Applied Catalysis B: Environmental 102 (2011) 572–583
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Applied Catalysis B: Environmental
journal homepage: www.elsevier.com/locate/apcatb
Photocatalytic degradation of organics in water in the presence of iron oxides:
Effects of pH and light source
Eva M. Rodríguez, Guadalupe Fernández, Pedro M. Álvarez, Rebeca Hernández, Fernando J. Beltrán
∗
Departamento de Ingeniería Química y Química Física, Universidad de Extremadura, 06006 Badajoz, Spain
article info
Article history:
Received 7 October 2010
Received in revised form
16 December 2010
Accepted 20 December 2010
Available online 27 December 2010
Keywords:
Bisphenol A
Photocatalytic oxidation
Iron oxides
Hematite
Magnetite
Carboxylic acids
Titanium dioxide
Hydrogen peroxide
abstract
The effects of pH on the performance of different photocatalytic oxidizing systems involving iron oxides,
oxalic acid, hydrogen peroxide and titanium dioxide for the removal of bisphenol A (BPA) and its degra-
dation phenolic intermediates, have been studied. For that purpose two photoreactors have been used:
one irradiated with black light lamps and the other with solar radiation.
Effects related to iron dissolution, generation/photoreduction of ferrioxalate and accumulated UV-A
energy in the photoreactors are discussed in terms of BPA and total polyphenol (TP) degradations, TOC
elimination (i.e., mineralization), accumulation of iron in solution and hydrogen peroxide disappearance
rate. Solar radiation was found to be more efficient than the black light lamps used due to the higher
flux of UV-A radiation supplied. When results were expressed as a function of the accumulated UV-A
energy, however, no significant differences were observed on organic degradation rates when using one
or another radiation source with the exception of the systems where hydroxyl radical formation goes
through, at least in some extent, iron oxides dissolution in the presence of oxalic acid. For these cases, in
addition to the accumulated UV-A energy, contact time between oxalic acid and iron oxides played a key
role in the process.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
In a previous paper two iron oxides, -Fe
2
O
3
(hematite) and
Fe
3
O
4
(magnetite), were used as sources of aqueous iron, which
triggered the formation of aqueous free radicals in photocatalytic
processes induced by black light [1]. It was found that the pres-
ence of oxalic acid and pH as low as 3 favored the leaching of iron
from the iron oxides (especially from Fe
3
O
4
) towards the solution.
In that work bisphenol A (BPA), an endocrine system disruptor
compound that has been frequently detected in aquatic bodies
[2–4], was chosen as model compound to study the performance
of some UV-A photocatalytic processes involving the use of iron
oxides as well as H
2
O
2
, TiO
2
and/or oxalic acid at pH 3. In some
instances (e.g., UV-A/Fe
3
O
4
/oxalic acid/TiO
2
/H
2
O
2
) fast complete
removal of BPA was observed. However, it should be considered
that the efficiency of these systems might highly depend on pH
as this can affect properties such as surface charge of catalysts (i.e.,
iron oxides and TiO
2
), dissociation of H
2
O
2
and organic compounds
in water, organic metal complexes formation (e.g., ferrioxalate) or
leaching of iron from iron oxides. All these factors greatly influence
the reaction mechanism of BPA photodegradation which proceeds
∗
Corresponding author. Tel.: +34 924 289 387; fax: +34 924 289 385.
E-mail address: fbeltran@unex.es (F.J. Beltrán).
mainly through the generation of hydroxyl free radicals. Therefore,
pH optimization should be considered in order to maximize the
process performance.
Accordingly, as second part of our previous work, the main aim
of this study was to observe the effects of pH on the degradation
and mineralization of bisphenol A and leaching of iron when the
photochemical advanced oxidation processes indicated above are
applied. The work was mainly conducted with black light lamps
as UV-A source but direct solar radiation was applied in some
experiments for comparative purposes. In addition to lower costs
for energy production, solar radiation has the advantage of sup-
plying a wider spectrum of radiation and high incident radiation
flux, especially in areas like Badajoz, in southwest Spain (lati-
tude: 38
◦
53
′
north, longitude: 6
◦
58
′
west), where this work has
been carried out. Literature extensively reports on solar detoxi-
fication systems with promising results for the removal of water
pollutants [5].
2. Experimental
Details of product suppliers, analytical methods and proce-
dures can be seen in our previous work [1]. In this research total
polyphenol content (TP) was also analyzed, its concentration being
determined by the Folin Ciocalteau method following a procedure
detailed in a previous work [6,7].
0926-3373/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcatb.2010.12.041