Adsorption behavior and self-aggregation of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin on quaternized polysulfone membrane

Adsorption of 5,10,15,20-tetrakis-(4-sulfonatophenyl)-porphyrin (TPPS) on the quaternized polysulfone (QAPSF) porous membrane based on the electrostatic interaction was investigated. TPPS species in solution showed different adsorption behavior. The diacid (H4TPPS2−) form of the porphyrin at pH 4.0 showed almost equal adsorption capacity, while slower adsorption rate on the QAPSF membrane, compared with the free-base (H2TPPS4−) form at pH 7.0; J-aggregates of TPPS in aqueous solution affected the adsorption. Compared with in the aqueous solution, the apparent pKa for the equilibrium between H4TPPS2− and H2TPPS4− of the adsorbed porphyrin was significantly decreased by the interaction between TPPS and QAPSF. J-type aggregation of TPPS can also occur on the membrane, while much lower pH is required. The pH dependency was considerably influenced by adsorption capacity; higher adsorption capacity was in favor of the protonation and J-aggregation at relative higher pH.