Optimizing Permeance of Graphene Oxide\Polymer Membranes

Growing water scarcity threatens thermoelectric power plants, municipal water supplies, agriculture, and energy production. These demands drive a need for diverse water treatment technologies as more users turn to water reuse and non-traditional water supplies. 2D-nanomaterials such as graphene oxide (GO) are a chemical (including chlorine) tolerant alternative to the polyamide salt-rejection layer of conventional thin-film composite reverse osmosis membranes (TFC). However, GO\polymer membranes have often lacked the permeance and salt rejection of TFC-RO membranes.

Sandia has simultaneously optimized the permeance (3 LMH/bar for DI water; 1.5 LMH/bar for saline) and rejection (up to 98% for MgSO₄) of GO\polymer membranes. Increasing the stiffness and uniformity of the porous polymer support allowed us to decrease the thickness of the laminar GO layer to <50 nm, increasing permeance 10x. Despite this thin layer, these membranes are mechanically robust, operating at 10-50 bar in cross-flow environments for weeks. In this presentation, we focus on how the optimizing the laminar GO thin-slit structure enabled these advances. At moderate pressures (10-30 bar), ion rejection is independent of pressure, allowing for lower-energy desalination. Permeance declines at 40 bar and above, indicating significant compression of the thin-slit structure, as confirmed by synchrotron x-ray diffraction measurements of pressurized GO\polymer membranes. These recent advances in permeance and salt rejection show GO\polymer membranes are a promising desalination technology for chlorinated waters.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.