Stacking-Controlled Spontaneous Polarization in Zn-In-S Nanosheets for Efficient Piezo-Photocatalytic H2O2 Production Toward Uranium Recovery.

Efficient uranium recovery from wastewater is vital for nuclear fuel sustainability and environmental protection. However, conventional photocatalytic and adsorption approaches suffer from sluggish charge separation, limited active sites, and poor selectivity. Piezo-photocatalysis, integrating light and mechanical stimuli, can address these issues by accelerating charge dynamics, which calls for piezo-photocatalysts with tunable polarization and well-defined crystal configurations. Herein, ternary Zn-In-S layered nanosheets (ZnIn2S4, Zn2In2S5, and Zn3In2S6) with tunable metal-layer stacking configurations are fabricated via chemical vapor transport (CVT). By adjusting the Zn/In stoichiometry, we precisely govern the stacking geometry and crystal symmetry, enabling programmable spontaneous polarization and piezo-photocatalytic activity. Among them, Zn2In2S5 exhibits the strongest spontaneous polarization (ΔV = 3.44 eV, µ = 3.534 Debye), delivering the highest hydrogen peroxide (H2O2) production rate (689 µmol·g-1·h-1) under combined ultrasonic and light irradiation. DFT reveals that Zn2In2S5 optimizes interfacial electron transfer to *O2 and *OOH intermediates and lowers the free‑energy barrier for the rate‑determining *OOH formation, rationalizing its superior two‑electron oxygen reduction activity. The in‑situ generated H2O2 selectively precipitates uranyl ions (UO2 2+) as metastudtite ((UO2)O2·2H2O), achieving an uptake capacity of 1709.3 mg·g-1. Our findings unveil the intrinsic structure-polarization-catalysis correlation induced by crystal stacking and symmetry, establishing a paradigm for designing efficient piezo-photocatalysts toward uranium recovery.