Construction And Photocatalysis Of HNB₃O₈ Nanosheets With Plasma Effect

With the rapid development of globalization and industrialization,energy crisis and environmental pollution have become two major problems that human beings have to confront.Seeking for renewable and clean energy is likely to be a desirable way to cope with the two problems.Hydrogen recognized as a new generation of clean energy in the world has attracted wide attentions due to its high efficiency,less pollution and recyclable use.The method of hydrogen production by semiconductor photocatalysis is a potential technology.It is a main issue to develop and design efficient catalysts for H₂production using water splitting.Niobic acid（HNb₃O₈）is a kind of layered solid acid.Its layered structure is more conducive to the separation and migration of photogenerated carriers,so it is a good photocatalyst.However,its photocatalytic activity needs to be further improved.In this paper,the new photocatalysts based on HNb₃O₈nanosheets are synthesized by doping Mo,Ag and graphene quantum dots,which show excellent photocatalytic performance of H₂production by water splitting.The main work of this paper is as follows:HNb₃O₈nanosheets and MoNb nanosheets composites were synthesized by hydrothermal method using commercial NbCl₅and MoCl₅as niobium source and molybdenum source,respectively.The morphology,structure and photocatalytic hydrogen evolution of the samples were researched.The results of XRD、Raman、FT-IR、SEM、AFM and TEM show that HNb₃O₈nanosheets and Mo-doped HNb₃O₈nanosheets were successfully synthesized and the Mo（V）was isomorphously substituted into the framework of HNb₃O₈nanosheets.The conclusion of XPS and ESR indicates the chemical states of HNb₃O₈and Mo-doped samples,implying the coordinately unsaturated Mo species might be the visible-light adsorption centers and photocatalytic active sites.Based on the results of UV-Vis-NIR、Mott-Schottky plots、VB-XPS and UPS spectra,the band structures of the HNb₃O₈and Mo-doped samples are schematically illustrated,indicating that the more absorptions might be associated with LSPR.MoNb-10 displays the highest hydrogen evolution rate(180.3μmol g^-1h^-1),which is 6.3 times of that for pure HNb₃O₈(28.4μmol g^-1h^-1).In order to study the reaction mechanism,irradiation lights with different wavelength range are employed to photocatalyze H₂evolution from water.LSPR effects over MoNb-10can efficiently promote the separation and transportation of photoinduced charge carriers（h⁺-e^-）and afford supererogatory kinetic energy to the electrons and holes excited by UV lightHNb₃O₈nanosheets composites were synthesized by a one-step hydrothermal method using commercial NbCl₅as niobium source.Ag/HNb₃O₈-PP and Ag/HNb₃O₈photocatalysts were prepared by means of photo-deposition and dipping with a certain proportion of Ag on HNb₃O₈nanosheets.Besides,the results of XRD、FT-IR、SEM and TEM show that:the Ag loaded HNb₃O₈nanosheets were successfully synthesized.The XPS and ESR exhibits the chemical states.By UV-Vis-NIR and Mott-Schottky plots,the band structures of photocatalyst were determined.Because of loading Ag atom,the more absorptions might be associated with LSPR.The photocatalytic tests are consistent with the characterization.the optimal Ag/HNb₃O₈displays the highest hydrogen evolution rate(889.7μmol g^-1h^-1),which is 31.3 times of that for pure HNb₃O₈(28.4μmol g^-1h^-1).Nitrogen-doped graphene quantum dots（NGQDs）were prepared by hydrothermal method with citric acid and urea.NGQDs-HNb₃O₈photocatalyst were prepared by adding a certain amount of NGQDs in the process of synthesis of HNb₃O₈nanosheets.Meanwhile,the results of XRD,FT-IR and SEM confirmed that NGQDs-HNb₃O₈nanosheet catalysts were successfully synthesized.The characterization result of XPS indicates the chemical states of each element.The results of photocatalytic test showed that NGQDs-HNb₃O₈exhibited the highest hydrogen evolution rate(243.3μmol g^-1h^-1),which is 8.6 times of pure HNb₃O₈(28.4μmol g^-1h^-1).This might originate from visible and infrared light raising the temperature of the reaction system,thus speeding up the reaction rate.