PVDF/magnetite blend membranes for enhanced flux and salt rejection in membrane distillation

This study reports on the enhancement of direct contact membrane distillation (DCMD) performance by incorporating magnetite nanoparticles (NP) in polyvinylidene fluoride (PVDF) membranes to render the membrane bulk hydrophilic while maintaining a hydrophobic top surface. Hansen solubility parameters (HSP) were first calculated to assess the affinity/compatibility of NP with the polymer, dope solution and aqueous feed. Extensive characterizations were done to elucidate the structural and physiochemical properties of the blend membranes. Energy dispersive spectrometry (EDS) analyses confirmed the uniform distribution of NP within the membrane matrix. Contact angle values showed that the NP did not compromise the hydrophobicity of the membrane top layer. The blend membrane had a 92% higher water uptake value, compared to the pristine sample, indicating the high hydrophilicity of the membrane bulk. Blend membrane also showed higher (ca. 36%) DCMD flux, due to their hydrophilic sub-layer, without compromising the salt rejection. Leaching tests were conducted using both water and concentrated acid to confirm the presence of nanoparticles and to demonstrate the membrane stability in aqueous medium.