Solvent-Free Process to High-Flux Ultrafiltration Membranes: Spray Coating of Water-Dispersed Carbon Nanotubes

Mainstream ultrafiltration (UF) membranes are typically produced from the phase inversion of polymer solutions and suffer from the extensive use of organic solvents and disposal of organic wastewater. Therefore, it remains highly demanding for clean processes to produce UF membranes at no expense of separation performances. Herein, we report the preparation of high-performance carbon nanotube (CNT)-based membranes without using any organic solvents. CNTs are first homogeneously dispersed in water with the assistance of an amphiphilic block copolymer. The CNT-based membranes, composed by a separation layer of stabilized CNT networks and macroporous supports, are obtained by spray coating aqueous CNT dispersions. The pore sizes of thus-prepared CNT UF membranes are easily tuned by controlling the diameter of CNTs or the spraying volumes of the CNT dispersions. The CNT membranes exhibit superior water permeance (460−7750 L m⁻² h⁻¹ bar⁻¹) compared with membranes produced by other methods with similar pore sizes. This solvent-free process enabled by spray coating is expected to extend to other water-dispersible low-dimensional building blocks in clean preparation of various high-performance membranes.