Polyamide Thin-Film Composite Janus Membranes Avoiding Direct Contact between Feed Liquid and Hydrophobic Pores for Excellent Wetting Resistance in Membrane Distillation

Abstract

Hydrophobic membranes are very susceptible to pore wetting when they contact the feed water containing surfactants or low-surface-tension liquids in membrane distillation (MD). Avoiding direct contact between feed water and hydrophobic membrane pores is a potential strategy to control membrane pore wetting. In this study, we successfully fabricated a polyamide thin-film composite (TFC) Janus membrane through interfacial polymerization, with a hydrophobic microporous membrane as the substrate. The fabricated TFC Janus membrane showed a super antiwetting ability when treating the hypersaline water containing surfactants (>0.4 mM sodium dodecyl sulfate) or ethanol (>40% v/v). The optical coherence tomography (OCT) observation revealed that no liquid water was present at the distillate-facing side of the polyamide layer. Therefore, we ascribed the super antiwetting ability to the fact that the polyamide layer could prevent the feed liquid from directly contacting hydrophobic pores. The TFC Janus membrane could also avoid the wetting induced by gypsum scaling because the polyamide layer could act as a barrier to hinder the intrusion of gypsum crystals into hydrophobic pores. In addition to the antiwetting ability, the TFC Janus membrane showed 10–20% increases in vapor flux, despite the existence of a dense polyamide layer. Because interfacial polymerization is the most commonly used method for the fabrication of commercial TFC membranes, this study provides a facile and scalable method to fabricate membranes with robust antiwetting ability.

Dense Thiourea–Graphene Oxide Wetting-Resistant Membrane for Photothermal Distillation

“…Previous research has indicated that the effects of electrostatic repulsion and attraction are rendered negligible in salt solutions due to the shielding effect of high ionic strength. , Therefore, size exclusion emerges as the predominant mechanism for wetting resistance, enabling the GO-TU layer to exhibit a satisfactory performance (Figure c). Furthermore, the dense layer also exhibited potential resistance ability of scaling-induced wetting (Figure S13), suggesting great advantages in wetting resistance …”

“…Furthermore, the dense layer also exhibited potential resistance ability of scaling-induced wetting (Figure S13), suggesting great advantages in wetting resistance. 28 In addition, a range of commonly used surfactants in the environment was investigated (Table S3), 45 and their molecular sizes were found to be larger than the nanochannel size of the GO-TU layer. It further supports the ability of the GO-TU/PVDF membrane to resist practical wetting scenarios.…”

“…Constructing a dense layer on a hydrophobic membrane surface is considered as a promising solution to prevent surfactant molecules entering the pores of the hydrophobic membrane, and this strategy has been proven in convention membrane distillation systems to improve the wetting resistance significantly. − However, additional demands should be considered when implementing the dense layer strategy in SDMD systems. Previous studies have shown that the application of dense layers, either through coating or blending into the photothermal layer, leads to a decrease in photothermal conversion efficiency. , This decline can be attributed to the shading effect caused by the presence of dense layers (Figure S1a,b).…”