Thermally Reduced Graphene Oxide Membrane with Ultrahigh Rejection of Metal Ions’ Separation from Water

Abstract

Because of the water swelling of graphene oxide (GO) membranes, the rejection of metal ions is generally low, especially for monovalent metal cations. We prepared a thermally reduced graphene (TrGO) membrane with excellent separation performance of water and NaCl by heat treating GO membranes. Its blocking ability for Na+ is 1529 times larger than that of the GO membrane with the same amount of GO, and it is also much better than the reduced GO membranes prepared by NH3 or HI reduction. Using 3 M sucrose as the draw solution, the 795 nm thick TrGO membrane has an ultrahigh rejection of more than 99.56% for Na+ and maintains a water flux of 0.42 L m–2 h–1. TrGO membranes maintain high stability during the penetration of a high-concentration salt solution, and they have good mechanical properties to maintain operational stability and can be used for a longer time. We characterized and analyzed the separation mechanism of the TrGO membranes and believe that the inner channels form three zones with different hydrophobicity and uniform distribution. The ratio of the three zones can be changed by adjusting the heat-treatment temperature, the duration to swelling force, and the π–π attraction force.