Modification And Photocatalytic Activities Of Layered HCa₂Nb₃O₁₀ Photocatalyst

In recent years,environmental pollution and energy shortage have become main factors limiting development of economic.It is a highly effective measure to relieve the pressure of environment and energy by developing new energy.Photocatalytic water-splitting for hydrogen production utilizing semiconducting materials is essential to answer global environmental pollution and the energy crisis as an economical technique.Photocatalysis technique relies mainly on redox reaction of photogenerated carriers that are produced by semiconductor photocatalyst and substances in the environment.Among the state-of-the-art photocatalysts,HCa₂Nb₃O₁₀ has been suggested as one of high-efficiency photocatalysts for hydrogen production for its special layered perovskite-type structure and high chemical durability.However,the photochemical water splitting capability of HCa₂Nb₃O₁₀ is limited by its rapid carrier recombination.In this work,different measures such as construction of heterojunction,loading noble and doping ion are took to modify hydrogen production performance of HCa₂Nb₃O₁₀.Sandwich-like HCa₂Nb₃O₁₀/Ca Nb2O6 heterostructured nanosheets are successfully fabricated through a facile calcination with sub sequent ion-exchange treatment.The TEM test results indicate interfacial lattice mismatch,which is helpful for the transition of carrier,might occur between?001?planes of layered perovskite-related type HCa₂Nb₃O₁₀ and Ca Nb2O6.It can be speculated that the connection of lattice planes in heterostructure is accomplished by niobium chemical bond from XPS test results.Furthermore,the PL emission intensity of HCa₂Nb₃O₁₀/Ca Nb2O6 reduced significantly compared with HCa₂Nb₃O₁₀ showing charge carrier separation efficiency is greatly improved.The photocurrent density of HCa₂Nb₃O₁₀/Ca Nb2O6 is 2 times higher than HCa₂Nb₃O₁₀.This is attributed to effective carrier separation in the heterostructure.Characterization of band gaps confirms that HCa₂Nb₃O₁₀ and Ca Nb2O6 own similar energy gap but diffierent band position,so there is a separation of carriers in the nanosheets leading to a higher hydrogen production.Pt-loaded HCa₂Nb₃O₁₀/Ca Nb2O6 photocatalyst is prepared by a photochemical reduction precipitation method and optimal conditions are found as,reaction time 2 h,mass ratio 0.3%.The loaded samples exhibit higher activity for hydrogenation than before under simulated sunlight.UV-vis spectra shows that samples with different reaction times and different mass ratios have respectively similar and gradually enhanced intensity of light absorption.The absorption edges of all samples are about 370 nm.The photocurrent density of Pt-loaded samples is higher obviously proving efficient separation of carrier.However,no changes have been made to morphology for the loaded samples.Ta-doped HCa₂Nb₃O₁₀/Ca Nb2O6 nanosheets are obtained by the same method as the first part.TEM indicates that the doped nanosheets exhibit sandwich-like structure without changes in phase composition and construction.XPS characterization proves that Ta replaces location of Nb and affect the binding energy of Nb and O leading to tiny skewing of peaks.The band gap of Ta-doped sample has not changed compared with before but the hydrogen producton is improved.The higher efficiency of carrier transfer is proved by results of photocurrent density.All the results indicate that doping Ta is helpful for separation and transfer of carriers leading to a higher photocatalytic activity.