Research On Preparation And Performance Of G-C₃N₄ Visible Photocatalyst Doped With Elements

With the increasing consumption of fossil fuels,the problem of energy shortage and environmental pollution have become increasingly prominent.Especially with the continuous increase in the discharge of various types of chemical waste water in recent years,it has led to a large area of water pollution in China,which requires us to solve the current severe problems-water pollution.Semiconductor photocatalytic technology utilizes natural sunlight to drive a series of photocatalytic reactions and is widely used in the treatment of organic wastewater.A new-type polymeric organic semiconductor,graphitic carbon nitride?g-C₃N₄?was investigated in this study.We selected the potassium and iodine elements were introduced into the g-C₃N₄,and then improved its photocatalytic properties.Firstly,used thiourea,dicyanodiamine,melamine and urea,as precursors,and g-C₃N₄ were prepared by thermal polymerization.They were analyzed by SEM,XRD,FT-IR.UV-Vis,BET and elemental analysis,and the photocatalytic degradation experiments with methylene blue as the target contaminant.The stability was investigated,too.The results showed urea had the largest surface area.The visible light had the widest range of response.The degradation rate of methylene blue was the highest.Therefore,the study selected urea as the precursor to dope modification of g-C₃N₄.A series of different potassium doping amounts of g-C₃N₄ were prepared by thermal polymerization with urea as the precursor and potassium nitrate as the dopant.A series of characterizations were carried out,and their photocatalytic activity and stability were studied.The mechanism of the reaction was presumed.The results showed that the introduction of potassium did not destroy the original crystal structure of g-C₃N₄,and the presence of potassium in the form of K-N bonds in g-C₃N₄.The photocatalytic degradation experiments showed that the degradation rate of methylene blue by K_0.3-C₃N₄ was the highest,reached to94%,after repeated use 4 times also reached to 80%.Urea was used as precursor and ammonium iodide as the dopant.A series of different iodide doping amounts of g-C₃N₄ have been prepared by thermal polymerization.A series of optical and electrical properties have been characterized.The catalytic activity and stability were investigated and the possible photocatalytic reaction mechanism was analyzed finally.The results showed that the presence of iodine did not destroy the original structure of g-C₃N₄.XPS showed that the I existed in the crystal structure of g-C₃N₄ with C-I covalent bond The surface area of I_0.02-C₃N₄ was the largest,had the strongest light absorption characteristics,the photoelectron-hole pair had the fastest separation and migration rate,the degradation rate of methylene blue was up to 84%in 120 min,and reached to 80%after 4 times recycle.