Upcycling agricultural waste into membranes: from date seed biomass to oil and solvent-resistant nanofiltration

Abstract

Membranes hold a great promise for replacing energy-intensive separations across various industrial sectors. However, membrane production heavily relies on petrochemical-based raw materials; the need for greener membranes is a challenge that is yet to be solved. In this work, we solubilized date seed biomass (abundantly available from the multimillion-metric-ton date industry) using ionic liquids and dimethyl sulfoxide (which are greener than traditional organic solvents) to fabricate biodegradable nanofiltration membranes. The resultant membranes were coated with mussel-inspired polydopamine (PDA) via a layer-by-layer deposition method. The obtained membranes demonstrated excellent performance for organic solvent nanofiltration (OSN) and oil-in-water separation. The deposition time and the number of PDA layers correlated with the molecular sieving performance of the membranes and allowed the fine-tuning of the molecular weight cutoff (MWCO). The best-performing membrane exhibited an acetonitrile permeance of 7.8 L m⁻² h⁻¹ bar⁻¹ and a 96% rejection of acid fuchsin (585 g mol⁻¹). Moreover, an oil-removal efficiency of up to 97% was achieved with a water permeance of 5.7 L m⁻² h⁻¹ bar⁻¹. The prepared membranes showed excellent stability for over seven days in continuous nanofiltration tests. The biodegradability of the membranes was demonstrated in an aqueous cellulase solution. Our work offers a sustainable production of waste biomass-based membranes for liquid-separation applications.