Synthesis Of Carbon Nitride Dased Photocatalysts And Their Photocatalytic Degradation Of Tetracycline

In the past few years,antibiotics have received widespread attention as an emerging pollutant.At present,the presence of antibiotics has been detected in environmental matrices around the world,indicating that conventional water treatment methods have poor removal of antibiotics.Therefore,it is necessary to develop new processes to remove antibiotics from the water environment.As one of the advanced oxidation technologies,semiconductor photocatalysis technology has been favored by researchers because it can directly use sunlight to degrade pollutants.In recent years,carbon nitride（g-C₃N₄）,as a new type of two-dimensional graphite material,has become an important material in photocatalytic applications due to its unique photoelectrochemical properties.However,due to the high recombination efficiency of photocatalytic electron-hole pairs,the photocatalytic efficiency of the pure g-C₃N₄is relatively low.In order to further improve the photocatalytic activity of g-C₃N₄,based on the theoretical basis of photocatalysis and the research status of g-C₃N₄,this paper constructed a composite semiconductor material based on g-C₃N₄ to improve its photocatalytic activity.After the successful preparation of the composite material,a series of characterization methods were used to characterize it.The photocatalytic properties of the composites were determined by photocatalytic degradation of tetracycline,and the influence of a series of factors on the photocatalytic degradation of tetracycline was investigated.Finally,the photocatalytic mechanism of the composite was discussed.The research results were shown as follows:A series of MoS₂/g-C₃N₄ and FeS₂/g-C₃N₄ composite photocatalytic materials with different doping ratios were prepared by impregnation-calcination method.The composites were characterized by XRD,SEM,TEM,BET,UV-vis,XPS,PL and EIS.The photocatalytic activity of the composites was determined by photocatalytic degradation of tetracycline（TC）.The effects of photocatalytic dosage,initial pH and anions on the degradation were investigated.Finally,the free radical quenching experiment and electron spin resonance（ESR）technique were used to detect the active free radicals generated during photocatalysis,and the photocatalytic mechanism of the composites was studied.（1）The results showed that the MoS₂/g-C₃N₄ composite had a larger specific surface area,stronger light absorption and higher separation efficiency of photogenerated-hole pairs,indicating that the composite had higher photocatalytic activity.When the doping amount of MoS₂ is 1.0%,the photocatalytic activity of the composite was the highest,and the degradation rate was about 4.7 times higher than that of pure g-C₃N₄.The optimal dosage of the catalyst was 2.0 g/L,and the optimum pH for degradation was 5.At the same time,the experimental results showed that SO₄^2-has a slight effect on the degradation of TC,and Cl^-has almost no effect in the range of 0-20 mM.After 5 cycles of experiments,the removal rate of TC could still reach about 70%.The quenching experiment and ESR results showed that superoxide radicals and holes played a major role in the degradation process.（2）The characterization results of FeS₂/g-C₃N₄ composites showed that the loaded of FeS₂ broadened the photoresponse range of the material and improves the separation efficiency of electron-hole pairs of the material.When the doping amount of FeS₂ was 20%,the composite exhibited the highest photocatalytic activity,and the photocatalytic degradation rate of TC was 1.93 times that of g-C₃N₄ and 3.89 times that of FeS₂.The optimum dosage of the catalyst was 1.0 g/L,and the optimum pH for degradation was 7.The experimental results showed that SO₄^2-and Cl^-within 20 mM had little effect on the degradation of tetracycline.5 cycles of experiments,the removal rate of TC could still reach 70%.The quenching experiment and ESR results showed that singlet oxygen played a major role in the degradation process,followed by superoxide radicals and holes.