Two-Dimensional Photothermal Nanosheets as Confined Gelation Platforms for Large-Scale, Ultrathin, and Uniform Lamellar Hydrogel Membranes

Hydrogels featuring abundant network chemistry and tailorable pore structure have emerged as appealing membrane materials for numerous fields including ion sieving, gas separation, and osmotic energy harvesting. Nevertheless, current hydrogel membranes suffer from high transport resistance and inferior selectivity, owing to the inability of conventional thermal-initiated and photoinitiated bulky gelation methods to reduce their micrometer-scale thickness and pore sizes. Herein, we discover a versatile confined gelation platform to elaborate ultrathin lamellar hydrogel membranes (LHMs) using two-dimensional photothermal nanosheets as triggers to replace conventional small-molecule thermal initiators and photoinitiators. The LHMs are fabricated by manipulating the assembly of photothermal nanosheets within hydrogel precursors into a thickness-tunable lamellar skeleton with subnanometer interlayer spacing on the surface of porous substrates that harness their size screening ability to reject nanosheets for assembly, followed by a photothermal-triggered confined gelation only occurring within this lamellar skeleton. This approach enables the manufacturing of large-scale and uniform LHMs with superstable subnanochannels and ultrathin thickness as low as 50 nm, which is about 3 orders of magnitude lower than that of conventional counterparts. By customizing hydrogel network chemistry, our LHMs can be applied for gas separation with an extraordinary CO 2 /N 2 selectivity of 175 as well as harvesting osmotic energy with an impressive maximum power density of 6.87 W/m 2 even under long-term services.