Polymer inclusion membranes (PIMs) containing purified dinonylnaphthalene sulfonic acid (DNNS): Performance and selectivity

The use of purified dinonylnaphthalene sulfonic acid (DNNS) as extractant in polymer inclusion membranes (PIMs) was investigated for the first time. DNNS is commonly supplied in 50 wt% water soluble diluent, which when applied in PIMs is expected to affect their stability. Purified and commercial DNNS were characterised by gas chromatography with flame ionization detection and thermogravimetric analysis coupled with Fourier transform infrared spectrometric detection. PIMs prepared with the purified DNNS reagent containing the same amount of membrane liquid phase as the commercial DNNS-based PIMs were able to accommodate more DNNS than the PIMs incorporating the commercial product which contained a significant percentage of diluent. This resulted in better extraction efficiency and slightly lower mass loss. The affinity of a PIM containing 35 wt% purified DNNS, 10 wt% 1-tetradecanol and 55 wt% poly(vinyl chloride) towards a range of monovalent and divalent cations in 0.001 M HCl solutions, based on the percentage extracted metal ion, was found to follow the order: Fe3+ (1:1, 93.9) > CO2+ (2:1, 63.4) > Pb2+ (2:1, 59.7) > Zn2+ (2:1, 48.5) > Cu2+ (2:1, 45.0) > Ni2+ (2:1, 40.6) > Mg2+ (2:1, 35.0) > Na+ (1:1,20.9) approximate to K+ (1:1, 20.1), where the numerical data in the brackets correspond to the stoichiometric ratio (DNNS: ion) and the percentage of metal ion extracted from the source solution, respectively. This order can be explained by the Hard and Soft Acids and Bases Theory and the hydration energy of the metal cations. The stoichiometric composition of the corresponding metal DNNS adducts was determined in solvent extraction experiments.