In-situ Fabrication Of Ultrathin G-C₃N₄/AgI Heterojunction With The Research Of Its Photocatalytic Performance

Semiconductor photocatalytic technology uses the inexhaustible solar energy as the driving force to achieve the efficient degradation of organic pollutants.Therefore,it can make up for the defects of traditional water treatment technology and has shown a good application prospect in the field of water treatment.Graphite-like carbon nitride（g-C₃N₄）is a kind of non-metallic photocatalyst with excellent performance in recent years.It has the characteristics of moderate band gap（～2.7 e V）,cheap raw materials,convenient preparation and good stability.However,due to the low utilization of solar energy,high recombination rate of photogenerated carriers in the same 3,s-triazine ring and small specific surface area in the practical application of single g-C₃N₄ semiconductor photocatalyst,its wide application in the field of photocatalytic degradation of organic pollutants is restricted.The research work is aimed at the above problems in this paper,we have successfully constructed ultrathin g-C₃N₄/Ag I heterojunction photocatalysts through the strategy of morphology control-ion complexation-in situ growth,based on which,the structure-activity relationship between the microstructure,physicochemical properties,photoelectric properties and catalytic activity of the catalyst were studied,and the mechanism of photocatalytic reaction based on charge transfer behavior was discussed.The main contents and results are as follows:（1）Ultrathin g-C₃N₄（UCN）was prepared by thermal polymerization-ultrasonic stripping,then the adsorption thermodynamics and kinetic properties of Ag⁺on the surface of UCN were studied by exploiting AAS（Atomic Absorption Spectroscopy）to monitor the change of Ag⁺concentration with time and catalyst concentration.Next,the mechanism of interaction between Ag⁺and UCN was explored by the same method.The results indicated that the adsorption capacity of Ag⁺on the surface of UCN in the range of its maximum adsorption capacity was independent of p H and ionic strength of suspending liquid,which suggested that the adsorption between Ag⁺and UCN was not a simple physical adsorption,but chemical surface complexation.The change of C 1s and N 1s binding energy of UCN after Ag⁺adsorption also confirmed the interaction of surface complexation.（2）Based on the special complexation of UCN with Ag⁺,a synthetic method of in situ growth was proposed to construct UCN/Ag I（UCNA）composites.The morphology and structure of the composites were characterized by XRD,TEM,FT-IR,XPS and other test methods.The results showed that the composite retains the thin layer structure of UCN,and the Ag I particles are evenly distributed on the surface of UCN.In addition,there is a strong interaction between UCN and Ag I based on Ag⁺complexation,which makes the composite form an obvious heterojunction structure,and it shows better visible light absorption performance,and has the better photogenerated charge separation and transmission performance of single UCN and Ag I.（3）Rh B was selected as the target pollutant for photodegradation experiment to evaluate the photocatalytic performance of the prepared samples.The results showed that UCNA-70%exhibited the best photodegradation performance of Rh B,and the reaction was in accordance with the first-order kinetics.Under the conditions of p H=7,C₀=20 ppm and catalyst/pollutant dosage of 33 mg/mg,the reaction rate constant is 0.0723 min^-1 for UCNA-70%,which is 4.02times and 2.62 times of UCN and Ag I,respectively.The results of TOC,GC-MS and UV full wavelength scanning show that the photocatalytic degradation of Rh B by UCNA-70%is not a simple decolorization process but accompanied by the destruction and mineralization of organic structure.Finally,the reaction mechanism of photocatalytic degradation of Rh B was proved to be the traditional type II heterojunction charge transfer mechanism by radical trapping experiment and the calculation of band edge position.