On the Lifetime of the Transients (NP)(CH₃)_n (NP=Ag⁰, Au⁰, TiO₂ Nanoparticles) Formed in the Reactions Between Methyl Radicals and Nanoparticles Suspended in Aqueous Solutions

Abstract

Methyl radicals react in fast reactions, with rate constants k>1×10(8) M(-1) s(-1), with Au(0), Ag(0) and TiO(2) nanoparticles (NPs) dispersed in aqueous solutions to form intermediates, (NP)-(CH(3))(n), in which the methyl groups are covalently bound to the NPs. These intermediates decompose to form ethane. As n≥2 is required for the formation of C(2)H(6), the minimal lifetime (τ) of the methyls bound to the NPs, (NP)-CH(3), can be estimated from the rate of production of the CH(3)(·) radicals and the NPs concentration. The results obtained in this study, using a very low dose rate γ-source for NP = Ag(0), Au(0), and TiO(2) point out that τ of these intermediates is surprisingly long, for example, ≥8 and ≥188 sec for silver and gold, respectively. These data point out that the NP-C bond dissociation energies are ≥70 kJ mol(-1). Under low rates of production of CH(3)(·), that is, when the rate of formation of ethane is very low, other reactions may occur, consequently the mechanism proposed is "broken". This is observed in the present study only for TiO(2) NPs. These results have to be considered whenever alkyl radicals are formed near surfaces. Furthermore, the results point out that the rate of reaction of methyl radicals with (NP)-(CH(3))(n) depends on n, that is, the number of methyl radicals bound to the NPs affect the properties of the NPs.

Coating Pt0 Nanoparticles with Methyl Groups: The Reaction Between Methyl Radicals and Pt0NPs Suspended in Aqueous Solutions

“…First it is noted that the Pt 0 NPs after the irradiation are considerably more stable than the non‐irradiated ones and do not precipitate even months after irradiation. This result differs from those reported for Ag 0 NPs and Au 0 NPs which precipitate several days after irradiation under similar conditions 5. Furthermore, centrifugation or the addition of an electrolyte, for example, MgCl 2 , does not induce precipitation of the irradiated NPs.…”

“…Relatively little information is available concerning the mechanisms of these reactions. Recent studies5, 6 point out that methyl radicals, the simplest model to alkyl radicals, react in fast reactions, with rate constants k >1×10 8 M −1 s −1 , with Au 0 , Ag 0 , and TiO 2 NPs dispersed in aqueous solutions to form intermediates, (NP)(CH 3 ) n , in which the methyl groups are covalently bound to the NPs via σ bonds. These intermediates decompose to form ethane.…”

“…Thus formally the particles efficiently “catalyze” the dimerization of the methyl radicals, that is, inhibit the reaction of the radicals with (CH 3 ) 2 SO, see below. The reported minimal lifetime of the (NP)CH 3 transients ( τ ) is surprisingly long, for example, τ ≥8 s and τ ≥188 s for Ag 0 and Au 0 NPs, respectively 5…”

The Chemical Properties of Hydrogen Atoms Adsorbed on M0‐Nanoparticles Suspended in Aqueous Solutions: The Case of Ag0‐NPs and Au0‐NPs Reduced by BD4−

“…the present study,t he mechanisms involved in M 0 -NPcatalyzed hydrogen evolution were studied by using BH 4 À in slightly alkaline aqueous solutions. ( All the water used was ultrapure;t he pH of the M 0 -NPs is % 9d ue to the borate present in the suspensions [46] ). Isotope labeling was used to elucidate the underlying mechanism.…”

Coating Platinum Nanoparticles with Methyl Radicals: Effects on Properties and Catalytic Implications

“…Details of the synthesis were reported previously. [23] The synthesized NPs were characterized by using JEOL (JEM-2010) TEM and further analyzed by using Gatan Micrograph software. The TEM imaging and analysis of type aN Ps was previously reported [25] and that of type bi ss hown in Figure S1 (in the Supporting Information) together with explanations in the results section;t he UV/Vis spectra of the NPs are shown in Figures S2 and S3 (in the Supporting Information), which are typically for Pt 0 colloidal suspensions with only an increase in the absorption in the UV region.…”