Nanoscience & Nanotechnology-Asia, 2011, 1, 31-40 31
2210-6820/11 $58.00+.00 © 2011 Bentham Science Publishers Ltd.
Photodegradation of Phenol, 2-Chlorophenol and o-Cresol by Iron Oxide
Nanoparticles
Raúl Suárez-Parra
a,
*
, Isaias Hernández-Pérez
b
, Esteban Montiel-Palacios
a
, Juán P. Pérez-Orozco
c
,
Alvaro Sampieri
d
, Daili Vázquez-Avella
a
, Antonio E. Jiménez-González
a
and René Guardián-Tapia
e
a
Centro de Investigación en Energía, Universidad Nacional Autónoma de México, Apartado Postal 34, Temixco,
Morelos 62580, Mexico;
b
Universidad Autónoma Metropolitana-A, Dpto. de Ciencias Básicas, Av. Sn. Pablo No. 180,
México, D.F. 02200, Mexico;
c
Instituto Tecnológico de Zacatepec, Departamento de Ingeniería Química y Bioquímica,
Calzada Tecnológico No. 27, Col. Centro, Zacatepec, Morelos, México, CP 62780;
d
Benemérita Universidad Autónoma
de Puebla, Facultad de Ingeniería Química, Av. San Claudio y 18 Sur, Puebla, Puebla 72592, Mexico;
e
Instituto de
Ciencias Físicas, Universidad Nacional Autónoma de México, Av. Universidad s/n Col. Chamilpa, Cuernavaca,
Morelos 62210, Mexico
Abstract: Iron oxide nanoparticles were prepared by mixing either aged iron(II) or aged iron(III) hydrated chlorides with
hydrogen peroxide at pH 4.2±0.1. Iron oxide nanoparticles were identified in the mixtures of iron(II/III) chlorides with
hydrogen peroxide by transmission electron microscopy (TEM) analyses. TEM analyses showed irregular sizes and the
formation of different phases of iron oxide (-Fe
2
O
3
, -Fe
2
O
3
, -Fe
2
O
3
, -Fe
2
O
3
…). The variety of iron(III) oxide phases
was a consequence of interactions of hydrogen peroxide with different ferric oligomers and iron oxohydroxides formed
during the aging of iron(II/III) chloride mixtures. In order to decompose phenol or 2-chlorophenol or o-cresol a
photocatalytic reaction was carried out in a “reactor” with iron oxide nanoparticles, visible radiation and hydrogen
peroxide. Each reaction was kept at room temperature and pH 3.8±0.1. The photocatalytic processes were analyzed
through UV spectrophotometry, chemical oxygen demand (COD) and total organic carbon (TOC) measurements. Iron
oxide nanoparticles, in the photodegradation of phenol, 2-chlorophenol and o-cresol, presented bifunctional catalytic
properties, such as a semiconductor photocatalyst and probably as Lewis acid catalyst.
Keywords: Acid lewis catalyst, ferric oligomers, heterogeneous photocatalysis, hydrogen peroxide, iron oxide nanoparticles,
phenol derivatives, semiconductor photocatalyst.
1. INTRODUCTION
Fenton reaction is a degradation process of organic
compounds, that occurs in aqueous solutions at pH 3
through an homogeneous reaction with hydrogen peroxide
and iron ions, Fe(II) or/and Fe(III). For instance, the removal
of organic compounds from aqueous solutions [1-14] by
applying a system Fe(III)/H
2
O
2
destroys organic pollutants
slower than the system Fe(II)/H
2
O
2
due to the lack of
reducing power of the iron(III) ions [3]. The accepted
mechanism of the Fenton’s reaction involves the reduction of
hydrogen peroxide molecules by the iron(II) ions forming
hydroxyl species (
•
OH). Then, these species are mainly
consumed during the degradation of organic pollutants, thus,
the formed iron(III) ions return to the initial oxidation state
by reacting/oxidizing some organic byproducts formed in the
degradation process [1-3]. In the literature, there are also
reports on degradation enhancement of different organic
compounds using Fenton’s reaction in combination with an
additional iron source. According to Barbusinski and
Majewski [15] the degradation rate of an azo-dye by
Fenton’s reaction was upgraded by the presence of iron
*Address correspondence to this author at the Centro de Investigación en
Energía, Universidad Nacional Autónoma de México, Apartado Postal 34,
Temixco, Morelos 62580, Mexico; Tel: (52) 55 56 22 98 20;
Fax: (52) 55 56 22 97 42; E-mail: rsp@cie.unam.mx
powder (Fe
0
), indeed, iron powder dissolves generating
additional Fe
2+
ions, which increases the formation of
hydroxyl species (
•
OH) and improves the azo-dye degrada-
tion process. He et al. [16] reported the degradation of the
Mordant Yellow 10 (azo-dye) using the photo-Fenton
process and iron oxide dispersion, here authors found that
the dye adsorption/desorption processes and the formation of
complexes H
2
O
2
/iron oxide play an important role in the
elimination of the pollutant. He et al. [17] also proposed to
eliminate Mordant Yellow 10 in a heterogeneous system
H
2
O
2
/-FeOOH under UV irradiation at neutral pH, in this
case hydroxyl radicals are released via photolysis of surface
complexes of H
2
O
2
with surface iron ions. Huang et al. [18]
reported the catalytic degradation of azo-dye reactive black
B (RBB) by immobilized iron oxide and hydrogen peroxide.
In this study Huang established that generation rate of the
hydroxyl radicals was proportional to the consumption of
hydrogen peroxide and as a consequence the degradation of
RBB. Chou and Huang [19] have explained the benzoic acid
oxidation as a heterogeneous reaction on the surface of iron
oxyhydroxide -FeOOH, additionally this iron oxyhydroxide
was partially dissolved to form Fe
2+
ions, leading the latter
process to simultaneous Fenton’s catalytic oxidation. Lu [20]
has found that the system of goethite/hydrogen peroxide (-
FeOOH/H
2
O
2
), followed by the Fenton process, shows a
better oxidation efficiency of 2-chlorophenol than using the