CAREER: Facilitated Ion Transport in Nanostructured Titanosilicates

显示量子尺寸效应的半导体纳米线被预测具有革命性的热电传输特性，可能导致固态冷却设备的效率高于蒸汽压缩制冷技术。然而，为了实现这样的器件，必须合成直径远小于其热德布罗意布罗意波长的连续线，以达到量子限制状态。正在研究的一种合成这种纳米线的技术是模板辅助方法，其中有序的纳米多孔材料如微孔沸石、中孔二氧化硅（即SBA-15、MCM-41）和阳极氧化铝用作被动主体以模板化线的直径和形式。然而，具有足够小直径的纳米线尚未实现，并且在最小孔材料中的尝试由于质量传输限制而失败。有人提出，这种限制可以克服通过使用电化学生长技术与一类新的钛硅酸盐的纳米结构的框架，促进阳离子传输。这种新的钛硅酸盐，命名为ETS，首次报道于1989年。已经鉴定了几种骨架拓扑结构，其具有从略低于0.4 nm到0.8 nm的微孔。特别是一种结构（Sr-ETS-4）最近已经显示出对于N2/CH 4、N2/O2和Ar/O2分离具有非凡的气体分离性能。所有ETS结构所独有的关键特征是存在平行于微孔的连续二氧化钛链（-O-Ti-O-Ti-）。链中的每个钛单元携带两个负电荷单元，并且必须由链中的阳离子平衡。这种独特的纳米结构从根本上不同于经典的沸石，并且被假设为通过充当绳索将阳离子拉过框架来促进阳离子通过结构的运输。通过还原孔一端的骨架阳离子，可以电化学地“拉动”该“绳”。这在结构中产生了电荷不平衡状态，并诱导了一系列相关的阳离子跳跃，将额外的阳离子拉入孔相对端的骨架中。在这个过程中，阴极穿过框架生长，形成模拟孔的纳米线阵列。这一现象将在一个拟议的研究机构进行调查，重点是：合成高品质的ETS-10，ETS-4和相关结构的单晶体。了解这些独特的纳米结构材料的基本离子传输通过使用复阻抗谱检查IA，IIA族，金，铅，铋和碲阳离子的离子电导率，活化能和弛豫频率。电化学生长的亚纳米线在ETS框架的孔热电器件的发展。这项多学科研究是在工程，化学，物理和材料科学的十字路口，是一个综合教育和研究计划的一部分，旨在：（1）在多学科环境中培养和指导研究生，使其成为具有发现和发展纳米技术领域新思想的背景和技能的创造性独立研究人员，（2）积极鼓励和支持本科生参与研究，（3）开发和实施一种新的教学方法，利用学生对基于网络的内容的作者身份，以促进终身学习，并在纳米结构材料化学新课程的背景下吸引学生参与。

AbstractCTS-0134255Hillhouse, Hugh W.Purdue UnivesitySemiconductor nanowires that exhibit quantum-size effects are predicted to have revolutionary thermoelectric transport properties, potentially resulting in solid-state cooling devices with efficiencies greater than vapor-compression refrigeration technology. However, in order to realize such devices, continuous wires must be synthesized with diameters much smaller than their thermal de Broglie wavelength to reach the quantum confinement regime. One technique being investigated to synthesize such nanowires is a template assisted approach in which ordered nanoporous materials such as microporous zeolites, mesoporous silica (i.e. SBA-15, MCM-41), and anodic alumina are used as passive hosts to template the diameter and form of the wire. However, nanowires with a sufficiently small diameter have not yet been realized, and in the smallest pore materials attempts have failed due to mass transport limitations. It is proposed that this limitation can be overcome by using electrochemical growth techniques with a new class of titanosilicate whose nanostructured framework facilitates cation transport. This new class of titanosilicate, designated as ETS, was first reported in 1989. Several framework topologies have been identified that have micropores ranging from just under 0.4 nm up to 0.8 nm. One structure in particular (Sr-ETS-4) has recently been shown to be possess extraordinary gas separation properties for N2/CH4, N2/O2, and Ar/O2 separations. A key feature that is unique to all of the ETS structures is the presence of continuous titania chains (-O-Ti-O-Ti-) that run parallel to the micropores. Each titanium unit in the chain carries two units of negative charge and must be balanced by cations in the micropore. This unique nanostructure is fundamentally different from classical zeolites, and is hypothesized to facilitate cation transport though the structure by acting as a rope to pull cations through the framework. This 'rope' may be 'pulled' electrochemically by reducing a framework cation at one end of the pore. This creates a state of charge imbalance in the structure and induces a series of correlated cation hops that pull an additional cation into the framework at the opposite end of the pore. In the process, the cathode grows through the framework forming an array of nanowires that mimic the pores. This phenomenon will be investigated in a body of proposed research that focuses on:Synthesizing high quality single crystals of ETS-10, ETS-4, and related structures.Understanding the fundamentals ion transport in these unique nanostructured materials by using complex impedance spectroscopy to examine ion conductivities, activation energies, and relaxation frequencies for Group IA, Group IIA, gold, lead, bismuth, and tellurium cations.Electrochemical growth of sub-nanometer wires in the pores of ETS frameworks for the development of thermoelectric devices. This multidisciplinary research is at the cross roads of engineering, chemistry, physics, and materials science, and is one part of an integrated education and research plan that seeks to: (1) train and mentor graduate students in a multidisciplinary environment to become creative independent researchers who have the background and skills to discover and develop new ideas in the area of nanotechnology, (2) actively encourage and support undergraduate research participation, and (3) develop and implement a new teaching approach that utilizes student authorship of web based content to facilitate lifelong learning and engage student participation in the context of a new course on nanostructured materials chemistry.