Bioinspired lignin-based loose nanofiltration membrane with excellent acid, fouling, and chlorine resistances toward dye/salt separation
Wenge Sun, Na Zhang, Qiang Li, Xinmin Li, Shunmei Chen, Li Zong, Yiliyasi Baikeli, Enguang Lv, Huining Deng, Xiaotai Zhang, Hussein Baqiah
Abstract
Exploring green, renewable, and low-cost raw materials has great significance on developing high-performance loose nanofiltration (LNF) membranes using a scalable fabrication approach . Lignin is the second most abundant biomacromolecule in the botanic field. In this report, a lignin-based LNF membrane is successfully fabricated using alkaline lignin and sodium ligninsulfonate as raw materials and dopamine (DA) as a surface modifier by a brush assisted layer-by-layer assembly. The driving forces for the assembly are hydrogen bonds between hydrophilic groups and π-π stacking in phenyl groups. The experimental results show that the membrane possesses ultrahigh pure water permeability (65.2 LMH bar −1 ), and high dye rejections (100% for brilliant blue R (BBR), 96.1% for congo red (CR)) and salt permeations (85.1% for NaCl, 96.7% for MgCl 2 ), exhibiting satisfactory dye/salt separation performance. The separation process is dominated by the synergistic action of the size exclusion and Donna repulsion between charged dye clusters and the membrane surface . The separation selectivity of the membrane can keep stable accompanied by a small permeate-flux fluctuation during immersed in HCl solution for 7 days. The membrane also shows low flux decline and excellent flux recoverability during a three-cycle CR fouling process. Moreover, the separation capability and permeate flux only show small fluctuations under 5500 ppm·h chlorination strength (pH = 5). The DA surface modification can significantly enhance the membrane permeability, fouling and chlorine resistances. The membrane possesses satisfactory performance stability on a long-term running process for the CR/NaCl separation.