Can lignin nanosphere be used as a recycled sacrificed template for constructing high performance loose nanofiltration membranes?

Sacrificed template strategy has become a promising pathway to construct high performance loose nanofiltration (LNF) membranes for dye-containing wastewater treatment. However, few studies have been conducted on the recycling of templates in the LNF membrane preparation. In this study, lignin nanoparticles (LNPs) with abundant biomass sources, low cost, renewable ability, were attempted to be used as a recycled sacrificed template for the first time. The LNPs were easily renewed by concentration and NaOH dialysis with smaller nano-size and more hydrophilic surface. The optimized P-LNF-50 membrane prepared by pristine LNPs templates exhibited high water permeability of 146.24 LMH·bar⁻¹, excellent separation of dye/salt (i.e. rejection: 97.79 % for CR, 0.48 % for Na₂SO₄, 0.25 % for NaCl), and superior long-term stability. Interestingly, the R1-LNF-70 membrane prepared by 1^st recycled LNPs templates can still maintain high water permeability of 132.97 LMH·bar⁻¹ and excellent separation of dye/salt (i.e. rejection rate: 98.31 % for CR, and 1.27 % for Na₂SO₄). While the 2^nd recycled LNPs can not produce satisfied LNF membranes due to its poor figuration and easy aggregation. The inherent relationships between LNPs templates and selective layers were deeply explored. Importantly, the Sankey chart of recycling LNPs template technique and cost analysis indicated that the LNPs could be used as green templates for two cycles with comparable permeability and selectivity of dye/salts. Overall, our study paves the way for recycling of sacrificed templates for the scalable fabrication of high performance LNF membranes.