David Behar

Nitric Oxide Reduction to Ammonia by TiO2 Electrons in Colloid Solution via Consecutive One-Electron Transfer Steps

The reaction mechanism of nitric oxide (NO) reduction by excess electrons on TiO2 nanoparticles (e(TiO2)(-)) has been studied under anaerobic conditions. TiO2 was loaded with 10-130 electrons per particle using γ-irradiation of acidic TiO2 colloid solutions containing 2-propanol. The study is based on time-resolved kinetics and reactants and products analysis. The reduction of NO by e(TiO2)(-) is interpreted in terms of competition between a reaction path leading to formation of NH3 and a path leading to N2O and N2. The proposed mechanism involves consecutive one-electron transfers of NO, and its reduction intermediates HNO, NH2O(•), and NH2OH. The results show that e(TiO2)(-) does not reduce N2O and N2. Second-order rate constants of e(TiO2)(-) reactions with NO (740 ± 30 M(-1) s(-1)) and NH2OH (270 ± 30 M(-1) s(-1)) have been determined employing the rapid-mixing stopped-flow technique and that with HNO (>1.3 × 10(6) M(-1) s(-1)) was derived from fitting the kinetic traces to the suggested reaction mechanism, which is discussed in detail.

Nitrite Reduction to Nitrous Oxide and Ammonia by TiO2 Electrons in a Colloid Solution via Consecutive One-Electron Transfer Reactions

The mechanism of nitrite reduction by excess electrons on TiO2 nanoparticles (eTiO2(-)) was studied under anaerobic conditions. TiO2 was loaded with up to 75 electrons per particle, induced by γ-irradiation of acidic TiO2 colloid solutions containing 2-propanol. Time-resolved kinetics and material analysis were performed, mostly at 1.66 g L(-1) TiO2. At relatively low nitrite concentrations (R = [eTiO2(-)]o/[nitrite]o > 1.5), eTiO2(-) decays via two consecutive processes; at higher concentrations, only one decay step is observed. The stoichiometric ratio Δ[eTiO2(-)]/[nitrite]o of the faster process is about 2. This process involves the one-electron reduction of nitrite, forming the nitrite radical (k1 = (2.0 ± 0.2) × 10(6) M(-1) s(-1)), which further reacts with eTiO2(-) (k2) in competition with its dehydration to nitric oxide (NO) (k3). The ratios k2/k3 = (3.0 ± 0.5) × 10(3) M(-1) and k2 > 1 × 10(6) M(-1) s(-1) were derived from kinetic simulations and product analysis. The major product of this process is NO. The slower stage of the kinetics involves the reduction of NO by eTiO2(-), and the detailed mechanism of this process has been discussed in our earlier publication. The results reported in this study suggest that several intermediates, including NO and NH2OH, are adsorbed on the titanium nanoparticles and give rise to inverse dependency of the respective reaction rates on the TiO2 concentration. It is demonstrated that the reduction of nitrite by eTiO2(-) yields mainly N2O and NH3 via consecutive one-electron transfer reactions.

The reaction of [Ir(C3,N′-bpy) (bpy)2]2+ with OH radicals and radiation induced covalent binding of the complex to several polymers in aqueous solutions

Irradiation of aqueous solutions of [Ir(C3,N′-bpy) (bpy)2]2+ (IrP) produces a variety of OH adducts to IrP. The OH adducts decay by two second order processes separated in time. In the presence of both IrP and a soluble polymer, the OH radicals are shared between the IrP and the polymer, simultaneously producing OH adducts and polymer radicals. This is followed by radical-radical reactions. The rate constants of the various reactions between the OH adducts and the polymer radicals have been determined. The products of reactions of the OH adducts with polyethylene glycals (PEG.), polybrene radicals (PB.), and polystyrene sulfonate radicals (PSS.) are the respective polymers covalently linked to the iridium complex. This has been shown by dialysis as well as by spectral measurements. IrP behaves similarly to Ru (bpy)2+3 which was studied before. This indicates that the radiation method may have a general use in the preparation of polymers with pendant bpy complexes.