【作者】 刘兆婷；

【导师】 张荻； 范同祥；

【作者基本信息】 上海交通大学 ， 材料学， 2008， 博士

【摘要】 分级多孔材料在分离提纯、选择性吸附、催化剂装载、光电器件、及传感器研制等多个领域具有重要的研究和应用价值。为了获得多孔结构,材料工作者设计出了多种人工造孔的方法,这些方法一般都需要利用特定的设备,工艺比较复杂,合成的材料孔径分布单一,因而所实现的功能也较单一。遗态转化工艺是一种加工过程简单却能实现精细分级多孔材料制备的方法。自然界的生物结构通过亿万年的进化及优胜劣汰的自然法则,已经形成了高度精细的分级多孔结构与复杂功能的完美统一体,为遗态转化工艺准备了大量结构模板。本研究以木材为模板,遗传其形态和结构,合成制备木材结构分级多孔Fe₂O₃、ZnO和NiO材料。本文通过对制备机理的研究、优化了遗态转化工艺,成功制备了具有不同木材精细结构的分级多孔氧化物,研究了氧化物的多尺度孔结构,探索了分级多孔氧化物的光学及气敏功能特性,并着重研究了功能特性与木材分级多孔结构的关系。主要研究结果如下:首先,采用典型针叶材和阔叶材这两大类天然木材为模板,通过遗态转化工艺,制备得到了具有不同木材精细结构的分级多孔Fe₂O₃、ZnO和NiO,实现了对木材微观孔结构从微米到纳米尺度的复制。详细研究了遗态转化工艺的各个过程及制备机理,并优化了各项工艺参数。木材不仅为氧化物提供了分级多孔的结构模板,而且具有抑制氧化物晶粒生长的作用,使分级多孔氧化物的晶粒尺寸远小于相同温度焙烧常规氧化物。在成功制备分级多孔氧化物的基础上,利用压汞仪-电镜-氮吸附联用的分析方法,对分级多孔氧化物多尺度的孔结构进行了研究,并利用分形的概念,通过计算压汞仪曲线获得了分级多孔结构的分形维数,用以研究多孔结构的网络连通性。分级多孔氧化物通过复制木材径向细胞、纹孔和木材横向细胞等,获得了20¹00μm和0.1¹μm的分级大孔分布。遗态转化工艺参数对氧化物孔结构产生显著影响:首先,木材种类决定了氧化物大孔结构的基本分布特征,并且各种600oC焙烧分级多孔氧化物都形成了10⁵0nm左右的介孔分布;其次,使用不同的金属前驱体溶液浸渍,可以获得具有不同孔壁形貌的氧化物;最后,浸渍率和焙烧温度的提高均会改变孔壁形貌、增大孔壁厚度,并大幅度减少介孔含量。通过分形研究发现,600oC焙烧杉木结构ZnO具有最高的分形维数,并且孔隙率最高,因而具有最佳的网络连通性。对氧化物的光学性能研究发现,分级多孔氧化物的紫外-红外光吸收及紫外发光性能均优于常规氧化物。由于分级多孔结构的各尺度孔对各波长光波的驻波共振消耗作用,使分级多孔氧化物具有比常规氧化物更强的紫外-红外光吸收性能:600°C焙烧杉木结构氧化物的紫外光吸收性能分别比常规氧化物提高了5.6%²0%;600°C焙烧杉木结构氧化物的红外光吸收性能分别是常规氧化物的2.0³.9倍。由于具有较强的紫外激发波长吸收能力、较小的晶粒度以及较好的表面结晶质量等,分级多孔氧化物的光致紫外发光强度比常规氧化物提高了2.4².7倍。杉木结构ZnO的阴极射线发光光谱同时存在390nm处的紫外波段和480⁴90nm左右的蓝光可见波段,并且通过调节焙烧温度,可以控制紫外-蓝光发光强度比例,获得紫外、蓝光单色发光或紫外-蓝光双色发光ZnO。随着ZnO焙烧温度的升高,一方面,ZnO晶粒尺寸增大并且表面结晶质量变差,因此阴极射线紫外发光强度明显减弱;另一方面,ZnO的氧空位和锌空位增多、孔体积大大减少,提高了缺陷跃迁的几率,因此阴极射线蓝光发光强度明显增强。对氧化物的气敏性能研究发现,分级多孔Fe₂O₃具有优于常规Fe₂O₃的气敏性能,并且由于强烈的氧吸附能力使分级多孔α- Fe₂O₃的多子由电子变为空穴,表面产生反型层,表现为p型半导体,不同于常规α- Fe₂O₃的n型半导体。分级多孔ZnO对H2S气体具有非常优异的气体选择性,在332oC的元件工作温度下,600oC焙烧杉木结构ZnO对H2S的敏感度高达200,对H2S的选择性系数达到8.5¹98.0,H2S的响应和恢复时间分别仅为4s和12s。而常规ZnO对H2S的敏感度最高只有35左右,响应和恢复时间也更长（6s和15s）。更多还原

