Preparation Of Carbon Nitride Composites And Their Water Purification Mechanism Study

With the development of society,the harm of refractory pollutants in wastewater to human health and environmental safety is gradually increasing.There is an urgent need to develop efficient and green water pollution control technology to deal with the current pollution problems.It is found that advanced oxidation process can effectively degrade refractory pollutants by improving biodegradability and reducing toxicity.Graphite carbon nitride is a non-metallic two-dimensional layered material,which has attracted much attention because of its unique electronic structure,high stability and easy synthesis.However,pure carbon nitride also has structural defects,such as easy carrier recombination,small specific surface area and large internal resistance.Therefore,the development of new water purification materials with high catalytic activity and stable performance is still facing great challenges.Aiming at the refractory organic pollutants and microorganisms in water,based on the composite modification of carbon nitride,two different carbon nitride matrix composites were prepared,and the material structure,catalytic performance and reaction mechanism were deeply analyzed.The main research contents and conclusions are as follows:Fe and Ni metals were coupled with g-C₃N₄ by simple calcination method,and then zero valent Pd was loaded by in-situ liquid deposition to obtain Fe Ni-Pd@CN compound material.Under the conditions of aeration and the presence of formic acid,the degradation rates of acid red 73(AR 73,200 mg/L)and tetracycline hydrochloride(TC,10 mg/L)reached 92.0%and 93.2%respectively.The composite has good catalytic performance and stable service performance.Through capture experiment,O₂-TPD and ESR,it is further analyzed that formic acid decomposes under Pd catalysis to produce H^*,which provides a hydrogen source for the reaction system.The advocated air is adsorbed on the metal surface as an oxygen source,and then H^*generates H₂O₂,which can reach 1.69 mmol/L.The experimental results show that·OH and·O₂^-are the main reactive oxygen species.In order to obtain high visible light photocatalytic activity and stability,nitrogen deficient C₃N₅(NVCN)was constructed and compounded with silver phosphate(Ag₃PO₄,APO).The close interface between APO and NVCN was observed by SEM,TEM and element distribution diagram,which proved the successful construction of NVCN/APO heterojunction.In addition,according to the UV-vis diffuse reflection spectrum,transient photocurrent response,photocurrent analysis and Mott Schottky characterization results,it is further speculated that the electrons between NVCN and APO are transferred through the Z-scheme mechanism,the photogenerated electrons in APO conduction band(CB)are transferred to the valence band(VB)of NVCN,and holes are generated on VB of NVCN.Therefore,photogenerated electrons accumulate on the CB of NVCN and react with O₂ to form·O₂^-.Capture experiments and ESR tests show that the main effective ROS components of the catalytic reaction are·O₂^-and H⁺.The degradation experiment shows that the degradation effect of NVCN/APO-3 is the best,and the k value of pseudo first-order reaction kinetics can reach 0.5123 min^-1.The corresponding generation of·O₂^-is 0.04852?mol/min,which can effectively degrade pollutants in water.The degradation efficiency was only reduced by 2.7%after three times of recycling,which had good stability.Further explore the sterilization ability of the filter solution that accumulates H₂O₂ after photocatalytic reaction.H₂O₂ production can reach 0.199 mmol/L for 20min.The experimental results show that the filter solution after photocatalytic reaction still has a certain sterilization ability,and the bacterial removal rate is 99%within 30 min.when the sterilization time is extended to 3 h,the sterilization effect reaches 99.99%.The morphology of E.coli cells after reaction was observed by SEM.It was found that the cell end was damaged and the middle part was concave,indicating that the active substance oxidized the cell membrane structure,and the leakage value of NVCN/APO-3 K⁺was 646.81?g/L further confirmed this conclusion.Therefore,it shows that the filter solution after NVCN/APO-3 reaction has sterilization ability,resulting in distortion of cell structure and rupture of cell wall.This result can provide a new exploration idea for carbon nitride based modification and water pollution treatment in the later stage.