Preparation of Nanostructured Membranes by Reactive Depositions from Supercritical Fluids

Watkins - 9811088功能性纳米结构金属复合膜的开发将对气体的分离、净化和回收以及富氧燃烧、受控部分氧化和平衡限制脱氢反应的新型膜反应器应用产生重大经济影响。 尽管到目前为止已经取得了进展，但还没有实现对载体内的存款微观结构、组成和分布的精确控制。 多孔无机载体/金属复合材料的挑战仍然是开发用于在规定深度和厚度的内部孔内控制纳米结构金属和金属合金的渗透和沉积的方法。 由于这些工艺的限制，包括化学气相沉积、金属溅射和无电镀覆的当前技术无法实现这些结构，这些工艺不允许优化存款微观结构或组成。 聚合物/金属复合材料膜受到差的困扰，为了纠正这种缺陷，需要导致梯度界面的方法。 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）概念的加工策略。 CFD是金属沉积的一种形式，涉及可溶性有机金属化合物在超临界二氧化碳溶液中的化学还原。 该过程的关键是溶剂的物理化学性质，其位于液体和气体的物理化学性质的中间。 溶液中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）溶液不存在表面张力和低粘度，非常适合于在多孔环境中递送相对高浓度的有机金属前体。 通过引入还原剂来触发沉积以产生金属沉积物。 该反应方案可用于通过精确调节可溶性前体的化学计量来直接控制成核和生长动力学来规定存款组成和微结构。 由于高前体浓度和类似于气体的SCF溶液的有利传输特性，在很大程度上消除了传质限制。 可以利用聚合物基底对SCF/有机金属溶液的渗透性来生产具有粘附性、梯度聚合物/金属界面和金属夹层的复合膜。

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.