Nanostructured polyaniline incorporated ultrafiltration membrane for desalination of brackish water

Abstract

A novel salt rejecting ultrafiltration (UF) membrane was prepared by a facile, scalable route involving in situ incorporation of negatively charged polyaniline (PANI) nanoparticles within polysulfone (PSF). The incorporated PANI acts as a porogen and charge inducing agent, improving the porosity, permeability, hydrophilicity as well as the surface charge, leading to an enhancement of the permeate flux and improvement of the salt rejection capability. Specifically, 2 wt% PANI loading leads to a 25 times increase in the molecular weight cut-off (from 0.2 to 4.8 kDa). Also, there is improvement in porosity (from 20% to 64%), and a 2-fold increase in permeability (from 8 × 10⁻¹² to 16 × 10⁻¹² m³ m⁻² Pa⁻¹ s⁻¹). Surface hydrophilicity (reduction of the contact angle from 82° to 69°) was enhanced as well. All of these effects ultimately lead to a 2.5 times enhancement in the permeate flux (from 21 l m⁻² h⁻¹ to 38 l m⁻² h⁻¹ at 690 kPa transmembrane pressure, TMP and 20 l h⁻¹ cross flow rate, CFR). This reflects the change in membrane behavior from nanofiltration (NF) to UF. An increase in zeta potential (from −4 mV to −28 mV at pH 7) results in salt rejection between 40–53%, equivalent to the NF performance. Developed UF membranes match the desalination performance of NF membranes showing a higher flux and lower energy requirement. Advantageously, these membranes are also found to be fouling resistant during salt solution filtration, requiring no extensive regeneration. Desalination performance of these membranes is also demonstrated using artificially synthesized seawater. These UF membranes may be exploited as a pretreatment for inlet load reduction to reverse osmosis or for the production of industrial process water. It is believed these charged membranes lay the foundation for the development of next generation desalination membranes possessing high flux and fouling resistant characteristics.