Metal nanoparticles (NPs) and nanoclusters (NCs) exhibit size-different properties, making them tunable and potentially useful for many applications. NCs are smaller than 2 nm in diameter and comprise of a precise number of metal atoms and stabilizing ligands. In recent years NCs have been synthesized in solutions using strongly-bound capping agents, such as thiols for Au NCs. While it is possible to produce monodisperse atomically-precise NCs using thiol stabilizers, the very strong metal-thiolate interaction limits applications, especially in catalysis, and greatly hinders electrochemical size analysis by anodic stripping voltammetry. Therefore, more weakly-bound ligands, such as phosphoniums and phosphines, have been used. In our work, we synthesized tetrakis(hydroxymethyl)phosphonium chloride (THPC)-stabilized Au NCs of 1.6 nm diameter. Their poor size stability leads to potential ripening and aggregation processes over time, which hinders the synthesize of THPC-stabilized Au NCs with high size uniformity. Solvent fractionation with different organic solvents (tetrahydrofuran and methanol) followed by centrifugation allow separation of the 1.6 nm diameter population from larger NCs and NPs in the sample. Use of methanol as the solvent allowed the smaller sized NCs to be seperated from the larger NPs or aggregates. Fractionation, centrifugation, and attachment to indium tin oxide-functionalized glass (glass/ITO) electrodes allows the development of the optimum fractionation conditions by performing size analysis using anodic stripping voltammetry (ASV), which allows size determination based on the Au oxidation potential. This simple method of separation allows purification of 1.6 nm diameter THPC Au NCs and concentration onto electrode surfaces for potential catalysis and sensing applications in the future.

Electrochemical size analysis of 1.6 nm diameter phosphonium-stabilized atomically precise gold nanoclusters purified by solvent fractionation

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