Journal of Hazardous Materials 173 (2010) 445–449
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Journal of Hazardous Materials
journal homepage: www.elsevier.com/locate/jhazmat
Degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous
solution by the UV/ZnO photocatalytic process
Emad S. Elmolla
∗
, Malay Chaudhuri
Dept. of Civil Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia
article info
Article history:
Received 27 April 2009
Received in revised form 25 June 2009
Accepted 25 August 2009
Available online 31 August 2009
Keywords:
Amoxicillin
Ampicillin
Cloxacillin
Photocatalysis
UV/ZnO
abstract
The study examined the effect of operating conditions (zinc oxide concentration, pH and irradiation time)
of the UV/ZnO photocatalytic process on degradation of amoxicillin, ampicillin and cloxacillin in aque-
ous solution. pH has a great effect on amoxicillin, ampicillin and cloxacillin degradation. The optimum
operating conditions for complete degradation of antibiotics in an aqueous solution containing 104, 105
and 103 mg/L amoxicillin, ampicillin and cloxacillin, respectively were: zinc oxide 0.5 g/L, irradiation time
180 min and pH 11. Under optimum operating conditions, complete degradation of amoxicillin, ampicillin
and cloxacillin occurred and COD and DOC removal were 23.9 and 9.7%, respectively. The photocatalytic
reactions under optimum conditions approximately followed a pseudo-first order kinetics with rate con-
stant (k) 0.018, 0.015 and 0.029 min
-1
for amoxicillin, ampicillin and cloxacillin, respectively. UV/ZnO
photocatalysis can be used for amoxicillin, ampicillin and cloxacillin degradation in aqueous solution.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
From an environmental engineering point of view, pharmaceu-
ticals including antibiotics are a new group of man-made chemicals
of concern entering the environment at concentrations such that
the health effects are unknown. Problem that may be created by
the presence of antibiotics at low concentration in the environment
is the development of antibiotic resistant bacteria [1]. Amoxicillin,
ampicillin and cloxacillin are semi-synthetic penicillin obtaining
their antimicrobial properties from the presence of a beta-lactam
ring. They are widely used in human and veterinary medicine.
Some authors have found amoxicillin and cloxacillin in wastewater
[2,3].
Certain semiconductors, notably zinc oxide (ZnO) and titanium
dioxide (TiO
2
) when illuminated by photons having an energy level
that exceeds their band gap energy excites electrons (e
-
) from
the valence band to the conduction band and holes (h
+
) are pro-
duced in the valence band. The photogenerated valence band holes
react with either water (H
2
O) or hydroxyl ions (OH
-
) adsorbed
on the catalyst surface to generate hydroxyl radicals (
•
OH) which
are strong oxidant. The photogenerated electrons in the conduc-
tion band may react with oxygen to form superoxide ions (
•
O
2
-
).
The superoxide ions can then react with water to produce hydro-
∗
Corresponding author. Tel.: +60 14 904 7313.
E-mail addresses: em civil@yahoo.com, emadsoliman3@gmail.com
(E.S. Elmolla).
gen peroxide and hydroxyl ions. Cleavage of hydrogen peroxide
by the conduction band electrons yields further hydroxyl radi-
cals and hydroxyl ions. The hydroxyl ions can then react with the
valence band holes to form additional hydroxyl radicals. Degrada-
tion of organic substances can be achieved by their reaction with
hydroxyl radicals (
•
OH) or direct attack from the valence band
holes. Recombination of the photogenerated electrons and holes
may occur and indeed it has been suggested that preadsorption of
substrate (organic substance) onto the photocatalyst is a prerequi-
site for highly efficient degradation. Reactions ((1)–(6)) show the
formation of
•
OH by photocatalytic process [4].
ZnO + h → ZnO (e
-
+ h
+
) (1)
h
+
+ H
2
O → H
+
+
•
OH (2)
h
+
+ OH
-
→
•
OH (3)
e
-
+ O
2
→
•
O
2
-
(4)
•
O
2
-
+ H
2
O + H
+
→ H
2
O
2
+ OH
-
(5)
H
2
O
2
+ e
-
→
•
OH + OH
-
(6)
Daneshvar et al. [4] reported ZnO to be a suitable alternative
to TiO
2
since its photodegradation mechanism is similar to that of
TiO
2
. ZnO can absorb a larger fraction of the solar spectrum than
TiO
2,
and hence ZnO photocatalyst is considered more suitable for
photocatalytic degradation in the presence of sunlight [5]. There
are many reported studies using ZnO as catalyst in photocatalytic
degradation of organic pollutants such as kraft black liquor [6],
2-phenylphenol fungicide [7], phenol and chlorophenols [8] and
0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jhazmat.2009.08.104