Xiuxiu Wang, Minmin Li,* Yuting Xiong, Haijuan Qin, Qiongya Li, Fusheng Zhang, Yongliang Yu,* Guangyan Qing*

Small 2024, DOI: 10.1002/smll.202408695

https://onlinelibrary.wiley.com/doi/epdf/10.1002/smll.202408695

  Access to clean and renewable energy, osmotic energy from salinity gradient difference, for example, is central to the sustainability of human civilization. Despite numerous examples of nanofluidic membranes for osmotic energy conversion, one produced from abundant and renewable biomass resources remains largely unexplored. In this work, cotton-derived cellulose nanocrystals (CNCs) were employed to fabricate a membrane by self-assembly with polyvinyl alcohol (PVA) and subsequent in situ growth of metal-organic frameworks, UiO-66-(COOH)2, to provide an example. The composite membrane exhibits excellent mechanical strength and toughness due to the long chains and hydrogen bonding interactions of PVA. Incorporation of UiO-66-(COOH)2 endows the composite membrane with abundant nano- and subnano-sized ion transport channels, resulting in a 150% increase in ion conductance, while also providing superior cation selectivity through collaboration with the sulfated CNCs. The composite membrane with 27.4% MOF content can achieve an osmotic energy conversion performance of 5.10 W·m−2 under a 50-fold KCl gradient condition and a monovalent cation selectivity of ~16 for K+/Mg2+. This work presents a solution for harvesting renewable osmotic energy by constructing nanofluidic membranes using plentiful renewable biomass materials and a simple, low-emission fabrication procedure.