Antiswelling and Mechanical Robustness Clay Membranes Using as Osmotic Energy Conversion

Clay-based nanofluidic membranes are a promising candidate for osmotic energy conversion (OEC) due to their inherent surface charge that enhances ion selectivity. However, practical applications of these materials were constrained by significant swelling and inferior durability in aqueous environments. Herein, natural halloysite nanotubes (HNTs) were intercalated into layered montmorillonite (MMT) membranes to boost the osmotic energy conversion efficiency. The spatial confinement provided by HNTs, along with electrostatic interactions between MMT and functionalized HNTs, mitigates the water swelling of nanofluidic membrane, and the interlayered spacing decreases from 1.60 to 1.26 nm after complete hydration. Furthermore, the hollow structure of HNTs offers short and efficient pathways that improve fluidic permeability and accelerate cation translocation. HNT/MMT achieved a maximum OEC power output of 5.12 W m^-2 under a 50-fold salinity gradient of KCl electrolytes, which significantly outperformed the one-component clay two-dimensional (2D) nanofluids. The composite clay membrane demonstrates robust performance across various electrolyte solutions and under extreme pH conditions. This study provides a strategy for designing clay-based 2D nanofluids.