Janus polymer membranes prepared by single-side polydopamine deposition for dye adsorption and fine bubble aeration

Mussel-inspired surface modification has attracted great attention in recent years. Porous membranes with opposite surface properties play an important role in various fields such as ion rectification, unidirectional oil/water separation, and nanofiltration. In this paper, we report a spray coating method to prepare a series of single-side modified membranes. Two solutions containing dopamine and NaIO4/NaOH are alternately sprayed onto membrane surfaces. Each spray process can be finished in tens of seconds. Results indicate that this method is suitable for various substrates varying from hydrophilic to hydrophobic surfaces. By introducing charged polymers such as poly(sodium 4-styrenesulfonate) into the spray solution for co-deposition, Janus membranes with differently charged surfaces have been fabricated. Such Janus membranes can remove both positively and negatively-charged dyes, while the traditionally bulk modified membranes adsorb only one kind of the dyes. We further demonstrated that the Janus membrane with asymmetric wettability has potential in promoting bubbling efficiency while reducing the energy consumption. The proposed spray coating method is fast and effective and can be applied to different membrane materials for various applications.