Tag Archives: metal nanoparticles

Selective Oxidation of Transient Organic Radicals in the Presence of Gold Nanoparticles

by Viacheslav Shcherbakov, Sergey A. Denisov and Mehran Mostafavi

Nanomaterials 202111, 727; doi.org/10.3390/nano11030727

The ability of gold nanoparticles (AuNPs) to catalyze reactions involving radicals is poorly studied. However, AuNPs are used in applications where chemical reactions involving transient radicals occur. Herein, we investigate AuNPs’ catalytic effect on 2-propanol oxidation and acetanilide hydroxylation in aqueous solutions under ionizing radiation at room temperature. In both cases, the presence of AuNPs led to selective oxidation of organic radicals, significantly changing the products’ composition and ratio. Based on these observations, we stress how AuNPs’ catalytic activity can affect the correctness of reactive oxygen species concentration determination utilizing organic dyes. We also provide a discussion on the role of AuNPs’ catalytic activity in the radiosensitization effect actively studied for radiotherapy.

Hot‐Electron Photodynamics in Silver‐Containing BEA‐Type Nanozeolite Studied by Femtosecond Transient Absorption Spectroscopy

by Farah Kawtharani, Svetlana Mintova, Richard Retoux, Mehran Mostafavi, Guy Buntinx and Vincent De Waele

CHEMPHYSCHEM 2020, 21, 2634-2643; doi.org/10.1002/cphc.202000822

Silver cations were introduced in nanosized BEA‐type zeolite containing organic template by ion‐exchange followed by chemical reduction towards preparation of photoactive materials (Ag0‐BEA). The stabilization of highly dispersed Ag0 nanoparticles with a size of 1–2 nm in the BEA zeolite was revealed. The transient optical response of the Ag‐BEA samples upon photoexcitation at 400 nm was studied by femtosecond absorption. The photodynamic of the hot electrons was found to depend on the sample preparation. The lifetime of the hot electrons in the Ag−BEA samples containing small Ag nanoparticles (1–2 nm) is significantly shortened in comparison to bear Ag nanoparticles with a size of 10 nm. While for the larger Ag nanoparticles, the energy absorbed in the conduction band is decaying by electron‐phonon coupling into the metal lattice, the high surface‐to‐volume ratio of the small Ag nanoparticles favors the dissipation of the energy of the hot electrons from the metal nanoparticles (Ag0) towards the zeolitic micro‐environment. This finding is encouraging for further applications of Ag‐containing zeolites in photocatalysis and plasmonic chemistry.

Mechanisms of metal nanoparticles nucleation and growth studied by radiolysis

by J.Belloni, J.-L.Marignier, M.Mostafavi

Radiation Physics and Chemistry 2020, 169, 107952; doi.org/10.1016/j.radphyschem.2018.08.001

The ultradivided matter is used for long in various applications, for example in colloids, inks and paints, cosmetics, stained glasses, catalysts, photographic emulsions, … But the progressive need of nanoparticles for various miniaturized devices and the different approaches for the synthesis have suddenly increased.

All of the bottom-up synthesis methods from a diluted precursor to metal nanoparticles imply several steps: a reduction reaction of ionic precursors by electron transfer, inducing the nucleation of atoms then the growth of the seeds into particles, more or less inhibited by stabilizers. The final size, shape, structure and dispersity of the particles strongly depend on the thermodynamics and the kinetics of these steps. The interaction of high energy radiation with the solvent provides, quantitatively and homogeneously distributed in the bulk, strong electron donors (solvated electrons, reducing radicals) which reduce metal ions as precursors into atoms. The radiation chemistry, on one hand in the steady state regime with an accurate knowledge of the yields of all the radiolytic products, and on the other hand in the pulse regime giving access to time-resolved data, constitutes a unique tool to elucidate the detailed mechanisms and to provide the keys of really controlling these processes in view of various applications.