Spontaneous ionization of N-alkylphenothiazine molecules adsorbed in channel-type zeolites: effects of alkyl chain length and confinement on electron transfer.

International audienceThe mere mixing of N-alkylphenothiazines with three channel-type acid zeolites with various structures (ferrierite, H-MFI, and mordenite) induces the spontaneous ionization of the heterocyclic molecule in high yield upon adsorption. The diffuse reflectance UV-visible absorption and Raman scattering spectra show that the accessibility of the highly polarizing acid sites is not indispensable to induce the spontaneous ionization process. Due to their particularly low ionization potential values (6.7 eV), the adsorption of the molecules on the external surface or in the inner volume is the key parameter to generate the radical cation. However, the ionization yield and charge stabilization are intimately correlated to the possibility of the zeolites accommodating molecules inside their channels. Moreover, the higher electrostatic field gradient induced by high confinement is required to favor the second ionization and dication formation. The alkyl chain length plays a decisive role by either slowing down the diffusion process or blocking the molecule at the pore entry. Therefore, the efficiency of the ionization process that depends on the number of adsorbed molecules decreases significantly from phenothiazine to the N-alkylphenothiazines. The spectral data demonstrate that deformation of the alkyl group is necessary to allow the diffusion of the molecules into the channels

Nanosecond probing of the early nucleation steps of silver atoms in colloidal zeolite by pulse radiolysis and flash photolysis techniques

International audienc

Photoreduction of Ag⁺ by diethylaniline in colloidal zeolite nanocrystals

The photoinduced formation and the subsequent early nucleation steps of silver atoms (Ag0) in nanosized zeolite Beta crystals stabilized in aqueous colloidal suspensions are studied by steady-state UV-Vis and Raman spectroscopy, and by transient absorption spectroscopy. The reduction of extra-framework silver cations is initiated by photoinduced electron transfer using organic electron donors such as N,N-diethylaniline or triphenylamine. The Ag0 species are formed in less than 100 ns and are found to be stable for more than one microsecond before beginning to aggregate, leading first to Ag2+ species in ∼1.1 μs. The data suggest that the reduction of extra-framework Ag+ arises only if the electron donor species is adsorbed on the zeolite particle surface or within the channels