Preparation of high-yield and ultra-pure Au25 nanoclusters: towards their implementation in real-world applications

Abstract

Colloidal approaches allow for the synthesis of Au nanoclusters (NCs) with atomic precision and sizes ranging from a few to hundreds of atoms. In most of the cases, these processes involve a common strategy of thiol etching of initially polydisperse Au nanoparticles into atomically precise NCs, resulting in the release of Au-thiolate complexes as byproducts. To the best of our knowledge, neither the removal of these byproducts nor the mass spectra in the relevant mass region were shown in previous studies. A thorough analysis of inorganic byproducts in the synthesis of [Au₂₅(PPh₃)₁₀(PET)₅X₂]²⁺ NC, abbreviated as Au₂₅ NC, reveals that published protocols lead to Au₂₅ NCs in vanishingly small quantities compared to their byproducts. Three purification methods are presented to separate byproducts from the desired Au₂₅ NCs which are proposed to be applicable to other promising Au NC systems. Additionally, critical factors for a successful synthesis of Au₂₅ NCs are identified and discussed including the role of residual water. An important finding is that the etching duration is very critical and must be monitored by UV-Vis spectroscopy resulting in synthetic yields as high as 40%.