Enabling Tailored Selectivity of Ion-Selective Membranes with Dual-Driving Force Operation

许多基本的能源、水和环境分离过程都需要能够选择性地分离水混合物中不同离子的技术。离子选择膜(ISM)是一种具有带电离子官能团的聚合物膜，允许带相反电荷的物种(反离子)通过膜，同时保留带相同电荷的离子(共离子)。施加驱动力(静电势)以通过膜传输离子。ISM已被用于燃料电池和电渗析海水淡化等商业应用，但它们存在性能限制，使其无法在许多工业相关条件下应用。首先，在较高的电解液浓度下，ISMS的反离子和共离子之间的选择性降低。ISM也无法区分具有相同价态的反离子。这个项目将研究使用第二个同时的驱动力(液压加压)来改变不同离子的相对渗透性。通过协调这两种驱动力的大小和方向，称为“双驱动力”运作，可以克服ISM选择性方面的上述两个缺点。开发更具选择性的离子分离技术可以释放从非传统源水中回收资源的机会，包括从地热卤水中回收锂，从城市和工业废水中回收氮和磷，从采矿废水中回收稀土元素，从海洋中回收铀酰离子。该项目的总体目标是通过有目的地控制离子传输的两种相反的驱动力，即双驱动力操作，来提高ISM分离的选择性。研究的具体目标是：1)开发双驱动力操作的复合离子选择膜的制膜平台；2)论证双驱动力操作的合理控制，以提高ISM对不同迁移率反离子的选择性；3)利用双驱动力操作来工程抑制共离子泄漏，以提高ISM的渗透选择性。该项目的成功实施将使ISMS能够：1)偏离反离子传输的亲和力-迁移率限制；2)即使在提高溶液离子强度的情况下，也能更好地排除共离子。这项研究将系统地研究ISMS中控制传输和选择性的潜在因素，并为膜设计和操作策略提供机械性的见解。该项目将把教育和研究结合起来，以培养和准备STEM的研究生、本科生和高中生。PI将参与的活动包括：(I)为K-12教育和公众宣传开发单元，(Ii)通过将研究的科学概念和技术原理纳入课堂教学大纲来加强本科和研究生课程，以及(Iii)通过结构化计划提供本科研究机会。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。

Technologies that enable the selective separation of different ions in aqueous mixtures are required for many essential energy, water, and environmental separations processes. Ion-selective membranes (ISMs) are polymeric films with charged ionic functional groups that allow the transport of oppositely-charged species (counterions) through the membrane while retaining like-charged ions (co-ions). A driving force (electrostatic potential) is applied to transport ions through the membrane. ISMs have been used in commercial applications such as fuel cells and electrodialysis desalination, but they exhibit performance limitations that preclude their application under many industrially-relevant conditions. First, ISMs suffer from diminished selectivity between counter- and co-ions at higher electrolyte concentrations. ISMs are also unable to discriminate between counterions with the same valency. This project will investigate using a second, simultaneous driving force (hydraulic pressurization) to alter the relative permeation of different ions. By coordinating the magnitude and direction of the two driving forces, termed “dual-driving force” operation, the two shortcomings in ISM selectivity above may be overcome. The development of more selective ion separation technologies can unlock opportunities for resource recovery from nontraditional source waters, including recovering lithium from geothermal brines, nitrogen and phosphorus from municipal and industrial wastewaters, rare earth elements from mining waste streams, and uranyl ions from seawater.The overall goal of this project is to achieve enhanced selectivities in ISM separations by purposeful control of two opposing driving forces for ion transport, i.e., dual-driving force operation. The specific objectives of the research are: 1) develop a membrane fabrication platform for composite ion-selective membranes in dual-driving force operation, 2) demonstrate the rational control of dual-driving force operation to enhance ISM selectivity for counterions with different mobilities, and 3) engineer the suppression of co-ion leakage using dual-driving force operation to improve ISM permselectivity. Successful execution of the project will enable the ISMs to i) depart from the affinity-mobility constraint on counterion transport and ii) attain improved exclusion of co-ions even at elevated solution ionic strengths. The research will systematically study the underlying factors governing transport and selectivity in ISMs and provide mechanistic insights into membrane design and operation strategies. The project will integrate education and research to train and prepare graduate, undergraduate, and high school students in STEM. The PI will engage in activities including: (i) developing modules for K-12 education and public outreach, (ii) enhancing undergraduate and graduate courses by integrating scientific concepts and technical principles of the research into class syllabus, and (iii) providing undergraduate research opportunities through structured programs.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.