The Controllable Preparation Of Carbon Nitride And Layered Double Hydroxides For Environmental Pollutants Control And Hydrogen Energy Development

Environmental pollution and energy crisis are two major obstacles hindering human development in modern society.The main reason is that the burning of fossil fuels not only causes environmental pollution but also makes energy increasingly exhausted.Among the various technologies of solving these challenge,photocatalytic and adsorption methods are widely used due to their advantages of high efficiency,low cost and environmental friendliness.Graphite carbon nitride（g-C3N4）,as a kind of non-metal semiconductor photocatalyst,attracted widespread attention because of its narrow band gap（2.7 eV）and high thermal stability,the unique properties make carbon nitride have potential applications in pollutant treatment and photocatalytic splitting of water.However,carbon nitride has the small surface area and the high electron and hole recombination rate,which severely inhibited its photocatalytic activity.Therefore,modification was considered to improve the activity.Layered double hydroxides（LDHs）is a special kind of inorganic layered materials.The properties of excellent interlayer anion exchange capacity enable them with high removing capacity in pollutions adsorption fields,but the traditional type of hydrotalcite materials has the low remove efficiency and utilization rate of recycling in the process of practical water treatment.Therefore,developing the hydrotalcite adsorption materials with new high adsorption efficiency,wide application range and easy recycling are very important.To solve the above problems,the photocatalytic activity of carbon nitride was improved by forming the composites or controlling their morpholiges.By combining the layered double hydroxides（LDHs）and polyvinyl alcohol（PVA）sponge,the adsorption performance and recycling performance were greatly improved.The contents are mainly divided into three aspects:（1）In this experiment,boron doped carbon nitride was prepared by doping-calcination method,and then it combined with self-assembled of zinc porphyrin micron rod to form composite material viaπ-πinteraction to realize photocatalytic degradation of methyl orange.As the photosensitizer,zinc-porphyrins enhanced the absorption of visible light,and the photoinduced electrons are transferred to boron-doped carbon nitride nanosheets to achieve the synergistic degradation effect.The obtained products were characterized by transmission electron microscope,X-ray diffraction and Fourier transform infrared spectroscopy.The results showed that the boron doping carbon nitride nanosheets successfully attached to the surface of the zinc porphyrin microrods.Through the experiments of photocatalytic degradation of methyl orange,under visible light excitation,ZnTPyP/B-C3N4 composite photocatalyst has excellent performance on photocatalytic degradation of organic pollutants.ZnTPyP/B-C₃N₄ composite has been widely used in bionic photocatalytic degradation of pollutants due to its high stability and light absorption performance.（2）The porous carbon nitride was prepared by freeze-drying the mixed solution of melamine and ammonium chloride which was then combined with polyvinyl alcohol（PVA）sponge prepared by mechanical stirring foaming agent to prepare porous g-C₃N₄/PVA composite sponge.Scanning electron microscopy,X-ray diffraction,Fourier transform infrared spectroscopy and UV-Vis spectroscopy were used to characterize the products.The results show that we have successfully prepared porous g-C₃N₄/PVA composite sponge.Based on the photocatalytic activity,adsorption ability and easy recovery property of the porous g-C₃N₄/PVA composite sponge,it can be further applied to the degradation of organic pollutants fields.（3）In this work,a novel Zn/Fe-LDH composite sponge was successfully fabricated using a simple in-situ hydrothermal method on the surface of the pristine polyvinyl alcohol（PVA）sponge.The composite sponge can not only absorbed well the anionic pollutants of water by anionic intercalation exchange method,but also can be easily recovered and reused.The products were characterized by scanning electron microscope,X-ray diffraction,Fourier transform infrared spectroscopy.Characterization studies revealed that the composite sponge contained flower-like Zn/Fe-LDH microspheres uniformly dispersed throughout a poly vinyl alcohol（PVA）sponge matrix.The specific surface area of the Zn/Fe-LDH composite sponge was 42.5 m²·g^-1,approximately 5 times higher than the pristine PVA sponge(8.9 m²·g^-1).Adsorption experiments revealed that Zn/Fe-LDH composite sponge exhibited a much higher adsorption ability for As（V）anions compared with a Zn/Fe-LDH powder or the pristine PVA sponge.The maximum adsorption capacity for As（V）was found to be 85.7 mg·g^-1.Furthermore,the Zn/Fe-LDH composite sponge showed high thermal stability,good mechanical stability and easy recoverability,thereby allowing reuse.Results guide the development of improved,low cost water treatment materials.（4）Ordered graphitic carbon nitride（g-C3N4）tubular bundles were successfully prepared by a two-step method.Melamine and PEG-PPG-PEG were found to readily form molecular crystals in hot water via self-assembly processes,which on heating at 550 ^oC in N₂ yielded high specific surface area g-C₃N₄ tubular bundles.The obtained products were characterized by X-ray diffraction,transmission electron microscope,fluorescent spectroscopy and X-rays photoelectron spectroscopy.The results demonstrated that the ordered parallel alignment of the individual g-C₃N₄ nanotubes（diameter¹00 nm,length>5μm）within the bundles delivered excellent electron transport properties as evidenced by photoelectrochemical and photoluminescence measurements under visible light excitation.The combination of high specific surface area and enhanced electron transport properties imparted the g-C₃N₄ tubular bundles with outstanding photocatalytic performance.A 1 wt.%Pt/g-C₃N₄ tubular bundle photocatalyst afforded the remarkable H₂ production rate of 16.07 mmol·h^-1·g^-1 in 10 vol.%triethanolamine（TEOA）under visible light（300 W Xe lamp,λ>420 nm）,almost 5 times higher than that of a conventional 1 wt.%Pt/bulk g-C₃N₄ photocatalyst.Results guide the development of improved g-C₃N₄ photocatalysts for renewable energy applications.