Atomic-Level Composition Engineering in M25 Nanoclusters for Photocatalytic Degradation of Methylene Blue: From Homometallic Au25, Ag25, and Cu25 to Heterometallic Au1Cu24

Abstract

Atomically precise metal nanoclusters provide an ideal platform for elucidating composition–activity relationships in photocatalysis. Herein, four structurally defined M₂₅ nanoclusters, Au₂₅, Ag₂₅, Cu₂₅, and Au₁Cu₂₄, were supported on g-C₃N₄ to establish an atomic-level composition-engineering model for photocatalytic methylene blue (MB) degradation. Among the homometallic clusters, Au₂₅ exhibited the highest activity, followed by Ag₂₅, whereas Cu₂₅ showed the lowest performance. Remarkably, substitution of a single Au atom into Cu₂₅ to form Au₁Cu₂₄ markedly enhanced the photocatalytic activity to a level comparable to that of Au₂₅. Au₁Cu₂₄/g-C₃N₄ achieved over 95% MB degradation within 120 min, a TOC removal efficiency of 71.6%, and retained above 88% degradation efficiency after five cycles. Photoelectrochemical measurements indicate that the improved performance of Au₁Cu₂₄ is associated with more efficient interfacial charge transfer and suppressed charge-carrier recombination relative to the Cu₂₅-based system. These results demonstrate that single-atom heterometal incorporation can effectively regulate photocatalytic function and provide a practical strategy for designing efficient and economical nanocluster-based photocatalysts.