POC/PIM-1 mixed-matrix membranes for water desalination: A molecular simulation study

As a new class of porous materials, porous organic cages (POCs) are dissolvable in common organic solvents and can be readily incorporated into polymers to fabricate mixed-matrix membranes (MMMs). Herein, we report a molecular simulation study on MMMs formed by a POC (PB-1A) and a polymer of intrinsic microporosity (PIM-1) for water desalination. Three MMMs with different PB-1A/PIM-1 ratios are constructed, namely MMM1 (1 cage/13 PIM-1 chains), MMM2 (1 cage/20 PIM-1 chains) and MMM3 (1 cage/28 PIM-1 chains). After swelling in water, the voids in the MMMs are observed to become larger. The swelling degrees are estimated to be 69.3%, 64.9% and 56.6% in MMM1, MMM2 and MMM3, respectively, which are greater than 20-30% in the pristine PIM-1. Due to the presence of PB-1A cage, water permeability is significantly enhanced in the MMMs, along with nearly complete salt rejection. Particularly, water permeability in MMM1 is 1.1 X 10(-5) kg m/(m(2)center dot h center dot bar), which is one order of magnitude higher than 8.6X10(-7) kg m/(m(2)center dot hr center dot bar) in the pristine PIM-1, and is also higher than those in a wide variety of reported membranes. This simulation study provides microscopic insights into the structural and dynamic properties of water and ions in the PB-1A/PIM-1 MMMs, suggests that the MMMs might be interesting candidates for water desalination.