Highly permeable carminic acid functionalized graphene oxide-based membranes for dye separation and desalination

Graphene oxide-modified membranes with tailored pore sizes have emerged as a promising solution for water purification. Here, we report a novel strategy by functionalizing graphene oxide (GO) nanosheets with carminic acid, a naturally occurring compound with an abundance of functional groups, to boost the filtration efficiency of GO-based membranes for organic dyes and salts. Carminic acid (CA) has a unique structure with oxygen- containing functional groups, such as OH, COOH, C=O groups, and anthraquinone backbone. Due to its versatile functional groups, CA increased the rejection efficiency of GO membranes several times, while its large aromatic benzene ring-based structure supports high water permeance by increasing the interlayer spacing between GO sheets. The as-prepared carminic acid-functionalized GO (CA/GO) membranes were characterized by EDX, SEM, FTIR, TGA, and XRD techniques. The CA/GO membranes exhibited exceptional performance, achieving 100 % rejection of methylene blue and Eriochrome black T dyes. Moreover, they demonstrated remarkably high water permeance, reaching similar to 2831 +/- 5 L m(- 2) h(- 1) bar(- 1) for DI water, which is substantially higher than that of reported GO-based membranes. Further, these membranes also demonstrated high salt rejection rates of 99 % for Pb(C2H3O2)(2), NiCl2, and MgCl2, due to the tailored functional groups and interlayer spacing. In addition, the CA/GO membranes also exhibited remarkable long-term stability, remaining effective under harsh conditions for up to 90 days. This remarkable stability, combined with their outstanding performance, makes these membranes an ideal choice for wastewater treatment applications.