Additive manufacturing of defect-healing polyamide membranes for fast and robust desalination

Polyamide membranes that can exclude salts from water have found significant success in desalination applications. The polyamide thickness is difficult to control, as it is closely coupled with other properties including monomer chemistries and substrate structures. In this work, an additive manufacturing strategy using spray-coating to prepare large-area polyamide composite membranes with tunable thickness is explored. Using spray-coating, composite membranes comprising polyamide layers and carbon nanotube (CNT) layers on top of porous substrates are additively constructed. In the context of mediation by CNT layers, thickness control is decoupled from other properties. As a result, the polyamide thickness can be independently adjusted by changing monomer concentrations, and water permeance is found to be related to the thickness. A large-area membrane with a size of 30 × 30 cm² is successfully prepared under optimal conditions, and exhibits large water permeance of 34.1 L m⁻² h⁻¹ bar⁻¹ and high Na₂SO₄ rejection rate of 95.6%. Importantly, the additive nature holds the ability to eliminate defects possibly existing through multiple spraying, affording defect-healing characteristic. This work allows envisioning a turning point that additive manufacturing is shifting the long-standing paradigm in the preparation of high-performance separation membranes.