US EPA

3537072 

Journal Article 

Accelerated methylene blue (MB) degradation by Fenton reagent exposed to UV or VUV/UV light in an innovative micro photo-reactor 

Li, M; Qiang, Z; Pulgarin, C; Kiwi, J 

2016 

Yes 

Applied Catalysis B: Environmental
ISSN: 0926-3373 

187 

83-89 

10.1016/j.apcatb.2016.01.014 

WOS:000371939500010 

This study presents the accelerated
discoloration/degradation of methylene blue (MB) in solution by Fenton reagent under exposure to
ultraviolet (UV) or Vacuum-UV/UV (VUV/UV) light in an innovative micro photo-reactor. The MB
degradation was kinetically faster when using VUV/UV light at 254/185 nm compared to UV-
irradiation at 254 nm. Oxidative radicals produced by the photo-Fenton process were identified
with appropriate scavengers. The addition of benzoquinone (BQ) at millimolar (mM) concentrations
to MB solutions precluded completely the MB photo-induced bleaching, while tert-butanol hindered
to a lesser extent the MB degradation suggesting that HO2 center dot was the predominant
intermediate leading to MB degradation. The VUV/UV micro photo-reactor comprised mercury
resonance lines at 185 and 254 nm. The photon percentages absorbed by water were estimated to be
16.8% at 254nm and 78.3% at 185 nm by water, while those absorbed by H2O2 were 0.9% and 2.2%,
correspondingly. The solution parameters affecting the features of MB degradation, such as MB,
Fe, and H2O2 concentrations, were explored and reaction mechanism was proposed. The lifetimes of
(OH)-O-center dot and HO2 center dot were estimated to be 2 ns and 0.38 s under an optimized
solution with 0.016 mM MB, 0.147 mM H2O2 and 0.05 mM Fe3+. Moreover, an estimation of the mean
free paths of these radicals in solution provided the evidence that it was the radical lifetimes
and mean-free paths, not their oxidation potentials that controlled the MB degradation kinetics.
This study shows the potential of this VUV/UV assistant photo-Fenton process for the degradation
of diluted organic compounds in aqueous solution. (C) 2016 Elsevier B.V. All rights reserved. 

Vacuum-UV (VUV); Photo-Fenton; Micro photo-reactor; Methylene blue; Oxidative radicals; Reaction mechanism