Tunable Interlayer-Spacing Graphene Oxide Membrane: Efficient Osmotic Energy Conversion Toward Metal Recovery.

2D material membranes show promise in osmotic energy (OE) conversion and separation technologies. However, low ion flux and swelling limit their applications. Herein, a polydopamine-crosslinked graphene oxide membrane (PDA@GO) with tunable interlayer spacing is developed to address these challenges. PDA expands the interlayer spacing, optimizes Debye length matching, and reduces ion transport barriers. Compared to pristine GO membranes, PDA@GO membranes achieve a 369% higher ion flux and a power density of 10.06 W m under a 500-fold NaCl gradient. Besides, PDA@GO membranes show excellent anti-swelling stability in aqueous solution up to 60 days. Furthermore, integrating green chemistry principles, PDA@GO enables dual energy-resource utilization, successfully recovering copper ions from wastewater via OE. This work highlights the potential of 2D membrane systems in high-efficiency energy conversion and sustainable wastewater treatment.