Mechanisms of Reduction of M(H₂O)_k ⁿ⁺ to Form M°-Nano-Particles in Aqueous Solutions Differs from That Commonly Assumed: The Reduction of Ag(H₂O)₂ ⁺ by H₂

The redox potentials of M(H₂O)_l ⁿ⁺/M°(H₂O)_k are far too negative for the reduction of M(H₂O)_l ⁿ⁺ by most common reducing agents. Therefore, the question raised is how do relatively weak reducing agents reduce M(H₂O)_l ⁿ⁺ to form M°-nanoparticles, M°-NPs? Density functional theory calculations concerning the mechanism of reduction of Ag(H₂O)₂ ⁺ by H₂ prove that AgH_aq is formed as an intermediate. The AgH_aq agglomerize to form a variety of {(AgH)_n}_aq and {(AgH)_nAg}⁺ _aq. H₂ release occurs only from these agglomerates. It is suggested that the first agglomeration step is {(AgH)_n}_aq + Ag(H₂O)₂ ⁺ → (Ag₂H)⁺ _aq. Thus, M°_(solvated) are not transients in the formation of M°-NPs except when very strong reducing agents, for example e^- _aq, are used. Therefore, one has to re-evaluate the results concerning the mechanisms of formation of M°-NPs.