Engineering Atomically Precise Cu4I4 Nanoclusters With Integrated Adsorption and Hydrogenation Functions for Efficient Photocatalytic Nitrate-to-Ammonia Conversion.

Photocatalytic nitrate reduction to ammonia offers a sustainable route that couples environmental remediation with nitrogen resource utilization. However, this transformation suffers from sluggish kinetics and insufficient hydrogenation, leading to poor selectivity and efficiency. Herein, we report the deposition of Cu4I4 nanocluster onto TiO2 (Cu4I4/TiO2) that achieves efficient and selective photocatalytic nitrate reduction to ammonia under mild conditions. The active site derived from an atomically precise Cu4I4Py4 (Py = pyridine) nanocluster introduces sterically accessible copper sites with intrinsically unsaturated coordination and enhanced Lewis acidity for nitrate adsorption and activation. The iodide ligands in Cu4I4 motif directly bonded to copper atoms are suggestive of promoting the generation of reactive hydrogen species (*H). The atomic-scale proximity of copper and iodide sites facilitates efficient *H utilization in the multistep hydrogenation toward NH3. Consequently, Cu4I4/TiO2 delivers an ammonia generation rate of 26.8 mmol·gcat -1·h-1 with good selectivity in a sacrificial-reagent-assisted photocatalytic nitrate reduction system. In situ characterizations and theoretical calculations support the plausible cooperative dual-site mechanism, which synergistically ensures the deep hydrogenation of nitrate and its intermediates to ammonia. This work establishes an atomic-level design paradigm for constructing multifunctional nanocluster catalysts that address the selectivity and efficiency challenges inherent to complex multiple proton/electron-involved reactions.