Self-cleaning membranes for water purification by co-deposition of photo-mobile 4,4′-azodianiline and bio-adhesive polydopamine

Stimuli-responsive membranes have been widely explored to mitigate fouling on the membrane surface to achieve the stable performance of water purification. Herein, a facile one-step coating of photo-mobile materials on membrane surface was developed to impart self-cleaning property upon exposure alternatively to ultraviolet (UV) and visible light. Specifically, photo-mobile 4,4′-azodianiline (AZO) and a bio-adhesive polydopamine (PDA) were co-deposited on the surface of ultrafiltration (UF) membranes. The effect of the coating layer on the surface hydrophilicity and pure water permeance was systematically evaluated. The photoresponsive properties of AZO in solutions and thin films with PDA was characterized using UV–Vis absorption spectroscopy. When exposed with UV light, AZO undergoes photoisomerization from trans-AZO to cis-AZO, decreasing the volume, while the exposure to visible light enables the transition from the cis- to trans- configuration, increasing the volume. The resulted self-cleaning behavior of the modified membranes through the reversible volume change is demonstrated in treating 1 g/L bovine serum albumin (BSA) solution. After exposure to the alternative UV/vis light, the AZO-coated UF membranes showed an increased water permeance by ~160%.