Preparation Of Catalytic Metal Oxide Electrodes And Their Performances In Photocatalytic/Microbial Fuel Cell Wastewater Treatment

Photocatalytic/microbial fuel cells are promising for wastewater purification and electricity generation from recovering chemical energy of wastewater,through photocatalysis or bio-catalysis.Recently,they have gained more attention in the fields of water pollution control and energy conversion.Constructing photo/electrocatalytic electrodes with high catalytic activity and stability is the key to efficiently remove pollutants and convert energy.Metal oxide electrodes possess high stability,low price and easy preparation,but they still suffer from insufficient catalytic activity.Moreover,the performance of single fuel cell is relatively limited in treating refractory wastewater.To solve these problems,metal oxide electrodes were designed including silver/zinc oxide nano-array/nickel foam photo-anode,carbon nanofiber/cobalt ferrite/carbon cloth cathode,carbon nanofiber/cobalt ferrite/polyvinylidene fluoride membrane cathode,for refractory pollutants removal and electricity generation in photocatalytic/microbial fuel cells.The activity and mechanism of fuel cells integrated with heterogeneous activation of peroxymonosulfate(PMS),microbial catalysis and membrane filtration were explored,respectively.The specific research contents and conclusions are as follows:(1)The three-dimensional nickel foam electrode was prepared with zinc oxide nanorod array decorated nanoscale Ag(AZN),through "crystal layer-hydrothermal-photoreduction"method.Experimental results indicated that the ordered morphology and heterostructure between metal and semiconductor enhanced the absorption ability of simulated solar-light and the separation efficiency of photogenerated carriers.Selecting berberine as the target pollutant,the degradation and mineralization rate were 98.9%and 89.6%(60 min)by AZN,respectively.The kinetic constant of AZN was 1.26 times that of electrode without Ag,which was higher than that of nickel sheet,carbon cloth flat electrode and ZnO catalyst.Electron paramagnetic resonance tests revealed that the photocatalytic activity of AZN benefited from the unique morphology,generating abundant hydroxyl radicals(·OH)and superoxide radicals(·O2-).The electrons transmission process was realized in photocatalytic fuel cell(PFC)with AZN photoanode and Pt cathode,with berberine as the fuel.(2)Considering the insufficient catalytic activity of traditional PFC(·OH oxidation),the PMS-PFC coupled system was constructed by the heterogeneous activation PMS of carbon nanofiber/cobalt ferrite/carbon cloth(CNF/CoFe2O4/CC)cathode,together with AZN photoanode.The PMS-PFC synergistically promoted the catalytic oxidation and electron transport:the berberine removal rate was more than 90.0%(10 min),and the degradation kinetic constant(9.18 h-1)and voltage output(0.50 V)were 7.29 times and 1.28 times to that of PFC.respectively.Mechanism analysis revealed that the metal sites at cathode mainly activated PMS to produce SO4·-,which promoted radicals generation by initiating the chain reactions of radicals.Meanwhile,the electrons from anode to cathode accelerated the process of catalytic oxidation.The PMS-PFC system possessed cyclic stability and its energy consumption indicators EEO was 5.25 kWh m-3.(3)The polyvinylidene fluoride(PVDF)membrane modified with CNF-CoFe2O4(CNFCFO-PM)was synthesized by the phase inversion method.The PMS activation with PFC/membrane reactor coupled system(PMS-PFC/MR)was constructed with the PMS activation and filtration function of CNF-CFO-PM.This membrane had a porous structure with loaded catalysts.The degradation performance under recycled filtration mode was higher than that under the static mode,verifying accelerated activity with membrane filtration.Under filtration mode,the PMS-PFC/MR with CNF-CFO/PM membrane obtained the highest catalytic activity compared to the unmodified and CNF modified membrane,with berberine degradation rate of 92.5%(30 min,volume:0.5 L).And its degradation kinetic constant was 9.39 times to that of PFC-MR.The cathodic reaction reduced metal leaching and effectively improved the reusability of membrane.The mechanism analysis revealed that ·OH,1O2,·O2and SO4·-were all responsible for pollutant degradation.The voltage output,maximum power density and energy consumption were 0.55 V,0.34 W m-2 and 1.18 kWh m-3,respectively,achieving low energy consumption and efficient treatment of refractory pollutants.(4)The catalytic and anti-fouling properties of the CNF-CFO/PM were further optimized by adjusting the ratio of catalyst.Considering the advantages of microorganisms for long-term operation,a cathodic membrane-microbial fuel cell system(CM-MFC)was constructed with activated carbon loaded electrogenic bacteria as an anode,using quartz sand separating layer(QSL)to replace expensive proton exchange membrane.The effect of hydraulic retention time(HRT)on the performance of system was investigated,and CM-MFC can effectively treat coking wastewater under HRT of 36 h.The COD of coking wastewater(4325.0-5074.3 mg L1)was reduced to 50.0-92.8 mg L-1.Driven by bio-anode,this system operation was stable with the output voltage of 0.40 V.The high-throughput sequencing results verified that the enriched electrogenic bacteria coexisted with other anaerobic bacteria in anodic chamber,and functioned for electron transfer and refractory organics removal in coking wastewater.Integrating with the cathodic catalysis and filtration process,the effluent quality was further improved.The cost of microbial fuel cell can be significantly reduced by using cheap QSL for wastewater treatment.