Study On The Performance Of Ammonia Nitrogen Removal From Water Via Photocatalytic Nitrification-denitrification Process By G-C₃N₄/Gr/TiO₂ Z-schematic System

Ammonia nitrogen is one of the main pollutants in surface water and the main inducement of eutrophication in lakes and reservoirs.And it will bring about acute toxicity to aquatic organisms as its concentration accumulates.Therefore,it is of great significance to study and develop efficient ammonia nitrogen removal technologies for ammonia nitrogen emission,alleviating eutrophication in water and enhancing drinking water safety.Photocatalysis technology using sunlight as energy source possesses the properties of high efficiency,energy saving and environmental friendliness,and can overcome a series of problems compared with the biological technologies,which is considered as one of the most promising pollutant treatment technologies.In this work,homemade g-C₃N₄,graphene oxide（GO）and TiO₂were used as raw materials,through electrostatic assembly method and hydrothermal reduction reaction process,we prepared g-C₃N₄/Gr/TiO₂photocatalytic materials successfully.The results provide a simple and feasible method for harm Less removal of ammonia nitrogen in wastewater.In addition,it provides experimental reference and theoretical basis for simulating oxidation-reduction two-stage degradation of other pollutants by Z-schematic system.Meanwhile,it is hoped to promote the application of photocatalytic technology in wastewater treatment.The main research contents are as follows:（1）The SEM images of g-C₃N₄/Gr/TiO₂（GO:g-C₃N₄=1:10）show the structure of this material is g-C₃N₄/Gr coated with TiO₂nanoparticles,peaks of TiO₂and g-C₃N₄appeared in the XRD pattern composite materials at the same time,DRS spectra manifest the absorptive capacity of composite material in the visible light enhanced obviously,the active free radicals were tested by means of electron paramagnetic resonance（EPR）,and the degradation mechanism is considered as:The superoxide anion radical and hydroxyl radical were generated on the composite photocatalyst under irradiation of xenon lamp,and they oxidize the adsorbed NH₃on the surface of the material directly,while Gr could conduct photoelectric charge carriers as the transmission medium of the photocatalytic material.（2）In the ammonia-nitrogen removal experiment of g-C₃N₄/Gr/TiO₂Z-type photocatalytic system,the ammonia-nitrogen removal efficiency of 50mg/L ammonia-nitrogen solution was highest when pH=9.5 with g-C₃N₄/Gr/TiO₂（GO:g-C₃N₄=1:10）photocatalytic material.At the same time,the possible NO₃^-production in the reaction process was studied and analyzed.When the pH in the reaction was 4.5,the NO₃^-removal rate of 10mg/L NO₃^-solution was low.However,when the ammonia nitrogen of 50mg/L was added,the NO₃^-removal rate of NO₃^-solution was improved,and ammonia nitrogen played the role of hole capture agent.The present of ammonia nitrogen benefits the removal of NO₃^-,which could be caused by the Z-schematic mechanism of g-C₃N₄/Gr/TiO₂photocatalytic system,and indicated NO₃^-could be one of the reaction intermediates during the removal of ammonia nitrogen in water.Particularly,the ammonia nitrogen in PS II produce NO₃^-,and photocatalytic denitrification of intermediate NO₃^-occurs in the conduction band of PSI to produce N₂.（3）In the degradation of actual wastewater by g-C₃N₄/Gr/TiO₂Z-type photocatalytic system,the existence of COD and its generated chromatism do not affect the degradation efficiency of ammonia nitrogen by the photocatalytic material,when the reaction conditions are consistent with that of simulated wastewater,the reaction performance is good.