Dual metals co-intercalated graphene oxide membrane with outstanding permeability and molecule selectivity for the high-salinity brine treatment

Abstract

Conventional membrane separation technology still encounters substantial challenges in removal of various dissolved organic matter in concentrated-saline brine due to their imperfect interlayer microstructure and inferior stability. Here, we demonstrate an ingenious design to build stable and defect-free interlayer structure inside the sodium alginate (SA)-crosslinked graphene oxide (GO) composite membranes by anchoring bimetallic ions as bridging center at different binding sites. SA can realize the ordered self-assembly of GO nanosheets through Van der Waals forces and hydrogen bonding, and provide more metal ion coordination sites. On this basis, Sr²⁺ preferentially bridges with the G-blocks of SA and the carboxylate groups on GO, while Fe³⁺ is precisely anchored in the residual G- and M−blocks on SA, the oxygen-containing groups and graphitic regions on GO nanosheets via strong coordination interaction. The synergistic coordination constructs additional water transport nanochannels, while also imparting the membrane with stable and regular interlayer structure, thereby improving permeability without sacrificing separation performance. This design endows the membrane with super-hydrophilicity, great tolerance toward high salts concentrations (372.4 g‧L⁻¹), strong acid-alkali resistance, excellent long-term structural stability and cycling performances. Notably, the composite membrane exhibits high rejection for various dissolved organic matter and diverse dyes, while maintaining a superhigh permeance (21130 L·m⁻²·h⁻¹·bar⁻¹), which is greatly superior to traditional membranes. Size sieving and electrostatic interaction provide the main support for molecule selective separation. This protocol highlights the practical application prospect of GO-based membrane in the field of high-salinity brine treatment.