Upcycling black liquor lignin into superwetting carbon layer with switchable wettability for on-demand emulsion separation with high flux

Abstract

The separation of multiple types of emulsions by the traditional two-dimensional superwetting membrane is a desired outcome but remains a challenge, because of the disadvantages of single wettability, low flux and high cost. In this work, black liquor lignin-based carbon pellet with switchable wettability was prepared through hydrothermal and calcination using black liquor lignin derived from a multitude of sources as raw material. The obtained carbon pellet was developed into a superwetting black liquor lignin-based carbon filter layer with switchable surface wettability between hydrophobicity and superhydrophilicity via calcination and steam modification alternately, without the use of toxic modification reagents. The porous structure caused by pellet accumulation ensures a high penetration flux of the emulsion, while the black liquor lignin-based carbon pellet layer could function as an adsorbent layer, facilitating the capture tiny droplets from emulsions. Thus, the as-prepared carbon pellet layer can effectively separate oil-in-water and water-in-oil emulsions by adjusting its wettability with high separation flux up to 18778 L m⁻² h⁻¹. After multiple cycles, it still maintains more than 95 % of the original separation performance. Its switchable wettability, high flux, wide range of raw materials sources and low cost suggest its potential applications for emulsions separation and great value in environmental protection and industrial applications.