Periodic Molecular-Level Asymmetric Channels for Synergistical Purification of Iodide Wastewater and Osmotic Power...

Heterogeneous structured nanofluidic membranes show an extraordinary potential for selective ion transport. In particular, heterogeneous membranes with periodically asymmetric nanofluidic channels are expected to exhibit optimal ion selectivity, yet have rarely been achieved to date. Herein, we designed a two-dimensional (2D) organic-inorganic superlattice-like membrane with periodically arranged molecular-level asymmetric channels that achieve high iodide-ion selectivity and permeability. The PDDA/Ti_0.87O₂ superlattice-like membranes (PDDA/Ti_0.87O₂ SLMs) were prepared from unilamellar Ti_0.87O₂ nanosheets with surface-modified poly(diallyldimethylammonium chloride) (PDDA) by a layer-by-layer assembly strategy, in which the PDDA layers and Ti_0.87O₂ nanosheets are alternatively stacked to form molecular-level asymmetric channels between the heterogeneous units periodically. Unlike conventional nonperiodic structures with discontinuous ion migration paths and high ion-diffusion resistance, superlattice-like membranes provide continuous, unobstructed transport channels, enabling I^- ions to follow a periodic adsorption-repulsion synergistic transport mechanism, thereby forming nearly frictionless continuous ionic flow. As a result, the PDDA/Ti_0.87O₂ SLMs produce a record I^-/SO₄^2- selectivity of ∼680, which is the highest among all reported materials. When applied to osmotic energy generators with the artificial iodine wastewater, the PDDA/Ti_0.87O₂ SLMs can facilitate sustainable osmotic power generation and maintain operation for at least 160 h. In addition, the resulting iodine solution can be effectively utilized as a sterilizing agent with a high bactericidal effect of 99.5% for Escherichia coli within 30 min. This study establishes a new paradigm for periodic molecular-level asymmetric channels, presenting an approach for maximizing resource utilization from industrial iodine wastewater.