Preparation Of Graphitic Carbon Nitride-based Composites And Its Photolysis Properties Of Tylosin

Antibiotics are widely used in the treatment of various infectious diseases and livestock husbandry.However,a large amount of antibiotics is abused,which leads to the gradual increase of antibiotic residues in the environment and potential harm to human and ecological environment.Traditional biochemical processes do not effectively treat antibiotic wastewater.But,the study found that the use of sufficient sun exposure to semiconductor photodegradation of antibiotics is the ideal solution to the global water pollution of antibiotics.Graphitic carbon nitride（g-C₃N₄）as a non-metallic semiconductor,due to its non-toxic,cheap and easy to prepare are widely used in the degradation of organic pollutants.However,g-C₃N₄ has some disadvantages such as small surface area,low light absorption capacity and low electron-hole separation efficiency,which will lead to low photocatalytic efficiency and affect its practical application.To improve the photocatalytic performance of g-C₃N₄,a variety of modifications were carried out around g-C3N4.The physical and chemical properties of composite materials prepared by the characterization analysis.In addition,the properties and mechanism of photodegradation of tylosin（TYL）in composites were studied.Specific research contents are shown as follows:（1）The goethite/g-C₃N₄ photocatalyst was successfully synthesized by thermal polymerization-hydrothermal synergistic method.By using the difference between the valence band（VB）and the conduction band（CB）of goethite and g-C₃N₄,the formation of a semiconductor heterojunction effectively suppresses the recombination of electron-hole pairs.When the mass ratio of goethite and g-C₃N₄ is 1:1,the prepared catalyst exhibits the strongest degradation efficiency,and its photodegradation efficiency is more than three times that of pure g-C3N4.In addition,the load of goethite greatly increases the specific surface area and light absorption capacity of the composite catalyst,and effectively suppresses the recombination of electron-hole pairs.Experimental studies have found that superoxide radicals(·O^2-)and hydroxyl radicals（·OH）produced by goethite/g-C₃N₄ composites under light irradiation are the main active groups for photodegradation of TYL.At the same time,the cycle experiment also confirmed that the goethite/g-C₃N₄ composite has good stability and recycling.（2）Modified carbon spheres with higher crystal structure were synthesized by surfactant modification using monosaccharide（glucose）,disaccharide（sucrose）and polysaccharide（cyclodextrin）as precursors.A small amount of modified carbon spheres embedded in g-C₃N₄ can form a heterojunction with an intimate interface.In addition,use carbon spheres as the carrier can promote the separation efficiency of electron-hole pairs.Furthermore,through characterization and photolysis experiments,it was found that the modified carbon spheres expands the visible light absorption range of g-C₃N₄by its own characteristics,and the electron transfer inhibits the recombination of electron-hole pairs,thereby improving the photodegradation efficiency of TYL.Free radical quenching experiments showed that the main active groups of TYL photodegradation were·O₂^-and·OH.In addition,the photodegradation process of TYL is in accordance with the pseudo first-order reaction kinetics.（3）Using dicyandiamide,melamine and urea as precursors,the modified g-C₃N₄was prepared by thermal polymerization using the oxidation and bursting properties of sodium nitrate.Through the characterization,it was found that the type of precursors and the molar ratio of sodium nitrate not only affected the crystal structure and chemical structure of the synthesized g-C3N4,but also affected the condensation degree and specific surface area of g-C₃N₄.Sodium nitrate can change the crystal structure of g-C₃N₄ and produce new chemical bonds,which induces changes in the physical and chemical properties of g-C3N4,thereby increasing its ability to photocatalytically degrade TYL.Under simulated sunlight irradiation,the photodegradation rates of g-C₃N₄ modified with dicyandiamide,melamine and urea were 5.05,5.32 and 12.93times that of unmodified g-C₃N₄,respectively.In addition,it was found that the modified g-C₃N₄ can produce more·O^2-and holes（h⁺）,which can significantly increase the efficiency of photodegradation of TYL.