Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Dye-sensitized photo-hydrogenation of aromatic ketones on titanium
dioxide under visible light irradiation
Shigeru Kohtani ⁎, Saki Nishioka, Eito Yoshioka, Hideto Miyabe ⁎
Department of Pharmacy, School of Pharmacy, Hyogo University of Health Sciences, 1-3-6, Minatojima, Chuo-ku, Kobe 650-8530, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 July 2013
Received in revised form 2 September 2013
Accepted 4 September 2013
Available online 14 September 2013
Aromatic ketones were photocatalytically hydrogenated on P25 TiO2 powder modified with metal free organic
dyes under visible light irradiation. The suitable combination of dye-TiO
tron donor successfully extended the photocatalytic UV response of TiO
2
and triethylamine as a sacrificial elec-
toward visible light region in the
2
photo-hydrogenation of acetophenone derivatives.
©
2013 Elsevier B.V. All rights reserved.
Keywords:
Dye-sensitization
Photocatalysis
Titanium dioxide
Hydrogenation
Reduction
Aromatic ketones
1
. Introduction
our recent review [26]. We have recently demonstrated that P25 TiO
2
exhibited the excellent activity to hydrogenate aromatic ketones
under UV light irradiation [17]. Furthermore, the study on adsorptive
and kinetic behaviors shows that the accumulated conduction band
(CB) electrons or those trapped at surface defect sites (Ti s4 d ) actually
take part in the hydrogenation [18]. Therefore, we expect that electron
injection from excited dyes into CB of TiO will appear to a promising
2
way to achieve the hydrogenation under visible light irradiation.
Here, we report the photo-hydrogenation of aromatic ketones using
Dye-sensitization of semiconductor materials has developed in the
application of photographs [1], solar cell devices [2–6], and photocatalysis
7–14] to extend UV light response of the materials toward visible light
region. In particular, dye-sensitization of titanium dioxide (TiO ) is re-
ceiving increased attention with respect to hydrogen production in
water splitting [7,8] and CO fixation [9–11] under visible light. However,
less is known about synthetically useful organic reactions catalyzed by
dye-sensitized TiO [12–14], thus, the development of efficient dye-
sensitized system has been a subject of current interest. In recent years,
the utility of TiO modified by Ru(II) complex as a transition metal dye
+
[
2
2
2
2
dye-sensitized P25 TiO photocatalyst in the presence of triethylamine
(TEA) as a sacrificial electron donor under visible light irradiation. In
this study, fluorescein (Fl) and rhodamine B (RhB) dyes were employed
as non-expensive and eco-friendly metal-free organics (Fig. 1). The
merit using this system is to obtain the catalysts by a simple and easy
mixing procedure as described in the Experimental section.
2
in organic reactions was reported by König's and Jang's groups, respec-
tively [12,13]. More recently, organocatalysis combining the metal-free
organic dye-sensitized TiO
study, the Texas-Red derived dye, which was covalently anchored on
TiO particle, was employed as an organic dye.
Photocatalytic hydrogenation on semiconductor particles has been
reported as highly efficient and selective reductions of CH C`CH to
CH CH_CH on Pt/TiO (rutile) [15], carbonyl compounds to corre-
sponding alcohols on the P25 TiO [16–18] or on zinc sulfide nano-
crystallite [19], nitroaromatics to corresponding amino-compounds on
TiO [12,20–25], and so on. These and other examples of photo-
hydrogenation on semiconductor particles have been summarized in
2
was studied by König's group [14]. In their
2
2. Experimental
3
Polycrystalline TiO
2
powder (Degussa P25, specific surface area:
50 m g ) was purchased from Japan Aerosil and used as received. A
ratio of anatase/rutile in TiO was roughly estimated to be 9/1 by pow-
der X-ray diffraction (Rigaku, Ultima IV, Cu Ka). The TiO powder was
previously heated at 120 °C in air for 2 h to remove adsorbed water
on the TiO surface. The dyes were adsorbed onto the P25 TiO powder,
silica gel (SiO , Silicycle, F60, particle size: 40–63 μm, 230–400 mesh),
or alumina powder (Al , Nacalai Tesque, Activated 200, ca. 200 mesh)
2
−1
3
2
2
2
2
2
2
2
2
2
2 3
O
3
by immersing 1.0 g of the powder into Fl in ethanol (13 mmol/dm )
or RhB in methanol (99 mmol/dm ) solution overnight at room tem-
3
⁎
perature in the dark. After repeating the centrifugation and washing