The Preparation Of CaTiO₃-based Nanocomposites And Their Photocatalytic Hydrogen Production Properties

Nowadays,due to the shortage of traditional energy sources,it is urgent to develop new energy sources to alleviate the current predicament.Among many options,hydrogen energy is the most ideal energy source.It not only burns pollution-free and zero-carbon emissions,but also can be obtained through various ways,especially photocatalytic splitting water,which can convert solar energy into chemical energy,and photocatalytic splitting water into hydrogen and oxygen without consuming conventional energy.Therefore,photocatalytic hydrogen production is considered to be one of the most promising hydrogen energy development pathways.Calcium titanate（CaTiO₃）is a typical perovskite with the appropriate bandgap of the conduction band negative to redox potential of H⁺/H₂ and valence band positive to redox potential of O₂/H₂O,so it is available to photocatalytic splitting water produces hydrogen.Due to its wide band gap,the utilization of visible light lowly,and the recombination rate of photogenerated electrons and holes highly,is resulting in low photocatalytic hydrogen production efficiency.Therefore,how to improve its light utilization rate and photo-generated carrier efficiency is the fundamental way to improve its photocatalytic hydrogen production,especially the surface heterojunction modification.By compounding with other materials,it can not only increase the visible light utilization rate,but also promote the migration and separation of photogenerated carriers,thus it is effective to improve photocatalytic hydrogen production.This thesis explores the application of CaTiO₃-based composites in the field of photocatalytic hydrogen production.The principle of preparation was Ca（NO₃）₂·4H₂O as calcium source and tetrabutyl titanate as titanium source with an appropriate amount of NaOH to prepare CaTiO₃ by one-step hydrothermal method.Through regulating the preparation parameters,it not only controlled its morphology,but also increased the specific surface area.Then,it is combined with a co-catalyst,a precious metal material or a carbon material to enhance the absorption of visible light,accelerate the migration efficiency of photogenerated carriers,and improve the photocatalytic hydrogen production efficiency.The main researches are as follows:（1）MoS₂/CaTiO₃ composites were prepared by hydrothermal co-deposition method,and the influence of MoS₂ content on photocatalytic hydrogen production efficiency were studied.The absorption band of the MoS₂/CaTiO₃ composites exhibit a red shift and increase the utilization of visible light.The photocatalytic hydrogen production activity of the MoS₂/CaTiO₃composites（⁸8.89μmol/g·h）expresses a higher improvement about 9 times,compared to the pure CaTiO₃（⁹.32μmol/g·h）.It was ascribed to MoS₂ as co-catalyst can drive the transfer of photon-generated carriers to promote the photon-generated carrier separation,accelerate the binding efficiency of e^-and H⁺to improve the efficiency of photocatalytic hydrogen production.（2）AgCl/Ag/CaTiO₃ nanocomposites were synthesized via simple preparation of hydrothermal-chemical co-deposition method,and the influence of AgCl/Ag loading on photocatalytic hydrogen production performance was investigated.The results of SEM,EDS,elemental mapping,XRD,TEM,XPS and Raman shift imply that the AgCl/Ag nanoparticles have deposited on the surfaces of CaTiO₃ nanosheets successfully.Compared with the unmodifiedsamples（¹3.05μmol/g·h）,theoptimalhydrogenproductionvalue（²26.53μmol/g·h）of AgCl/Ag/CaTiO₃ nanocomposites increased by 17 times,and the best hydrogen production of samples were tested for cycle stability and the average hydrogen production was about 220μmol/g·h.The mechanism is explored,which could be ascribed to the Z-scheme heterojunction.The metal Ag⁰could act as a cross-linking bridge to contact the two semiconductors and promote the recombination of electrons（CB of AgCl）and holes（VB of CaTiO₃）,which could promote the remaining holes（VB of AgCl）and electrons（CB of CaTiO₃）separation,so that the photocatalytic hydrogen production activity improved remarkably.（3）g-C₃N₄/CaTiO₃ composites was synthesized via simple preparation using the hydrothermal co-deposition method.The results of SEM,EDS,elemental mapping,XRD,TEM,XPS,FT-IR and Raman shift imply that the g-C₃N₄ nanoparticles have deposited on the surfaces of CaTiO₃ successfully.The photocatalytic activity of the g-C₃N₄/CaTiO₃ composites（¹89.38μmol/g·h）exhibits an enhancement of 18 times than that of the unmodified samples（¹0.58μmol/g·h）,and the best hydrogen production of samples were tested for cycle stability and the average hydrogen production was about 187.64μmol/g·h.Further,the photocatalytic process and the mechanism of the photocatalytic hydrogen production enhancement has been studied,which could be ascribed to the nano-heterojunction at the interface and proved by the transient photocurrent,PL,EIS and Motty-Scotty plots.