Download Iron oxides: new perspectives as heterogeneous photocatalysts

GIFC 2010
CP-12
Iron oxides: new perspectives as heterogeneous photocatalysts
A. Bedini, V. Maurino, C. Minero, D. Vione
Department of Analytical Chemistry and NIS Centre of Excellence, Torino – Italy
[email protected]
Iron oxides and hydroxides are widespread in nature and play an important role in a variety of disciplines,
including environmental and industrial chemistry, corrosion science, soil science, biology and medicine.[1] Iron
oxides have been widely studied in metallurgy and soil chemistry for their importance as colloids to adsorb a
broad variety of chemical species. Non-systematic or incomplete studies are present in the literature regarding
their photocatalytic activity.[2 3] In particular, the correlation between different shapes of iron oxides colloids and
their catalytic activity has not yet been explored.[4] The present study demonstrates that two photocatalytic
reactions carried out in the presence of iron oxides, namely solid-gas phase decomposition of NO and benzene
hydroxylation in aqueous media, can be considered as valid methods to assess the photoreactivity of novel ironbased
materials
and
as
possible
solutions
to
the
problem
of
pollution
in
urban
areas.
30
α FeOOH
β FeOOH
γ FeOOH
25
NO conversion %
20
15
10
5
0
0
10
20
30
40
50
60
Irradiation time, min
The growth of well-defined iron polymorph nanostructures can be obtained through simple hydrothermal
processes, using an aqueous medium and anions or organic compounds as shape controllers. The synthesized
materials shows very different shapes and expose different planes. Although it is still difficult to establish a
correlation between the shape of the nanoparticles and their photocatalytic properties, species with a high
concentration of surface hydroxyl groups such as α-FeOOH and β-FeOOH show the highest photoactivity. In
contrast, α-Fe2O3 specimens show generally minor or poor photoreactivity. It has also been observed that iron
oxides undergo photodissolution processes. In particular, the higher the photoactivity, the higher is the catalyst
photodissolution or photoreductive dissolution in the presence of organic ligands and reductive agents. Future
studies will be devoted to the understanding of the role of the exposed planes at the semiconductor-reaction
medium interface and of how they affect both the efficiency of the photooxidation reactions and the rate of
photodissolution through the presence of singly, doubly or triply coordinated surface hydroxyl groups.
The author is thankful to Rockwood Italia, Divisione SILO for the financial support of his Ph.D. thesis.
1
Schwertmann, U.; R.M. Cornell The Iron Oxides WILEY-VCH GmbH & Co. KGaA, 2003, Weinheim.
Bahnemann, D.W.; Hoffmann, M.R.; Kormann, C.; J. Photochem. Photobiol. A, 1989, 48, 161-169.
3
Leland, J.K.; Bard, A.J.; J. Phys. Chem., 1987, 91 (19), 5076-5083
4
Egglestone, C.M. Science, 320, 2008, 184-185
2