All-wood-based hybrid membrane derived from waste sawdust for efficient emulsion separation

Oriented toward the demand for safe and sustainable oily wastewater separation, biomass-based composite membranes have received widespread attention due to the advantaged properties of green biodegradability, multifunctionality and easy modification, offering great application potentials in wastewater treatment. However, present studies still need to be done to enhance separation efficiency and to address the potential environmental risks from synthetic nanomaterials in biomass-based composite membranes. Herein, this work presented an “split and reorganization” strategy to prepare an all-biomass-based hybrid membrane for efficient emulsion separation using waste sawdust as raw materials, inspired by whole wheat bread. In this strategy, wood cellulose was extracted from waste sawdust via alkali elutriation, and lignin microparticles were prepared by hydrothermal process using black liquor formed from the extracting process of wood cellulose. Then, the all-wood-based hybrid membrane with super-wettability was fabricated for emulsion separation via vacuum-filtration of wood cellulose and lignin microparticles suspension. The lignin microparticles were uniformly distributed inside the all-wood-based hybrid membrane, which enhanced the surface roughness and endowed exceptional superhydrophilic/underwater super-oleophobic properties of the membrane. The obtained hybrid membrane exhibited superhydrophilicity with a water contact angle of 0° and underwater superoleophobicity with an oil contact angle of 140°. It can effectively separate oil-in-water emulsions with permeances up to 6673 L·m⁻²·h⁻¹ and high separation efficiency of greater than 98.8 %. More importantly, all-wood-based hybrid membrane demonstrated excellent demulsification and cycle ability after 10 cycles, which match well with the requirements for industrial oily wastewater. This study shows that the developed all-wood-based hybrid membrane and corresponding design strategy can be extended for preparing other biomass-based materials for applications in research and industrial fields.