Study On The Surface Hybridization And Photocatalytic Performance Of 2D Ultrathin Carbon Nitride

Currently,human beings are facing the two major problems of the world's severe environmental pollution and energy crisis.In order to achieve energy catalytic conversion and pollutant removal to realize sustainable development,the materials and technologies have been developed in the field of materials chemistry and environmental science.Among them,the two-dimensional graphite carbon nitride?2D g-C₃N₄?exhibits photocatalytic properties and effectively achieves energy catalysis and pollutant conversion due to its graphene-like structure,unique electronic and optical properties.However,low carrier transport rate and high carrier recombination rate result in a lower catalytic effect of 2D g-C₃N₄.At the same time,it is also affected by the quantum size effect,exhibiting lower visible light absorption,resulting in lower solar energy conversion efficiency.In order to improve the catalytic performance of 2D g-C₃N₄,the thesis regulates the material element composition and optimizes the design table/interface structure precisely from the micro-molecular level hybridization to the macro-material surface structure,from point to surface,from part to whole.It effectively increases the number of captured photons,effectively and precisely regulates the position of catalytic active sites,and promotes the separation of photogenerated electron-hole pairs.Optimizing the regulation table/interface structure to improve the transfer rate of carriers in the 2D g-C₃N₄ plane,and the photo-generated carrier can be utilized efficiently to catalyze reaction.The contents are as follows:?1?Synthetic surface nitrogen modification 2D g-C₃N₄,the molecular structure of2D g-C₃N₄ can be optimized from the molecular level to adjust the band gap structure and improve the visible light utilization rate.Under visible light,more photogenerated electron-hole pairs are generated,and surface nitrogen modification promotes the?-conjugated delocalization effect in the 2D g-C₃N₄ plane,thereby accelerating the carrier transport rate and improving the utilization rate.Finally,the catalytic effect is greatly improved.The NCNS using Pt?3 wt%?as a co-catalyst exhibit a hydrogen production rate of 19.8 mmol h^-1 g^-1,which is 2.19 times and 21.3 times higher than that of 2D g-C₃N₄ and the bulk g-C₃N₄,respectively,and the external quantum efficiency?EQE?of NCNS is also achieved to 10.7%at 420 nm.Furthermore,the NCNS also show excellent photocatalytic activity in the degradation of organic pollutants,80%methylene blue can be mineralized and decomposed after 3h illumination.?2?Synthesis of Fe₂O₃ QDs surface hybrid modification 2D g-C₃N₄ composite.In view of 2D g-C₃N₄ with large layered structure,the 0D Fe₂O₃ quantum dots can be uniformly dispersed on the surface of 2D carbon nitride material,providing more catalytic active sites.The photoelectrons transferring quickly promote carrier separation.Fe₂O₃ QDs can also broaden the absorption range of visible light and improve the utilization of visible light.Fe₂O₃ QDs attached on the surface of 2D g-C₃N₄ can rapidly transfer the photogenerated electrons,thereby inhibiting the photo-generated electron-hole recombination,and at the same time producing more O₂·^-to obtain good catalytic degradation of pollutants finally.75%methylene blue can be mineralized and decomposed in 3h duration under visible light irradiation.Importantly,this 0D/2D still maintains a good crystal structure and satisfying stability with negligible activity reduction after four photoreactions.?3?Synthesis of 2D/2D Ni?OH?₂/g-C₃N₄ photocatalyst nanocomposite.To further optimize the surface structure characteristics of 2D g-C₃N₄ and accelerate the surface/interface reaction.Starting from 2D g-C₃N₄ as a whole,2D Ni?OH?₂ was grown in situ on the surface of 2D g-C₃N₄ to construct a 2D/2D composite structure.By utilizing the characteristics of the variable-valence metal,this is,mutual conversion between Ni²⁺and Ni³⁺by redox reaction,the photo-generated carrier transport and conversion are accelerated,the performance of the catalytic degradation pollutant is effectively promoted,and the catalytic water decomposition performance of the non-platinum system is also improved greatly.Above all,the as-obtained Ni?OH?₂/2D g-C₃N₄ system exhibited a hydrogen evolution rate of 921.4?mol h^-1 g^-1using 10%triethanolamine as a sacrificial agent.And the external quantum efficiency of 5.21%at 400 nm is superior to the previously reported in 3h duration under visible light irradiation.At the same time,after 15 hours visible light irradiation,15?mol hydrogen gas can be generated,which can catalyze the decomposition of pure water under visible light irradiation to achieve a sustainable hydrogen production performance.Moreover,under visible light irradiation for 3 h,50%MB can be mineralized and decomposed,which is increased by 23%than pure 2D g-C₃N₄.Last but not the least,Ni?OH?₂/2D g-C₃N₄ composites can maintain good stability and cycle performance.