Understanding Gas Transport through Nanopores in Graphene Membranes

分离化学混合物的工业过程对文明至关重要，包括例如能源，材料和商品化学品的生产。因此，开发更具选择性和能源效率的分离工艺是一项重要的技术挑战，有望大幅节省成本以及减少能源消耗和有害排放。大多数工业分离是能源密集型的热过程，占世界总能耗的10-15%。基于膜的分离方法由于其降低的能量消耗和优异的可靠性而提供了热分离技术的有吸引力的替代方案。然而，传统气体分离膜的气体通量和选择性之间的权衡在历史上限制了膜分离单元的整体性能，以及用这些更有效的替代品替代能量密集型工艺的动机。石墨烯是碳原子的原子薄层，被认为是气体分离膜效率的潜在极限。石墨烯和其他二维材料是单个原子或晶胞厚度，并且代表候选膜材料中绝对最低的传质阻力（或最高的通量）。 因此，这种最终的薄度可以产生比使用常规膜材料获得的气体通量高几个数量级的气体通量。为了实现这一潜力，该项目的目标是通过实验在石墨烯层中产生纳米孔，其尺寸分布可控，用于气体分离。气体渗透的测量将用于获得通过这些新型的纳米孔使用理论和模拟框架的分子运输的基本理解。该项目将有助于麻省理工学院校园正在进行的教育工作，包括一门名为工程纳米技术的课程的学习模块，并将通过高中实习和本科生研究机会，吸引麻省理工学院和剑桥学术界代表性不足的学生。该提案的首要目标是使用实验，分子模拟和理论分析的组合方法来促进对气体分子通过二维膜（如石墨烯）中分子大小的纳米孔的运输的理解。首先，理论和模拟将用于研究石墨烯中的纳米孔形成，并研究不同气体物种通过这些纳米孔的渗透动力学，最终创建一个综合理论来预测通过实际孔径分布的气体渗透。其次，将制备纳米多孔石墨烯膜，并测量通过这些膜的气体渗透率。最后，将研究石墨烯孔的形成、修饰和功能化，以进一步了解通过不同石墨烯孔结构的气体传输。理论、分子模拟、膜制造、表征和气体通量测量的结合将提供孔隙结构和分布与观察到的气体渗透性之间的第一个基本联系，并阐明分子-孔隙相互作用的潜在机制。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Industrial processes that separate chemical mixtures are essential for civilization, including, for example, the production of energy, materials, and commodity chemicals. The development of more selective and energy efficient separation processes is therefore an important technological challenge, promising the potential for substantial cost savings as well as reductions in energy consumption and harmful emissions. Most industrial separations are energy-intensive thermal processes, which account for 10-15% of the world's overall energy consumption. Membrane-based separation processes offer attractive alternatives to thermal separation techniques due to their reduced energy consumption and excellent reliability. However, the trade-off between gas flux and selectivity of conventional gas separation membranes has historically limited the overall performance of a membrane separation unit, as well as the motivation for replacing energy-intensive processes with these more efficient alternatives. Graphene, an atomically thin layer of carbon atoms, is regarded as the potential ultimate limit of membrane efficiency for gas separation. Graphene and other two-dimensional materials are a single atom or unit cell thick and represent the absolute lowest mass transfer resistance (or highest throughput) among candidate membrane materials. Hence, this ultimate thinness can yield orders of magnitude higher gas fluxes than those attained using conventional membrane materials. To fulfill this potential, the goal of this project is to experimentally generate nanopores in the graphene layer with controlled size distributions for gas separation. Measurements of gas permeation will be used to gain fundamental understanding about molecular transport through these new types of nanopores using a theoretical and simulation framework. The project will contribute to ongoing educational efforts on the MIT campus, including learning modules for a course called Engineering Nanotechnology, and will engage under-represented student populations at MIT and the Cambridge academic community through high school internship and undergraduate research opportunities. The overarching goal of this proposal is to use a combined approach of experiment, molecular simulation, and theoretical analysis to advance the understanding of transport of gas molecules through molecularly sized nanopores in two-dimensional membranes such as graphene. Firstly, theory and simulations will be used to investigate nanopore formation in graphene and to study the permeation kinetics for different gas species through these nanopores, eventually creating a comprehensive theory to predict gas permeation through a realistic pore size distribution. Secondly, nanoporous graphene membranes will be fabricated, and the gas permeances through these membranes will be measured. Lastly, the formation, modification, and functionalization of the graphene pores will be investigated to further understand gas transport through different graphene pore structures. The combination of theory, molecular simulation, membrane fabrication, characterization, and gas flux measurements will provide the first fundamental links between pore structure and distribution with observed gas permeance, and elucidate the underlying mechanisms of molecular-pore interactions.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.