Co-depositing polyvinylamine and dopamine to enhance membrane performance for concentration of KAc solutions via sweeping air pervaporation

Polydopamine (PDA) has been used as a tool for engineering surfaces due to its good adhesive characteristics onto various surfaces and abundant functional groups for further improvement. However, its weak hydrophilicity and long term stability in an alkaline environment were a concern for membrane applications. To address the issues, we proposed to use polyvinylamine (PVAm) as a co-depositant with dopamine to fabricate thin film composite (TFC) membranes in order to take advantage of the covalent bonding between polydopamine (PDA) and PVAm and the adhesive properties of PDA oligomers. The membranes were investigated for concentrating KAc solutions via sweeping air pervapoation. It was shown that both the hydrophilicity and stability of the membrane were improved by incorporating PVAm into the membrane during the coating/deposition process. It was shown that a PVAm content of 20–30 wt% (solvent free basis) in the PVAm/dopamine depositing solution (i.e., PVAm/dopamine ratio in the range of 2:8 to 3:7) was appropriate for fabricating TFC pervaporation membranes for concentrating aqueous KAc concentrations. At a high salt concentration of 70 wt% in the feed solution, the membrane showed a water flux of 1.2–1.4 kg/m2.h and essentially a complete retention of the salt when tested over a period of over 200 h. The membranes were characterized in terms of surface hydrophilicity, permeance and activation energy for water permeation. In addition, the mass growth rate of the membrane skin layer during membrane buildup was determined as well to provide an insight into the general behavior of dopamine adhesion and polymerization in surface engineering.