Study On Photocatalytic Degradation Of Organic Residue In Water By Modified Graphite Carbon Nitride

The rapid development of social economy and a large number of productive activities have caused serious harm to the ecological environment and human health.Synthetic organic dye is a kind of common organic pollutant,which is the main culprit of water degradation and aquatic organism damage.Solar energy is a kind of sustainable,easy to operate,clean and pollution-free energy,which is considered to be the main energy in the future.Photocatalysis is a method of converting solar energy into chemical energy.It is considered as one of the most promising advanced oxidation technologies because of its green,high efficiency,simple operation and strong sustainability.The realization of solar energy conversion needs to find the right catalyst,graphite carbon nitride is a kind of non-metallic semiconductor material,because of its suitable band gap value,simple preparation,high stability and low price,it has been used in the degradation of organic pollutants,bacterial disinfection,CO₂ reduction,decomposition of water to produce H₂and production of capacitors.However,the serious accumulation and low electrical conductivity in the carbon nitride layer of the graphite phase lead to the shortcomings of slow carrier migration rate and easy recombination of photogenerated electron hole pairs,which seriously reduce the utilization rate of solar energy.Graphite carbon nitride can improve the catalytic performance by changing the band gap and specific surface area of the catalyst through element doping,morphology regulation and heterojunction construction.In this paper,the precursor of carbon nitride was prepared by the combination of hydrothermal method and solvothermal method,and the bubble carbon nitride was prepared by calcination precursor.The photocatalytic performance of the catalyst was further improved by in-situ deposition of iron oxyhydroxide quantum dots on the bubble carbon nitride.The catalysts were characterized by phase analysis,morphology analysis,composition analysis and the photocatalytic properties of the synthesized catalysts were tested.The main research content of this paper consists of the following two parts:In the first part,melamine was used as a nitrogen-rich precursor,the two-dimensional bubble structure of carbon nitride was prepared by combining hydrothermal,solvothermal and calcination methods.When Rhodamine B concentration is 20 mg/L and catalyst concentration is 50 mg/L,the kinetic rate constants of bulk carbon nitride,rod carbon nitride and bubble carbon nitride are 0.002min^-1,0.016 min^-1 and 0.070 min^-1,respectively.The results of photocatalytic degradation experiment and cycle experiment show that the prepared bubble carbon nitride has the best photocatalytic degradation performance and good stability.Finally,the active groups and related degradation mechanisms of the bubble carbon nitride were investigated by free radical capture experiment and paramagnetic resonance spectroscopy test.In the second part,the catalyst was loaded with iron oxyhydroxide quantum dots by in-situ precipitation method at room temperature.A series of composite catalysts were prepared by changing the content of iron oxyhydroxide quantum dots,and the effect of iron oxyhydroxide content on photocatalytic degradation efficiency was investigated.The experimental results show that under the conditions of 40 mg/L Rhodamine B,2 mmol/L H₂O₂ and 50 mg/L catalysts,the kinetic rate constant of the bubble carbon nitride containing 5%iron oxyhydroxide quantum dots is 0.166 min^-1.The catalyst not only has good photocatalytic activity,but also has good stability when the content of iron oxyhydroxide quantum dots supported on the bubble carbon nitride is 5%.Finally,the active substances in the degradation process were tested by free radical capture experiment,and the relevant degradation mechanism was proposed.