Research On Modification Of Carbon Nitride And Photocatalytic Degradation Of Organic Pollutants

Photocatalytic technology has been widely used in environmental pollution control.Semiconductor photocatalytic technology can utilizesolar energy to degrade dye wastewater and antibiotic pollutants,and can remove low concentrations of NO.However,the photocatalytic efficiency of carbon nitride is limited because its recombination rate of photogenerated electrons and holes is high.Therefore,it is studied in this paper how to promote the separation of charge carriers in order to improve the photocatalytic activity of carbon nitride,the following modifications are made to carbon nitride:(1)physical modification of carbon nitride;(2)preparation of Mg/O co-modified carbon nitride;(3)Na~+-doped carbon nitride.The as-prepared samples are systematically characterized by XRD,SEM,TEM,XPS,FT-IR,BET,UV-vis DRS,PL,ESR,photocurrent,impedance spectroscopy and so on.The characterizations above contribute to the analyses of microstructure,charge carriersseparation,radical species.The researchconclusions are as follows.(1)Physically modified carbon nitride:The thermal carbonization method is used to prepare the bulk carbon nitride with melamine as the precursor,and the physical modification of the carbon nitride by ultrasonic wave and microwave can be used.Increasing the specific surface area of the sample and reducing the recombination rate of the photogenerated electrons and holes of the samples,thereby improving the photocatalytic performance of the sample.By comparing the efficiency of photocatalytic degradation of tetracycline hydrochloride antibiotic wastewater and methylene blue dye wastewater by different ultrasonic modification and microwave modified catalysts,CN-M-12H and CN-M-30min showed the highest photocatalytic activity at 12W.The degradation rate of MB in the LED light reaches 94.1%and85.2%,and the degradation efficiency of TC can reach 81.4%and 82.4%,which are higher than CN before modified.(2)Preparation of Mg/O modified carbon nitride:a method combining experimental characterization with theoretical calculation,using Mg/O in situ thermal polymerization to prepare amorphous carbon monoxide modified by Mg/O.The in-plane electronic structure of carbon nitridemakes the localized electrons in the original carbon nitride plane localized,realizes directional transport of electrons,and realizes high separation rate of electron-hole.This unique Mg/O electronic structure can be extended.The fluorescence life time of the flux promotes electron-hole separation,and the amorphous structure of the carbon nitride structure enhances light absorption.The modification method can improve the photocatalytic degradation ability of the antibiotic tetracycline hydrochloride and the dye wastewater methylene blue.The degradation rate of the photocatalytic activity of the sample MgO-CN-1.2 to the 30 mg/L tetracycline hydrochloric acid solutionreaches 82%,The MgO-CN-1.2photodegradation rate constant is 5 times that of purecarbon nitride.(3)Preparation of Na~+doped modified carbon nitride:The amorphous carbon nitride modified by the combination of Na~+doping and N-defect was prepared by thermal polymerization using melamine and NaOH solution as precursors.As the amount of NaOH increases,the carbon nitride gradually becomes amorphous.Melamine is polymerized under NaOH solution to introduce Na~+and N defects to promote the transport of photogenerated electrons between the carbon nitride layers.The CN-NaOH-30 sample has the largest specific surface area,the lowest fluorescence intensity of the sample,the highest photocatalytic activity,the degradation rate of tetracycline hydrochloric acid solution is 89.6%,and the photo-degradation rate constant of CN-NaOH-30 is purecarbon nitride 3.6.At the same time,carbon nitride and CN-NaOH-30 were used to purify NO,and it was found that CN-NaOH-30 also had a good photocatalytic effect on photocatalytic oxidation of NO.The work of this research provides a new way to improvevisible light responsive semiconductors for efficient visible light photocatalysis.It has obvious practical effects on solving environmental pollution problems.