Interface Modulation Of Metal/g-C₃N₄ Photocatalytic Materials And Their Hydrogen Evolution Performance

Since the 20th century,the over-consumption of fossil fuels has caused increasing energy crisis and environmental pollution.Therefore,it is desired to find effective ways for the production of clean and renewable energy.Semiconductor photocatalysis,converting solar energy into hydrogen energy and other chemical energy,has been considered as one of the most promising strategies to address the afore-mentioned issues.Recently,graphitic carbon nitride?g-C₃N₄?has been regarded as an attractive photocatalyst due to its visible-light absorption ability,suitable band positions,high chemical stability,easy preparation,low cost and nontoxicity.However,g-C₃N₄ still suffers from the poor solar energy utilization and low quantum efficiency,which limits the large-scale application.In particular,the low quantum efficiency is mainly due to the rapid recombination of electrons and holes.Coupling cocatalyst onto the photocatalyst can greatly improve the photocatalytic performance by promoting the separation of photogenerated electrons and holes.Nevertheless,commonly used and efficient cocatalysts are noble metals,of which the loading amount is relatively high.Therefore,how to reduce the loading amount of noble-metal cocatalyst is one of the meaningful research topic of photocatalysis.Recently,a number of research groups have reported the single-atom-based catalysis,which shows that the single-atom catalyst can largely reduce the amount of noble metals and achieve maximum atomic efficiency.Such single-atom engineering strategy could also be employed in photocatalysis.On the other hand,g-C3N4 has several drawbacks such as poor crystallinity,non-uniform polymerization,poor dispersion in water and poor hydrophilicity.Therefore,it is necessary to improve the crystallinity and water dispersity of g-C₃N₄ by effective ways such as the molten salt method.Furthermore,a highly efficient interface could be established between g-C3N4 and noble metal cocatalyst,which enables the interface to be a fast electron-transfer channel rather than the recombination center,through the strong interaction between the metal and support.The main contents of this thesis are as follows:1.Urea was used as the precursor material and was calcined to obtain the bulk g-C₃N₄.The g-C₃N₄ nanosheets were then prepared by a secondary calcination method.Pd/g-C₃N₄ hybrid was obtained via an impregnation-reduction method.By employing a facile thermo-driven diffusion approach,the simultaneous interlayer and surface modulation of g-C₃N₄ framework by Pd single atoms has been successfully acheived.The prominent advantage of this single-atom engineered Pd/g-C3N4 photocatalyst is its capability of constructing a vertical channel for directional charge transfer from the bulk to the surface by the interlayer Pd atoms and establishing the targeting active sites for the catalytic reactions of water reduction by the surface Pd atoms.Such unique structure efficiently boosts the electron transport and separation and enhances the affinity towards reactant molecules,thus greatly enhancing the photocatalytic activity of g-C₃N₄ photocatalyst.2.Firstly,melamine as the precursor material was mixed with KOH through oil-bath drying treatment under stirring.The resultant mixture was then mixed with NaCl and was put into a tube furnace for calcination under N₂ atmosphere.It was shown that defect-engineered crystalline g-C3N4 could be obtained by tuning the content of KOH.The as-obtained g-C3N4 possess abundant terminal groups,which can not only improve its hydrophilicity toward better adsorption of water molecules,but also modulate the strong interaction between the cocatalyst and photocatalyst,further tuning interfacial electron-transfer ability.