Photocatalytic Hydrogen Evolution Of Fluorinated G-C₃N₄ Catalyst

Energy is related closely to the progress of human society and the development of the national economy.The development of each country and region is inseparable from the support of energy.Energy not only provides convenience for production and daily life but also accompanied by negative effects.The exhaustion of energy and environmental pollution caused by over-exploitation and utilization of energy is imminent.As a kind of renewable clean energy with high combustion value,hydrogen energy has attracted wide attention from countries.Water splitting for hydrogen evolution converts endless solar energy into clean hydrogen energy,which is an effective means to solve energy crisis and environmental pollution.A polymeric semiconductor,namely graphitic carbon nitride（g-C₃N₄）,has a layered graphite-like phase structure.Due to its chemical and physical stability and unique energy band structure,g-C₃N₄ is widely used in photocatalysis.However,g-C₃N₄ still has some disadvantages,such as small specific surface area,high probability of photocarrier recombination,low quantum efficiency,and weak visible light response capability,which limits the application range in photocatalysis.F atoms are very stable and difficult to be oxidized by active oxygen species such as photogenerated holes etc.,becoming an excellent modulator of g-C₃N₄ photocatalyst.In this dissertation,the bandgap was adjusted by fluorinated g-C₃N₄,the visible light response range was widened,the recombination probability of photogenerated electrons and holes was reduced,and the photo-quantum efficiency of the catalyst was increased.Fourier transform infrared（FT-IR）,UV-VIS Diffuse Reflectance Specatrum（UV-vis DRS）,X-ray diffraction（XRD）,Field emission scanning electron microscopy（SEM）,Raman spectroscopy（Raman）,Fluorescence Spectroscopic（PL）,X-ray photoelectron spectroscopy（XPS）,Transmission electron microscopy（TEM）,and electrochemical characterizations are used to analyze the chemical structure,morphology,and optoelectronic properties of fluorinated catalysts,and g-C₃N₄ is examined water splitting for hydrogen evolution activity under visible light（λ≥420 nm）.The main research content is as follows:（1）X（X=F,Cl,Br,I）-g-C₃N₄ is prepared by simple thermal polymerization using melamine and KX（F,Cl,Br,I）and analyzed by a series of characterizations.The dopant of heteroatoms increases the visible light response of the catalyst and suppresses the recombination of photogenerated carriers.Through hydrogen evolution activity,the results show that the enhancement of the photocatalytic performance of g-C₃N₄ by halogen atoms with increasing electronegativity and with the increase of the atomic radius of the halogen element,the smaller the doping rate.The K atoms also have a certain role in improving the photocatalytic performance of the catalyst,in which the fluorinated g-C₃N₄ compared to the hydrogen evolution activity of g-C₃N₄ increased by 7.6 times.（2）The fluorinated g-C₃N₄ is prepared by thermal polymerization using melamine and potassium fluoride as the raw materials in a highly polar environment provided formed deep eutectic solvents（DESs）.F ion and K atoms have higher migration rate in the DESs environment and they contribute to heteroatoms doping.Through a series of characterization results,the doping of F atoms and K atoms enhances the visible light absorption range of the g-C₃N₄ photocatalyst,reduces the recombination probability of photogenerated carriers,and accelerates the rate of photoelectron migration.The results of hydrogen production performance shows that the fluorinated g-C₃N₄ formed in the DESs environment has higher photocatalytic activity and stability,in which the hydrogen evolution of the modified g-C₃N₄was increased by 8.2 times.