Preparation Of Carbon Nitride With High Specific Surface Area By Solvothermal Method And Study On The Photodegradation Of Tetracycline Hydrochloride

The abuse of tetracycline antibiotics has become an urgent problem of environmental pollution.Using semiconductor photocatalysis technology to degrade tetracycline antibiotics is a method of using clean energy,high removal efficiency and complete photolysis and mineralization of pollutants.Among all kinds of catalysts,g-C₃N₄ has become a research hotspot because of its suitable band structure,no heavy metal components,visible light availability and low cost.However,toxic solvents such as acetonitrile and dimethyl sulfoxide are often used in the preparation of g-C₃N₄ by solvothermal method.There are still some disadvantages in the photocatalytic process,such as serious photogenerated electron hole recombination,low quantum efficiency and low utilization of visible light.In order to solve these problems,we designed green synthesis routes with water and ethanol as solvent respectively from the perspective of morphology control of g-C₃N₄,and prepared two kinds of g-C₃N₄ photocatalysts with high specific surface area and unique structure by solvothermal method.The effects of heating time on the morphology,photoelectric properties and catalytic performance of g-C₃N₄ catalyst were studied and the structure of the catalyst was characterized.The photocatalytic activity and stability of g-C₃N₄ for tetracycline hydrochloride under simulated sunlight were investigated,and its degradation mechanism was proposed.（1）Carbon nitride with high specific surface area was prepared by solvothermal method using melamine as raw material and water as solvent and reactant.The effects of heating time on the morphology,photoelectric properties and catalytic performance of the catalyst were studied.The results show that the heating time is the key factor affecting the structure and morphology of carbon nitride prepared by solvothermal method.Too short heating time will lead to incomplete hydrolysis reaction and self-assembly process,and the surface structure of the catalyst will aggregate into blocks;too long heating time will lead to complete hydrolysis of melamine to produce cyanuric acid,which will affect the formation of precursors.The g-C₃N₄（DM18）prepared by heating for 18 h has high specific surface area(33.5 m²·g^-1)and high light absorption properties.Its unique dense bubble structure is conducive to the refraction and repetition of light in the catalyst and effectively inhibits the recombination of photogenerated electrons and holes.The results of photocatalytic degradation of tetracycline hydrochloride showed that the degradation rate of tetracycline hydrochloride by DM18 was 61%within 2 h,among the DMX catalysts prepared by solvothermal method,the photocatalytic activity was the highest.The active group capture experiments showed that·O₂^-and H⁺were the main active groups in the photocatalytic degradation of DM18 and BCN.（2）High specific surface area carbon nitride（CCMx）with porous structure was prepared by solvothermal method using melamine and cyanuric chloride as raw materials,ethanol as solvent and reactant.Different heating time leads to the change of the morphology,photoelectric properties and catalytic performance of the catalyst.The specific surface area of g-C₃N₄（CCM18）with heating time of18 h is 107.4 m²·g^-1,which has a unique mesh like structure.The results of photocatalytic degradation of tetracycline hydrochloride showed that the degradation ability of all the catalysts in CCMx series was higher than that of BCN.The degradation rate of tetracycline hydrochloride by CCM18 was 82%in2 h,which was higher than that of BCN and DM18.The active group capture experiment showed that the photocatalytic degradation mechanism of CCM18 was different from that of DM18 prepared with water as solvent.The main active group was·O₂^-and·OH.The results of cyclic experiments show that the structure of CCM18 as photocatalyst was stable.