Sustainable, biocompatible, and mass-producible superwetting water caltrop shell biochars for emulsion separations

The separation of oily wastewater, specifically emulsions, is a crucial global issue. Possible strategies for the efficient separation of emulsified oil/water mixtures through sustainable and environmentally friendly materials have recently drawn considerable attention. In our study, we prepared superwetting water caltrop shell biochar (WCSB) via a top-lit-updraft carbonization procedure. The as-prepared WCSB was characterized by superhydrophilicity, underwater superoleophobicity, underoil superhydrophilicity, and underoil water adsorption ability. Because of its superwetting properties, WCSB was used for the separation of both surfactant-stabilized oil-in-water emulsions (SOIWEs) and surfactant-stabilized water-in-oil emulsions (SWIOEs) with very high fluxes (up to 74,700 and 241,000 L m^-2 h^-1 bar^-1 for SOIWE and SWIOE, respectively). The separation performances were excellent, with oil contents in all SOIWE filtrates lower than 10 ppm and oil purities in all SWIOE filtrates higher than 99.99 wt%. Moreover, WCSB was applied to separate dye-spiked emulsions. Due to their high emulsion separation ability, sustainability, good biocompatibility, and ease of mass production, the as-prepared WCSBs have notable potential for utilitarian applications.