PPS/TA-PEI/CaAlg/ZIF-8 composite membranes with under-liquid dual superlyophobicity for on-demand separation of oil-water emulsions

Polyphenylene sulfide (PPS) membrane materials have attracted significant attention for separating oily wastewater due to their remarkable separation precision and permeation capability. Nevertheless, the inherent hydrophobic characteristics result in a single wetting property, which restricts their broad applicability in treating diverse types of oily wastewater. In this study, the PPS/TA-PEI/CaAlg/ZIF-8 composite membranes exhibit outstanding under-liquid dual superlyophobicity, which were formed via constructing a composite coating containing polyphenol-polycation and calcium alginate (CaAlg) hydrogel, and assembling ZIF-8 nanocrystals with suitable surface chemistry. Through the solvent pre-wetting approach, the surface wettability of the PPS composite membranes can be flexibly transitioned between under-water superoleophobicity and under-oil superhydrophobicity, thus realizing on-demand separation of oily wastewater. It is noteworthy that the treatment efficiency of the PPS/TA-PEI/CaAlg/ZIF-8 composite membranes for the various oil-water mixtures (surfactant-free) and emulsions (stabilized by surfactants) attained greater than 98.1%. Meanwhile, the rapid transport capability of diverse types of oil-water emulsions can also be exhibited, with a permeance of 1652.4 L m -2 h -1 bar -1 for water-in-oil (W/O) emulsions and 2087.5 L m -2 h -1 bar -1 for oil-in-water (O/W) emulsions. In addition, the PPS composite membranes demonstrated outstanding anti-fouling capacity, recyclability, and switchable separation capacity. This work extended the utilization of the PPS membrane material in the controllable treatment of oily wastewater.