【Abstract】 Hierarchical porous materials have displayed important researching and application values at the fields of separation and purification, selective adsorption, optical function, and sensor design etc. Some preparation methods have been designed to fabricate porous materials. But these traditional methods have to use specific equipments and complicated techniques, and obtained porous materials have single pore size distributions with single functions. The morph-genetic transformation technology is a simple processing technology to fabricate refined hierarchical porous materials using organisms as template. The organisms in nature are the perfect unities of highly delicate structures and effectively complex functions through millions of years of evolution and natural survival law, which prepare plentiful structural templates for morph-genetic hierarchical porous materials. In the present work, wood was used as template to fabricate hierarchical porous Fe₂O₃, ZnO and NiO to inherit wood’s morphology and structure. The synthetic mechanism was studied to optimize the parameters of morph-genetic technology, and the hierarchical porous oxides with wood structure were fabricated successfully. The porous structures in multi-scales, the optical properties and the gas sensing properties of hierarchical porous oxides were researched in detail. The contents and results are summarized as follows:1. The hierarchical porous Fe₂O₃, NiO, and ZnO have been synthesized successfully using wood templates to retain the wood’s porous structures fromμm scale to nm scale. The parameters of morph-genetic technology have been optimized on the basis of synthetic mechanism research. Wood template not only provided the structural template for oxides, but also restrained the grain growth of oxides to cause much smaller grains of hierarchical porous oxides than ordinary oxides. 2. The combination of mercury intrusion / electron microscopy / nitrogen adsorption measurement has been used in the present work to characterize hierarchical porous structures in multi-scales. The fractal dimensions of oxides were calculated from mercury intrusion data to research the network connectivity of porous structures. Oxides obtained hierarchical macroporous structures with pore size distributions of 20¹00μm and 0.1¹μm through duplicating wood’s radial cells, pits and cell walls etc. It’s proved that the parameters of morph-genetic technology have obvious influences on porous structures of oxides. Firstly, wood template type decided the basic characteristics of oxides’structures. But all of hierarchical porous oxides calcined at 600oC have mesopores distributed at 10⁵0nm. Secondly, oxides with different morphologies of pore walls can be obtained through infiltrating different precursor solutions. Thirdly, increases of infiltration rate and calcination temperature could change the morphologies of pore walls, increase pore wall thickness and decrease the quantities of mesopores. Fractal research discovered that Fir-templated ZnO calcined at 600oC had both the highest fractal dimension and porosity to prove its best network connectivity.3. Hierarchical porous oxides have much better UV-IR absorption and luminescence abilities than ordinary oxides. Due to the standing wave resonance absorption ability of pores in various scales, hierarchical porous oxides have much better UV-IR absorption properties. UV absorption abilities of Fir-templated oxides calcined at 600oC have been improved about 5.6%²0% compared with ordinary oxides. IR absorption abilities of Fir-templated oxides calcined at 600oC were 2.0³.9 times higher than ordinary oxides. Photoluminescence abilities of hierarchical porous oxides were 2.4².7 times higher than ordinary oxides due to higher UV excitation wave absorption ability, smaller grains and better surface crystal quality.4. Hierarchical porous ZnO measured with cathodoluminescence was detected both UV emission at 390nm and blue visible emission at 480⁴90nm. Both emissions strongly depended on the calcination temperature of ZnO. On one hand, with the increase of calcination temperature, larger grains and worse crystal quality of ZnO decreased UV emission intensity. On the other hand, with the increase of calcination temperature, more defects including oxygen vacancies and zinc vacancies and smaller pore volume increased the defect transition probability and enhanced the blue emission intensity as the result.5. Hierarchical porous Fe₂O₃ has better gas sensing ability than ordinary Fe₂O₃. Strong oxygen absorption ability made hierarchical porous Fe₂O₃ produce surface inversion layer and display p-type semiconductor, different from n-type of ordinaryα-Fe₂O₃. Moreover, the higher free carrier concentration of hierarchical porous p-type Fe₂O₃ led to better gas sensing properties than ordinary n-type Fe₂O₃.6. Hierarchical porous ZnO showed excellent gas selectivity to H2S. At working temperature of 332oC, Fir-templated ZnO calcined at 600oC has high H2S sensitivity of about 200, high selectivity coefficient of H2S over other gases of 8.5¹98.0, and short response and recovery time of 4s and 12s. In contrast, ordinary ZnO has H2S sensitivity of only 35 with longer response and recovery time （6s and 15s）.更多还原