Optimized hybrid PVDF/graphene membranes for enhancing performance of AGMD process in water desalination

Abstract

Hybrid membranes consisting of polyvinylidene fluoride (PVDF) and electrochemically-fabricated graphene were prepared via phase inversion technique. The important parameters in manufacturing unfilled PVDF membranes including polymer concentration and content of additives were initially assessed. The effects of adding graphene to the PVDF membrane on its performance for desalination of a 3.5 wt% NaCl solution were then investigated using an air gap membrane distillation setup. The simultaneous effects of three individual parameters in membrane preparation including ethanol concentration in the coagulation bath, the coagulation bath temperature, and graphene content on membrane characteristics such as contact angle, porosity, and permeation flux were investigated. By increasing ethanol concentration in the coagulation bath and graphene content in the polymeric solution, the contact angle and thus hydrophobicity of the membrane were increased. Also, by increasing graphene content up to 0.5 wt%, the membrane permeation flux was increased while further increase in the graphene content resulted in decrease in the permeation flux. It was found that coagulation bath temperature has the highest effect on the membrane porosity. The parameters for manufacturing optimum membrane were determined by experimental design. The optimum membrane could yield a permeation flux of 3.54 kg m−2 h−1 and a salt rejection of 99.88%, which are in good agreement with the predicted results. The performance of optimized membrane was superior to those by PVDF and GO/PVDF membranes reported previously in literature.