements.Therefore,it is urgent to prepare a cathode catalyst with excellent ORR activity and long-term stability to improve the output performance of MFC and the degradation efficiency of pollutants.The carbon source of biomass used in this paper is waste pomelo peel,melamine is used as nitrogen source,and Co Cl₂·6H₂O is used as cocatalyst.Nitrogen-doped biomass carbon(NBC)catalysts are prepared by two-step synthesis method and treated with different concentrations(0,0.5,2 M)of nitric acid.The electrochemical performance tests of catalysts treated with different acid concentrations shows that NBC-0.5 shows the best electrochemical activity.In combination with the structural characterization,it can be seen that NBC-0.5 presents a stable porous spherical structure after proper acid treatment.And nitrogen atoms are successfully introduced into the stable carbon skeleton,resulting in uneven electron density distribution around the adjacent carbon,which is conducive to electron transfer and ORR process in the interface reaction.Applied to the actual running MFCs,NBC-0.5 has the maximum power density(0.996 W m^-2),the output voltage(0.486 V),and the smaller mass transfer resistance(43.3?).After stable operation for1200 h,the maximum power density only decreases by 7.83%.Compared with Pt/C and AC,it has excellent power generation performance and long-term stability.Meanwhile,when the initial concentration of phenol is 0.2 g/L,the removal efficiency of phenol by NBC-0.5 cathode MFC can reach 90.8%,which is significantly higher than that of Pt/C and AC.In order to improve the efficiency of MFCs degradation of phenol and the performance of electricity generation,the cathode catalyst is further improved based on the above experiments.Based on the same carbon source,nitrogen source and co-catalyst,boric acid is introduced as boron source to prepare nitrogen-boron co-doped biomass carbon(BNBC)by using two-step synthesis method and treating carbonized samples with0.5 M HNO₃.The control variables are the molar ratio of Co Cl₂·6H₂O,boric acid and melamine(1:1.5:3,1:3:3 and 1:6:3).BNBC-1 has a large number of defect structures due to the successful doping of boron and nitrogen atoms as well as abundant pore structure,which leads to faster mass transfer efficiency and better electrical conductivity.Meanwhile,BNBC-1 has the highest current density and nearly four electron reaction pathway,which shows good ORR catalytic activity.When BNBC-1 is used as MFC cathode,its long-term operation stability is the best,and the final periodic power density only decreases by 6.41%.When the initial concentration of phenol is 0.2 g/L,the degradation efficiency of BNBC-1 cathode MFCs reaches 98.2%,which is higher than that of NBC-0.5 cathode MFCs,and the treatment effect of high concentration phenol wastewater is improved to some extent.This is due to the synergistic effect brought by the co-doping of boron atom and nitrogen atom,as well as the catalytic ability of boron atom with stronger electronegativity,which realizes the efficient,energy-saving and harmless treatment of phenol wastewater.