Facile preparation of water-proof paper with tunable surface properties for water/oil separation

Highlights: • Water-proof paper was prepared by using a self-crosslinkable polyelectrolyte. • Water-resistance of paper was one magnitude improved by incorporating 1.2 wt% polymer. • The modified paper was stable in 6 M HCl, featuring tunable surface properties. • The modified paper served as an efficient membrane for separating oil/water mixtures. Paper sheets are economic and sustainable materials alleviating the world's reliance on petroleum plastics, yet the facile preparation of water-proof paper combing high strength with tunable surface properties is difficult. This work exploited a self-crosslinkable polyelectrolyte (poly[1-cyanomethyl-3-vinylimidazolium], PCMVIm) to circumvent this problem. The PCMVIm solution was filled into paper sheets, dried, and treated by mild ammonia (NH₃) vapor at 25 °C. Paper sheets incorporated with 0.6 wt% PCMVIm were rendered water-proof (80 °C, 1 week) and acid-resistant (6 M HCl), exhibiting a wet strength that is 6 times higher than pristine paper without PCMVIm. In addition, the hydrophilicity and oleophilicity of NH₃-treated paper were easily tuned by modulating the counter anions of PCMVIm. The modified paper sheets show high permeability, selectivity and stability in separating water/oil emulsions containing toluene, petroleum ether, hexane and chloroform, respectively. The facile method of NH₃ vapor treatment confers wet-resistance, high strength, and tunable surface properties to paper valorization, leading to sustainable paper sheets for efficient oil/water separation.