Preparation Of Bi₂WO₆-based And G-C₃N₄-basedcomposites And Their Degradation Properties To Tetracycline

At present,the contradiction between global energy and environmental issues is becoming increasingly prominent,the ecosystem on which human beings depend is facing a huge threat.As the catalyst of life on earth and the source of all thing,aquatic ecosystems are facing environmental problems such as the surge of organic pollutants.The treatment of organic pollutants in water has become one of the hot topics in the field of environmental protection.Photocatalytic technology is widely used in the degradation of organic pollutants in water,removal of atmospheric pollutants and catalytic hydrogen production due to its advantage such as high degree of mineralization efficiency,mild reaction and utilizing sunlight.However,the related research showed that the single photocatalyst has the problems of low quantum efficiency and low photocatalytic activity.Therefore,researchers in the field of photocatalysis are committed to modifying photocatalysts,further widening their absorption range of sunlight,increasing the rate of photogenerated holes and electrons,and thereby improving photocatalytic performance.As the new type of photocatalytic materials,Bi2WO6 and g-C3N4 have great potential in photocatalytic degradation of organic pollutants in water,such as simple preparation process,wide light response range and strong stability.At present,researchers have done a lot of studies on the modification of Bi2W06 and g-C3N4 to improve the light absorption capacity of materials and the transfer of photocarriers,thereby improving their photocatalytic degradation performance of organic pollutants.Based on above analysis,we synthesized Bi2W06 and g-C3N4 based composites by different cocatalysts.The morphology,structure and optical properties of the composites were analyzed by relevant characterization.The photocatalytic performance of the composites was measured by the degradation of TC.The degradation mechanism of TC was discussed by analyzing the degradation product and the capture experiments.The main research contents are as follows:(1)Ni/Ti/Bi2WO6 photocatalysts were successfully prepared by facile hydrothermal reaction and impregnated method.SEM,XRD,XPS,PL,UV-vis and other characterizations showed that cocatalysts significantly improved the light absorption capacity and transfer of photogenerated carriers of Bi2WO6.On one hand,Ti-Ni as hole-electron cocatalysts could promote the transfer of photogenerated carriers and inhibit the recombination of photogenerated electrons and holes;On the other hand,the light absorption ability of the composites was enhanced by Ni-Ti modification.In addition,the larger specific surface area promoted the absorption of organic pollutants by the composites.In the potocatalytic degradation of TC,it was found that the removal rate of TC by Ni/Ti/Bi2WO6 reached 93.47%,which was 29.15%higher than that of single Bi2WO6.(2)NCDs were synthesized by the one-step hydrothermal method,and the new ternary h-BN/NCDs/g-C3N4 composites were synthesized by calcination.Due to the special optical characteristics of NCDs,the light absorption capacity of composites in the visible light region became stronger and there was a significant red shift phenomenon.In addition,the effective transport of photogenerated carriers between h-BN,NCDs and g-C3N4 inhibited the recombination of electrons and holes,thereby further enhancing the photocatalytic performances of composites.The results of photocatalytic degradation of TC showed that when the content of NCDs was 0.5wt%,the h-BN/NCDs/g-C3N4 composite exhibited the best photocatalytic performance.The degradation efficiency of TC reached 74.48%in 1h,and the reaction rate constants were 2.93 times and 1.98 times that of g-C3N4 and h-BN/g-C3N4,respectively.It was proved that h+ and·O2-were the main active species in photocatalytic reactions by the radical scavenge experiments and ESR.The degradation path and mechanism of TC were predicted through the HPLC-MS and characterization.(3)Ti/NCDs/g-C3N4 composites were prepared by calcination.The composites were characterized by XRD,TEM,UV-vis and PL.The photocatalytic activity of the samples was determined by the degradation of TC under simulated sunlight.The results showed that when the content of Ti was 0.75 mmol and the content of NCDs was 1 wt%,the Ti/NCDs/g-C3N4 exhibited the best photocatalytic performance,and the degradation rate reached 81%in 90 minutes.