Carbon Nanomaterial Composite Photocatalytic System And Preparation Of Graphene Quantum Dots And Their Properties

The energy crisis and environmental pollution are two major issues facing the world.Photocatalysis is an important technology that is expected to use solar energy to achieve decomposition of water to produce hydrogen and degrade pollutants.The development of efficient,low-cost and stable photocatalytic materials is the key to advancing the development and application of this technology.Carbon nanomaterials including graphene and carbon nanotubes have excellent photoelectricity,electrical conductivity,adsorption ability,and have important applications in many fields.This paper aims at the application of carbon nanomaterials in the field of photocatalysis and fluorescence detection.It is dedicated to the development of high-efficiency photocatalytic systems based on carbon nanomaterials and the exploration of the simple preparation technology of graphene quantum dots.The following research results have been achieved.A TiO₂ nanosheets/graphene foam composite photocatalytic system has been designed and prepared,which has dual functions of both adsorption and photocatalytic degradation.The TiO₂ nanosheets/graphene foam composites were prepared by one-step hydrothermal method using graphene oxide and tetrabutyl titanate as raw materials.The morphologies of the samples were studied by scanning electron microscopy and transmission electron microscopy.The removal ability of hexavalent chromium and methylene blue was also tested.The composite material contains a large amount of graphene,so that the composite material has a strong physical adsorption effect on pollutants.The excellent electron transport ability of the graphene also greatly enhances the photocatalytic efficiency of the composite material.In the process of photocatalytic degradation of organic matter,TiO₂ nanosheets and graphene foam can play a synergistic role,so that the photocatalytic efficiency can be more significantly improved.The composite material has good removal ability for hexavalent chromium ion and methylene blue,which are 1.3 times and 2.1 times of the removal capacity of TiO₂ nanosheets of the same quality.The complex catalyst is easy to handle and has good cycle stability,it can be reused multiple times.The composite material can simultaneously remove hexavalent chromium ions and methylene blue molecules in water,and has a good effect on the treatment of mixed sewage containing both.In order to improve the photocatalytic activity under visible light,a combination of sulfur doping and graphene composite was developed to develop a photocatalytic system of sulfur-doped TiO₂ nanosheets/graphene composite.A simple one-step hydrothermal method was used to prepare anatase TiO₂ nanoparticles that exposed a large number of?001?crystal faces.X-ray diffraction,scanning electron microscopy,transmission electron microscopy,photoelectron spectroscopy and ultraviolet-visible diffuse reflectance spectroscopy were used to characterize the morphology of the samples.The methylene blue was used as a template for organic pollutants to explore the photocatalytic degradation of organic pollutants.In this paper,we have realized the omni-directional control of TiO₂ forbidden band width,carrier recombination rate,morphology and crystal plane by a convenient method,which greatly improves its photocatalytic efficiency under visible light.The?001?facet has the highest photocatalytic activity.Sulfur doping expands the response range of the light from the ultraviolet region to the visible region by reducing the bandgap width?from 3.3 eV to 3.0 eV?,and the introduction of graphene helps to enhance carrier separation rate,thereby improving the photocatalytic activity of the catalyst in multiple ways.The composite exhibited high photocatalytic activity when methylene blue was degraded under simulated sunlight,and all the methylene blue in 50 mL of 10.0 mg/L methylene blue solution could be degraded in 12 minutes.A simple and convenient process for the synthesis of g-C3N4/carbon nanotube composite photocatalytic system with close contact interface by microwave assisted heating has been explored.The morphological structure,light absorption and elemental composition of the obtained composite photocatalytic system were characterized by scanning electron microscope,transmission electron microscopy,X-ray diffraction and other test methods.The optical properties of the composite were characterized by UV-Vis diffuse reflectance and fluorescence emission spectra.The photoelectrochemical properties of the samples were characterized by measuring transient photocurrent and impedance.The photocatalytic hydrogen production rate and cycle stability of the composite were tested.Compared with other methods,the g-C3N4 and carbon nanotubes in the composite photocatalyst obtained by this method have a more intimate contact interface and higher crystallinity.The composite photocatalyst can effectively increase the number of photogenerated carriers and increase the photocurrent response.The composite photocatalyst has good photocatalytic stability and photocatalytic performance,its hydrogen production rate under visible light can reach 45.1 ?mol/h,and its photocatalytic activity is also higher than that of g-C3N4/carbon nanotubes prepared by other preparation methods previously reported.A simple one-step synthesis of graphene quantum dots using low-cost biomass waste rice husks as raw materials was attempted.Graphene quantum dots were prepared by one-step hydrothermal method,and their reaction conditions?temperature,duration?were optimized.The reuse of biomass waste in a green and facile way has been achieved.The morphology of graphene quantum dots was studied by scanning electron microscopy and transmission electron microscopy.By measuring fluorescence emission and absorption spectra,the luminescence properties of graphene quantum dots were investigated.The degree of fluorescence quenching of a series of metal ions by graphene quantum dots was tested.The fluorescence intensity of the graphene quantum dots dispersion after contact with a series of solutions of ferric ions with different concentrations was measured.The relationship between the concentration of ferric ions and the fluorescence quenching degree of graphene quantum dots was investigated.The obtained graphene quantum dots have a narrow particle size distribution,they have an average particle diameter of 3.9 nm,contain 2-3 layers of graphene,and can produce specific fluorescence quenching of trivalent iron ions.The produced graphene quantum dots can be used as fluorescent sensors for detecting ferric ions in water.Meanwhile,the residue from the synthesis of the graphene quantum dots can be used to prepare amorphous silica nanoparticles.A comprehensive utilization of the organic and inorganic components in the rice husk has been achieved.