Synthesis of photocatalytic cysteine-capped Cu_≈10 clusters using Cu₅ clusters as catalysts

We report an easily scalable synthesis method for the preparation of cysteine-capped Cu_≈10 clusters through the reduction of Cu(II) ions with NaBH₄, using Cu₅ clusters as catalysts. The presence of such catalytic clusters allows controlling the formation of the larger Cu_≈10 clusters and prevents the production of copper oxides or Cu(I)-cysteine complexes, which are formed when Cu₅ is absent or at lower concentrations, respectively. These results indicate that small catalytic clusters could be involved, as precursor species before the reduction step, in the different methods developed for the synthesis of clusters. The visible light-absorbing Cu_≈10 clusters, obtained by the cluster-catalysed method, display high photocatalytic activities for the decomposition of methyl orange with visible light.