The removal of Indigo Carmine from water by solvent sublation

Indigo Carmine (IC, C16H8N2Na2O8S2), an anonic dye, was removed from an aqueous solution by solvent sublation of Indigo Carmine-Cetyltrimethyl Ammonium Bromide (CAB) complex (sublate) into 2-octanol. A stoichiometric amount of surfactant (surfactant: dye = 2:1) was the most effective for the removal, with over 93% IC removed from the aqueous solution in 5 min by solvent sublation. The removal rate was somewhat enhanced by higher air flow rates and almost independent of the volume of the organic solvent floated on the top of the aqueous column. The effects of electrolytes (e.g., NaCl), nonhydrophobic organics (e.g., ethanol), and pH of the solution upon the process were studied. The solvent sublation process followed first-order kinetics. A characteristic parameter, apparent activation energy of attachment of the sublate to bubbles, was estimated at a value of 1.3 kJ/mol.