Photoexcited Carriers Spatial Seperation Of Heterogeneous Micro-nanomaterials For Photocatalytic Reduction Of CO₂

Photocatalytic conversion of CO2 into renewable hydrocarbons using solar energy is perhaps one of the potential solutions to both global warming and energy shortage concerns. Generally, in the presence of water vapor, CO2 could be photoreduced into renewable hydrocarbons using the appropriate bandgap semiconductor as a photocatalyst with narrow bandgap could absorb more sunlight to generated photoexcited electron and hole, but photocatalytic reaction demand sufficient redox ability for photocatalysts. The recombination of photoexcited carriers is one of the most important factors restricting the photocatalytic reaction. Semicontors, meeting both thermodynamic and dynamic requirements and having strong ability of photoexcited-carriers, is the starting point of the thesis. In this dissertation, Fe2V4O13 nanoribbons was synthesized by simple hydrothermal reaction and Fe2V4O13-based nanocomposite was fabricated via introducing materials such as graphene, CdS particles. An unprecedented, crystal facet-based CeO2 homoj unction consisting of hexahedron prismanchored octahedron with exposed prism surface of{100} facets and octahedron surface of{111} facets was fabricated through solution-based crystallographic-oriented epitaxial growth. Monoclinic phase Bi6Mo2O15 sub-microwires consisting of MoO4 tetrahedra have been successfully synthesized by a molten salt method. The photocatalytic activity and mechanism of CO2 reduction of Fe2V4O13 nanoribbons, Fe2V4O13-based nanocomposite, crystal facet-based CeO2 homojunction and BiMo2O15 microwires were studied. The details are summarized as follows:(1) One-dimensional Fe2V4O13 nanoribbons of 10-20 mm long and 20-30 nm thick growing directly on a stainless-steel mesh (SSM) have been successfully obtained by a simple and facile hydrothermal reaction without any templates or surfactants. The SSM served as not only the Fe source but also the substrate for the deposition of vanadium and oxide elements. The Fe2V4O13 nanoribbon as an easily reused photocatalyst shows great potential for the efficient photoreduction of CO2 into renewable hydrocarbon fuel (CH4) and for the removal of organics from air under visible-light illumination.(2)An all-solid-state Z-scheme system array consisting of an Fe2V4O13 nanoribbon (NR)/reduced graphene oxide (RGO)/CdS nanoparticle grown on the stainless-steel mesh was rationally designed for photoconversion of gaseous CO2 into renewable hydrocarbon fuels (methane:CH4).(3)An unprecedented, crystal facet-based CeO2 homojunction consisting of hexahedron prism-anchored octahedron with exposed prim surface of{100} facets and octahedron surface of{111} facets was fabricated through solution-based crystallographic-oriented epitaxial growth. The photocatalysis experiment reveals that growth of the prism arm on octahedron allows to activate inert CeO2 octahedron for an increase in phototocatalytic reduction of CO2 into methane. The pronounced photocatalytic performance is attributed to a synergistic effect of the following three factors:(1) Band alignment of the{100} and{111} drives electrons and holes to octahedron and prism surfaces, respectively, aiming to reach the most stable energy configuration and leading to a spatial charge separation for long duration; (2) Crystallographic-oriented epitaxial growth of the CeO2 hexahedron prism arm on the octahedron verified by the interfacial lattice fringe provides convenient and fast channels for the photogenerated carrier transportation between two units of homojuntion; (3) Different effective mass of electrons and holes on{100} and{111} faces leads to high charge carrier mobility, more facilitating the charge separation. The proposed facet-based homoj unction in this work may provide a new concept for the efficient separation and fast transfer of photoinduced charge carriers, and enhancement of the photocatalytic performance.(4)Monoclinic phase Bi6Mo2O15 sub-micro wires consisting of MoO4 tetrahedra have been successfully synthesized by a molten salt method. The wide-bandgap sub-microwire exhibits photocatalytic activity toward the photoreduction of CO2 into CH4. The existence of surface oxide vacancies enhanced the photocatalytic activity, which can be easily tuned via different post-heating temperatures, through capturing photo-generated electrons at the surface, thus being beneficial for the separation of electrons and holes and prolonging the lifetime of the electrons.