A reformulation of the equation of state for interfacial tensions

Highly efficient treatment of oil-water emulsions in severe environments (organic solvents, strong acids) is recognized as a challenging subject. Polyphenylene sulfide (PPS) is an ideal membrane material with superior thermal stability as well as chemical resistance that is expected to settle this challenge. However, the hydrophobicity of PPS (h-PPS) membrane inherently prevents its efficient treatment of oil-in-water (O/W) emulsions. In this study, superhydrophilic modification of PPS substrates was achieved by in situ electrostatic self-assembly of hydrophilic Zr-MOFs to obtain UiO-66-NH2@h-PPS membranes. The introduction of UiO-66-NH2 crystals constructed the micro/nanoscale hierarchical structure for the substrate, which transforms the PPS substrate from a hydrophobic to a superhydrophilic state (water droplets require only 0.6 s to be completely immersed in the membrane). Meanwhile, the UiO-66-NH2@h-PPS membranes gain under-water superhydrophobicity (the under-water oil contact angle exceeds 150° for toluene, hexane, dichloromethane, and carbon tetrachloride, of which toluene reaches 163.1°), thereby improving wettability selectivity and decreasing oil adhesion, permitting the fabricated UiO-66-NH2@h-PPS membranes to effectively separate different types of O/W emulsions. The UiO-66-NH2@h-PPS membranes acquire excellent permeate fluxes (for the surfactant-free toluene-in-water emulsion, it reaches up to 7638.1 L m−2 h−1) and separation accuracy (99.1% oil rejection). Moreover, the UiO-66-NH2@h-PPS membrane exhibited outstanding harsh environment resistance. Interestingly, the combination of UiO-66-NH2 and h-PPS substrate was applicable to degrade the organic compound in water, and the degradation efficiency of the methylene blue achieved 85.7% under visible light within 120 min. In summary, loading Zr-MOFs onto h-PPS substrates provides a novel strategy for the efficient treatment of wastewater under complex conditions with great potential for practical applications.