Adsorptive removal of anionic dye by inorganic–organic hybrid anion-exchange membranes

Anion-exchange membranes with quaternary ammonium groups were prepared by coating a precursor with secondary amino groups (the product of N-[3-(trimethoxysilyl)propyl] ethylene diamine and 3-(triethoxysilyl)propyl isocyanate) on porous glass fiber membranes and further treated with bromoethane. The precursor coating and bromoethane treatment have been proved successful by membrane characterization such as Fourier-transform infrared (FTIR) spectrum, scanning electron microscopy (SEM) photo, contact angle, water content, and ion-exchange capacity. The optimal feed precursor/dimethyl formamide (DMF) ratio was found as 1:3 (w/w) based on the batch adsorption results of anionic dye Cibacron blue 3GA. The membrane ion-exchange capacity for this condition was 6.8 μmol/cm2 (or 104.2 μmol/cm3) and the maximum dye adsorption capacity was 2.12 mg/cm3. Different desorption solutions were tested in batch desorption process, and the use of 1N KSCN in 60% methanol attained a better performance (70% desorption). In the chromatography process with two pieces of 47 mm modified anion-exchange membrane discs (loading at 1 mL/min; washing and elution at 8 mL/min), more than 92% of dye molecules could be recovered from a 20 mL feed aqueous solution with an initial dye concentration of 0.05 g/L. Moreover, the membrane performance remained unaltered over 10 successive cycles of dye adsorption, washing, and elution.