Metal-organophosphate biphasic interfacial coordination reaction synthesizing nanofiltration membranes with the ultrathin selective layer, excellent acid-resistance and antifouling performance

Abstract

Phytate as a natural strongly charged organophosphate has recently attracted much attention in diverse fields including membrane separations towards water-energy-food nexus. However, the ideal phytate-based nanofiltration membrane with defect-free and ultrathin selective layer for highly-efficient water treatment is still much challengeable due to the typical aggregation of metal ions and uncontrolled reaction between metal ion and organophosphate via conventional coating method. Herein, metal-organophosphate biphasic interfacial coordination reaction is proposed to construct ultrathin (13.4 nm) selective layer of phytate-based nanofiltration membranes with high permeance and excellent stability by controllable coordination assembly. Iron acetylacetonate (Fe(acac)3) as an organic phase monomer with powerful electron-gaining ability is exploited to avoid the aggregation of traditional Fe(III) in aqueous phase, which can also coordinate with phytic acid (PA) to ensure a defect-free ultra-thin selective layer. The architecture of the phytate-based selective layer can be well regulated by optimizing the coordination metal source, the concentration of PA and Fe(acac)3, reaction time, so as to achieve the ultrahigh permeation flux of 190 L m−2 h−1 with excellent dye rejection (99.6%). Most interestingly, our phytate-based nanofiltration membranes with plenty of hydrophilic phosphate groups on the surface and high binding energy of P–O–Fe bond (−315.1 kJ mol−1) exhibited the long-term separation stability, excellent acid-resistance and anti-pollution ability, realizing the stable membrane separation process under harsh conditions.