Preparation Of Carbon Nitride-based Composites And The Properties Of Visible Photocatalytic Degradation Of Bisphenol A

Bisphenol A（BPA）is a typical environmental endocrine disruptor that can have a huge impact on the human body and organisms,even at low doses present in the environment.Therefore,there is an urgent need to find a green,clean and efficient removal method without secondary pollution,and photocatalytic oxidation technology has this advantage.In recent years,due to the low cost,high stability and environmental harmlessness of carbon nitride（g-C₃N₄）,it has received widespread attention in the field of photocatalytic degradation of organic pollutants,but its photocatalytic activity has been limited due to its own structural defects,and its photocatalytic performance is not ideal.Therefore,this paper uses a simple in situ deposition method to composite silver phosphate（Ag₃PO₄）with excellent light absorption capacity and high quantum yield with g-C₃N₄,so as to improve the photocatalytic activity of g-C₃N₄,and CNQDs of zero-dimensional nano-scale semiconductor materials with excellent optical performance are also introduced to further modify Ag₃PO₄/g-C₃N₄（ACN）composites.On this basis,the performance of the prepared photocatalysts in the degradation of BPA in photocatalytic and its coupling systems was investigated,and the reaction mechanism of photocatalytic degradation of BPA in different systems was explored by combining various characterization analysis and experimental results.The main conclusions drawn in this paper are as follows:（1）CNQDs/Ag₃PO₄/g-C₃N₄composite photocatalytic materials were successfully prepared by calcination-in situ deposition-solvothermal method,and their physical morphology,crystal structure and chemical properties were systematically analyzed by various characterization methods.All the diffraction peaks of g-C₃N₄and Ag₃PO₄were found in the XRD plot,and the losses during the preparation of the material made the crystal surface characteristic peak strength of Ag₃PO₄/g-C₃N₄and CNQDs/Ag₃PO₄/g-C₃N₄lower than that of pure g-C₃N₄;The results of SEM and TEM analysis showed that Ag₃PO₄and CNQDs were evenly distributed on the lamellar g-C₃N₄,and the agglomeration phenomenon of Ag₃PO₄was improved;Ft-IR and XPS analysis results showed that no peaks of other impurities appeared in the atlas,indicating that no change in the crystal structure occurred during the preparation of the catalyst and no new substances were generated;Bet analysis data show that the addition of Ag₃PO₄and CNQDs increases the specific surface area of the composite.（2）Taking BPA as the target pollutant,the degradation performance of CNQDs/Ag₃PO₄/g-C₃N₄composites under photocatalytic systems was investigated.The experimental results show that when using a composite catalyst with a g-C₃N₄mass fraction of 20%,after 30 min of dark reaction and 60 min of light reaction,BPA was completely removed,the degradation rate was 0.05228 min^-1,the mineralization rate reached 49.7%,and after five times of reuse,the catalyst still maintained a high photocatalytic activity of 79.8%.The reaction conditions in the photocatalytic process were carried out by univariate experimental method,and the results showed that the optimal degradation effect could be achieved when the pH was11,the dispersion concentration of the photocatalyst was 0.5 g/L,the initial concentration of BPA was 5 mg/L,and the light intensity was 500 W.The quenching experiment of active species was carried out by quenching agent,and the results showed that the contribution order of active species in the process of biodegradation of BPA by photocatalytic system was·O₂^->h⁺>·OH.（3）Using BPA as the target pollutant,the degradation performance of CNQDs/Ag₃PO₄/g-C₃N₄composite catalysts in photocatalytically coupled persulfate systems was investigated.BPA was completely removed within 20 min of light reaction,the mineralization rate was improved,reaching 57.6%,and the BPA degradation rate of the composite catalyst after five cycles was still 85.7%;The univariate experimental results show that the optimal degradation of BPA can be achieved by reacting for 20 minutes in acidic and neutral environments,with a persulfate concentration of 2 mmol/L,an initial concentration of BPA of 10 mg/L,and a light intensity of 500 W.Quenching experiments on active species show that·O₂^-,h⁺,and·OH is the main active species in the system and·SO₄^-is produced in small quantities.（4）The reasons for the increase in the activity of CNQDs/Ag₃PO₄/g-C₃N₄composite photocatalysts were further explored by means of ultraviolet-visible diffuse reflection spectroscopy（UV-vis）and electrochemical performance tests.The results were as follows:UV-vis spectroscopy showed that the absorption intensity and range of the composite catalyst increased significantly.The results of EIS and transient photocurrent tests showed that the composite catalyst had a smaller electrochemical impedance value and a larger photocurrent density,and the band structure of the composite photocatalyst was analyzed by using the Tauc curve and M-S curve,and the mechanism of photocatalytic degradation of BPA and its coupling system was derived by combining the active species composition of different systems.