Reduction of Pb2+ in Aqueous Solution: Early Steps and Colloid Formation, and the Atom -> Metal Transition

Article abstract of DOI:10.1021/j100191a004

Aqueous solutions of Pb(ClO4)2 containing sodium formate were investigated pulse radiolytically.Pb⁺ (absorption maximum at 320 nm, ε = 2.5 x 10³ M^-1 cm^-1) is formed at the first reduction product via the reactions of e_aq^- and CO2^- with Pb²⁺.The bimolecular reaction between two Pb⁺ ions to yield Pb⁰ occurs with 2k = 8.2 x 10⁹ M^-1 s^-1.Pb⁰ has an absorption maximum at 290 nm(ε = 1.2 x 10⁴ M^-1 cm^-1) and a weaker one at 660 nm (ε = 9.7 x 10² M^-1 cm^-1).During the second-order disappearance of the Pb⁰ absorption, stronger absorption bands at shorter wavelengths build up, which are attributed to oligomeric precursors and finally metallic particles of lead.The metallic particles have an absorption maximum at 220 nm which is attributed to a plasmon oscillation.The first appearance of this band occurs at a particle agglomeration number slightly smaller than 10; thus, lead is found to possess a giant dipole oscillation band at rather small particle sizes as was first found for silver particles in solution and alkali metal particles in molecular beams.