Multi‐Scale Water Modulation for Regulating Water Reactivity and Suppressing Nanoscale Zero‐Valent Iron (nZVI) Corrosion

ABSTRACT Water is not a passive solvent but an actively tunable participant in aqueous‐phase redox processes, whose reactivity can be regulated by modulating its molecular states and dynamics. Here, we introduce a multi‐scale water modulation strategy using a hydrophilic polysaccharide network to reorganize the aqueous environment and suppress the corrosion of nanoscale zero‐valent iron (nZVI). At the molecular scale, the polysaccharides tune free water (FW) into bound and intermediate water (BW/IW), which together account for ∼45% of total water. This water‐state redistribution elevates the reaction barrier for H ₂ O–Fe(0) interactions from 8.2 eV (FW) to 10.5 eV (BW), and the observed reaction rate constant (k _obs ) shows a strong linear dependence on the BW+IW fraction (R ² ≈ 0.99). At the nanoscale, the network imposes hydrophilic confinement (mesh size ≈ 1.1 nm) that restricts water access to reactive Fe(0) sites, causing a rapid attenuation of early‐stage reactions (<12 days). At the macroscale, the modulated water forms a viscoelastic matrix (G′ > G″) that retains in situ‐generated H ₂ microdomains, creating interfacial shielding that suppresses prolonged reactions (>12 days). By linking water's molecular organization to macroscopic redox behavior, this work provides a framework for using the water modulation to stabilize corrosion‐sensitive nanoparticles.