Preparation of Nanostructured Membranes by Reactive Depositions from Supercritical Fluids

功能化纳米结构金属复合膜的发展将对气体的分离、净化和回收，以及用于富氧燃烧、可控部分氧化和平衡有限脱氢反应的新型膜反应器的应用产生重大的经济影响。尽管迄今为止取得了一些进展，但尚未实现对支架内沉积物微观结构、成分和分布的精确控制。多孔无机载体/金属复合材料面临的挑战仍然是如何在规定深度和厚度的内部孔隙中控制纳米结构金属和金属合金的渗透和沉积。目前的技术，包括化学气相沉积、金属溅射和化学镀，都无法实现这些结构，因为这些工艺的限制不允许优化沉积的微观结构或成分。聚合物/金属复合膜性能差，为了纠正这一缺陷，需要采用导致梯度界面的工艺。PI计划整合材料合成、表征和多尺度模拟，以开发基于化学流体沉积（CFD）概念的处理策略。CFD是金属沉积的一种形式，它涉及在超临界二氧化碳溶液中对可溶性有机金属化合物的化学还原。这个过程的关键是溶剂的物理化学性质，它位于液体和气体的中间。溶液的运输和还原提供了低工艺温度，高试剂浓度，并消除了与气相技术相关的前体挥发性要求。超临界流体（SCF）溶液没有表面张力，粘度低，非常适合在多孔环境中输送相对高浓度的有机金属前驱体。沉积是通过引入还原剂来产生金属沉积物而引发的。该反应方案可以通过精确调整可溶前驱体的化学计量来直接控制成核和生长动力学，从而指示沉积物的组成和微观结构。由于高前驱体浓度和SCF溶液类似于气体的良好输运性质，在很大程度上消除了质量输运的限制。聚合物基质对SCF/有机金属溶液的渗透性可以用于生产具有粘附、梯度聚合物/金属界面和金属中间层的复合膜。

Watkins - 9811088 The development of functional, nanostructured metal composite membranes will have a substantial economic impact on the separation, purification and recovery of gases as well as novel membrane reactor applications for oxygen-enriched combustion, controlled partial oxidation and equilibrium limited dehydrogenation reactions. Despite progress that has been achieved to date, precise control of deposit microstructure, composition and distribution within the support has not been realized. The challenge for porous-inorganic support/metal composites remains the development of methodologies for the controlled infiltration and deposition of nanostructured metal and metal alloys within interior pores at a prescribed depth and thickness. These architectures are inaccessible by current techniques including chemical vapor deposition, metal sputtering and electroless plating due to constraints of these processes that do not allow for optimization of deposit microstructure or composition. Polymer/metal composites membranes are plagued by poor and to rectify this deficiency, processes leading to gradient interfaces are required. The PI's plan to integrate materials synthesis, characterization and multi-scale simulations for the development of a processing strategy based on the concept of chemical fluid deposition (CFD). CFD is a form of metal deposition that involves the chemical reduction of soluble organometallic compounds in supercritical carbon dioxide solution. The key to the process is physicochemical properties of the solvent which lie intermediate to those of liquids and gases. Transport and reduction in solution offers low process temperatures, high reagent concentrations and eliminates precursor volatility requirements associated with vapor phase techniques. The absence of surface tension and low viscosity of supercritical fluid (SCF) solutions are well suited to the delivery of relatively high concentrations of organometallic precursors within porous environments. Deposi tion is triggered by the introduction of a reducing agent to produce metal deposits. This reaction scheme can be used to dictate deposit composition and microstructure via direct control of nucleation and growth kinetics by precise adjustments in stoichiometry of the soluble precursors. Mass-transport limitations are largely eliminated due to high precursor concentration and favorable transport properties of the SCF solution which is similar to those of a gas. The permeability of polymer substrates to SCF/organometallic solutions can be exploited to produce composite membranes with adherent, gradient polymer/metal interfaces and metal interlayers.