Electrochemical/chemical synthesis, purification, characterization and properties of atomic quantum clusters of different sizes

Resumo

The main objective of this PhD thesis was the synthesis of Cu clusters in water and without any ligand or stabilization agent, which could mask many of their properties (catalytic, biomedical, etc.). For this purpose, electrochemical methods were used, because the electrochemical synthesis seems to be optimal for the production of small size clusters (less than ≈ 5-10 atoms), which is the main goal of this work. To achieve the control of the cluster growth, without protecting agents, the synthesis of clusters was carried out by an optimal kinetic control of the reaction. Such optimal conditions were accomplished through an exhaustive study of the key electrochemical parameters controlling the reaction. In this way very monodisperse samples of naked Cu5 clusters in water could be synthesized and characterized. The second goal of this work was the synthesis of larger amounts of larger clusters (> ≈ 10 atoms). For this purpose, a two-step process was developed, taking benefit of one of the main properties of small clusters, namely their exceptional catalytic activities. By this way, using Cu metal salts as starting material and small Cu5 clusters as catalytic agents, together with cysteine as capping agent, almost quantitative amounts of Cu10 clusters could be produced by chemical reduction of the corresponding metal salt. Cluster samples were characterized by a combination of different methods: UV-Vis and fluorescence spectroscopy, Mass Spectrometry, X-ray photoelectron spectroscopy, Atomic force microscopy and Advances synchrotron techniques (EXAFS, XAS and XANES). Finally, several properties of the synthesized samples (HOMO-LUMO gaps and Photocatalysis for the degradation of contaminants) were studied.