Effects of process parameters on polyaniline nanofiltration membranes synthesis via phase inversion-immersion precipitation method

Polymer membranes are commonly used for selective separations in many world’s major industries as they are cheap and easily fabricated. However, the common use of polymers, such polyamide and cellulose acetate, means membrane selectivity is fixed once cast. To increase the in-use flexibility of this unit operation, new membranes that allow changeable separation selectivity are required. Using conducting polymers (CP) like polyaniline (PANI) as the membrane polymer is one way of achieving this. This is because PANI has the ability to be electrochemically switched between the conducting and insulating states as a function of protonation from emeraldine salt to emeraldine base, which can influence the surface energy, charge, free volume and/or the pore size of a membrane incorporating it. Therefore PANI nanofiltration (NF) membranes were aimed to be fabricated from in-house PANI synthesis followed by phase inversion via immersion precipitation method. The membrane formation variables namely polymer concentration, casting thickness, heat treatment and type of acid dopant used for the synthesis were linked to the micro-structural properties of the membranes in a way to find the best NF membranes with better separation selectivity. The PANI membranes all had a typical integrally skinned layered asymmetric membrane structure. The addition of different dopants: anthraquinone sulfonic acid (ASA), dodecyl benzene sulfonic acid (DBSA) and maleic acid (MA) followed by secondary doping with conventional dopant hydrochloric acid (HCl; 1M) to improve the electrical conductivity in PANI membranes had changed the thickness of these PANI layers, with the HCl and ASA doped membranes having almost the same structure; and these were the best membranes for comparison in filtration study.