Modification Of Graphitic Carbon Nitride Skeleton For Efficient Photocatalytic Hydrogen Evolution

Two of the preoccupations of modern human society are the ever-increasing energy demand and global warming.Researchers have extensively endeavored to use inexhaustible and renewable solar energy to address these concerns.Solar intermittency and uctuations have urged scientists to suggest and develop numerous techniques to provide permanent sources of electrical energy.Conversion of sunlight to electricity via solar cells and subsequent storage in batteries and supercapacitors are among the conventional strategies.Storage of sunlight in the form of hydrogen via room temperature-based photoelectrochemical reactors,however,has proved to be the most propitious technique due to its cost effectiveness compared with other conventional methods.Hydrogen can be further employed in CO₂ production sites for the synthesis of hydrocarbon fuels or in fuel cells for generation of electric power.On the other hand,two dimensional?2D?materials have become the frontiers of materials science due to their excellent photocatalytic and photoelectrocatalytic properties,making investigations into solar energy conversion and storage devices based on 2D materials more prevalent than ever before.Since its discovery by Wang et al.,graphitic carbon nitride?g-C₃N₄?has attracted immense attention in the field of heterogeneous photocatalysis due to its excellent optical properties,high thermal physical-chemical stability in basic/acidic media,Earth abundance and environmentally friendly nature.Discontentedly,pristine g-C₃N₄exhibits limited visible-light absorption and fast recombination of photoinduced electron-hole pairs,which results in mediocre catalytic activity.To remedy these disadvantages,triamterene-doped g-C₃N₄ and strong organic acid-assistant synthesis of holey graphitic carbon nitride were prepared,characterized and evaluated for photocatalytic evolution of hydrogen in this dissertation.Details of this thesis are summarized briefly as follows:?1?In this study,we report a photocatalyst with distorted skeleton,which was synthesized by grafting triamterene onto graphitic carbon nitride?g-C₃N₄?frameworks.Pteridine ring of triamterene-based nitrogen-enriched organic structure,functions as trapped electron sites due to its inductive effect.Benzene ring in triamterene plays an important role on even dispersion of electrons by conjugative effect.Intramolecular electronic potential redistribution caused by synergistic effect between pteridine ring and benzene ring of triamterene promotes separation and migration of photo-induced charge carriers.After coupling with triamterene,the?-electrons of g-C₃N₄ were relocated.That is,its intrinsic electronic and band structure were effectively modulated.The modified polymeric photocatalyst shows a higher photocatalytic H₂ evolution rate of 157.5?mol/h,which is 4.3times of that of the pristine g-C₃N₄?36.8?mol/h?,with an apparent quantum efficiency of 9.7%at 450 nm.The incorporation of triamterene into the g-C₃N₄ frameworks significantly expands its?-delocalized system by electronic potential redistribution,expands visible light absorption range and effectively promotes the separation and migration of photo-induced charge carriers.?2?A facile and cost-effective approach was developed for the preparation of holey N-deficient g-C₃N_x nanosheets using trifluoroacetic-acid-treated urea as a precursor.Various techniques were utilized to investigate the multifaceted influences of trifluoroacetic acid modification.The obtained sample FCN-400 displayed laminated porous morphology with nitrogen defects,which enlarged specific surface areas and extended range of spectral response,and enhanced electron transportation and photocatalytic activity.Consequently,FCN-400 exhibited superior photocatalytic performance and excellent cycling stability.The hydrogen evolution rate of FCN-400 reached 309.3?mol/h,which is 11.3-fold of that of bulk g-C₃N₄?27.3?mol/h?.