Hollow Multi-shelled Structures Of Complex Metal Oxide:Preparation And Application In Photocatalysis

Harvesting and converting the solar energy into electric,thermal or chemical energy with more flexible application is an important method to alleviate the nowadays global energy crisis.During the various converting routes,converting and restoring solar energy into solar fuels like hydrogen,carbon oxide or organic compounds by photocatalytic reactions and thus realizing the conversion of solar energy to chemical energy is much promising.In this process,photocatalysts is the main factor in dealing the final efficiency.As a result,the composition and morphology design of photocatalysts,promoting the light harvesting ability,enhancing the charge separation efficiency,and accelerating the surface reaction rate,will greatly increase the catalytic activity of photocatalyst.Aiming to these aspects,we synthesized series of hollow multi-shelled structured(HoMSs)photocatalysts and applied them in photocatalytic water splitting reactions.By adjusting the compositions and morphologies of these photocatalysts,we improved the photocatalytic activity of these HoMSs materials.The main contents are listed as follows:(1)With abundant electronic energy level,unique 4f5d orbital features,and suitable band positions,CeO2 was chosen as the research subject.By controlling the morphology,creating surface oxygen vacancies,and embedding heterojunctions,cage-like CeO2 HoMSs photocatalysts were synthesized.X-ray diffraction(XRD),transmission electronic microscope(TEM),and scanning electronic microscope(SEM)were used to characterize the morphology and composition of the photocatalyst.Furthermore,the presence of oxygen vacancies existing at the surface of nanoparticle was confirmed by the high-resolution spherical aberration-corrected STEM images on the atomic scale.The introduction of CeFeO3 phase and the rich oxygen vacancies on the surface enhanced the light absorption capacity of the photocatalyst.At the same time,the heterostructure improved the efficiency of photogenerated electron-hole separation.The surface oxygen vacancies enhanced the adsorption of water molecules on the catalyst surface.Excellent photocatalytic performance of O2 evolution rate of 4.0 mmol/h/g was achieved and the activity could be maintained for 5 h.(2)The TiO2 HoMSs was used as raw material to convert TiO2 into SrTiO3 by hydrothermal process.The synthesis of perovskite-type HoMSs was realized for the first time.By adjusting the hydrothermal time,we could obtain HoMSs photocatalysts with both TiO2 phase and SrTiO3 phase with different ratios.Thanks to the unique light scattering ability of the HoMSs structure,the multi-shelled hollow structure can significantly improve the light absorption capacity of the SrTi03 photocatalytic material.The as-prepared SrTiO3-TiO2 HoMSs heterostructure could effectively separate photogenerated electrons and holes.Finally,by controlling the type of solvent in the hydrothermal process,we can also control the exposed facet to spatially separate the photoreduction and photo-oxidation active sites,thereby improving the overall water splitting performance of SrTiO3-TiO2 HoMSs.After testing by overall water splitting system,SrTiO3-TiO2 HoMSs loaded with Pt co-catalysts can stably generate H2 and O2 in stoichiometric ratio.Thanks to the stable structure of the perovskite SrTiO3,the photocatalyst maintained a good stability for more than one day.(3)In order to realize the overall water splitting under visible light,a Z-type composite photocatalyst with SrTiO3 HoMSs co-doped with La and Rh as the HER catalyst and BiVO4 nanoplates as the OER catalyst was designed and synthesized.XRD,UV-visible absorption spectra and electrochemical tests showed that the impurity energy levels of La and Rh co-doped in the SrTiO3 phase can effectively shorten the band gap and enable SrTiO3 to generate excellent response to visible light.With the introduction of HoMSs,the ability of photocatalyst to capture light is significantly enhanced.In Fe3+/Fe2+ redox shuttle solutions,the SrTiO3:La,RhHoMSs/BiVO4 photocatalysts loaded with noble metal co-catalysts exhibited better overall water splitting performance than SrTiO3:La,RhHoMSs/BiVO4 nanoparticles both under visible and simulated sunlight illumination.