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

Abstract

Methyl radicals react with TiO(2) nanoparticles (NPs) immersed in aqueous solutions to form transients in which the methyls are covalently bound to the particles. The rate constant for this reaction approaches the diffusion-controlled limit and increases somewhat with the number of methyls bound to the particle. The transients decompose to yield ethane. Thus, formally the particles "catalyse" the dimerization of the radicals, a reaction that is diffusion-controlled. Rutile powders behave similarly to the TiO(2) NPs whereas the mechanism for the decomposition of the transients formed in the analogous reaction of the radicals with anatase powders differs. These results are of importance as alkyl radicals are formed near the surface of TiO(2) in a variety of important photocatalytic processes. The results imply that the reactions of alkyl radicals with TiO(2) have to be considered in these processes.

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

“…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.…”

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

“…These results are of importance as radicals are formed near surfaces (including NPs) in a variety of processes, for example, heterogeneous radical induced catalytic processes, [7,8] electrochemistry [9] (e.g., Kolbe reaction), [10,11] photochemistry at semiconductor surfaces [12,13] (e.g., TiO 2 ), environmental processes [14] (treatment and degradation of organic pollutants, for example, de-halogenations of chloro-organics by granular zero valent iron), [15,16] corrosion of tanks during the storage of radioactive aqueous wastes containing organic materials. [17] Recent results [5] point out that the observed rate constant of Reaction (2), for NP = TiO 2 , decreases slightly when the dose rate of the g source decreases or the concentration of the NPs increases. These results suggest that the rate constant of Reaction (2) depends on "n".…”

“…Recent results point out that alkyl radicals react with metal powders, [1,2] noble-metal NPs, [3,4] and TiO 2 NPs [5] immersed in aqueous solutions to form intermediates in which the radicals are bound covalently to the surfaces. [1][2][3][4][5] The rate constants of the reactions of methyl radicals with Ag 0 , Au 0 , and TiO 2 NPs are very high (k > 1 10 8 m À1 s À1 ).…”

“…Recent results point out that alkyl radicals react with metal powders, [1,2] noble-metal NPs, [3,4] and TiO 2 NPs [5] immersed in aqueous solutions to form intermediates in which the radicals are bound covalently to the surfaces. [1][2][3][4][5] The rate constants of the reactions of methyl radicals with Ag 0 , Au 0 , and TiO 2 NPs are very high (k > 1 10 8 m À1 s À1 ). [3,5] The mechanisms of decomposition of the intermediates thus formed depend on the nature of the metal, [1][2][3][4] on the substituents on the radical, [1,2] on the composition of the solution (including the pH), [2] on the temperature, [2] and on the electrical bias, if applied, on the metal particle.…”

“…[1][2][3][4][5] The rate constants of the reactions of methyl radicals with Ag 0 , Au 0 , and TiO 2 NPs are very high (k > 1 10 8 m À1 s À1 ). [3,5] The mechanisms of decomposition of the intermediates thus formed depend on the nature of the metal, [1][2][3][4] on the substituents on the radical, [1,2] on the composition of the solution (including the pH), [2] on the temperature, [2] and on the electrical bias, if applied, on the metal particle. [6] The intermediates formed in the reactions of methyl radicals with Ag 0 , Au 0 , and TiO 2 NPs decompose to yield ethane, [3,5] that is, the reaction mechanism is:…”