Effect of Silica-Supported Silver Nanoparticles on the Dihydrogen Yields from Irradiated Aqueous Solutions

Abstract

Metal nanoparticles (NPs) are used to catalyze the formation of molecular multielectron transfer products, for example, H 2 , from single-electron reductants, such as radicals. Noble metals, like silver and gold, were very instrumental in unraveling the mechanism of this interfacial process. In this study, we explore the effect of the support, silica nanoparticles, on the catalytic production of H 2 on silver from radiolytically produced • C(CH 3 ) 2 OH radicals and water. We obtain very high concentrations of stable silica-supported silver nanoparticles that remain suspended in solution for long periods of time. The presence of metallic silver particles on the silica surface further induces a very effective deposition of silver particles on the same silica particle leading to cooperative deposition of the silver. The silica support changes appreciably the reactivity of the silver NPs, reducing the yield of the molecular hydrogen produced at the high concentrations of the supported NPs to that of the primary molecular hydrogen G(H 2 ) ) 0.45 molecules/100 eV from water radiolysis indicating that H 2 production at the surface of the silver is inhibited. A possible explanation is that the catalyst (Ag on SiO 2 ) catalyzes the disproportionation of the reducing radicals or the reduction of acetone at the expense of the H 2 evolution catalysis.

Pd0‐ and Au0‐Nanoparticles Catalyze the Reduction of Perchlorate by ·C(CH3)2OH Radicals

“…Sect., Reactions (12–14)]. These radicals disproportionate (or recombine) in the absence of particles, but reduce water to molecular H 2 when the catalytic process dominates . The effect of NaClO 4 addition to the suspensions on the radiolytic H 2 and Cl – yields was measured.…”

“…The addition of NPs to the blank solutions, in the absence of ClO 4 – , increases G (H 2 ), as expected from Reactions (4–6). The maximal yield of H 2 under these conditions is: G (H 2 ) = G (H 2 ) p + G ( · H) + 0.5{ G [ · C(CH 3 ) 2 OH]} – G (H 2 O 2 ) ≈ 3.2,, , , , where G [ · C(CH 3 ) 2 OH] = G (e – aq. ) + G ( · H) + G ( · OH); see Reactions (12–14).…”

“…Metal nanoparticles (NPs) have been used as catalysts for multielectron redox reactions using radicals generated by light or by ionizing radiation (e.g., M = silver,, , , gold,, , etc.). The mechanism of water‐reduction catalysis by the one‐electron reducing radical, · (CH 3 ) 2 OH, has been proposed by Henglein , , .…”

On the Reactions of Methyl Radicals with TiO2 Nanoparticles and Granular Powders Immersed in Aqueous Solutions

“…Indeed, recent results that indicate that the properties of Ag 0 and Au 0 as catalysts for the reduction of water by ketyl radicals are affected by the inert SiO 2 support [22] suggest that the study of the reactions of radicals with metal NPs on different supports might contribute to the elucidation of the factors affecting the catalytic properties of composite NPs. Clearly such a study first requires knowledge of the mechanisms of the reactions of the radicals with the metal NPs and with the support.…”

Behavior of fluorescent molecules bound to the interior of silica nanocapsules in various solvents

“…If so, the interior of the nanocapsule can be modified at a much higher rate than the surface. Although surface modification is easy since the condensation of a silanol group on the surface is readily achieved in a nonaqueous solution, it is not easy to uniformly increase the rate of modification of the surface in an aqueous solution [15,16].…”