Three-dimensional superhydrophilic polyvinyl alcohol–formaldehyde composite sponges with suitable pore sizes for high efficiency emulsion separation

Abstract

Compared with membrane separation materials, three-dimensional (3D) sponge materials have a higher emulsion separation efficiency, better water flux, and stronger antifouling ability. In this work, 3D superhydrophilic polyvinyl alcohol–formaldehyde composite sponges with suitable pore sizes and distribution are successfully prepared through the crosslinking reaction of polyvinyl alcohol (PVA) and carboxyl modified polyvinyl alcohol (PVA–COOH) in the polyvinyl alcohol–formaldehyde (PVF) network under acidic conditions. The introduction of PVA and PVA–COOH can effectively decrease the average pore size of PVF sponge from 74.6 μm to 18.9 μm, while maintaining the porosity above 83.1%. These PVA/PVF and PVA–COOH/PVF composite sponges with suitable pore sizes are applied to separate surfactant-free and surfactantstabilized oil-in-water emulsions including low-polarity kerosene-in-water emulsion, medium-polarity toluene-in-water emulsion and high-polarity chloroform-in-water emulsion solely by gravity. The separation efficiency can reach up to 96.88% with a high water flux of 3.82 × 10⁴ L m⁻² h⁻¹ bar⁻¹. Meanwhile, the separation efficiency of the electrically neutral PVA/PVF and the negatively charged PVA–COOH/PVF composite sponges for different types of surfactant-stabilized oil-in-water emulsions, including anionic, nonionic, and cationic surfactants, is also investigated for further practical evaluation. The PVA/PVF and PVA–COOH/PVF composite sponges with outstanding hydrophilicity, excellent stability, simple preparation method and low cost can be regarded as new candidates for emulsion separation materials in practical applications.