【作者】 王新震；

【导师】 刘久荣；

【作者基本信息】 山东大学 ， 材料学， 2014， 博士

【摘要】 由于具有较高的孔隙率和比表面积,多孔金属氧化物半导体材料如ZnO、SnO2、 MnO等因其优异的物理化学性质在气敏传感器、锂离子电池、光催化剂及太阳能电池等领域具有广泛的应用前景。对于表面电阻控制型气敏传感器,具有多孔结构的半导体材料可以为检测气体和半导体之间的反应提供更多的接触面积,这有利于提高器件的灵敏度。同时多孔结构还可以为气体在半导体层的扩散提供通道,有利于提高响应和恢复速率。对于锂离子电池电极而言,多孔结构有助于促进活性物质与锂离子之间的反应,对活性物质体积变化起到缓冲作用,从而提高材料的电化学性能。由此可见,氧化物半导体材料的结构和比表面积对其气敏和电化学性能具有很大影响。因此,设计和合成具有一定形貌的多孔氧化物半导体材料成为目前半导体材料研究领域的热点之一。本论文合成了具有多孔结构的ZnO、SnO2和MnO半导体材料,对合成机理和相关性能进行了探讨,具体研究内容如下：(1)以乙酸锌和碳酸铵为主要原料,采用水热法制备了Zn5(CO3)2(OH)6前驱体,通过煅烧前驱体制备了三维多孔ZnO鸟巢型结构。该鸟巢型结构具有很好的分散性和均匀性,尺寸约为1-3μm,比表面积为36.4m2g-1,每一个鸟巢型结构由二维纳米片状多孔ZnO组成,二维纳米片的厚度约为20nm,其表面具有许多不规则的孔隙结构。这种多孔鸟巢型结构为半导体材料和检测气体之间反应提供更多的反应场所,此外,鸟巢型多孔结构还可以为气体在半导体的吸附脱附提供通道。对制备的鸟巢型多孔ZnO材料进行气敏性能测试,结果表明三维鸟巢型多孔ZnO对乙醇和丙酮灵敏度高于二维纳米片状结构多孔ZnO材料。(2)以四氯化锡为主要原料,无水甲醇为溶剂,聚乙烯吡咯烷酮(PVP)为表面活性剂,采用溶剂热工艺制备了前驱体,通过对前驱体热处理制备出Sn02介孔球。前驱体和分解后产物的形貌和尺寸一致,所制备的Sn02介孔球具有很好的分散性和均匀性,直径约为500-700nm,比表面积为78.2m2g-1。对Sn02介孔球的生长机理进行了分析,对比实验表明,反应体系中表面活性剂PVP对Sn02介孔球的物相和孔结构没有明显影响,但对产物的分散性和均匀性起到关键作用。对SnO2介孔球进行气敏性能测试,结果表明SnO2介孔球对CO和H2气敏性能优异,灵敏度高于商业Sn02纳米颗粒。(3)以氯金酸为原料,对SnO2介孔球进行修饰,制备了Au修饰的SnO2介孔球。样品的整体形貌和尺寸在修饰前后没有发生明显的变化,比表面积由78.2m2g-1降为33.6m2g-1。测试结果表明,Au纳米颗粒沉积在SnO2表面和孔隙中,尺寸约为5nm。对Au修饰SnO2和SnO2介孔球的气敏性能进行测试,Au纳米颗粒修饰后样品的气敏性能在灵敏度和响应速率方面都有很大的提高。一方面是由于SnO2介孔球可以为气体和氧离子之间的反应提供更多的场所,另一方面是由于Au纳米颗粒对检测气体和氧离子之间的反应起到催化作用。(4)以乙酸锰和碳酸铵为原料,以PSS为表面活性剂,Na2SO4为静电稳定剂,甘氨酸为络合剂,室温条件下采用化学沉淀的方法制备了MnCO3前驱体,通过煅烧MnCO3前驱体制备了多孔Mn2O3微米球,再以吡咯为碳源,在真空条件下对Mn2O3多孔微球进行包碳处理,合成了MnO@C多孔微球。对比实验结果表明添加剂对MnCO3前驱体的分散性和均匀性有很大影响。对所制备的Mn203和MnO@C微球进行电化学性能测试,结果显示MnO@C的循环性能明显优于Mn2O3多孔微球。对于MnO@C电极材料,循环使用60次后其可逆容量依然可以保持在625mAhg-1而Mn203样品在循环20次后即降到355mAh g-1,此外,MnO@C还表现出良好的倍率性能,在电流密度为200,400and800mA g-1时,其可逆容量分别为560,422and308mAh g-1。更多还原

【Abstract】 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.更多还原