| Inspired by natural photosynthesis,semiconductor photocatalysis that converted solar energy to chemical energy was widely applied in the area of pollutants degradation,water splitting into H2 and O2,CO2 reduction and N2 fixation,etc and considered as effective strategy to solve environmental problems and produce renewable energy.Photocatalytic H2 generation via water splitting could convert solar energy to storable and transportable hydrogen energy in green and sustainable way,which showed great potential for the future sustainable energy society and had received extensive attention from scientists.The development of photocatalysts with low cost,visible light response and high energy conversion efficiency is the core issue for the research on photocatalytic H2 production systems.Graphitic carbon nitride(g-C3N4)had been considered as a promising photocatalyst towards photocatalytic H2 evolution due to its visible light response,suitable band edge,good chemical stability and thermal stability,etc.However,limited by visible light harvesting wavelength less than 460 nm,low dielectric property and high resistivity,pristine g-C3N4 suffered from insufficient visible light adsorption,high recombination rate of photoexcited charge carriers,high transport resistance and thus low photocatalytic activity.The modification and optimization of the g-C3N4 based photocatalysts to improve its photocatalytic efficiency is of great significance to promote its application in clean energy and industrial production.In this thesis,p block element(In)and oxide(In2O3)were employed to modify g-C3N4 based photocatalysts through ion doping and/or heterojunction construction to extend visible light harvesting capacity and optimize photoelectric conversion efficiency.The morphology,composition,band structure,optical property,electrical property and photoelectric response of modified g-C3N4 based photocatalysts were investigated and mechanism on improved H2 generation performance was illustrated.The main research contents and achievements are as follows:1.Mechanism investigation on promoted H2 production realized by In3+ doped g-C3N4 based photocatalyst.In the second part of the thesis,uniform In3+ doping within g-C3N4 substrate was achieved via in-situ copolymerization.The content of doped In3+ and separation and migration efficiency of photoexcited charge carriers could be tuned by altering amount of indium precursor added.DFT stimulation revealed doped indium tended to approach the bottom layer and far away the top layer,which we would like to term as a quasi-interlayer doping fashion.The interaction between indium and the bottom g-C3N4 layer was identified to be weak coordination and that between indium and the top layer to be ion-dipole one.The doped In3+ effectively increased electron density of?conjugated system via charge transfer from In to N and promote separation and transportation of photoexcited charge carriers without altering energy band structure and visible light harvesting ability.The In-g-C3N4 photocatalyst doped with optimal amount of indium ions,i.e.,2.18 wt.%,exhibited a hydrogen evolution rate of 1.35 mmol·h-1·g-1,17 times of that of pristine g-C3N4 (0.08mmol·h-1·g-1),attributed to the synergistically promoted separation and migration of the photogenerated charge carriers.This work demonstrated special doping pattern of p block element(In)and mechanism on elevated H2 evolution performance.2.Mechanism investigation on enhanced H2 production of g-C3N4 based photocatalyst induced by indium and phosphorus co-doping.In the third part of the thesis,indium and phosphorus co-doped g-C3N4 photocatalyst was prepared by facile post-treatment.The theoretical simulations revealed that the doped indium ions were located between the planes of g-C3N4 and the phosphorus atoms were introduced into the g-C3N4 plane by replacing the carbon atoms,existed in the form of P=N bond.DOS calculation results indicted new occupied electronic state emerged in the VB and CB,contributed by 5s orbital of the doped indium and 3p orbital of doped phosphorus,which may act as new transport channel for the photogenerated holes and electrons.Metal and non-metal co-doping contributed increased electron density,narrowed band gap,extended visible light adsorption and elevated separation and migration of photoexcited charge carriers.As a result,the In,P-g-C3N4 photocatalyst exhibited a hydrogen evolution rate as high as 4.03 mmol·h-1·g-1,ca.50 times of that of pristine g-C3N4(0.08 mmol·h-1·g-1).3.In2O3-g-C3N4 Z-scheme heterojunction fabrication and mechanism investigation on improved H2 generation performanceIn the forth part of the thesis,In2O3-g-C3N4 heterojunction was constructed by hydrolysis and calcination procedure using g-C3N4 as support and In Cl3 as indium precursor.The morphology of In2O3-g-C3N4 exhibited one-dimensional In2O3 nanorod supported on sheet-like g-C3N4.The content of In2O3 could be tuned from 3wt.%to 18 wt.%in the In2O3-g-C3N4 heterojunction by altering amount of In Cl3 added.With optimal amount of In2O3,i.e.,12 wt.%,In2O3-g-C3N4 heterojunction exhibited optimal separation and migration efficiency of photogenerated charge carriers and highest hydrogen evolution rate of 1.29 mmol·h-1·g-1,12.9 times of that of pristine g-C3N4(0.10 mmol·h-1·g-1).The enhanced photocatalytic H2 production performance was attributed to separation and transportation promotion driven by interfacial electric field and maintained strong redox ability,originating from Z-scheme heterojunction formation due to matched energy band structure and work function difference.4.Fabrication of In2O3-g-C3N4 heterojunction with enhanced local electric field and mechanism investigation on improved H2 generation performance.In the fifth part of the thesis,g-C3N4 supported cubic In2O3 heterostructure was constructed by hydrothermal and calcination procedure using ultrathin g-C3N4 nanosheet as support and In(NO3)3 as indium precursor.The In2O3-g-C3N4 heterojunction exhibited extended visible light adsorption.The interfacial electric field between In2O3 and g-C3N4 could effectively improve the photogenerated charge carrier separation and transport owing to type II heterojunction formation.Meanwhile,accumulation of photoexcited electrons in plasmonic In2O3 contributed to localized electric field enhancement on the In2O3-g-C3N4.These factors contributed to superior photocatalytic H2 evolution activity of In2O3-g-C3N4 heterojunction(3 mmol·h-1·g-1),7.5 times higher than that of nanosheet(0.4 mmol·h-1·g-1).The apparent quantum yield of In2O3-g-C3N4 reached up to 5.27% at 400 nm and remained 0.7% at 660 nm. |
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