Photoinduced electron-hole recombination in zeolites: Marcus theory applied to DCB@MFI systems

The adsorption of DCB in MZSM-5 (M = H+, Na+) and silicalite-1 channel zeolites takes place without chemical or structural modification of the zeolite. Upon UV photoexcitation, a radical anion - hole pair is stabilized as demonstrated by time resolved diffuse reflectance UV-visible spectroscopy. The photogeneration of the radical anion DCB center dot- is assigned to the dual (ambivalent) role of the zeolite framework as electron donor and hole stabilizator. The observation of such electron transfer only in the aluminated zeolite highlights the key role of the aluminum and of charge balancing cations. By studying the recombination of the radical anion - hole pairs at different temperature, the activation energy has been determined as a function of the nature of the chargebalancing cation. The values of the free enthalpy have been calculated using the Marcus theory from which the local redox potential of the zeolite has been estimated.