Enhanced Photoreduction of Nitro-aromatic Compounds by Hydrated Electrons Derived from Indole on Natural Montmorillonite

Abstract

A new photoreduction pathway for nitro-aromatic compounds (NACs) and the underlying degradation mechanism are described. 1,3-Dinitrobenzene was reduced to 3-nitroaniline by the widely distributed aromatic molecule indole; the reaction is facilitated by montmorillonite clay mineral under both simulated and natural sunlight irradiation. The novel chemical reaction is strongly affected by the type of exchangeable cation present on montmorillonite. The photoreduction reaction is initiated by the adsorption of 1,3-dinitrobenzene and indole in clay interlayers. Under light irradiation, the excited indole molecule generates a hydrated electron and the indole radical cation. The structural negative charge of montmorillonite plausibly stabilizes the radical cation hence preventing charge recombination. This promotes the release of reactive hydrated electrons for further reductive reactions. Similar results were observed for the photoreduction of nitrobenzene. In situ irradiation time-resolved electron paramagnetic resonance and Fourier transform infrared spectroscopies provided direct evidence for the generation of hydrated electrons and the indole radical cations, which supported the proposed degradation mechanism. In the photoreduction process, the role of clay mineral is to both enhance the generation of hydrated electrons and to provide a constrained reaction environment in the galley regions, which increases the probability of contact between NACs and hydrated electrons.

Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-acetic-acid in Organomodified Montmorillonite

“…The HDTMA-derived hydrocarbon phase present in clay interlayers is known to be an effective sorbent for a wide variety of organic compounds via a phase partition process 31 32 . These results are consistent with our previous study 24 demonstrating that the photoreduction by hydrated electron occurs predominantly in the interlayer regions of montmorillonite clay, and that the sorption of PFCs and IAA by montmorillonite is a prerequisite for the effective photoreduction of PFCs in the reaction system described here.…”

“…5d,e,g,h and see Supplementary Figs S6–S9 ). Hence, this new light-induced peak was attributed to the formed IAA radical cations 24 38 .…”

“…We recently demonstrated that hydrated electrons can be generated when indole or its derivatives are irradiated with sunlight, especially in the presence of the montmorillonite clay 24 . The clay mineral provides a planar negatively-charged surface that can stabilize indole radical cations, consequently inhibiting their recombination with hydrated electrons.…”

“…The clay mineral provides a planar negatively-charged surface that can stabilize indole radical cations, consequently inhibiting their recombination with hydrated electrons. Moreover, the photoreduction process is strongly dependent on the interaction between contaminants and clay mineral, higher adsorption increases the contact possibility of contaminants with hydrated electrons 24 . However, in our previous study, under natural conditions, the quantum yield of hydrated electrons is low and the reaction must occur in the absence of oxygen.…”

Rapid degradation of atrazine by hydroxyl radical induced from montmorillonite templated subnano-sized zero-valent copper

“…S2), which could be explained that since dried montmorillonite is less hydrated and atrazine can form direct interaction with the opposing basal surface of the clay mineral (Chappell et al, 2005). The enhanced adsorption of atrazine on montmorillonite would increase the contact possibility between atrazine and ZVC, hence increasing the degradation rate, similar phenomenon has also been observed in our previous studies (Gu et al, 2010;Yu et al, 2012;Tian et al, 2015). In addition, other factors may also contribute to the higher reactivity for freeze dried ZVCMMT.…”