Study On Preparation And Photocatalytic Performance Of Modified Carbon Nitride Photocatalytic Material

Graphitic carbon nitride,a metal-free photocatalytic material,is favored by researchers due to its advantages of nontoxicity,stable physical and chemical properties,abundant and availability of raw materials,moderate band gap and so on.However,the further improvement of g-C3N4 photocatalytic activity is restricted to its limited specific surface area and rapid recombination performance of photo-generated carriers.Therefore,the preparation of carbon nitride based photocatalyst was explored in this paper,aiming to improve the ability of carbon nitride photocatalytic degradation of pollutants,and tetracycline was selected as the target pollutant to explore the photocatalytic degradation of prepared carbon nitride based photocatalytic materials under visible light irradiation.The main research contents are as follows:(1)The photocatalytic materials g-CN/GQDs-X were prepared by one pot mixed calcination method through the pre-prepared GQDs calcined with melamine,the prepared samples were analyzed through XRD,FTIR,TEM,XPS,PL and UV-Vis spectroscopy,etc.The conclusions showed that the incorporation of GQDs had no significant effect on the crystal structure and surface functional groups of carbon nitride,but its ability to assist electron transfer significantly reduces the PL intensity of the composites,and the visible light absorption property and the separation capability of carriers were enhanced.The degradation experiment results showed that the degradation rate of tetracycline(TC)of prepared g-CN/GQDs-X was better than that of carbon nitride,among which g-CN/GQDs-5 possessed the best degradation effect,78%TC can be degraded after 60 min visible light irradiating,the degradation rate increased by 27%compared with carbon nitride,and the kinetic constant was 1.8 times that of carbon nitride.Cyclic experiments showed that g-CN/GQDs-5 had good cycling stability,and the degradation rate of TC did not change after four times of reuse.The capture experiment of active species showed that superoxide radicals played a major role in the degradation of TC in this system.Combined with the characterized results and experimental results,it is concluded that the improvement of photocatalytic performance of g-CN/GQDs-5 is due to the enhancement of visible light utilization of carbon nitride with the introduction of GQDs,as well as the excellent electron-receiving ability of GQDs,which inhibits the recombination of photo-generated carriers.(2)The photocatalytic materials PCN-X were prepared by selected melamine and urea as precursors,NH4H2PO4 was used as phosphorus source.The samples were characterized by XRD,FTIR,XPS,SEM and BET.The results showed that the prepared PCN-X had a unique tubular structure,a large specific surface area(39.58 m2/g)and a relatively low recombination speed of photo-generated carriers.Meanwhile,in the evaluation experiment of photocatalytic performance,PCN-5 showed the best degradation effect of TC,and the degradation rate was 83.8%:In order to further improve the degradation effect of TC,the oxidant K2S2O8 was added to investigate the degradation of TC by prepared photocatalysts in different systems,and the influence of reaction conditions on the degradation of TC was explored.Research found that the maximum degradation effect of TC could reach 96.4%under PCN-5/K2S2O8/Vis system,the degradation process of tetracycline conforms to the pseudo first order kinetic equation.And the reaction kinetics constant of PCN-5/K2S2O8/Vis system is 1.6 times,3.5 times,9.3 times that of PCN-5/Vis,g-CN/K2S2O8/Vis and g-CN/Vis.And found that the reaction conditions such as catalyst dosing quantity,TC initial concentration,initial pH and K2S2O8 dosing quantity will affect the PCN-5/K2S2O8/Vis system photo-degradation TC.The capture experiments of active species showed that·O2,followed by h+andSO4-·,played a major role in the degradation of TC in PCN-5/K2S2O8/Vis system.Based on the comprehensive analysis of the experimental and characterization results,the increases of specific surface area and the improvement of the transport efficiency of photo-generated carriers caused by the morphology change were the main reasons for the improvement of the photocatalytic performance of PCN.