Vol:.(1234567890)
Catal Lett (2017) 147:1608–1614
DOI 10.1007/s10562-017-2029-1
1 3
Photocatalytic Degradation of Hexaethylene Glycol
Drocilia Ednah Simangoye Ngobissi
1
· Jihène Souf
1
· Laurent Vanoye
1
·
Dominique Richard
1
Received: 29 November 2016 / Accepted: 8 March 2017 / Published online: 29 March 2017
© Springer Science+Business Media New York 2017
1 Introduction
Photocatalysis, especially with TiO
2
as the catalyst is very
efective for the abatement of organic pollutants in water
but much less for the degradation of polymers mainly due
to the hydrophobic nature of the latter [1]. On the con-
trary polyethylene glycols (PEGs) constitute a family of
mostly water-soluble polymers available over a wide range
of molecular weights from 300 to 10,000,000 Da used in
many areas such as additives in the plastic industry, excipi-
ents in pharmaceuticals, surfactants or lubricants. PEG are
generally considered non toxic and biocompatible, however
they may become potential contributors to environmental
problem if discarded after use into solid waste or as aque-
ous solutions [2, 3]. The smaller oligomers with a few gly-
col units, especially the monodisperse ones are good model
molecules to use in order to describe the degradation of the
larger ones.
Some studies of PEG oxidation are reported but very
few using photocatalysis with TiO
2
. The degradation of
tetraethylene glycol, choosen as a model of PEG, under
thermal conditions is reported by Glastrup [4]. The oxida-
tion of ethylene glycol using various advanced oxidation
processes such as ozone [5], or Fenton’s reagent and H
2
O
2
/UV [3, 6] have also been reported. Wu et al. [7–9] report
the photocatalytic degradation of PEG with TiO
2
nanopar-
ticles as the photocatalyst. They observed the formation of
esters and other intermediates and a zero order reaction.
Vijayalakshmi and Madras [10] report the photocatalytic
degradation of high molecular weight PEG in solution and
propose a random mode of chain scission. Yuan et al. [1]
studied the photocatalytic degradation of heavy PEG (PEG-
4000–10000) in solid phase where the catalyst (TiO
2
or
Fe–TiO
2
) is dispersed in a PEG matrix. The degradation
was monitored by gel permeation chromatography and no
Abstract Polyethylene glycol (PEG) photodegradation
was studied in water under UV irradiation in the presence
of catalytic amount of TiO
2
using hexaethylene glycol as
a model compound. Full conversion was achieved in 7 h
with an average quantum yield around 1%. Formic acid
was found to be the main intermediate and was slower to
oxidize into CO
2
(traces remains after 24 h). The other
intermediates [lower PEG, oxidized PEG (formates, alde-
hydes and acids, acetic acid)] of the photodegradation have
also been identifed and quantifed. A mechanism based on
previous literature but also taking into account these new
observations is proposed.
Graphical Abstract
HO
O
O
O
O
O
OH
HO
O
O
O
O
OH
HO
O
O
O
OH
HO
O
O
OH
HO
O
O
O
O
O
O
HO
O
O
O
O
O
O
OH
HO
O
O
O
O
O
O
O
H
H
O
O
O
O
O
O
O
O
H
H
O
OH
hexaethylene glycol
glycols
aldehydes
acids
formates
formic
acid
hν
TiO2
Keywords Photocatalysis · Hexaethylene glycol · PEG ·
Mechanism · TiO
2
* Dominique Richard
dri@lgpc.cpe.fr
1
Laboratoire de Génie des Procédés Catalytiques,
UMR5285, CNRS, CPE Lyon, Université de Lyon,
69616 Villeurbanne cedex, France