Adsorptive removal of fluoride by activated alumina doped cellulose acetate phthalate (CAP) mixed matrix membrane

Flat sheet mixed matrix membranes were prepared using cellulose acetate phthalate (CAP) and activated granular alumina using phase inversion technique. The membranes were characterized using porosity, permeability, molecular weight cut off (MWCO) and contact angle. Compositional analysis of the membrane was carried out by X-ray diffraction and the morphology and surface roughness were investigated by scanning electron microscope and atomic force microscope, respectively. The permeability of the membrane was reduced from 3.0 × 10−11 to 1.4 × 10−11 m/Pa s as alumina concentration increased from 0 to 35 wt% for constant CAP concentration at 20 wt%. Decrease in porosity from 75% to 45% supported the above fact. Membrane hydrophilicity was improved and most importantly, fluoride rejection from contaminated water increased to 91% using 35 wt% of alumina. Maximum adsorption capacity for fluoride was 2.3 mg/g for the mixed matrix membrane at room temperature. Continuous cross flow experiments revealed that the virgin membrane (24 kDa), having a surface area of 0.01 m2, could produce water well within the safety limit for a time of 11 h. Regeneration study was conducted for five cycles. Effect of other co-existing anions on fluoride removal efficiency of the membrane was also studied.