Synthesis, Modification And Gas Sensing Investigation Of Metal Oxides

The design of simple, economic, efficient, environmental/user-friendly synthesisapproaches and exploit novel micro/nanomaterials are meaningful for thedevelopment of micro/nanotechnology. This dissertation concentrates on themodification of the structure and composition of semiconducting metal oxidesmicro/nanomaterials to exploit novel gas sensing materials with high performance.The structure modification mainly focuses on the fabrication of micro/nanomaterialswith different structures such as one-dimensional （1D）,3D hierarchical, porous, andcore-shell architectures, and micro/nanocrystals with exposed high-indexed facets.The composition adjustment is realized by metal oxides-based micro/nano hybridswith complex morphology, such as noble metal （NM） nanoparticles （NPs）functionalized metal oxides and multiple metal oxides hybrids. The main researchcontents are summarized as follows:1. Several porous materials have been fabricated via different routes, and theirstructure or composition have been modified to improve the gas sensingperformance:（1） Porous α-Fe₂O₃has been obtained via a precursor-calcination route and utilizedas support for the catalytic Au NPs. The Au/porous α-Fe₂O₃has been firstinvestigated for gas sensing application. The porous structure of α-Fe₂O₃andthe catalytic activity of Au NPs endowed the Au/porous α-Fe₂O₃with excellentgas sensing performance, such as high sensitivity and good reproducibility.（2） Ni-SnO₂hollow spheres were synthesized by a carbon spheres-templatedstrategy. The p-n junction between p-type NiO and n-type SnO₂as well as thehigh accessibility of3D hollow spheres provides the Ni-SnO₂hollow sphereswith good selectivity to high alcohols and high response.（3） The brochantite tabular microspindles were synthesized by hydrothermalmethod and investigated by changing the concentration, hydrothermal duration,and surfactants. Worm-like CuO microstructures were prepared by thecalcination of precursor, and exhibited good gas sensing performance to ethanoland methanol, with better performance to ethanol.2. ZnO3D hierarchically porous superstructures, with controlled morphology anddimensionality as well as large surface area of193.7m2/g, were first synthesizedvia an amino acid-assisted biomimetic hydrothermal method combined with subsequent calcination of the3D hierarchically basic zinc carbonate precursor, theformation of which has been systematically investigated. The ZnO3Dhierarchically porous superstructures were employed as support for Au NPs toconstruct hybrids. Due to the high accessibility of porous structures and catalyticactivity of Au NPs, the Au/ZnO3D hierarchically porous superstructuresexhibited excellent sensor properties with higher sensitivity and fast response.This strategy provides a new pathway to develop advanced nanomaterials forimproved applications.3. Au（Pt）/ZnO submicrorods and Pt/WO3nanorods were fabricated via a facilelysine assisted one-pot strategy for the assembly of NM NPs onto varioussupports using a non-toxic lysine as the capping agent. Small NM NPs （Au/Pt）capped by lysine are formed and simultaneously anchored onto the surface ofsupport. No pre-functionalization of the support/NM NPs is needed, hencesimplifying the synthesis and reducing the fabrication cost. Due to the special1Dstructure, the promotion and spillover effect of the catalytic NM NPs, as well asthe improved Schottky barriers and electron interaction at the interface of metaland semiconductor, Au（Pt）/ZnO submicrorods and Pt/WO3nanorods haveexhibited superior gas sensing performance.4. Novel α-Fe₂O₃@SnO₂/Au ternary core–shell hetero-nanospindles with α-Fe₂O₃nanospindles as cores and Au-decorated SnO₂coatings as shells, have beensuccessfully fabricated via two steps of hydrothermal and subsequent decorationof Au NPs. Due to the special core–shell architectures and multiple compositions,the α-Fe₂O₃@SnO₂/Au hetrostructures demonstrated enhanced gas sensingperformances with higher sensitivity and faster response-recovery than pristineα-Fe₂O₃nanospindles. This proposes an example for the design of complexnanostructures with controlled structure and compositions for both theoreticalinvestigation and practical application.5. Single α-Fe₂O₃submicron crystals bounded by six {104} high-index facets（denoted as: α-Fe₂O₃/{104}） were prepared by a simple formamide-assistedhydrothermal method, and the formation mechanism has been systematicallystudied. The α-Fe₂O₃crystals are formed via an aggregation-phasetransformation-recrystallization mechanism in which formamide has played acrucial role. As the special atomic arrangement of {104} plane with large amountof unsaturated coordination of Fe and oxygen vacancies could promote theadsorption of oxygen species, the unique α-Fe₂O₃/{104} are highly advantageousfor high performance gas sensors. This work sheds some new light towardhigh-index faceted crystals for high performance functional device applications.