Study On Modification And Photocatalytic Properties Of Graphite Phase Carbon Nitride

Graphite-phase carbon nitride?g-C₃N₄?is an environment-friendly photocatalyst with a graphite-like lamellar structure.However,due to its inert surface and low specific surface area,its further application is limited.Therefore,the modification of g-C₃N₄ has become a research hotspot.In this paper,firstly,Thiourea?TH?,urea?CU?,citric acid?CA?and acetic acid?HAc?were selected as pore-forming agents and mixed with melamine.g-C₃N₄-TH,g-C₃N₄-CU,g-C₃N₄-CA and g-C₃N₄-HAc were in-situ prepared by thermal polymerization.The results of X-ray diffraction?XRD?and scanning electron microscope?SEM?exhibited that g-C₃N₄-TH,g-C₃N₄-CU,g-C₃N₄-CA and g-C₃N₄-HAc samples displayed the similar lamellar structure.Ultraviolet-visible diffuse reflection absorption spectrum?UV-Vis DRS?analysis showed that the band gap values of the prepared samples were as follows:g-C₃N₄>g-C₃N₄-TH>g-C₃N₄-CU>g-C₃N₄-HAc>g-C₃N₄-CA.Photoluminescence?PL?spectrum and Photocurrent test analysis indicated that the separation ability about photogenic electron-hole of g-C₃N₄-CU was higher than that of g-C₃N₄.Selecting 15 mg/L methyl orange as the simulated pollutant,the visible light catalytic performance of the material prepared was investigated,and it was found that the degradation performance of g-C₃N₄-CU was the best among the above-prepared samples,and the degradation efficiency of g-C₃N₄-CU was nearly as three times as that of g-C₃N₄.Then,the concentrated nitric acid?NA?was used to treat and modify g-C₃N₄.The effects of reaction time,temperature and concentration on the degradation properties of g-C₃N₄ had been investigated.The optimal conditions of 24 h,80?and 10 mol/L were ultimately selected.g-C₃N₄-CU had treated under the optimal condition and made as g-C₃N₄-CU-NA.The characterization results of XRD,SEM,UV-Vis DRS,X-ray diffraction spectroscopy?XPS?found that comparing with g-C₃N₄,g-C₃N₄-CU-NA had thinner layers,UV-Vis absorption peak with shorter wavelength and wider band gap.The results indicated that HNO₃ not only plays the role of protonation,but also plays the role of oxidation.Through photodegradation experiments,the degradation efficiency of g-C₃N₄-CU-NA towards organic dye MO?15mg/L?reached 94%,which was 15 times higher than that of g-C₃N₄.The related reasons could be attributed to the surface function groups and high separation efficiency of g-C₃N₄-CU-NA.The main active species were·O₂^-,then h⁺,and the smallest contribution is the·OH during the photocatalytic degradation process.Finally,in order to further explore the role of concentrated HNO₃,the g-C₃N₄-CU was further treated and modified by concentrated HCl or H₂SO₄.The XPS,ammonia gas-temperature programmed desorption?NH₃-TPD?and thermo gravimetric analysis?TG?further indicated that the excellent photocatalytic properties of g-C₃N₄-CU-NA treated by the concentrated HNO₃ could be due to not only the protonation role of conventional acids,but also the surface modification of several acid oxygen functional groups and stripping actions caused by strong oxidizing properties of concentrated HNO₃.