Progress, Challenge, and Perspective of Bimetallic TiO2-Based Photocatalysts
Hindawi Publishing Corporation
Journal of Nanomaterials
Volume 2014, Article ID 208920, 17 pages
http://dx.doi.org/10.1155/2014/208920
Research Article
Progress, Challenge, and Perspective of
Bimetallic TiO2-Based Photocatalysts
Anna ZieliNska-Jurek
Department of Chemical Technology, Gdansk University of Technology, Narutowicza 11/12, 80-233 Gdansk, Poland
Correspondence should be addressed to Anna Zielińska-Jurek;
Received 17 March 2014; Accepted 28 April 2014; Published 11 June 2014
Academic Editor: Arash Dehghan Banadaki
Copyright © 2014 Anna Zielińska-Jurek. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited.
Bimetallic TiO2 -based photocatalysts have attracted considerable attention in recent years as a class of highly active catalysts and
photocatalysts under both UV and Vis light irradiation. Bimetallic noble metal structures deposited on TiO2 possess the ability to
absorb visible light, in a wide wavelength range (broad LSPR peak), and therefore reveal the highest level of activity as a result of
utilization of a large amount of incident photons. On the other hand they can enhance the rate of trapping photoexcited electrons
and inhibit the recombination process due to the capability of the storage of photoexcited electrons. Based on literature two groups
of bimetallic photocatalysts were distinguished. The first group includes bimetallic TiO2 photocatalysts (BMOX ), highly active under
UV and Vis light irradiation in a variety of oxidation reactions, and the second group presents bimetallic photocatalysts (BMRED )
exceptionally active in hydrogenation reactions. This review summarizes recent advances in the preparation and environmental
application of bimetallic TiO2 -based photocatalysts. Moreover, the effects of various parameters such as particle shape, size, amount
of metals, and calcination on the photocatalytic activity of bimetallic TiO2 -based photocatalysts are also discussed.
1. Introduction
Titanium (IV) oxide (TiO2 ) is one of the most important photocatalytic materials in the area of environmental
purification, hydrogen generation, and CO2 photoconversion
to methane and low hydrocarbons. The limitation in its
application is resulting from low quantum yield (fast recombination of charge carriers: e− /h+ ) and necessity to use UV
irradiation, which may be overcome since modified titania
often possesses higher activity and ability of working under
visible light irradiation. Over the past decades physical,
chemical, and photocatalytic properties of TiO2 were intensively investigated to enhance the efficiency of degradation of
organic pollutants [1–7]. Among various organic and inorganic compounds used as dopants or surface modifiers, noble
metal particles especially attracted attention, since they may
enhance the transfer of photogenerated electrons extending
the lifetime of charge carriers [8, 9]. Noble metal nanoparticles, such as gold, silver, platinum, and palladium, possess the
ability to absorb visible light due to localized surface plasmon
resonance (LSPR) [10–12] and therefore may also activate
wide bandgap semiconductors (e.g., TiO2 ) towards visible
light.
Metallic nanoparticles, particularly these of silver, gold,
and platinum, or a combination of these metals (Ag-Pt, AuPt, and Au-Ag) and various oxides (TiO2 , SiO2 ) are used as
templates for the creation of complex and ordered nanomaterials with tailored and tunable structural, optical, and surface
properties [13].
Since the pioneering work of Haruta, Au clusters supported by oxides (Au/oxides) have perhaps become the most
interesting systems in heterogeneous catalysis because of
their unique catalytic properties at low temperatures for many
reactions. Gold nanoparticles less than 5 nm in size are very
active catalysts. However, large gold nanoparticles supported
on metal oxide with diameter of about 50 nm and more
exhibit photocatalytic activity for hydrogen production, environmental pollution degradation, and reduction of nitrogen
oxides [11, 14].
Many reports on this subject using platinum cluster dispersions or nanoparticles have been published [15–17]. Platinum is one of the most active metals for photocatalytic
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enhancement, which can produce the highest Schottky barrier among metals that facilitate electron capture and, therefore, hinders the recombination rate between electrons and
holes [18, 19].
Although platinum is a very promising metal, which can
increase TiO2 activity, it is more expensive than gold [20].
Certain solution is to use bimetallic structure of platinum
with another metal, which can greatly enhance the photocatalytic performance, particularly with respect to activity and
selectivity [21]. Bimetallic nanoparticles revealed unique catalytic, electronic, and optical properties distinct from those of
the corresponding metallic particles as used in photocatalysis,
photonics, electronics, optics, drug delivery, and others [22–
27]. The positive effect of metal deposits on TiO2 surface
results from the improved separation of electrons and holes
on the surface of the photocatalyst. Additionally, modification of TiO2 with noble metal nanoparticles (NPs) such as
gold and silver, which exhibit plasmon absorption band at
560 nm (Au) and 410 nm (Ag), is beneficial, due to enabling
the absorption of visible light in a wider range of wavelengths
and thus with higher levels of activity [28]. Bimetallic NPs
deposited on TiO2 are expected to display not only the combination of the properties associated with two distinct metals,
but also the new properties due to synergy between two
metals.
Recently, alloying or bimetallization of platinum with
gold has been reported to improve the catalytic activity of
platinum clusters for visible light-induced hydrogen generation and degradation of organic dyes or phenol [15, 29].
However, the improvement of photocatalytic activity of TiO2
modified with noble metal nanoparticles by bimetallization is
observed not only between platinum and gold, but also
between platinum and palladium [30, 31], palladium and gold
[32, 33], platinum and copper [34], platinum and nickel [35],
platinum and tin [36], platinum and iron [35], palladium and
copper [37, 38], gold and silver [11, 39], and copper and silver
[40].
Reports on preparation of Au/TiO2 , Pt/TiO2 , Ag/TiO2 ,
and Cu/TiO2 nanocomposites with different morphological
forms are progressively increasing with the focus on preparation of catalysts and photocatalysts modified with bimetallic
nanoparticles of an alloy or core-shell structure. Several
research targets on TiO2 responsive to visible light or to
enhance the photocatalytic efficiency in oxidation and reduction processes were reported.
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