Controlling reduction degree of graphene oxide membranes for improved water permeance

Tailoring the pore structure and surface chemistry of graphene-based laminates is essentially important for their applications as separation membranes. Usually, pure graphene oxide (GO) and completely reduced GO (rGO) membranes suffer from low water permeance because of the lack of pristine graphitic sp² domains and very small interlayer spacing, respectively. In this work, we studied the influence of reduction degree on the structure and separation performance of rGO membranes. It was found that weak reduction retains the good dispersion and hydrophilicity of GO nanosheets. More importantly, it increases the number of pristine graphitic sp² domains in rGO nanosheets while keeping the large interlayer spacing of the GO membranes in most regions at the same time. The resultant membranes show a high water permeance of 56.3 L m^-2 h^-1 bar^-1, which is about 4 times and over 10⁴ times larger than those of the GO and completely reduced rGO membranes, respectively, and high rejection over 95% for various dyes. Furthermore, they show better structure stability and more superior separation performance than GO membranes in acid and alkali environments.