Gas Sensing And Photocatalytic Properties Of Hydrogenation Enhanced TiO 2 {001} And MnO{111} Crystal Planes And Their Mechanisms

TiO₂ nanosheets with exposed {001} facets and MnO octahedron with exposed{111} facets were obtained by solvothermal method,then annealed in H2 atmosphere to obtain hydrogenated TiO₂ nanosheets and MnO octahedron.The morphology and structure of those nanostructures were characterized by using field emission scanning electron microscopy?FESEM?,desktop scanning electron microscopy?SEM?,X-ray diffraction?XRD?,field transmission electron microscopy?FETEM?,X-ray photoelectron spectra?XPS?and Infrared spectrometer?IR?.The properties of gas sensing and photocatalytic reduction CO₂ by hydrogenated TiO₂ nanosheets and the photocatalytic degradation of organic dyes of hydrogenated MnO octahedron were studied.The relationship between their properties and structures was discussed.?1?Through heating Ti?C4H9O?4-HF aqueous mixtures at 200 ? for 24 h,TiO₂ nanosheets with exposed {001} facets were synthesized.Then the TiO₂ nanosheets were hydrogenated at different temperature for 24 h to obtain hydrogenated TiO₂ nanosheets.It was found that the hydrogenated TiO₂ nanosheets show significantly higher response towards ethanol,acetone,triethylamine or formaldehyde than the samples without hydrogenation,and the response further increases with an increase on the hydrogenation temperature.The excellent sensing performances are ascribed to an increase on the density of unsaturated Ti5c atoms on the TiO₂ {001} surface resulted from the hydrogenation process.The unsaturated Ti5c atoms are considered to serve as sensing reaction active sites.?2?Hydrogenated TiO₂ nanosheets were obtained by hydrogenating TiO₂ nanosheets with exposed {001} facets at 600 ? for different time.Their photocatalytic activities on reducting CO₂ were studied.It was found that the hydrogenated TiO₂ nanosheets had better photocatalytic activity on reducting CO₂ than unhydrogenated TiO₂ nanosheets,and the photocatalytic activity further increaseed with an increase on the hydrogenation time.And the photocatalytic activity further increaseed by photoselsctive loading Ag nanoparticals on unhydrogenated TiO₂ nanosheets.Atomic structure of TiO₂ {001} high active facets was calculated by using periodic density functional theory?DFT?,in order to investigate the relationship between the crystal structure and properties.A charge separation model between TiO₂ polar {001} facets was proposed.The enhaced photocatalytic.mechanism is described in detail.?3?MnO octahedrons with exposed {111} facets were obtained by heating Mn?Ac?2-C2H5OH aqueous solution at 200 0C for 48 h.Then the MnO octahedrons were annealed in H2 atmosphere at 600 ? for different time to obtain hydrogenated MnO octahedrons.Their photocatalytic activities on degradation of malachite green were studied.It was found that hydrogenated MnO octahedrons showed superior photoreactivity on degradation of organic dyes,compared with unhydrogenated MnO octahedrons.And the photocatalytic activity further increased with an increase on the hydrogenation time.In order to investigate the relationship between the crystal structure and properties,the atomic structure of MnO polar {111} facets was researched.A charge separation modle is proposed.This model can well explain the mechanism of the enhanced photocatalytic activity of hydrogenated MnO octahedrons.