Study On Controllable Synthesis And Visible Photocatalytic Properties Of Modified Carbon Nitride-based Photocatalytic Materials

Water pollution has become a major problem that human beings have to face.At the same time,the energy crisis seriously restricts the development of human to solve the water pollution problem.Semiconductor photocatalytic technology has a broad application prospect in solving water pollution and energy problems because of its can use inexhaustible solar energy and excellent environmental purification ability.So far,many excellent photocatalysts have been developed and show exciting photocatalytic properties,but none of them are perfect.As the graphite phase carbon nitride（g-C₃N₄）,known as the"photocatalytic star",has many advantages,such as low manufacturing cost,simple preparation method,visible light activity,no biological toxicity,stable properties.In this paper,a series of modifications to the g-C₃N₄are carried out from the aspects of morphology construction,introduction of vacancies,surface modification of carbon materials,surface acidification,element doping and so on,which improve g-C₃N₄exciton separation ability,conduction ability of photogenerated carriers,light absorption ability and redox ability.The photocatalytic properties of the modified materials were tested with a variety of pollutants as substrates,and the oxidation and reduction ability of the modified materials were comprehensively evaluated.The findings are summarized as follows:1.Carbon nitride nanosheets with uniform nitrogen vacancy modification（g-C₃N₄-V_NNs）were prepared by calcination in H₂atmosphere.All kinds of characterization and experiments have proved that the introduction of nitrogen vacancies has changed the potential distribution inside the material,effectively enhanced the dissociation of excitons,and produced more hydroxyl radicals（·OH）,thus greatly enhancing the oxidation ability of the material against organic pollutants（4-chlorophenol（4-CP）,bisphenol A（BPA）,tetracycline（TET）and phenol（Ph））.2.The bio-based carbon quantum dots（BCQDs）were prepared from the waste Camellia oleifera shell.Then the BCQDs was loaded onto carbon nitride by low temperature hydrothermal method,and ultrathin carbon nitride nanosheets loaded with acidic bio-based carbon quantum dots（H⁺/BCQDs/g-C₃N₄）were prepared by simple dilute hydrochloric acid acidification.Through characterization and experimental proof,BCQDs can effectively improve the light absorption ability of g-C₃N₄and the transfer ability of photogenerated carriers.More importantly,the BCQDs and H⁺on H⁺/BCQDs/g-C₃N₄material after acidification will have a synergistic effect,which allows H⁺/BCQDs/g-C₃N₄to rapidly reduce heavy metal Cr（Ⅵ）without acid addition.3.Porous sulfur-doped graphitic carbon nitride（P-C₃N₄-_xS_x）was prepared by pretreatment of precursor melamine with carbon disulfide（CS₂）and acidified with dilute hydrochloric acid to prepare acidified porous sulfur-doped graphitic carbon nitride（H⁺/P-C₃N₄-_xS_x）.By various characterization and experiments,it can be proved that the doping of S elements can significantly reduce the band gap and thus enhance the light absorption.Moreover,the process of doping is also a pore-forming process,and the specific surface area of the material increases significantly after doping.The oxidation and reduction ability of sulfur-doped materials are obviously improved relative to g-C₃N₄through the degradation experiments of four fluorine phenol（4-FP）and the reduction experiments of Cr（Ⅵ）.