Fabrication of novel Janus membrane by nonsolvent thermally induced phase separation (NTIPS) for enhanced performance in membrane distillation

Abstract

This study proposed to use the nonsolvent thermally induced phase separation (NTIPS) method to fabricate a novel Janus membrane for MD applications. The as-prepared dual-layer membrane consisted of a thin hydrophobic PVDF top-layer and a relatively thick hydrophilic PVDF-PVA sub-layer. By adopting a facile one-step co-casting technique and water soluble diluent ε-caprolactam (CPL), delamination-free dual-layer membrane was obtained. The SEM morphologies and FTIR crystalline analyses suggested the membrane formation mechanisms, where the hydrophobic top-layer was formed via NTIPS process, resulting in an ultra-thin dense skin with finger-like pores formed beneath; while the hydrophilic sub-layer was induced by TIPS, producing highly porous cellular structure with high degree pore interconnectivity. Combining the structural observation and MD performance results, suitable fabrication parameters were identified as a PVDF concentration of 15 wt% for the hydrophobic layer and coagulation temperature between 20-40 o C. The total membrane thickness was optimized as 100-150 μm, given the thickness of hydrophobic layer kept within an optimal range of 30-60 μm to ensure minimal mass transfer resistance. The Janus membrane exhibited stable salt rejection above 99.5% over continuous MD runs and superior permeation flux up to 165.3 kg•m-2 •h-1 at 80 o C, which was remarkably higher than reported MD membranes.

Porous Hydrophobic–Hydrophilic Composite Hollow Fiber and Flat Membranes Prepared by Plasma Polymerization for Direct Contact Membrane Distillation

“…The water flux achieved with a 30 g/L salt solution was 12.2 L/m 2 -h with a salt rejection of 99.9% for a feed temperature of 60 °C and distillate temperature of 17 °C [ 29 ]. A novel dual-layer flat membrane consisting of a thin hydrophobic top-layer of PVDF and a relatively thick hydrophilic PVDF-PVA sub-layer was fabricated using the non-solvent thermally induced phase separation (NTIPS) method [ 30 ]; the water vapor flux achieved was quite high.…”

Alteration of the morphology of polyvinylidene fluoride membrane by incorporatingMOF‐199 nanomaterials for improving water permeation with antifouling and antibacterial property

“…[35] The cross-sectional structures of the membranes are shown in Figure 3. The pristine PVDF membrane, M0, possessed typical asymmetric structure of finger-like sublayer on the top and sponge-like structure on the bottom (Figure 3a), [36] and the composite membrane, M3, showed the similar structure compared with M0 ( Figure 3b). However, as for the M5 and M7 membranes, the finger-like structure was replaced by the sponge-like structure (Figure 3c,d).…”

Effect of Additives on Hydrophobicity of PVDF Membrane in Two-stage Coagulation Baths for Desalination

“…29 Surface hydrophobicity can be enhanced by in phase inversion method (dual coagulation bath method) exhibiting hydrophobic characteristics with a higher contact angle. 30 It should be noted that membrane immersed in softer precipitation such as ethanol, methanol, octanol, etc., prevents the asymmetric structure which leads to improving the wettability of membrane. The droplet images can be seen in Figure 4 for M-3, M-4, M-5 and the values were listed in Table 3 indicating that all PVDF membranes prepared by dual CB resulted in the hydrophobic membrane.…”