Sustainable Antibacterial\nSurface of Transparent PMMA\nMembranes with α‑ZrP Nanosheets Adsorbing Tetraalkylammonium\nIons

We fabricated composite membranes containing inorganic\nnanosheets\n(NSs) and polymers and demonstrated their outstanding antibacterial\nperformance against several opportunistic pathogens. Layered α-zirconium\nphosphate [Zr(HPO<sub>4</sub>)<sub>2</sub>, α-ZrP] as a pristine\ncompound of NS was exfoliated by ion-exchanging protons in the interlayer\nspace of α-ZrP with bulky tetraalkylammonium ions (TRA<sup>+</sup>: R = butyl, hexyl, and octyl). During the exfoliation process, TRA<sup>+</sup> was electrostatically adsorbed onto α-ZrP NS with a\nnegative surface charge (ZrP-TRA-NS). The produced PMMA membrane including\nα-ZrP NS (PM-ZrP-TRA-NS) was optically transparent and prohibited\nbacterial growth, and the effect was stronger for Gram-positive Staphylococcus aureus than Gram-negative Escherichia coli. The antibacterial activity of PM-ZrP-TRA-NS\nwas based on physical damage induced by both 2D ceramic NSs and sharp\nalkyl chains of TRA<sup>+</sup>. Despite the inherent flexibility\nof alkyl chains, when adsorbed onto the NSs, they can act in a manner\nthat effectively pierces the bacterial cell wall. The piercing force\nof TRA<sup>+</sup> was greater for the longer alkyl chains (TBA<sup>+</sup> < THA<sup>+</sup> < TOA<sup>+</sup>). Focusing on the\ndifference in the cell wall structure between these bacteria, the\ngrowth of Gram-positive S. aureus with\nloose peptidoglycan layers as an outer membrane could be easily inhibited\nby contact with the composite film. In contrast, Gram-negative bacteria E. coli, surrounded by a relatively dense outer cell\nwall composed of peptidoglycan and lipopolysaccharide layers, could\nnot be damaged easily. In this study, the antibacterial mechanism\nof PM-ZrP-TRA-NS membranes was elucidated, and their usefulness as\nantimicrobial coatings for existing solid surfaces was demonstrated.