Study On The Preparation Of C₃N₄ Based Photocathodes For Photoelectrochemical Selective Oxidation Of Glycerol

In the past five years,China has continuously strengthened ecological environmental protection,promoted green ecological development,and pushed carbon neutrality forward in a scientific and orderly manner.At present,with the depletion of fossil fuels and the increasing seriousness of environmental pollution,the development of clean,low-pollution,renewable sustainable green energy is an increasingly urgent requirement.Biodiesel is one of the current development directions to solve the global energy crisis.In recent years,with the rapid increase in demand and production of biodiesel,a large number of glycerol,a by-product,has been produced.Therefore,the conversion of glycerol into other value-added products,including 1,3-dihydroxyacetone,ethanol and methanol,has important application value for extending the biodiesel industry chain and promoting a green and low-carbon economy.Graphite carbon nitride（g-C₃N₄,abbreviated CN）has been widely used in energy-related fields such as photocatalytic water splitting and organic pollutant degradation due to its simple synthesis method,good chemical stability and adjustable band structure.In this study,CN thin film photoelectrodes were first prepared by depositing different contents of CN on carbon paper,and the physicochemical properties and photoelectric properties of the materials were characterized by various analytical methods.The selective decomposition of glycerol of CN thin film photoelectrodes was analyzed and evaluated by high performance liquid chromatography.Then,the CN film deposited on carbon paper was modified by Cu,which was coordinated with CN to promote the adsorption of O₂and form a singlet oxygen active center.Thereby the selectivity of three-carbon compounds in glycerol oxidation products was improved.The main research contents are as follows:（1）Firstly,CN thin films photoelectrodes were prepared by depositing different contents of CN on carbon paper,and the physical and chemical properties and photoelectric properties of the materials were characterized by X-ray Diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,Fourier transform infrared（FT-IR）,Scanning Electron Microscope（SEM）,Ultraviolet and visible spectrophotometry（UV-vis）,Electrochemical Impedance Spectroscopy（EIS）,Mott-Schottky,Electron paramagnetic resonance（EPR）and other characterization methods,and then the stability of different content CN films deposited on carbon paper was explored under acidic and neutral conditions,which paved the way for further research on the catalytic decomposition of glycerol by different content of CN films deposited on carbon paper.Finally,under oxygen conditions,the photocatalytic selective decomposition experiment of glycerol was carried out,and the liquid phase products were analyzed and evaluated by high performance liquid chromatography.It is found that the photocurrent density of the 80 mg CN film deposited on carbon paper is optimal when V_RHE=0 V.In the experiment of glycerol decomposition,the glycerol conversion rate of the40 mg CN film deposited on carbon paper was the highest,reaching 43.59%,and the 20 mg CN film deposited on carbon paper had the highest selectivity,and the product was mainly methanol.（2）In order to further improve the selectivity of the three-carbon product in glycerol oxidation,Cu-modified CN film deposited on carbon paper was first prepared,and then its photoelectric performance was analyzed by XRD,XPS,FT-IR,UV-vis and other characterization methods,and then under oxygen conditions,the Cu modified CN film deposited on carbon paper was subjected to photocatalytic selective oxidation glycerol experiment,and high performance liquid chromatography was used to analyze and evaluate the factors affecting the liquid product and the reaction process.Finally,the factors affecting the oxidation of glycerol in Cu-modified CN film deposited on carbon paper were analyzed,and the reaction mechanism was speculated by free radical trapping agent experiments and EPR tests..Result shows that the doping of Cu is conducive to improving the photoelectric properties of CN film deposited on carbon paper and promoting the selective oxidation of glycerol.Under suitable conditions（O₂for 30 min before reaction,electrolyte p H=2,O₂flow rate of 6 m L/min during reaction）,the selectivity of dihydroxyacetone reached 93.59%,and the conversion rate of glycerol was 54.64%.