Tailored Molecular Transport In Low-Dimensional Hybrid Materials From 1D Nanocrystals And 2D Nanosheets

在精细化学、制药研究和其他复杂的纯化过程中，许多重要的应用依赖于有效地将分子从溶液和悬浮液中分离出来的分离过程。目前的无定形聚合物或纸基薄膜具有随机的形态，孔隙率控制不佳，并且缺乏机械强度。使用这些材料平衡膜的渗透和选择性性能也是具有挑战性的。这些综合因素限制了无定形聚合物和纸基薄膜在高压应用中快速有效地进行分子分离的用途。具有不同孔径大小、形状和表面化学成分的多孔聚合物材料的随机形态使得很难合理地设计分子传输特性。因此，本项目将研究具有长程有序低维结构元素的膜的分子传输现象和材料性质，以增进基础知识，并开发使用纤维和二维材料的新型膜。此外，该研究项目将为来自不同背景的研究生和本科生提供跨学科研究培训机会，帮助他们为在工业领域的职业生涯做好准备。佐治亚理工学院的本科生也将受益于研究人员的软纳米材料课程开发工作。该项目的最终研究目标是了解具有有序纳米通道和纳米片以及快速和对映选择性的高度组织的一维和二维(1D和2D)纳米结构中定向、空间和尺度相关的分子传输的原理。这种介质有可能用于从纳滤和超滤过渡到中间区域内的离子、有机分子甚至手性物种的膜分离。这项研究将探索材料的有组织的孔隙率、孔形状和取向(通道状或狭缝状)、窄的尺寸分布以及潜在的手性偏置相互作用等因素，以调整分子传输和膜分离性能。第一个研究目标是合成纳米晶和纳米片，并对材料的表面进行修饰，以调整它们的组织、表面化学和结构间的相互作用，实现具有可控孔组织的有序形态。第二个目标是制备具有有序螺旋和堆积结构的坚固的超薄膜。这些膜将使用化学修饰的针状(1D)纤维素纳米晶和2D碳化钛纳米片来制备，这些纳米片具有手性向列结构，并具有定制的孔洞形状和取向、节距长度和局部手性。将使用一组常见的溶液染料来评估其性能。第三个目标是表征有序低维材料的内部纳米级组织、孔隙率、取向和机械性能。这些信息可用于通过缩短的曲折度、定向通道和手性偏置来控制局部和全球分子-纳米尺度的传输，从而用于研究选定的金属离子、染料和手性分子的传输。该项目将对具有远程有序纳米晶体和纳米片状组件的有序多相膜中的复杂传输现象有深刻的基本理解；这些知识对于设计具有高渗透率、选择性和截留率的机械坚固的分子分离膜是必不可少的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Many important applications in fine chemistry, pharmaceutical research, and other sophisticated purification processes rely on separation processes that effectively separate molecules from solutions and suspension. Current amorphous polymer- or paper-based membranes have random morphologies, poorly controlled porosities, and lack mechanical strength. Balancing the membrane’s permeance and selectivity performance using these materials is also challenging. These combined factors limit the utility of amorphous polymer- and paper-based membranes for fast and effective molecular separations in high-pressure applications. The random morphology of porous polymeric materials with varied pore sizes, shapes, and surface chemistries makes it difficult to rationally design molecular transport properties. Therefore, this project will examine the molecular transport phenomena and materials properties of membranes with long-range ordered low-dimensional structural elements to advance fundamental knowledge and develop new membranes using fibrous and two-dimensional materials. Additionally, this research project will provide graduate and undergraduate students from diverse backgrounds with interdisciplinary research training opportunities, helping prepare them for careers in industry. Undergraduate students at Georgia Tech will also benefit from the investigator’s soft nanomaterials curriculum development efforts.The ultimate research goal of this project is to understand the principles of directional, spatial, and scale-dependent molecular transport in highly organized one- and two-dimensional (1D and 2D) nanostructures with ordered nanochannels and nanosheets as well as fast and enantiotropic selectivity. Such media can potentially be used in membrane-based separations of ions, organic molecules, and even chiral species within the intermediate region at the transition from the nanofiltration and ultrafiltration regimes. The research will explore factors such as the materials’ organized porosity, pore shapes and orientation (channel-like or slit-like), narrow size distribution, and potential chiral-biased interactions to tailor molecular transport and membrane separation performance. The first research objective is synthesizing nanocrystals and nanosheets and modifying the materials’ surfaces to tailor their organization, surface chemistries, and inter-structural interactions, achieving ordered morphologies with controlled pore organization. The second objective is fabricating robust ultrathin membranes with organized helicoidal and stacked structures. The membranes will be fabricated using chemically modified needle-like (1D) cellulose nanocrystals and 2D titanium carbide nanosheets with chiral nematic organization and tailored porosity shape and orientation, pitch length, and local chirality. The performance will be assessed using a set of common dyes in solution. The third objective is to characterize the organized low-dimensional materials' internal nanoscale organization, porosity, orientation, and mechanical performance. This information can be applied to control local and global molecular-nanoscale transport through shortened tortuosity, directional channels, and chiral bias and, thus, for studying the transport of select metal ions, dyes, and chiral molecules. The project will yield a deep fundamental understanding of the complex transport phenomena in organized multiphase membranes with long-range organized nanocrystal and nanosheet assemblies; such knowledge is essential to the design of mechanically robust molecular separation membranes with high permeance, selectivity, and rejection rate.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.