Chemical Synthesis And Doping Of Porous G-C₃N₄ Nanosheets And Their Use As A Metal-free Catalyst For Water Treatment

With the continuous progress of science and technology and the rapid economic development,human demand for natural resources is growing,while the development and utilization of natural resources at the same time,a large number of organic pollutants also will enter the natural environment.These substances not only pollute the environment,destroy the ecology,but also on human life and health have brought a huge threat.Semiconductor photocatalytic oxidation technology as a promising"green technology" has been widely used in environmental pollution control and solar energy conversion areas,such as photocatalytic degradation of organic pollutants and water splitting to produce hydrogen.Conventional semiconductor metal catalytic materials are constrained of the extensive application of photocatalytic technology due to the limited nature resources and easy to cause secondary pollution.Recently,the graphitic carbon nitride?g-C₃N₄?,a kind of conjugated polymer semiconductor,has been used in many fields,such as environmental remediation and solar energy conversion,etc,due to its metal-free property,chemical inertness,thermal stability and superior photocatalytic activity.However,the photocatalyst activity of bulk g-C₃N₄ is still limited due to its low specific surface area and fast recombination of photogenerated electron-hole pairs.Furthermore,the application form of g-C₃N₄,such as micro-nanometer powder and sheets,limits its industrial applications.Therefore,the development of efficient,stable and recyclable catalysts is an important direction for the development of photocatalytic technology.In order to improve the photocatalytic activity of g-C₃N₄,porous g-C₃N₄ nanosheets and g-C₃N₄-TiO2 composite catalysis with larger specific surface area were synthesized.The microstructure,crystal structure and photoelectric properties of the as-prepared samples were characterized by a series of modern advanced instrument,such as X-ray diffraction?XRD?,transmission electron microscopy?TEM?,Atomic force microscopy?AFM?,X-ray photoelectron spectroscopy?XPS?,nitrogen adsorption,UV-vis diffuse reflectance absorption spectra?UV-DRS?and photoluminescence spectroscopy?PL?.The results show that the large surface area and abundant pore structure can effectively enhance the adsorption ability of g-C₃N₄.And composited with one-dimensional TiO2 continuous fiber successfully solved the difficult problem of recycling.In this paper,the bulk g-C₃N₄ was synthesized by the thermal condensation polymerization of melamine at 550 ?.Two different methods were used to prepare porous g-C₃N₄ nanosheets with larger specific surface.In order to realize the application of g-C₃N₄,the nanosheets were used to form the heterojunctions with TiO2 continuous fibers which were easy to be recycled and used as photocatalytic materials.The synergic effects of g-C₃N₄ and TiO2 contributed to the superior photocatalytic activity of composite continuous fibers.The main researches as follows:?1?Anionic polyacrylamide?APAM?as the intercalator and carbon source for synthesis of high quality carbon doped g-C₃N₄ nanosheets with large specific area and broadband response for visible light?NSs-APAM?.The average thickness of the ultrathin nanosheets in NSs-APAM is about 4 um.The effective doping of carbon broadening its responding to visible light.The successful insertion of APAM was demonstrated by a series of characterization methods.The physical and chemical properties of the obtained catalyst were analyzed,such as morphology,crystal form,photoelectric properties and chemical composition.The specific surface area of the obtained catalyst is 118.6 m2/g,which is about 5 times that of the bulk g-C₃N₄.Compared with the non-carbonated g-C₃N₄ nanosheets?NSs-Water?,the effective doping of carbon is effective expand the ? electronic conjugate structure,lead to the maximum absorption band of the NSs-APAM band red shift,the band gap be reduced by 0.34 eV,and the visible light response range is wider.The results of PL test show that the recombination of photo-generated electron-hole pairs is suppressed.The photocatalytic activity of NSs-APAM was higher than that of NSs-Water and CN,and the free radicals were surveyed by photocatalytic reaction under visible light irradiation.The experimental results show that the hole plays a major role in the photocatalytic reaction.?2?PCN with high specific surface area and rich pore structure was obtained by KOH reaction with g-C₃N₄ under 450?500 ? and further acid treatment.G-C₃N₄ was activated at a low temperature of KOH to obtain a porous structure of g-C₃N₄.The activation temperature is 450-500 ?,lower than conventional 800?.Not only shorten the experimental cycle,reduce energy consumption,and the reaction is more simple,safe and easy to operate.?3?The obtained g-C₃N₄ nanostructure colloidal liquid was homogeneously mixed with the TiO2 sol,and the composite fiber precursor was prepared by centrifugal distillation method.The composite fiber precursor was heat treated under the water vapor atmosphere.The formation of g-C₃N₄/TiO2 heterojunction effectively broadens the response of TiO2 to visible light and enhances its adsorption enrichment to contaminants.The degradation rate of X-3B dye is higher than that of TiO2 and g-C₃N₄,and the composite fiber is easy to facilitate the recycling to show the convenience of recycling.