MOF Membrane Ion Selectivity via Sub-Nanometer Pore Control
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Solution Overview
Problem
Current synthetic membranes are ineffective in efficiently separating atomic ions of the same valence and similar sizes due to limitations in ion selectivity and permeation rates.
Innovation Solution
Development of metal organic framework (MOF) membranes with sub-nanometer pore windows and tailored selectivity, integrated with a substrate and electrodes to apply a potential difference, enhancing ion transport and selectivity through controlled pore sizes and shapes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional synthetic membranes are used for ion separation, then the membrane structure is simple and easy to manufacture, but the ion selectivity and permeation rates are insufficient for efficiently separating atomic ions of the same valence and similar sizes
Solution Approach 1:
The patent employs metal-organic framework (MOF) materials with precisely controlled porous structures. The MOF membranes feature uniform pore sizes in the angstrom range (e.g., 3.4 Å for ZIF-8), which are specifically designed to match the hydrated diameters of target ions. This porous structure enables size-based sieving mechanisms that achieve high ion selectivity while maintaining permeation rates, directly resolving the contradiction between selectivity and structural complexity.
Solution Approach 2:
The invention creates composite membranes by integrating MOF layers with support substrates (such as porous ceramics, metals, or polymers). This composite structure combines the size-selective properties of MOF materials with the mechanical strength and structural stability of support materials, achieving both high ion selectivity and practical manufacturability without requiring the entire membrane structure to be complex.
2Manufacturing precision
If MOF membranes with sub-nanometer pore windows are used, then ion selectivity is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The patent employs a seeding approach where MOF nanocrystals are pre-formed and deposited onto support substrates before the final membrane formation. This preliminary action creates nucleation sites that guide the subsequent growth of uniform MOF layers with controlled pore sizes, simplifying the overall fabrication process while achieving precise pore size control necessary for high ion selectivity.
Solution Approach 2:
The invention uses templating agents or surfactants as intermediaries during MOF membrane fabrication. These intermediaries facilitate the formation of uniform porous structures by controlling nucleation and growth processes, enabling the production of membranes with precise sub-nanometer pore windows without requiring complex direct fabrication methods.
3Quantity of substance
If pressure-driven gas separation processes are used with MOFs, then gas adsorption capacity and selectivity are improved, but the application to ion separation has not been explored
Solution Approach 1:
The patent transitions the application of MOF membranes from gas separation to ion separation by changing the operational parameters (from pressure-driven gas flow to electric field-driven ion transport) while maintaining the core size-selective mechanism. The sub-nanometer pore windows that provide excellent gas adsorption capacity and selectivity are similarly effective for ion separation, demonstrating the adaptability of MOF structures across different separation modes and expanding their versatility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The MOF membranes demonstrate significant selectivity and transport efficiency for monovalent ions over multivalent ions, achieving high selectivity ratios and fast ion transport rates, overcoming previous limitations in ion separation technologies.
Implementation Method 1
the respective pore windows have a pore size that is less than the hydrated diameter of the ion for which the ion selective separation membrane is selective
Implementation Method 2
first and second electrodes to apply a potential difference across the membrane... the application of a potential difference across the ion selective separation membrane enhances the selective passage of ions
Implementation Method 3
a metal organic framework layer formed on, in, and/or around a substrate, the metal organic framework having a crystal structure that includes a first surface and a second surface
Implementation Method 4
first and second electrodes to apply a potential difference across the membrane... the application of a potential difference across the ion selective separation membrane enhances the selective passage of ions
Data Source
AI summary
Disclosed herein is an ion selective separation membrane including: a metal organic framework layer formed on, in, and/or around a substrate, the metal organic framework having a crystal structure that includes a first surface and a second surface and includes ion transport channels formed between respective pore windows in the first surface and the second surface; first and second electrodes to apply a potential difference across the membrane; wherein the respective pore windows have a pore size that is less than the hydrated diameter of the ion for which the ion selective separation membrane is selective.