Strengthen The Bioelectricity Generation Of Bioelectrochemical Systems By N-containing Functional Carbon Materials:performance And Mechanisms

Bioelectrochemical systems(BESs)are emerging and promising technology that uses electroactive microbes(EAMs)as catalysts to drive redox reactions for wastewater treatment and simultaneous current generation.However,lower current density and power output,compared with other sources of energy,have severely hampred the practical application of BESs.The anode that serves as the habitat for biofilm formation is one of the determinants of BES performance,and structural optimization and interfacial modification of the anode have proven to be an effective method to enhance the performance of BES.However,most of the reported anode materials in BES have the disadvantages of poor performance,complex preparation method and high cost,which are inconvenient to practical application.Therefore,it is necessary to develop high-efficiency,easy-preparation and low-cost anode materials for BES,so as to lay a foundation for the practical application of BES.In view of the problems existing in BESs at present,a series of N-containing functional carbon materials were prepared to improve the bioelectricity generation capacity of BESs through structural design and surface modification of electrode materials,and moreover the promotion mechanisms were explored in depth.The main contents and results of this thesis are as follows:1.The mechanism of N dopant states in N-doped graphene(NG)regulating the EET process of S.oneidensis MR-1 was analyzed.A series of NG materials were prepared and employed as anode modifiers of BESs.The electricity generation performance of different NG anode materials in S.oneidensis MR-1 inoculated BESs were investigated,and the impacts of different active N species on the EET process of S.oneidensis MR-1 were explored.The results showed that there was a linear positive correlation between the content of pyrrolic N in NG-modified electrode and the electricity generation capacity of BES.The NG500 sample with the highest pyrrolic N content most significantly promoted the current generation of the BES,achieving a current density of 6.46 A/m2,which was about 5 times that of the undoped graphene one.The mechanism study showed that the pyrrolic active N species in the electrode played an important role in promoting the DET and MET processes of S.oneidensis MR-1.Molecular dynamics simulation(MDS)results verified that the pyrrolic active N species possessed the lowest kinetic and thermodynamic resistance in both DET and MET processes,which could promote the DET and MET processes of S.oneidensis MR-1 more effectively.2.A N-containing conductive polymer/porous carbon composite anode material was prepared to improve the bioelectricity generation capacity of BESs,and the promoting mechanisms were analyzed.Using sodium citrate(SC)and polyaniline(PANI)as raw materials,a honeycomb-like porous carbon coated with PANI nanoparticles composites(PANI@SC)were prepared by high temperature pyrolysis and in-situ polymerization,which was then used as the surface modifier for carbon paper(CP)to obtain the PANI@SC-CP composite electrode.The PANI@SC-CP composite electrode showed excellent electricity generation capacity in three-electrode electrochemical cells(ECs)inoculated with Shewanella oneidensis MR-1,and its maximum current density reached to 4.41 ± 0.15 A/m2,which was about 6 times that of the traditional CP electrode.This improvement was mainly attributed to the higher biocompatibility resulting from the large Brunauer-Emmet-Teller(BET)surface area of the SC and the outstanding hydrophilicity of PANI,and the increased extracellular electron transfer(EET)efficiency of S.oneidensis MR-1 owing to the enhanced interaction between electroactive microbes(EAMs)and the PANI@SC-CP composite electrode.The excellent performance of the PANI@SC-CP composite electrode for bioelectricity generation was also verified in microbial fuel cells(MFCs)inoculated with S.oneidensis MR-1 or mixed culture.3.The feasibility and mechanism of using poultry feather solid waste-derived N-doped activated carbon anode material to improve bioelectricity generation of BESs were explored.Using goose feather solid waste as raw material,N-doped activated carbon(GFNAC)was prepared by a simple pyrolysis method and then used as the anode modifier of BESs.By using S.oneidensis MR-1 inoculated BESs with the GFNAC-modified CP anode,a current density of 0.96±0.03 A/m2 was achieved,which was about 2 times that of the CP one.It was found that the excellent electricity generation performance of the GFNAC-CP electrode was mainly attributed to the increased loading capacity of EAMs on the electrode surface and the enhanced EET efficiency of S.oneidensis MR-1.The improved EET efficiency of S.oneidensis MR-1 would be attributed to not only the improvement of direct electron transfer(DET)efficiency caused by the strong interaction between outer membrane protein OmcA/MtrC and GFNAC,but also the promotion of flavins mediated electron transfer(MET)process caused by the increased flavins' adsorption capacity of the GFNAC-modified electrode.4.A novel highly efficient 3D N-doped graphene aerogel(NGA)anode material was developed to enhance power generation performance of BESs.The 3D NGA was fabricated by a two-step method,including hydrothermal reaction and freeze-drying process,using graphene oxide as the raw material and ethylene diamine(EDA)as the nitrogen source.By using S.oneidensis MR-1 inoculated BESs with the NGA anode,a current density of 1 A/m2 was achieved,which was about 2 times that of graphene aerogel,and much higher than that of the conventional carbon-based electrode(0.34 A/m2).The excellent electricity generation performance of NGA anode was mainly attributed to the good biocompatibility owing to its 3D macroporous structure,and the improved EET efficiency of S.oneidensis MR-1 resulting from its abundant mesoporous structure,excellent electrical conductivity the enhanced interaction between microbes and the electrode.In addition,the excellent electricity generation capacity of the 3D NGA anode was further verified in mixed-culture MFCs.5.Using nitrogen-rich corn straw solid waste as precursor,a three-dimensional(3D)N-doped macroporous carbon anode was fabricated to improve electricity generation of mixed-culture MFCs,and the regulation mechanism of N doping states on the MFC performance was also analyzed.Using nitrogen-rich corncob as raw material,3D N-doped macroporous carbon foams(NMCFs)were prepared by pyrolysis at high temperature.In addition,PANI and polypyrrole(PPy)were used as external N sources to further regulate the contents of different N species in NMCFs.The optimized 3D NMCF anode achieved a maximum power density of 4.99 ± 0.02 W/m2 and a maximum current density of 12.30±0.01 A/m2,which represents the best performance among the reported carbon-based ones for MFCs to date.Moreover,there was a positive correlation between the pyrrolic N content in 3D NMCF electrode and the power output of MFC.Such improvements would likely be originated from not only the good biocompatibility of 3D NMCFs for the enrichment of electroactive Geobacter species,but also the enhancement of extracellular electron transfer(EET)efficiency of the Geobacter with anode doping of N atoms especially for pyrrolic N,as indicated by density functional theory calculation.