Effects of embedding functionalized multi-walled carbon nanotubes and alumina on the direct contact poly(vinylidene fluoride-co-hexafluoropropylene) membrane distillation performance

Flat-sheet membranes were fabricated by incorporating alumina (Al₂O₃) and functionalized multiwalled carbon nanotubes (MWCNTs; MWCNTs-COOH) in PVDF-co-HFP membrane via the phase-inversion method for application in membrane distillation (MD) application. Scanning electron microscopy and atomic force microscopy were performed on the resulting membranes to investigate the effects of functionalized MWCNTs. The results revealed that the embedding of functionalized MWCNTs led to a significant modification of the membrane characteristics, including the structural morphology, thickness, roughness, porosity, pore size, and pore size distribution. The effects of operational parameters such as the hot feed solution temperature (47–67?°C), feed flow rate (0.35–0.55?L/min), and feed concentration (0–100?g/L) on the performance of the fabricated membrane were tested using the DCMD system. The experimental results demonstrated that the permeate flux was enhanced by approximately 32.43% by using functionalized MWCNTs, reaching a value of 16.35?kg/m² h at 35?g/L feed concentration, 67?°C hot feed temperature, and 0.55?L/min feed flow rate, at the constant temperature of 20?°C and 0.35?L/min flow rate. The functionalized MWCNTs embedded within the membrane successfully modified the interactions between water and the membrane to improve the water vapor transport while inhibiting salt penetration into the pores.