Interface Properties Of G-C₃N₄ Based Eterostructured Functional Materials And Their Organic-Inorganic Nanocomposites

Since graphite phase carbon nitride（g-C₃N₄）has a good ability to absorb visible light and is also a narrow band gap semiconductor,it has become one of the research hotspots in the field of photocatalysis in recent years.It can not only completely degrade organic pollutants and not cause secondary pollution under mild conditions,but also decompose water to generate hydrogen under light.It can be applied to environmental protection and in line with the concept of sustainable economic development.However,g-C₃N₄ has the disadvantages of small specific surface area,relatively narrow response range to visible light,fast recombination rate of photogenerated electrons and holes,and low photon efficiency,which makes the advantages of g-C₃N₄ material not significant.Therefore,by using different modification methods to inhibit the recombination of g-C₃N₄ photogenerated electron-hole pairs,thereby improving the photocatalytic performance of the material,the material is more widely used.Among the many methods for modifying g-C₃N₄ materials,constructing heterostructure nanocomposites is one of the effective ways.Among them,some transition metal oxides and metal sulfides are good semiconductor materials,and some metal oxides and metal sulfides belong to P-type or N-type semiconductors depending on the electrons to be lost.The g-C₃N₄ is an N-type semiconductor.The P-N junction nanocomposites were prepared by modifying the graphite phase carbonitride carbon with P-type transition metal oxides and metal sulfides,which is more conducive to inhibiting the recombination of g-C₃N₄ photogenerated electron-hole pairs.Therefore,this study formed a nanocomposite of metal sulfide or metal oxide with g-C₃N₄ by chemical doping or other modification means to form a heterojunction between the two,and inhibited the recombination of photogenerated electron hole pair by the regulation of heterojunction microstructure.Organic-inorganic composite functional materials are one of the important development directions in the field of materials,and can exert the respective characteristics of inorganic and organic materials,thereby achieving synergistic or complementary effects.Chitosan is a kind of resource-rich polymer material.It has many hydroxyl groups and amino groups in the polymer segment of chitosan,and it has good applications in environmental and biomedical fields.Therefore,the composite of g-C₃N₄ and chitosan is expected to develop an organic-inorganic nanocomposite functional material with low cost and excellent performance.In addition,solving the dispersibility of nanocomposites in polymers is the key to developing organic-inorganic composite functional materials with excellent performance.It is a simple and attractive effective way to prepare materials by simple synthesis and one-pot method with improved material synthesis,dispersion and performance.In this study,a series of nanocomposites were prepared by different synthesis methods.Through the characterization of the microstructure and evaluation of some properties,an effective way to inhibit the composite part of photo-generated electron-hole pairs of g-C₃N₄ was found.（1）CuO/g-C₃N₄ nanocomposites were synthesized by hydrothermal method.It was characterized by SEM,XRD,UV-Vis and so on.The results show that the nanocomposite has good light absorption properties for visible light.Its response mechanism to weak light shows that the photoconductive switching ratio is 3-4 times,indicating that the separation and transmission ability of the photogenerated electron-hole pairs of the material is obvious,which is attributed to the formation of P-N junction at the CuO/g-C₃N₄ interface.（2）In this study,CuO/g-C₃N₄/chitosan graft polymer nanocomposites were prepared by blending method and characterized by series.The experimental results show that the nanocomposite has good absorption of visible light.However,its response mechanism to weak light shows that it is difficult to obtain obvious photoconductive switching phenomenon,indicating that the interface optimization of organic-inorganic nanomaterials is not enough,which is not conducive to the separation and transmission of photogenerated electron hole pairs.（3）CuO/g-C₃N₄/chitosan graft polymer nanocomposites were prepared by one-pot method with simpler,more convenient and less synthetic steps.The results show that CuO/g-C₃N₄/chitosan graft polymer nanocomposites are compared with CuO/g-C₃N₄/chitosan graft polymer nanocomposites prepared by two-step hydrothermal blending.The photoconductive switching behavior of the material prepared by one-pot method is more obvious.The photoconductive switching capability is increased to two orders of magnitude,indicating that the preparation method can effectively inhibit the recombination of photogenerated electron hole pairs and improve the separation efficiency of photogenerated electron hole pairs.（4）Extend the one-pot method to prepare sulfide（oxide）/g-C₃N₄/chitosan graft polymer nanocomposites,such as CuS/g-C₃N₄/chitosan graft polymer nanocomposites,NiS/g-C₃N₄/Chitosan grafted polymer nanocomposites,etc.,gave similar results.And the photoconductive switching behavior is obvious,can reach two orders of magnitude,which shows that the recombination of photogenerated electron hole pairs is effectively suppressed,and the performance of the material is improved.In summary,the one-pot method can improve the dispersibility of the nanocomposite and enhance the charge transfer at the interface of the organic-inorganic nanomaterial compared to physical blending.The formation of heterojunction is to inhibit the recombination of the photogenerated electron-hole pairs of the nanocomposite,thereby improving the photoelectric properties of the nanocomposites.