Preparation Of Non-metal Doped Carbon Nitride With Broad Spectrum Response And Study On Photodegradation Of Organic Pollutants In Water

With the progress of chemical industrialization,the wastewater pollution generated from refractory organic pollutants,such as the endocrine-disrupting chemicals,xenobiotic and antibiotics,become a significant threat to ecosystem,which could persist in the environment for many years and cause a host of health problems.Photocatalysis and photocatalysis with persulfate are green and sustainable advanced oxidation technology,using solar energy to efficiently degrade organic pollutants.Among various novel photocatalysts,g-C₃N₄ has come into notice on account of its particular electronic and optical nature,which can efficiently activate persulfate without loading and doping any metal.However,it is faced with huge challenges such as narrow light absorption threshold and high photogenerated carrier recombination rate.Non-metallic doping can continue the non-metallic characteristics of g-C₃N₄.g-C₃N₄ has easy-to-tune band gap energy,by non-metallic doping,which can be adjusted by introducing levels in the middle gap to further increase the light utilization rate and improve the electronic structure.The previous doping of non-metallic g-C₃N₄ mainly concentrated on single element doping,and there are few reports on double element doping.In this paper,firstly,oxygen-doped carbon nitride was synthesized by cyanoacetic acid treatment.Based on this research,oxygen and halogen co-doped g-C₃N₄ were prepared by one-step polycondensation and applied to photocatalysis and photocatalysis with persulfate for degrading organic pollutants.The main research contents are as follows:1.The oxygen doped and porous defect co-modified broad-spectrum g-C₃N₄（CN-CA）was synthesized by a facile bottom-up copolymerization of urea and cyanoacetic acid for the first time.The results suggest that with the increase of cyanoacetic acid content,the light absorption intensity and range of CN-CA are enhanced significantly.The CN-CA-0.3 displays an outstanding photocatalytic degradation of BPA under visible light,whose degradation rate reaches 99.8%in 150 minutes and reaction rate constant is 6.77 times higher than g-C₃N₄.Similarly,the degradation rate of MBT over CN-CA-0.3 can achieve 99.1%within 20 minutes.Moreover,the degradation efficiency of CIP over CN-CA-0.3 is improved compared to CN.It was found that under blue light（450-462 nm）and green light（510-520 nm）,CN-CA-0.3 can still also has a certain improvement activity,which manifests CN-CA-0.3 is equipped with broad-spectrum response.Free radical quenching test and electron spin resonance（ESR）spectra show that active oxygen groups play an important role in the photocatalytic degradation process.2.The oxygen and bromine co-doped（CN-Br）,oxygen and iodine co-doped（CN-I）porous g-C₃N₄ were successfully prepared using bromoacetic acid and iodoacetic acid to modify the urea.CN-Br-0.05 and CN-I-0.05 process the ability to efficiently degrade bisphenol A,2-mercaptobenzothiazole,and bisphenol E.For bisphenol A,the reaction rate constant of them are 12.48 and 14.46 times higher than that of CN,respectively.The degradation performance of pollutants under blue LED,green LED and red LED and the photocurrent response under the light of different wavelengths were explored,further confirming that the co-doping modification of oxygen and halogen is a strategy to broaden the spectrum response.PL,electron paramagnetic resonance（EPR）and electrochemical tests show that co-doping strategy makes carriers easy to transfer and can hinder the recombination process.Trapping experiment and ESR study the active species in the photocatalytic reaction.3.A oxygen and chlorine co-doped porous g-C₃N₄（CN-Cl）was synthesized by a one-step polycondensation method of using chloroacetic acid and urea as precursors,and it is combined with activated persulfate to synergistically degrade pollutants in water.CN-Cl-0.05 shows an improved electronic structure,an appropriate redox potential and an enlarged specific surface area.In activated persulfate photocatalysis,bisphenol A,2-mercaptobenzothiazole,and bisphenol F can be degraded within 18 min,12 min and 36 min.The degradation rate of BPA is 71.18 times higher than that before modification.This broad-spectrum responsed g-C₃N₄ also has excellent performance under different wavelengths of red,blue and green LED,and exhibits an increased photocurrent under the illumination of different wavelength.Cycling experiments proved the stability and durability of CN-Cl-0.05.And the influencing factors and degradation mechanism of photocatalysis with persulfate were evaluated.Finally,the catalyst was used for actual application,achieving 100%degradation of bisphenol A within 12 minutes under solar.