Coupling Fuel Cell And Photocatalysis In Removing Inorganic Nitrogen In Water

With rapid urbanization and economic development,the nitrogen pollution in water has become a severe problem.In addition,the high cost and energy consumption in nitrogen pollution control is an obstacle for changing the situation.New energy-saving wastewater treatment technologies should be developed.MFCs?Microbial Fuel cells?can be used to treat wastewater and generates electricity simultaneously.However,the low power output and waste removal are the problems to be solved.Therefore,a photocatalysis-MFC system was developed for highly efficient pollutants removal and electricity production.Based on these,three kinds of photocatalytic electrodes were prepared.And photocatalytic fuel cell systems were constructed to remove inorganic nitrogen in water.The reaction conditions,electricity production and the mechanism of nitrogen removal were studied.The main achievements of this paper are as follows:?1?With carbon fiber cloth as the base material,a simple sol gel method was used to prepare g-C₃N₄-TiO₂ photocatalytic electrodes.The nitrate was removed by electrons from the microbe in the anode chamber and photocatalysis reaction under visible light.The nitrate nitrogen removal rate was 72.57% after 3.5 h?initial concentration of 100 mg/L?and the nitrogen gas selectivity in product was 99.54%.The maximum power density reached 33 m W/m2.From the repeated experiments,the catalysts showed good stability.?2?A simple hydrothermal synthesis method was used to prepare MoS₂-Ti O₂ and MoS₂-Bi VO₄ photocatalyst.Photocatalytic electrodes were prepared by coating on stainless steel net as the base and with silica sol as the binder.The catalytic activity and stability were best when the ratio of catalyst and silicon sol is 1 mg: 1 1?L.In the ammonia oxidation system,MoS₂-TiO₂ and MoS₂-BiVO₄ served as the photo-anode and photocathode,respectively.The removal rate of ammonia nitrogen reached 78.21% after 4 h,under the light intensity of 30000 Lux,and the selectivity of produced nitrogen gas was97.12%.The photocatalytic electrode stability was good after the repeated experiment.?3?The nitrogen removal mechanism was studied.The nitrate nitrogen was removed by reduction by the electrons produced from the anode and the photoelectron produced by the cathode.Most of the nitrate was reduced to nitrogen gas directly,a minor part was firstly turned into nitrite and then nitrogen.The ammonia maybe directly oxidized to nitrogen gas or firstly oxidized into nitrate by active species produced by photo-generated holes,and then reduced into nitrogen by photo-generated electrons.Above all,the visible light responses,nitrogen removal and nitrogen gas selectivity of the two photocatalytic fuel cell systems were good.As a new type of high efficiency nitrogen removal method with low energy consumption,it showed great potential in practical application.