Synthesis,Characterization And Photocatalytic Performance Of Modified G-C₃N₄ Composites

Semiconductor photocatalysis can use the sunlight as an energy source,mild reaction conditions and and can effectively avoid secondary pollution.Therefore,it offers the possibility of accomplishing energy cycles without pollution of the environment and additional heating of the earth.Therefore,photocatalysis with important application foreground in environmental protection and energy storage and transformation.Among the various of semiconductor materials,titanium dioxide?TiO₂?has been widely investigated and applied owing to the relatively strong chemical and thermal stability,good biocompatibility,non-toxic and low cost and so on.But TiO₂ has a relatively wide band gap?³.2 eV?,which makes it can only be activated by ultraviolet light irradiation,does not respond to the majority of the visible light in the solar spectrum.In addition,the quantum yield of the semiconductor is low,and h the recombination rate of photogenerated electrons and holes is high.Accordingly,in order to absorb and utilize solar energy more efficiently,it is very urgent and critical to design and develop new,efficient,and stable visible-light-driven photocatalytic materials.Graphitic carbon nitride?g-C₃N₄?is a new type of metal free semiconductor photocatalytic material,with?-conjugated plane formed by the stacking of stacked structures.g-C₃N₄ has execellent thermal and chemical stability,as well as unique band structure,which make it has numerous potential applications in the fields of photocatalytic hydrogen production and organic degradation and has been widely concerned.However,as an organic polymer semiconductor,g-C₃N₄ has small specific surface area and a large number of defects,resulting in severe photogenerated recombination and poor photocatalytic activity.In order to improve the photocatalytic activity of g-C₃N₄,Therefore,many modification methods have been trided to improve its photocatalytic activity,it can be modified by semiconductor compound,organic and inorganic elements such as doping,surface modification and other methods.In this paper,g-C₃N₄ was modified by the method of semiconductor composite.If the different coupling materials conduction bands and valence bands position were matched,which is beneficial to the photo-generated electrons and holes separated and transferred through the heterostructure interface to improve the system photocatalytic activity.This thesis mainly consists two chapters as fllows:?1?A certain amount of tungsten trioxide modified carbon nitride carbon composites were prepared by one-step calcination method,and the microstructure and microstructure of the as-synthesized samples were characterized X-ray powder diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,UV-visible diffuse reflectance spectrum?UV-vis DRS?,nitrogen adsorption desorption and other characterization methods.Melamine and hydrated ammonium tungstate through high temperature calcination will produce ammonia,forming a reducing atmosphere,so that tungsten trioxide hypoxia to form non-stoichiometric nitrogen oxides(WO_3-x).The results of SEM showed that the two components were tightly bonded to form a smooth phase interface.The photocatalytic degradation activity of the composite system was stronger than that of pure tungsten trioxide and carbon nitride,and the photocatalytic degradation effect of WO_3-x/g-C₃N₄-15%on rhodamine B was the strongest,was 3.3times and 2 times that of pure WO_3-x and pure g-C₃N₄.The photocatalytic activity enhanced may be related to the increase of the specific surface area,the matching band structure and the tubular microstructure.The active species trapping experiments indicated that the superoxide radicals?·O₂^-?and holes?h⁺?were the main active species during photocatalytic process and photocatalysis mechanism was finally proposed.?2?SiC-g-C₃N₄ hybrids with different SiC nanosheets contents were synthesized via high temperature calcination method and then characterized by a collection of analytical techniques.The results revealed that the SiC-g-C₃N₄ composites have been prepared successfully.The enhanced photocatalytic acitivity of these SiC-g-C₃N₄ hybids could be attributed to the synergetic effects between SiC and g-C₃N₄ as well as favorable optical property and suitable energy-band structure.SiC-g-C₃N₄-8%hybrids exhibited the highest photocatalytic activity,the pseudo-first-order kinetic constant was about 30.95and 1.23 times as high as those of individual SiC and g-C₃N₄ under identical conditions.Active species trapping measurements revealed that superoxide radicals?·O₂^-?and hydroxyl radical??OH?played important roles in photocatalytic degradation of RhB dye,and apossible photocatalytic mechanism was proposed.