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Chemistry Letters Vol.32, No.8 (2003)
Radiation-induced Degradation of Nitrobenzene in Aqueous Solutions
Shao-Hong Feng, Shu-Juan Zhang, Han-Qing Yu,ꢀ and Qian-Rong Liy
Department of Chemistry, University of Science & Technology of China, Hefei, Anhui 230026, P. R. China
yResearch Center for Physics & Chemistry, University of Science & Technology of China, Hefei, Anhui 230026, P. R. China
(Received May 6, 2003; CL-030378)
Both the efficiency and pathways of nitrobenzene degrada-
tion induced by g-ray irradiation were significantly influenced
by the addition of reactive species scavengers. Experimental re-
sults showed that the degradation of nitrobenzene was more fa-
vorable under oxidative conditions than under reductive condi-
tions. Based on the product analysis by GC–MS, possible
degradation mechanisms of nitrobenzene under both oxidative
and reductive conditions were proposed.
DB-5 column [Split ratio: 10:1; Injection temperature: 250 ꢁC;
Carrier gas: Helium (1 mL minÀ1)]. The irradiated samples were
extracted with ethyl acetate, and dehydrated with anhydrous
magnesium sulfate for 24 h. Thereafter, the filtrate was concen-
trated using a spin evaporator. The extracts with a volume of
0.2-mL were subjected to GC-MS analysis.
Irradiation of dilute NB aqueous solutions produces several
À
reactive species, such as ÁOH, eaq and HÁ. When reactive spe-
cies scavengers, e.g., H2O2, i-PrOH or t-BuOH, were presenÀt,
according to the principles of competitive kinetics, ÁOH, eaq
or HÁ was discriminately scavenged. Figure 1 illustrates the in-
fluences of the addition of H2O2, t-BuOH or i-PrOH on the deg-
radation efficiency of NB. There was an optimal H2O2 concen-
tration at a certain dose rate for the degradation of NB, e.g.,
20 mM H2O2 at a dose rate of 55.75 Gy minÀ1. This can be in-
terpreted by the competition between NB and H2O2 for reactive
species produced from water radiolysis. With the addition of ap-
propriate amount of H2O2, the degradation efficiency of NB en-
Nitrobenzene (NB), widely present in waste water from
chemical industries, is a highly toxic compound.1 Because of
the strong electron-withdrawing character of the nitro-group,
the biodegradability of NB is poor.2 Therefore, conventional bi-
otechnology is not effective for the treatment of NB-rich waste
water. Utilization of ionizing radiation to treat waste water has a
major advantage over other treatment methods: A complete
degradation of NB can be achieved without consumption of
any chemicals and resulting in no further pollution.3–5 Radioly-
sis of NB aqueous solutions has been investigated, focusing on
the determination of rate constants between NB and the reactive
species generated from water radiolysis,6 and the identification
of the degradation products.7–9 However, information about ra-
diolytic Àdecomposition of NB, especially reductive degradation
with eaq and HÁ and the identification of degradation products,
is still sparse.6–8,10 In this work, in order to clarify which spe-
cies generated from water radiolysis play the key roles in the
degradation of NB and to elucidate the mechanisms of NB deg-
radation under both oxidative and reductive conditions, experi-
ments were conducted to investigate the respective effects of
addition of H2O2, t-BuOH and i-PrOH on the radiation-induced
degradation of NB. Based on the analysis of the products, the
degradation mechanisms of NB under both oxidative and reduc-
tive conditions were suggested.
À
hanced due to the conversion of eaq to ÁOH induced by H2O2.
On the contrary, at an excessive dosage, H2O2 would compete
with NB for ÁOH. As a result, the degradation of NB was inhib-
ited. As shown in Figure 1, with the addition of i-PrOH or t-
BuOH, the NB degradation rate gradually reduced until it di-
minished to an invariable value. This is due to the removal of
ÁOH by i-PrOH or t-BuOH. Furthermore, the effect of i-PrOH
on the degradation of NB was more drastic than that of t-BuOH,
because i-PrOH removed not only ÁOH but also HÁ. On the other
hand, even if the removal of ÁOH and HÁ was complete (with the
addition of i-PrOH up to 30 mM), the NB solution still had a re-
duction rate of about 20%. Therefore, it can be concluded that
À
eaq played an important role in the reductive degradation of
All the reagents, purchased from Shanghai Chemical Re-
agent Co., were of analytical reagent grade and used without
further purification, except that ethyl acetate was redistilled be-
fore use. Throughout the irradiation experiments, the samples
were prepared with doubly distilled water in Pyrex glass vessels
and irradiated by a 60Co-g-source with an activity of approxi-
mately 60 kCi (2:22 Â 1015 Bq). The dose rate was determined
by a Fricke-dosimeter using G (Fe3þ) = 15.6.
NB concentration was determined by High Performance
Liquid Chromatography (HPLC) (Agilent 1100, VWD detector)
with an ODS column. The mobile phase was a mixture of water
with 0.1% acetic acid and methanol (40:60) delivered at a flow
rate of 1 mL minÀ1. The detecting wavelength was 254 nm. To-
tal organic carbon (TOC) measurements were carried out using
a TOC analyzer (TOC-VCPN, Shimadzu Co.). Analysis of final
products was performed on a GC–MS (an Agilent 6890 GC cou-
pled with a Micromass MS) with a 30 m  0.25 mm  0.25 mm
Figure 1. Effect of reactive species scavengers
on the degradation of NB as a function of their
concentration (Initial NB concentration (C0):
2 mM, dose rate: 55.75 Gy minÀ1, irradiation time:
100 min, scavengers: 1: H2O2, 2: t-BuOH, 3: i-
PrOH).
Copyright ꢀ 2003 The Chemical Society of Japan