Unlocking internal Zr sites via pH-triggered coordination-hydrolysis: A metal-phenolic network confinement strategy for high utilization HZO adsorbents toward heavy metal remediation in real wastewaters.

Hydrous zirconium oxide (HZO) holds great promise for heavy metal sequestration, yet its practical application is severely limited by the underutilization of interior Zr(IV) sites. Herein, we develop a metal-phenolic network (MPN) confinement strategy to construct sub-10 nm HZO nanodomains within a tannic acid-Zr(IV)-functionalized polystyrene matrix (PS@TA-HZO), substantially enhancing interior-site accessibility. The TA-Zr network confines Zr-O condensation and restricts HZO growth, generating ultrafine nanodomains that shorten diffusion pathways to interior Zr sites. Meanwhile, the pH-modulated electronegative interface generates a strong electrostatic field that enriches Pb(II) toward the interior HZO regions. The TA-Zr-confined environment further provides favorable electronic and coordination characteristics for Pb(II) binding, evidenced by enhanced Zr-O hybridization, charge redistribution, and stable Zr-O-Pb configurations. The optimized PS@TA-HZO delivers a Pb(II) capacity of 261.6 mg/g and a distribution coefficient (Kd) of 18,714 mL/g under high-salinity conditions, 92-fold higher than conventional PS@HZO. XPS depth profiling reveals increasing Pb/Zr ratios from 2.81 at the surface to 3.03 at 6 nm depth, contrasting sharply with the decline to ∼0.33 in PS@HZO, confirming preferential utilization of interior sites. Fixed-bed tests with real electroplating and photovoltaic wastewaters achieve a treatment capacity of 3290 L/kg, reducing effluent Pb(II) below 10 μg/L over eight regeneration cycles. This work establishes MPN confinement as a strategy for unlocking latent interior capacity in metal oxides for practical heavy metal removal.