Underwater superoleophobic all-cellulose composite papers for the separation of emulsified oil

All-cellulose paper-based composites with underwater superoleophobicity and high-wet-strength were developed by casting a barrier layer of bacterial cellulose (BC) on a filter paper substrate. To optimize the pore structure of barrier layer, slow gel process of BC dispersion was conducted via acidification and solvent exchange. 1,2,3,4-butanetetracarboxylic acid was used to improve the wet strength and surface hydrophilicity through the crosslinking reaction between fibers. The underwater oil contact angles are higher than 150° in neutral environment, and slightly decrease under acid and alkali conditions. Combined with the micron-sized pore structure of BC barrier layer, the composite papers show good separation performance of oil-in-water emulsion. A denser BC layer can significantly improve the separation efficiency, but also lead to the reduction of flux. During the gelation of BC barrier layer, the increase in the ethanol/water ratio of the dispersion medium is able to increase the flux without obvious negative impact on the separation efficiency. When the ethanol/water ratio is 80%, the separation efficiency and water flux reach 99.2% and 1320 L m−2 h−1·bar−1 for the emulsified soybean oil with the average size of 13 μm, respectively. This type of all-cellulose composite papers provides a new idea for the fabrication of membrane materials for oil–water separation.