Research Article
Photocatalytic Degradation of Trifluralin, Clodinafop-Propargyl,
and 1,2-Dichloro-4-Nitrobenzene As Determined by Gas
Chromatography Coupled with Mass Spectrometry
Niyaz A. Mir,
1
A. Khan,
1
M. Muneer,
1
and S. Vijayalakhsmi
2
1
Department of Chemistry, Aligarh Muslim University, Aligarh, Uttar Pradesh 202002, India
2
SAIF, CRNTS, IIT Bombay, Powai, Mumbai 400076, India
Correspondence should be addressed to M. Muneer; readermuneer@gmail.com
Received 30 May 2014; Revised 17 July 2014; Accepted 17 July 2014; Published 31 August 2014
Academic Editor: Teresa Kowalska
Copyright © 2014 Niyaz A. Mir et al. Tis is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Phototransformation is considered one of the most key factors afecting the fate of pesticides. Terefore, our study focused on
photocatalytic degradation of three selected pesticide derivatives: trifuralin (1), clodinafop-propargyl (2), and 1,2-dichloro-4-
nitrobenzene (3). Te degradation was carried out in acetonitrile/water medium in the presence of titanium dioxide (TiO
2
)
under continuous purging of atmospheric air. Te course of degradation was followed by thin-layer chromatography and gas
chromatography-mass spectrometry techniques. Electron ionization mass spectrometry was used to identify the degradation
species. GC-MS analysis indicates the formation of several intermediate products which have been characterized on the basis
of molecular ion, mass fragmentation pattern, and comparison with NIST library. Te photocatalytic degradation of pesticides
of diferent chemical structures manifested distinctly diferent degradation mechanism. Te major routes for the degradation of
pesticides were found to be (a) dealkylation, dehalogenation, and decarboxylation, (b) hydroxylation, (c) oxidation of side chain,
if present, (d) isomerization and cyclization, (e) cleavage of alkoxy bond, and (f) reduction of triple bond to double bond and nitro
group to amino.
1. Introduction
Te contamination of water bodies due to the presence
of pesticides constitutes a pervasive problem and there-
fore advanced methods are in demand for the efective
treatment of these pesticide polluted ground and surface
waters. Advanced oxidation processes have proven efective
for the removal of organic pollutants. During the last two
decades, photocatalytic processes involving semiconductor
particles under UV light illumination have been shown to
be potentially advantageous and useful in the degradation
of organic pollutants [1–3]. Te process occurs as a result
of the interaction of a semiconductor photocatalyst and UV
radiation that yields highly reactive hydroxyl and superoxide
radical anions, which are believed to be the main species
responsible for the oxidation of organic substrates. Te most
commonly used photocatalyst is TiO
2
, which is inexpensive,
abundant, photostable, and nontoxic [4]. Te mechanism of
photocatalysis is well documented in the literature [4, 5].
Briefy, when a semiconductor such as TiO
2
absorbs a photon
of energy equal to or greater than its band gap energy, an
electron may be promoted from the valence band to the
conduction band (e
−
) leaving behind an electron vacancy
or “hole” in the valence band (h
+
), as shown in (1). If
charge separation is maintained, the electron and hole may
migrate to the catalyst surface where they participate in
redox reactions with sorbed species [6, 7]. In particular, h
+
may react with surface-bound H
2
O to produce the hydroxyl
radical and e
−
is picked up by oxygen to generate superoxide
radical anion (O
2
−
), as indicated in (2) and (3):
TiO
2
+ℎV → TiO
2
∗
(e
−
+ h
+
) (1)
e
−
+ O
2
→ O
2
∙−
(2)
H
2
O + h
+
→ OH
∙
+ H
+
(3)
Hindawi Publishing Corporation
Chromatography Research International
Volume 2014, Article ID 261683, 9 pages
http://dx.doi.org/10.1155/2014/261683