Preparation Of G-C₃N₄/Fe⁰/TiO₂ And Optimization Of Systems For Efficient Electricity Generation From Pollutant Degradation

Environmental pollution and energy crises have become worldwide concerns.To tackle these problems,scientific research about photocatalysis(PC),photocatalytic fuel cell(PFC),microbial fuel cell(MFC),and integrated catalyst systems indicating great potentials has been conducted.Especially,catalytic fuel cell technologies serving as advanced oxidation processes(AOPs)can integrate pollutants degradation with electricity generation that recovers energy from wastewater.Catalyst properties are the critical factor for such fuel cell technologies.By using non-noble metal materials such as Fe,g-C₃N₄ and TiO₂,Z-scheme catalyst of low cost and high activity can be constructed.The electrode with excellent photo-electrocatalyst can improve the efficiency of fuel cells,in-situ integrate catalysis with biological process,and enhance pollutant degradation and energy recovery.Thus,a novel environmental-friendly triple component g-C₃N₄/Fe⁰(1%)/TiO₂ catalyst was prepared and optimized.It was applied in PC,PFC and/or MFC-PFC for pollutants degradation as well as electricity generation.The results and conclusions are as follows:(1)Catalyst g-C₃N₄/Fe⁰(1%)/TiO₂ was prepared using a simple process involving the formation of zero valence iron by chemical reduction.This triple component catalyst demonstrated high-visible-light activity in a wide range of pH conditions.It can photo-catalytically degrade rhodamine B(RhB),tetracycline hydrochloride(TC),and berberine chloride(BC)with degradation rate of 0.037,0.027,and 0.022 min-1 and efficiency of 98%,92%,and 90%,at optimum pH 5 in 90 min under visible light,respectively.This triple component catalyst has excellent photocatalytic property and stability compared with those reported catalysts.The high activity arises from the increased harvest of visible light and the enhanced separation of photo-excited electrons and holes,via Z-scheme and heterojunctions mechanism.The addition of 3.18 mM Na2SO3 in PC reactor made possible the generation of more reactive oxidizing species thus improved the degradation of pollutants.(2)Degradation of pollutants can be integrated with electricity generation in PFC using Z-scheme g-C₃N₄/Fe⁰(1%)/TiO₂ as an anodic catalyst and WO3 as a cathodic catalyst under light irradiation or in the dark in self-powered fuel cell at different pH values(1,2,5,7,10,11,and 13).RhB,BC,TC(10 mg L-1),and coking wastewater were treated.With light,removal of RhB(0.026 min-1 and 98%in 100 min),BC(0.025 min-1 and 91%in 90 min)at optimum pH 2,and TC(0.034 min-1 and 97%in 90 min)at optimum pH 5 were accompanied with 0.95,0.81,and 0.98 V cell voltages and 22.6,16.4,and 24.0 W m-2 power densities,respectively(in 0.05 M Na2SO4,with 10 ? external resistance).However,without light irradiation,all the RhB,BC and TC degradation efficiencies(60%,76%and 80%),kinetic constants(0.005,0.013 and 0.014 min-1)and electricity generation(0.50,0.68 and 0.76 V)of the PFC were decreased.This PFC exhibited higher performance in cell voltage,current density,and degradation efficiency in comparison with others.The influence of pH on photocatalytic degradation performance and cell voltage was evaluated.With TC(10 mg L-1),the chemical oxygen demand(COD)and total organic carbon(TOC)removal rates with light were 95%and 91%,respectively.In the dark,the removal of COD and TOC was 65%and 48%,indicating that the fuel cell was self-driven and self-biased,forming potential gradient and degrading pollutants.In PFC treating real coking wastewater,91%COD and 89%TOC were removed in 240 min and 0.35 V cell voltage and 3.1 W m-2 power density were generated in 120 min,at initial pH 5.(3)The g-C₃N₄/Fe⁰(1%)/TiO₂ was tested as cathode in MFC-PFC treating real coking wastewater under alternate light and without light condition.The continuous up-flow reactors,with granular activated carbon as bio-anode and flat membrane photo-cathode(carbon fiber cloth cathode with g-C₃N₄/Fe⁰(1%)/TiO₂).The volumetric ratios of cathode chamber to anode chamber were different.The continuous 28 days performances for Reactor A with a bigger anode chamber and for Reactor B with a bigger cathode chamber,treating an acidic pH 3.18 coking wastewater(initial COD 3070 mg L-1)were compared.The higher biomass and lower internal resistance in Reactor A led to a power density of 14.5 W m-2 when connected with 5? external resistance.The Reactor A and Reactor B respectively has a cell voltage of 0.51 V and 0.31 V,removed 95%and 85%COD,and 90%and 80%TOC under light irradiation.The light irradiated cell voltage,power generation and COD removal in Reactor A were respectively 0.20 V higher,2 times and 20%higher than without light.The MFC-PFC system(using a small surface area of cathode)shows high performance in pollutant removal and electricity generation compared with other studies.After stopping Reactor A for 5 months,the test was restarted treating slightly alkaline coking wastewater(pH=7.65),with light and without light.After 28 days of continuous operation for reviving and acclimating the microbes,this reactor was capable to recover its performances and generate a maximum power density of 6.18 with light and 2.53 W m-2 without light,with 10 ? external resistance.The COD removal with light was 93%.This combined system may treat other refractory wastewaters.