Res. Chem. Intermed.
, Vol. 29, No. 5, pp. 467– 475 (2003)
Also available online - www.vsppub.com
Mixed oxide /sul de systems for photocatalysis
AGATINO DI PAOLA
, MAURIZIO ADDAMO and LEONARDO PALMISANO
Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Università di Palermo,
Viale delle Scienze, 90128 Palermo, Italy
Received 8 April 2003; accepted 23 April 2003
and ZnO/ZnS powders have been prepared by sul dation of H
or ZnO. Photocatalytic degradation of phenol has been employed to test the photoactivity of the
samples. The results indicated that the coupling of the two tungsten chalcogenidesenhanced the rate of
disappearanceof the organic substrate. Unlikely, the ZnO/ZnS systems exhibited lower photocatalytic
activitiy than pure ZnO. The different photocatalytic behaviour of the two mixed oxide/ sul de
systems can be explained by a simultaneous displacement of electrons and holes between two different
: Photocatalysis; electron displacement; mixed oxide/ sul de systems.
Heterogeneous photocatalysis is a promising and alternative method for the treat-
ment of gaseous and liquid wastes [1 – 4]. Many different semiconductor particu-
lates have been used for the degradation of environmental pollutants and TiO
ZnO have been proven to be very ef cient catalysts for the photodegradation of
several organic substrates [5– 10].
One of the limiting factors that control the ef ciency of a photocatalyst is the
quick recombination between photogenerated electrons and holes as it impedes the
charge transfer at the semiconductor surface. An interesting approach for achiev-
ing an ef cient charge separation involves coupling two separate semiconductors
possessing different energy levels for their corresponding conduction and valence
bands . The improvement of photocatalytic activity has been attributed to the
transfer of electrons and holes from a semiconductor to another.
To date, a large variety of coupled semiconductors has been investigated [10 – 20].
Recently, polycrystalline WO
systems [21 – 23] have shown signi cantly
higher activities than pure WO
. An improved charge separation has
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