Biological membranes achieve both rapid transport and high selectivity. Synthetic membranes cannot approach such performance due to basic gaps in understanding the underlying primary and secondary molecular interactions necessary to impart high selectivity without sacrificing permeability. Thus, materials cannot be designed with predictive control over separation efficiency for targeted solutes, especially in complex fluids. Complementing the detailed studies of hydration at interfaces from GAP 1, the objective of GAP 2 is to design specific molecular affinity/reactivity interactions towards solutes, including uncharged species and (multivalent) ions, in complex fluids to discern basic molecular factors governing specificity in synthetic membranes.
1. How do pore size, molecular geometry, and chemical functionality in molecular scale pores lead to ion selectivity? What design rules fundamentally control interaction of molecular pores with charged and uncharged solutes? Templated synthesis of porous aromatic frameworks (PAFs) is now robust enough to provide control over binding pocket size, shape, and chemistry. Are there opportunities to bias selectivity in multi-component systems towards solutes of interest to beneficially treat complex aqueous mixtures? Can specific chemistry and processing conditions lead to efficient release of solutes preferentially bound to PAFs for recovery of valuable ions (e.g., Li+)? If so, are these mechanisms dominated by thermodynamics or kinetics, and how can they be biased to maximize resource recovery with minimum energy?
2. How do transition metal catalyst electronic structure and ligand geometry impact efficacy of reactive membranes that “capture & kill” recalcitrant contaminants such as hydrocarbons and inorganic oxyanions? Can reaction pathways be controlled to manipulate the product distributions, and, if so, are these routes sensitive to complex fluid composition?
3. How does attaching interactants to polymer matrices influence their behavior? What is the connection between bulk matrix properties - including chemistry, charge, and interactant density - and separation efficiency? What specific degradative mechanisms most effectively operate in polymer-bound catalysts with efficient reactivity, selectivity, and stability? In what way are these effects correlated to surface hydration as deduced in GAP 1?
GAP 2 integrates small molecule and polymer synthesis, physical measurements to evaluate structure-function relationships, and theory to provide inverse design of ideal chemical building blocks. “Interactant” platforms are designed to “catch & release” solutes, and “capture & kill” specific solutes. Polymer membrane platforms for these interactants, will designed and synthesized. Molecular simulation and modeling will inform experimental design by predicting the influence of charge density, binding geometry, and polymer/interactant structure on solute partition, diffusion, and permeability coefficients as well as ionic conductivity (for charged solutes). Deliverables include rules for designing: (1) interactants with tailored solute selectivity/reactivity, and (2) polymers supporting these interactants and maximizing performance in contact with complex aqueous fluids. These studies will inform inverse design of novel polymers and interactants to prepare highly permeable, selective membranes.
Project #1: 'Capture and Kill or Release' Solutes
Catalysts that can oxidize organics; catalysts that can reduce oxyanions
Selective binding motifs for F-, and metal ions including Ca2+
Binding strategy for neutral contaminants such as B
Knowledge to design selective reactivity into membranes
Project #2: Incorporating Specific Interactions to Membrane Framework
Understand how specific interactant performance in solution (Project 1) translates to dense polymeric membrane materials.
Understand the connection between polymer architecture, interactant density, and interactant sequence on fundamental membrane properties/performance.
Development of new chemistry and materials to improve specificity.