Modeling of Adsorption in Templated Porous Materials

具有可控孔结构的材料作为吸附剂、催化剂和传感器是非常有用的。一个挑战是设计一个适合特定应用的孔结构。一种有前途的新方法是在可去除模板的存在下通过单体单元的凝胶化形成材料。 一旦凝胶化完成，模板被移除，并且理论上，最终的孔结构将模拟模板的结构。 通过选择正确的模板，原则上可以创建具有特定于给定目的的孔结构的材料。模板材料在吸附剂、传感器、气体分离膜和分子识别剂等方面具有巨大的应用潜力，但目前模板材料研究的一个局限性是缺乏对模板形貌和浓度对材料孔结构以及随后的分子吸附行为的普遍、定量的了解。所需要的是一个理论上的描述足够普遍，使模板策略可以智能地制定不同的化学成分的新材料。目前可用的多孔材料模型是次优的，因为它们没有考虑模板的影响。 模板多孔材料通常是在模板分子存在下通过凝胶化形成的，因此，本文试图建立一个理论框架来模拟模板多孔材料的结构及其吸附分子的行为。 老化和干燥后，通过热处理或其他处理将模板从固体中除去，留下它们的分子尺度印记。这个过程启发了我们提出的模型。我们的模型开始于一个二进制系统的粒子代表矩阵和模板组件。平衡后，颗粒被淬灭，即在空间中冻结。这模拟了实验凝胶化步骤。接下来，去除模板颗粒。剩余的基质颗粒是模型多孔材料。向这些不移动的基质颗粒中加入移动的（模型）吸附质分子，并研究它们的性质。 本计画首先建立分子电脑模拟与积分方程技术来探讨此模式系统。基质、模板和吸附物被认为是简单形状的颗粒（球体、球柱和/或球体的链接链），其通过势函数（诸如硬颗粒、Lennard-Jones和连续体Lennard-Jones）相互作用。 将使用大正则Monte Carlo和Ornstein-Zernike积分方程技术计算吸附等温线、相图和吸附热。巨正则分子动力学将用于计算通过模板材料的渗透速率。主要目标是了解模板的大小、形状和浓度对吸附相行为的影响。接下来，将努力模拟实验数据可用的特定系统：吸附在有机模板硅胶中的小分子[2，3]。基质颗粒的密度将作为一个单一的可调参数;我们打算将此参数与合成条件（干燥速率，模板去除温度等）。这里的主要目标是在我们的模型和实验之间建立联系。 最后，将建立一个网页，其他研究人员可以在其中获得我们的计算机程序，这些程序专门用于将此处开发的模型应用于实验数据。这项工作的意义在于建立和传播一个通用的理论框架-捕捉无序，孔隙空间连通性和模板去除的基本特征-用于模拟模板化多孔材料中的吸附现象。

ABSTRACTCTS-9876599VanTassel, P. RWayne State U.Materials with controllable pore structures are extremely useful as adsorbents catalysts, and sensors. A challenge is to engineer a pore architecture tailored to a specific application. A promising new approach is to form the material via a gelation of monomer units in the presence of a removable template. Once the gelation is complete, the template is removed and, in theory, the final pore structure will mimic the structure of the template. By selecting the right template, one can in principle create a material with a pore architecture specific for a given purpose. Templated materials have tremendous potential as adsorbents, sensors, gas separation membranes, and molecular recognition agents.A current limitation to developing template approaches is the lack of a universal, quantitative understanding of the influence of template morphology and concentration on the material's pore structure and, subsequently, on the behavior of molecules adsorbed in the material. What is needed is a theoretical description sufficiently general so that template strategies may be intelligently formulated for novel materials of diverse chemical compositions. Currently available models of porous materials are suboptimal because they do not accountexplicitly for the influence of the template. It is proposed to establish a theoretical framework through which the structure of templated porous materials and the behavior of their adsorbedmolecules may be modeled.Templated porous materials are usually formed by gelation in the presence of template molecules. Following aging and drying, the templates are removed from the solid by thermal or other treatment, leaving behind their molecular scale imprints. This process inspires the model that we propose. Our model begins with a binary system of particles representing matrix and template components. Following equilibration, the particles are quenched, that is, frozen in space. This mimics the experimental gelation step. Next, the template particles are removed. The remaining matrix particles are the model porous material. To these immobile matrix particles mobile (model) adsorbate molecules are added and their properties are investigated. The project begins by establishing molecular computer simulation and integral equation techniques to investigate this model system. Matrix, template, and adsorbate are considered to be simply shaped particles (spheres, spherocylinders, and/or linked chains of spheres) that interact via potential functions such as hard particle, Lennard-Jones, and continuum Lennard- Jones. Grand canonical Monte Carlo and Ornstein-Zernike integral equation techniques will be used to calculate the adsorption isotherm, phase diagram, and heat of adsorption. Grand canonical molecular dynamics will be used to calculate the rate of permeation through a templated material. The principal goal is to understand the effect that template size, shape, and concentration have on the behavior of adsorbed phase.Next, efforts are to be directed toward modeling specific systems for which experimental data are available: small molecules adsorbed in organic templated silica gels [2,3]. The density of matrix particles will serve as a single adjustable parameter; we intend to relate this parameter to the synthesis conditions (drying rate, temperature of template removal, etc.). The principal goal here is to establish a connection between our model and experiment. Finally, a web page is to be established where our computer programs, written specifically to apply the models developed here to experimental data, can be obtained by other researchers. The significance of this work is in establishing and disseminating a universal theoretical framework - capturing the essential features of disorder, pore space connectivity, and template removal - for modeling adsorption phenomena in templated porous materials.