Synthesis And Photocatalytic Properties Of G-C₃N₄-based Composite Materials

Environment and energy are one of the reasons that restrict the sustainable development of modern society.Considering that solar energy is not only relatively abundant in itself,but also easy to obtain,develop and utilize.At present,substantial progress has been made in the field of heating and power generation,which has been applied effectively on a large scale.Therefore,the researchers consider that the use of solar light to degrade refractory pollutants is a favorable technology to control the environment based on semiconductor photocatalysis.As a metal-free photocatalyst,graphitic-like carbon nitride?g-C₃N₄?not only has the band structure characteristics of absorption to the visible light band,but also has strong ability to resist chemical corrosion and high temperature environment,which wide application value in the field of photocatalysis.But g-C₃N₄ also has two major limitations,one is that the band gap width is larger,the utilization of uv and visible light is low,and it is difficult to respond to infrared light at the same time;the second is that the crystallization is incomplete,which makes its conductivity poor,which is not conducive to the migration of photogenerated electrons.Therefore,in view of the two main problems existing in the g-C₃N₄,the g-C₃N₄-?NH₄?_XWO₃ binary heterojunctions are first constructed to expand the range and intensity of light response,and effectively utilize the solar band in the range of200 nm-2500nm;secondly,the g-C₃N₄-?NH₄?_XWO₃/GO ternary heterojunctions are constructed to promote photogenerated electron migration and improve photocatalytic activity.The structure and morphology were analyzed by X ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and X ray photoelectron spectroscopy?XPS?.Meanwhile,uv-vis diffuse reflectance absorption spectroscopy?UV-Vis-DRS?,fluorescence spectroscopy?PL?and photoelectrochemical characterization were performed to investigate the photoabsorption and photogenerated carrier separation efficiency.And then,the photocatalytic activity and its mechanism were characterized by using rhodamine B as pollutants.For thin film samples,the transmission and absorption characteristics of different bands of light in the solar spectrum,as well as the thermal insulation and photocatalytic degradation effect of the thin film were analyzed.The main contents of the study are as follows:?1?The graphitic-like g-C₃N₄ prepared by thermal condensation and hydrothermal method and ammonium tungsten bronze?NH₄?_XWO₃ prepared by hydrothermal method.And the g-C₃N₄-?NH₄?_XWO₃ binary photocatalysts were prepared by simple method using different surface electrical properties of g-C₃N₄ and?NH₄?_XWO₃.Studies have shown that g-C₃N₄ have a typical layer-like structure of two dimension bulk graphene,and?NH₄?_XWO₃ consists of many agglomerated nanoparticles and randomly oriented distributed nanorods.After recombination,the specific surface area of the sample was increased.The two surfaces are in close contact at the same time,which is beneficial to the migration of photogenerated carriers.The heterojunction formed,which can well combine the light absorption characteristics of both,not only enhances the light absorption of g-C₃N₄ ultraviolet and visible light,but also has?NH₄?_XWO₃ infrared absorption characteristics.Therefore,the photocatalytic degradation rate of rhodamine B was significantly improved under different illumination,among which g-C₃N₄-2%?NH₄?_XWO₃ had the best effect.Under ultraviolet light,after 10 min of light,the degradation was 79.7%;under 20 min of visible light,the degradation was 67.1%;after 180 min of infrared light,the degradation was 47.8%,which the degradation rate were superior to pure phase g-C₃N₄.At the same time,the composite sample has good stability and repeatability.In addition,the as-prepared thin film samples also have good photodegradation activity.At the same time,they can absorb harmful ultraviolet light,and maintain high visible light transmittance and can block infrared light,so they have the versatility of self-cleaning and heat insulation.?2?Based on the g-C₃N₄-?NH₄?_XWO₃ binary heterojunction structure,the g-C₃N₄-?NH₄?_XWO₃/GO ternary heterojunction was constructed to further enhance the photocatalytic activity by selecting graphene oxide GO which can be used as electron support and transfer conductor while absorbing visible light.The g-C₃N₄-?NH₄?_XWO₃/GO ternary composites were synthesized in aqueous solution of binary g-C₃N₄-?NH₄?_XWO₃ composite using the advantages of good dispersion of GO in aqueous solution.Studies have shown that GO have large specific surface area and good adsorption,and can effectively form heterojunctions with g-C₃N₄??NH₄?_XWO₃.After doping GO,the spectral response range and intensity are effectively improved.Meanwhile,GO has a large carrier conductivity,which can be used as a channel for electron transport of composites to construct Z heterojunctions to participate in the degradation of pollutants,further improving the redox ability of photogenerated carriers.With rhodamine B as the pollutant dye,the photocatalytic activity of the samples was tested.The photodegradation of g-C₃N₄-2%?NH₄?_XWO₃/0.1%GO was the best.Under ultraviolet light,90.1%can be degraded after 10 min of illumination,and 79.8%can be degraded after only 20 min of visible light,which indicates that the three have better synergistic effect after composite GO.