Preparation Of Ag Doped G-C₃N₄ By In-Situ Composition Method And Their Photocatalytic Properties

With the increasing environmental pollution,water pollution has become an indispensable part of the battle for environmental governance.Semiconductor photocatalysis is an effective way to solve environmental pollution problem due to its unique advantages.Graphite carbon nitride（g-C₃N₄）,a mental-free polymeric semiconductor with a high chemical stability,low cost,and visible light catalytic activity,has become the research focuses of photocatalysis in recent years.However,the photocatalysis properties of g-C₃N₄ is seriously hindered by its small surface area,high photogenerated electron-hole recombination rate and insufficient utilization of sunlight.Herein,g-C₃N₄ was doped by metal Ag using an in situ composite method.Ag/g-C₃N₄ composite photocatalyst with different surface area was prepared via different routes,which effectively improved the photocatalytic activity of g-C₃N₄ in visible light degradation of organic dyes in water.The main research contents are as followed:1.Ag/g-C₃N₄（Ag-UCN,Ag-MCN）composite photocatalysts with different doping ratios were prepared by ball-milling mixing and high-temperature thermal polymerization using nitrogen-rich urea and melamine as the polymerization precursor and AgNO₃ as the Ag source respectively.XRD,FT-IR,SEM and UV-Vis DRS were used to characterize the structure,morphology and optical properties of the composite photocatalyst.The photocatalytic performance of the composite photocatalyst under visible light was studied with methyl orange as the target pollutant.The results showed that the Ag doped composite photocatalyst can broaden the light absorption range and effectively inhibit the photogenerated electron-hole recombination.Meanwhile,the photocatalytic activity of Ag-UCN and Ag-MCN in visible light was significantly improved.Moreover,the Ag-UCN composites have much larger surface area and better photocatalytic activity than Ag-MCN.Under the optimal ratio,the degradation rate of methyl orange in water by 2wt%Ag-UCN within 100min was up to 96.3%,far higher than that by 3wt%Ag-MCN（200min,72.73%）.2.The intermediate product of g-C₃N₄ was obtained by calcining urea at a low temperature,and then mixed with AgNO₃ by ball-milling,subsequatly Ag/g-C₃N₄（Ag-InterCN）composite photocatalysts with different doping ratios were prepared by a high temperature thermal polymerization.the obtained Ag-InterCN photocatalysts were characterized by XPS,TEM and PL,and their photocatalytic properties were investigated.The results showed that the doping modification of Ag is beneficial to reduce the photogenerated electron-hole recombination rate,regulate the band structure of Ag-InterCN and broaden the visible light absorption range.In addition,the high temperature conversion of the intermediate endows Ag-InterCN a larger surface area.Therefore,The photocatalytic performance of Ag-InterCN is significantly enhanced compared with that of the unmodified InterCN.When the mass ratio of AgNO₃ to intermediates is 2%,Ag-InterCN shows the best photocatalytic activity.The degradation rate of methyl orange reaches 94.72%in 60 minutes,and the photocatalytic reaction rate constant is about 2.69 times that of unmodified InterCN.In addition,compared with Ag-UCN,the photocatalytic activity of Ag-InterCN was further improved.3.Based on the self-assembly of melamine and cyanuric acid via hydrogen bond in solvent,Ag/g-C₃N₄（Ag-CAM-CN）composite photocatalyst microspheres were prepared by introducing AgNO₃ with different mass ratios and calcining at a high temperature.The chemical composition,morphology and optical properties of the catalyst were characterized.The results showed that Ag-CAM-CN presented a uniform microsphere with a diameter of about 2μm.The significantly increased surface area not only increased the adsorption of organic dyes,but also provided more photocatalytic activity sites.The C-Ag bond formed in the structure of CAM-CN by Ag atom promotes the separation of photogenerated electrons and holes.Meanwhile,under the synergistic effect of localized surface plasmon resonance,the band gap width of Ag-CAM-CN decreases and the visible light response of the catalysts increases.The 3wt%Ag-CAM-CN with an optimized ratio of AgNO₃ can degrade methyl orange up to 89.21%within 25min.