Bio-Inspired Amino Acid Promoted Nanofluidic Ion Transport and Energy Conversion in Free-Standing Layered Vermiculite-based Membranes

Two-dimensional nanofluidic membranes have garnered considerable interest due to their potential for cost-effective osmotic energy harvesting. One promising approach to enhancing ion conductivity and selectivity is the incorporation of guest additives. However, the traditional host-guest configuration can undermine the structural integrity of nanochannels owing to the inconsistent size and shape of these additives. Drawing inspiration from the intricate design of biological protein channels, which utilize small amino acid molecules as guests, we have addressed this issue by incorporating glycine, a common amino acid, into a vermiculite membrane using a simple vacuum-assisted infiltration method. The resulting vermiculite-glycine membrane demonstrates 1.8 times greater ionic conductivity and twice the power density compared to pure vermiculite membranes. Analysis based on glycine content, coupled with spectroscopic examination, reveals that ion conductivity is linked to the distribution of glycine molecules across three specific sites within the membrane. This suggests that glycine molecules—whether confined in voids, adsorbed onto nanochannel surfaces, or intercalated within multilayered vermiculite nanoparticles—enhance nanofluidic ion transport by modulating surface and space charge density, as well as strengthening hydrogen bonding, electrostatic interactions, and steric effects. This work reveals the specific interactions between amino acids and vermiculite, offering a novel path for advancing nanofluidic composite membranes and highlighting critical considerations for the proposed strategy.