Synthesis Of G-c₃n₄-based Photocatalyst And Its Visible-light Photocatalytic Treatment Of Environmental Pollutants

With the human's exploitation,many concerns have been gained about environment pollution and energy problems.Therefore,the study of environmental pollution control and purification has become the world important topic.Photocatalytic technology has been widely studied as a green and eco-friendly advanced oxidation technology because it use renewable solar energy to degrade pollutants without any disinfection by-products during the degradation process.At present,graphite phase carbon nitride?g-C₃N₄?as non-metallic layered materials has attracted much attention,.g-C₃N₄ with the band gap 2.7 eV,achieve the response of visible light.Under the irradiation of visible light,g-C₃N₄ is an ideal photocatalyst which could split water into hydrogen and degrade kinds of organic pollutants.However,g-C₃N₄ with narrow scope of spectral absorption,small specific surface area and the high electron-hole recombination rate hinds its photocatalytic performance.Based on the characterization of microstructure materials and their photocatalytic degradation of organic pollutants were systematically investigated.The main work was shown in the following parts:The Bi₄Ti₃O₁₂/g-C₃N₄ composites with 2D/2D microsheets and nanosheets structure were prepared through facile ultrasonic-assisted method.The SEM and TEM results suggested that the nanosheets g-C₃N₄ were stacked on the surface of regular Bi₄Ti₃O₁₂2 sheets.Comparing with pure Bi₄Ti₃O₁₂2 and g-C₃N₄,the Bi₄Ti₃O₁₂/g-C₃N₄ composites showed significant enhancement in photocatalytic efficiency for the degradation of RhB in solution.Its photocatalysis reaction constant was approximately 2 times higher than the single component Bi₄Ti₃O₁₂2 or g-C₃N₄.Meanwhile,good stability and durability for the Bi₄Ti₃O₁₂/g-C₃N₄-10%were confirmed by the recycling experiment and FT-IR analysis.The possible mechanism for the improvements was the matched band positions and the effective separation of photo-excited electrons?e^-?and holes?h⁺?.Furthermore,based on the results of active species trapping,photo-generated holes?h⁺?and superoxide radical?·O₂^-?could be the main radicals in reaction.Sulfur and halogen codoped g-C₃N₄ was synthesized by thermal condensation method.The S/Cl co-doped g-C₃N₄ sample exhibited the best photocatalytic activities for degradation of rhodamine B?RhB?and 4-nitrophenol?4-NP?among all samples.According to the DRS,UPS and VB-XPS investigation,S and Cl co-doping could narrow the band gap to improve visible-light absorption,meanwhile,lead to positively shifted valence band?VB?with enhanced oxidation ability.From the first principles calculation,the narrower band gap and better charge separation ability could be attributed to Cl 3p orbital as the doping level.Moreover,the generation of the main active species·OH was enhanced via direct oxidation of h⁺on valence band?VB?and reduction of O₂ on conduction band?CB?in S/Cl co-doped g-C₃N₄.Based on the strong oxidizability of the S/Cl co-doped g-C₃N₄,the possible formation of reactive chlorine-based species in photocatalysis process was proposed.Series of chlorine doped g-C₃N₄ nanosheets were synthesized by thermal condensation and ultrasonic exfoliating methods using melamine and ammonium chloride.The nano-structure and morphology was detected by A series of characterization.The photocatalytic activities of samples with different doping ratio and exfoliation time were evaluated under visible light.Moreover,the mixed pollutant solution containing rhodamine B?RhB?and hexavalent chromium?Cr?VI??were photocatalytic degraded by the modified samples.Compared with single pollutant in solution,the treatment efficiency of chlorine doped g-C₃N₄ nanosheets for RhB and Cr?VI?in the mixed solution are 1.4 times and 2.2times,respectively.In comparison to bulk g-C₃N₄,chlorine doped g-C₃N₄ nanosheets sample obtain larger specific surface,better optical absorption proformances and better charge separation capabiliities.The separation of photo-excited holes and electrons is promoted by the simultaneously photocatalytic oxidation of RhB and reduction of Cr?VI?,which lead to the synergistic treatment of RhB and Cr?VI?in mixed solution.