(447d) Balanced Reduction and Oxidation of Graphene Oxide Membranes to Achieve Excellent Dye Desalination Performance

Graphene oxide (GO) membranes have been extensively investigated for dye removal from textile wastewater because of their tunable interlayer spacings to permeate water and salts and reject dyes. However, GO can be dispersed in water, and thus, they are often reduced or cross-linked to improve their stability, which inevitably lowers water permeance. Herein we demonstrate an effective approach for in-situ oxidation of the reduced GOs (rGO) using peracetic acid (PAA) to enhance water permeance while retaining dye rejection rates. Specifically, rGO nanosheets were prepared using hydrazine in a solvation state and vacuum-filtrated onto a nylon substrate. The obtained rGO membranes were then exposed to PAA solutions at different concentrations and times to obtain oxidized rGO (OrGO) membranes. The effects of the PAA content and exposure time on the membrane chemistry, nanostructures, and dye/salt separation properties are thoroughly examined. For example, 100 nm-thick rGO membrane shows water permeance of 35±11 LMH/bar, congo red (CR) rejection of 99.8% and 3w% Na₂SO₄ rejection of 10 %, while the PAA oxidation of 10 min increases water permeance by 180% to 93±11 LMH/bar, retaining a CR rejection of 99.6%, but decreasing the 3w% Na₂SO₄ rejection to 3.3 %,. The OrGO membranes exhibit stable water permeance of 80 LMH/bar and dye rejection over 99.0% in multi-cycle continuous tests in cross flow, superior to state-of-the-art commercial NF membranes and GO membranes reported in the literature. The membranes also display stability in long-term continuous tests with aggressive chemical washing. This work demonstrates an interesting approach to flexibly fine-tune the oxidation and reduction degree of the GO membranes to achieve superior molecular sieving ability.