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Reduction Kinetics of Nitroaromatic Compounds by Titanium Substituted Magnetite

Abstract : Although there is a growing interest in environmentally friendly catalytic processes based on magnetic solids, the reactivity of titanomagnetite (Fe-3,TixO4) having a "tunable" solid-state Fe(II)/Fe(III) ratio for reductive transformation of nitroaromatic compounds has been never investigated. This study, for the first time, comprehensively examines the reduction kinetics of nitroaromatic compounds by titanium-substituted magnetite and compares with that of Fe(II) amended-unsubstituted magnetite at equal amounts of total Fe(ll). First, we demonstrated that Ti substitution in magnetite increased considerably the ability of magnetite to reduce 4-nitrophenol (4-NP) as well as nitrobenzene (NB) in a surface-mediated electron transfer pathway. However, Fe(II) amendment of magnetite (x = 0) to have an equivalent amount of total Fe(II) as in the corresponding titanomagnetite (0.25 <= x <= 0.75) resulted in higher reduction rate constants for both substrates (4-NP and NB). Initial k(obs) was shown to increase exponentially with (Fe(II)/Fe(III))(bound) in magnetite, while for titanomagnetites a logarithmic dependence of k(obs) with increasing (Fe(II)/Fe(III))(bound) was observed. Only the early-stage kinetic behavior differs between titanomagnetite and Fe(II)-amended magnetite at the same total Fe(II) amount. Changes in Fe2+/Fe3+ electron delocalization properties or electron hopping, presumably due to the mixing of Fe' and Ti4+ on the octahedral sites, may affect the surface-mediated electron transfer between the solid-state and the redox-sensitive species in solution. These bulk-controlled mechanisms drive the electron transfer process both within the solid phase and across the solid/ water interface, thereby altering the regeneration of active sites and ongoing reduction reaction on the magnetite surface.
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https://hal-univ-rennes1.archives-ouvertes.fr/hal-01559202
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Submitted on : Thursday, July 13, 2017 - 3:00:18 PM
Last modification on : Thursday, March 5, 2020 - 2:04:20 PM
Long-term archiving on: : Friday, January 26, 2018 - 5:52:53 PM

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Rémi Marsac, Mathieu Pasturel, Khalil Hanna. Reduction Kinetics of Nitroaromatic Compounds by Titanium Substituted Magnetite. Journal of Physical Chemistry C, American Chemical Society, 2017, 121 (21), pp.11399-11406. ⟨10.1021/acs.jpcc.7b01920⟩. ⟨hal-01559202⟩

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