Preparation of a Main-Chain-Type Polybenzoxazine-Modified Melamine Sponge via Non-Solvent-Induced Phase Inversion for Oil Absorption and Very-High-Flux Separation of Water-in-Oil Emulsions

Abstract Cost-effective, high-performance materials for the removal of oil contamination from water, specifically oil/water emulsions, in an environmentally friendly way are urgently required, but their development remains a major challenge. In this study, a facile water-based non-solvent-induced phase inversion method was applied to fabricate main-chain-type polybenzoxazine-modified melamine sponge (PBZMS). The as-prepared PBZMS possesses superhydrophobicity and superoleophilicity and can remove oil/organic solvents from the surface of water, as well as underwater. PBZMS has an outstanding absorption capacity (up to 170 times its weight), and, after long-term immersion tests in organic solvents, PBZMS maintained its superhydrophobicity. By compressing the PBZMS sponge, we achieved excellent oil–water separation of surfactant-stabilized water-in-oil emulsions (SWOEs) at very high permeation fluxes of 13,900 ± 300 L m-2 h-1 and 1,353,000 ± 27,700 L m-2 h-1 bar-1 via gravity-driven and pressure-driven (0.025 bar) processes, respectively, yielding an oil purity ≥ 99.96 wt.%. The excellent absorption capacities for various organic solvents and oils, outstanding separation performance for emulsions, stability in harsh chemical environments, and recyclability of PBZMS make it a promising candidate for large-scale applications.