Applied Surface Science 258 (2012) 5010–5024
Contents lists available at SciVerse ScienceDirect
Applied Surface Science
jou rn al h om epa g e: www.elsevier.com/locate/apsusc
Synthesis, characterization and UV-A light photocatalytic activity of
20 wt%SrO–CuBi
2
O
4
composite
Elaziouti Abdelkader
a,∗
, Laouedj Nadjia
b
, Bekka Ahmed
a
a
LCPCE Laboratory, Faculty of Sciences, Department of Industrial Chemistry, University of the Science and the Technology of Oran (USTO M.B), BP 1505 El M’naouar, 31000 Oran,
Algeria
b
Dr. Moulay Tahar University, Saida, Algeria
a r t i c l e i n f o
Article history:
Received 25 November 2011
Received in revised form
21 December 2011
Accepted 7 January 2012
Available online 8 February 2012
Keywords:
20 wt%SrO–CuBi2O4 composite
TG/TDA
XRD, EDX
SEM
Electrical measurements
Congo red
Photocatalytic activity
p–n heterojunction
a b s t r a c t
A novel nanoscale powder 20 wt%SrO–CuBi
2
O
4
has been successfully synthesized for the first time by
ion exchange through doping Sr(NO
3
)
2
into CuBi
2
O
4
matrix and characterized using TG/DTA, XRD, EDX,
SEM and electrical measurements. The as-prepared 20 wt%SrO–CuBi
2
O
4
composite exhibit much higher
photocatalytic activity than 20 wt%SrO–CuBi
2
O
4
synthesized via physical process and pure phase CuBi
2
O
4
under UV-A light irradiation ( = 365 nm) in the course of the photocatalytic redox activity of Congo red
(CR). Maximum degradation was achieved within 220 min of irradiation time under UV-A light as a
result of 97.22% of photocatalytic efficiency of CR. The mechanisms of the enhancement of photocatalytic
activity of the nanocomposite photocatalyst will be discussed by the p–n heterojunction principle (charge
separation and photochemical diode models) and the valance band theory. The pure nanocomposite
systems have been also reported for a comparative purpose.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Since Fujishima and Honda reported a TiO
2
photochemical elec-
trode for splitting water in 1972 [1] advanced oxidation processes
are of great scientific and practical interest in terms of ecology and
sustainable development [2]. Among the various advanced oxida-
tion processes, heterogeneous photocatalysis oxidation performed
with irradiated semiconductors dispersions has been extensively
studied, and proved to be efficient and potentially advantageous,
as it leads to fully decompose the organic and inorganic pollu-
tants present in water or air stream. This is because of the fact
that semiconductors are: (i) inexpensive, (ii) non-toxic, (iii) having
high surface area, (iv) having broad absorption spectra with high
absorption coefficients, (v) exhibiting tunable properties which can
be modified by size reduction, doping, sensitizers, etc., (vi) afford-
ing facility for multi electron transfer process and (vii) capable
of extended use without substantial loss of photocatalytic activ-
ity. In addition, semiconductor particles recovered by filtration or
∗
Corresponding author. Tel.: +213 41 54 24 78; fax: +213 041 56 00 50.
E-mail addresses: elaziouti a@yahoo.com (E. Abdelkader), nlaouedj@yahoo.fr
(L. Nadjia), bekka ahmed@hotmail.com (B. Ahmed).
centrifugation or when immobilized in a fluidized bed reactor
retain much of their native activity after repeated catalytic cycle.
Semiconductor (SC), on irradiation with photon of sufficient
energy, greater than or equal to the band gap energy of the semicon-
ductor (h ≥ E
g
), a free electron (e
-
) and electronic vacancy-a hole
(h
+
) are generated and recombine or migrate in the semiconduc-
tor surface being partially localized on structural defective centers
of its crystalline lattice Eq. (1). The photogenerated electrons take
part in the reduction reaction with dissolved oxygen, producing
superoxide anion (O
•-
2ads
), hydroperoxide (HO
2ads
) radicals and
hydrogen peroxide (H
2
O
2ads
) Eqs. (2)–(4), while the photogener-
ated holes can oxidize either the organic compound directly Eq.
(5) or both hydroxylic ions and water molecules adsorbed on the
photocatalyst surface Eqs. (6) and (7) forming the organic cation-
radicals (R
•+
ads
) and hydroxylic radicals (HO
•
ads
). The stepwise
photocatalytic mechanism is illustrated below:
Semiconductor (SC) + h → Semiconductor (SC) (e
-
(CB)
+ h
+
(VB)
)
(1)
O
2ads
+ e
-
→ O
•-
2ads
(2)
O
•-
2ads
+ H
+
→ HO
2ads
(3)
O
•-
2ads
+ 2H
+
+ e
-
→ H
2
O
2ads
(4)
0169-4332/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.apsusc.2012.01.044