Nanodiamond hybrid nanofiltration membranes: Synergistic enhancement of permeability and selectivity for sulfate-selective separation

Polydopamine-coated ethylenediamine-modified nanodiamonds (NDs-EDA@PDA) were incorporated into nanofiltration (NF) membranes, leading to enhanced permeability and selectivity. NDs boost mechanical attributes, preserving salt rejection under high temperature and pressure. PDA, with strong adhesion, improves compatibility. EDA and PDA amino groups and phenolic hydroxyl groups form additional covalent bonds, refining smaller pores (0.469 nm) for size-sieving. PDA’s hydrophilic groups accelerate water transfer and its oxygen anions amplify Donnan effect, repelling divalent anions. Molecular dynamics simulations confirm that NDs-EDA@PDA hinder piperazine diffusion, thereby resulting in the formation of a thinner polyamide layer. Consequently, NDs-EDA@PDA NF membrane achieves enhanced permeability (7.02 L m⁻²h⁻¹ bar⁻¹, 1 g L⁻¹ Na₂SO₄, 5 bar, 25 ℃, pH 6.5) and NaCl/Na₂SO₄ selectivity (97.49, single salt, 1 g L⁻¹ Na₂SO₄ and 1 g L⁻¹ NaCl, 5 bar, 25 ℃) through the aforementioned synergistic effect, achieving a dual improvement in permeability-selectivity. This research provides valuable theoretical and experimental insights into NDs’ application in NF membranes. And it deepens understanding of molecular mass transfer within membranes, and facilitates future development of high-performance NF membranes.