Effect of solvent type on the physicochemical properties and performance of NLDH/PVDF nanocomposite ultrafiltration membranes

The effect of different solvents e.g. N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), dimethylacetamide (DMAc) and dimethylformamide (MDF) on the physicochemical properties of Mg-Al nanolayered double hydroxide (NLDH)/PVDF nanocomposite ultrafiltration membranes was investigated. The Mg-Al NLDH was applied as a hydrophilic nanofiller with the purpose of improving PVDF-based ultrafiltration membranes. The main purpose of this study was to find which solvent could better highlight effect of the nanoparticle in the membrane preparation. Scanning microscopy (SEM), energy dispersive X-ray (EDX), atomic force microscopy (AFM) and water contact angle techniques were used for analyzing the surface and cross-sectional morphology, the NLDH distribution in matrix of nanocomposite membrane, surface roughness and hydrophilicity of the prepared PVDF/NLDH nanocomposite membranes, respectively. The permeability and the antifouling properties of the prepared membranes were investigated via determination of pure water flux and flux recovery ratio (FRR), respectively. The results showed that the morphology, dispersion of NLDH in the matrix of polymer and the properties of the nanocomposite are mainly affected by the type of the solvent. This research demonstrates that when NMP is used as solvent the NLDH can significantly improve the performance of the PVDF membrane, while by using other solvent the NLDH is not able to affect the performance of the PVDF membrane significantly. Indeed, in the case of using NMP as the solvent, beside the surface porosity enhancement in the presence of NLDH, the cross sectional morphology of the membrane was significantly affected and the pores changed from sponge-like to finger-like, resulting in significant permeability improvement of this membrane.