Fabrication Of Porous Metal Oxide Semiconductors And Analysis Of Their Properties

With the advantages of high porosity and specific surface area, porous metal oxide semiconductors usually exhibit unique physical and chemical properties different from solid structures, which make them have potential applications in various areas such as photocatalysts, gas sensors, Li-ion battery electrodes, solar cells and so on. For surface-resistance controlled type gas sensors, the voids and interspaces exiting among porous semiconductors facilitate the gas adsorption and desorption, and porous structures provided large contacting surface area for electrons, oxygen and target gas molecules. In addition, the network of interconnected pores and voids in sensor films fabricated from porous semiconductor provide abundant channels for gas diffusion and mass transport. Thus, porous structures with high porosity and large surface area are critically important to obtain superior gas sensing performance. For lithium ion batteries anode material, porous structures existing in semiconductor usually facilitate the diffusion of Li+and accommodate volume change. Thus, porous metal oxide semiconductors have attracted remarkable attentions.In this work, several mesoporous n-type metal oxide semiconductors have been synthesized successfully, e.g. ZnO, SnO2and MnO. The growth mechanisms have been proposed based on experimental evidence, and the related properties have been tested.The main content of this thesis is as follows:(1) Nestlike3D ZnO porous structures with size of1.0-3.0μm have been synthesized through annealing the zinc hydroxide carbonate precursor, which was obtained by a one-pot hydrothermal process with the assistance of glycine, Na2SO4, and polyvinyl pyrrolidone (PVP). The nestlike3D ZnO structures are built of2D nanoflakes with the thickness of ca.20nm, which exhibit the nanoporous wormhole-like characteristic. The measured surface area is36.4m2g-1and the pore size is ca.3-40nm. The unique nestlike3D ZnO porous structures provided large contacting surface area for electrons, oxygen and target gas molecules, and abundant channels for gas diffusion and mass transport. Gas sensing tests showed that the nestlike3D ZnO porous structures exhibit excellent gas sensing performances such as high sensitivity and fast response and recovery speed, suggesting the potential application as advanced gas sensing materials.(2) Mesoporous tin oxide (SnO2) spheres with a size of500-700nm have been successfully synthesized through annealing a tin hydroxide precursor was obtained by a one-pot solvothermal process from a methanol system containing the surfactant polyvinyl pyrrolidone (PVP). Experimental studies revealed that polyvinyl pyrrolidone plays a pivotal role in controlling the size and agglomeration of mesoporous spheres. The mesoporous SnO2spheres with a surface area of78.2m2g-1and an average pore size of ca.10nm are monodispersed and the mesoporous structure can be maintained even after annealing at500℃for2h in air. Gas sensing tests showed that the SnO2mesoporous spheres exhibit high sensitivity to H2, enhanced response to CO and also fast response and recovery rates, suggesting potential application as an advanced gas sensing material.(3) Au decorated mesoporous SnO2spheres with a size range of400-700nm have been synthesized for gas sensing. Specifically, the mesoporous SnO2spheres were fabricated through a solvothermal route followed by a thermal treatment process. The surface area of the mesoporous SnO2spheres is78.2m2g-1and the pore size is ca.10nm. After being decorated by Au, the Au nanoparticles with sizes of ca.5nm were deposited on the surface and the inner wall of pores. Gas sensing tests showed that the Au decorated SnO2mesoporous spheres exhibited superior gas sensing performances to CO and H2in terms of high sensitivity and fast response and recovery speed, mainly attributed to the facts that the SnO2mesoporous structure provides a high reaction surface area and abundant mesochannels for the probe gas and oxygen, and Au nanoparticles act as the catalyst to improve the reaction rate of the probe gas molecules with the oxygen ion.(4) Porous manganese oxide (Mn2O3) microspheres with a narrow size distribution have been successfully synthesized by the decomposition of a MnCO3precursor, which was obtained by a facile process with the assistance of glycine, Na2SO4and poly(sodium-p-styrenesulfonate)(PSS). Experimental evidence reveals that the additive agents are beneficial to control the size and agglomeration of microspheres. The growth mechanism has been proposed on the basis of control experiments. The porous MnO microspheres with carbon coating (MnO@C) were generated after a carbonization process using pyrrole as a carbon source. Electrochemical results showed that the as-prepared MnO@C achieves a reversible capacity of625mAh g-1after60cycles at a current density of100mA g-1and capacities of560,422and308mAh g"1at current densities of200,400and800mA g-1, respectively. Compared with porous Mn2O3, the enhanced cycling and rate performances are mainly attributed to the carbon coating, which could efficiently buffer the volume change during the lithiation/delithiation and improve the electronic conductivity among MnO particles.