Photocatalysis of titanium dioxide modified by catechol-type interfacial surface complexes (ISC) with different substituted groups

Article abstract of DOI:10.1016/j.jcat.2015.05.010

Visible-light responsive TiO₂ photocatalyst modified by catechol-type interfacial surface complexes (ISC) was designed by the reaction of TiOH moieties with catechol and such derivatives as 3-methoxycatechol involving electron-donating groups (

Full text of DOI:10.1016/j.jcat.2015.05.010

Journal of Catalysis 329 (2015) 286–290
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Journal of Catalysis
journal homepage: www.elsevier.com/locate/jcat
Photocatalysis of titanium dioxide modified by catechol-type interfacial
surface complexes (ISC) with different substituted groups
a
a
a
b
Shinya Higashimoto a, , Takuya Nishi , Miki Yasukawa , Masashi Azuma , Yoshihisa Sakata ,
⇑
Hisayoshi Kobayashi c
a College of Engineering, Osaka Institute of Technology, 5-16-1 Omiya, Asahi-ku, Osaka 535-8585, Japan
b Graduate School of Science and Engineering, Yamaguchi University, 2-16-1 Tokiwadai, Ube 755-8611, Japan
c Department of Chemistry and Materials Technology, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Visible-light responsive TiO2 photocatalyst modified by catechol-type interfacial surface complexes
(ISC) was designed by the reaction of TiAOH moieties with catechol and such derivatives as
3-methoxycatechol involving electron-donating groups (EDG) and 3,4-dihydroxybenzonitrile involving
electron-withdrawing groups (EWG). The visible-light response of the ISC is attributed to excitation from
the donor levels created in the TiO2 midband. The phenyl-ring-substituted groups strongly influence the
electronic structures of the ISC: the catechols with substituted EWG induce an anodic shift of the donor
levels accompanied by an enlargement of the energy gaps, compared with catechol without substituted
groups. The photocatalytic activities for H2 evolution from triethanolamine aqueous solutions were sys-
tematically investigated. It was confirmed that the more anodic the oxidative potentials of photoinduced
holes in the ISC are, the higher the photocatalytic activities they exhibit.
Received 13 April 2015
Revised 11 May 2015
Accepted 13 May 2015
Keywords:
Photocatalytic H2 production
Titanium dioxide
Interfacial surface complex
Catechol
Ó 2015 Elsevier Inc. All rights reserved.
Visible light
DFT calculation
1. Introduction
[20–24] and theoretical studies on its reaction mechanisms by
DFT calculations [25]. The visible-light response of the ISC formed
TiO2. photocatalysts are known to promote such photoreactions
as decomposition of volatile organic compounds (VOC), H2 produc-
tion from aqueous solutions, and selective transformation of
organic compounds [1–5]. In general, TiO2 photocatalysts operate
by band-gap excitation (3.0–3.2 eV or more) under UV irradiation,
of which only a few percent reaches the earth’s surface. Therefore,
the development of visible-light-sensitive TiO2 photocatalyst has
been a great concern for efficient utilization of solar light [6–9].
Visible-light-responsive TiO2 photocatalysts have been designed
by several methods such as doping with nitrogen and other
elements [10–14], organic dye sensitizer [15], plasmonic Au and
Ag nanoparticles [16–19], and interfacial surface complexes (ISC)
[20–30].
Recently, attention has been paid to photocatalysis due to the
ISC formed by the interaction of TiO2 surface with such colorless
organic compounds as aromatic alcohols [20–25], amine [26,27],
and phenolic compounds [28–30]. We previously reported the
selective photocatalytic oxidation of benzyl alcohol into benzalde-
hyde with high selectivity on TiO2 under visible-light irradiation
by the interaction of benzyl alcohol with the TiO2 surface is attrib-
uted to excitation from the donor levels in the TiO2 midband, and
the ISC is selectively converted into benzaldehyde.
Unlike the photocatalytic system employing the ISC as men-
tioned above, the binaphtol-modified and hydroxynaphthalene-
modified TiO2 photocatalysts exhibit hydrogen production from
triethanolamine (TEA) aqueous solutions [29] and selective
reduction of nitrobenzene into aminobenzene [30], respectively,
under visible-light irradiation.
The ISC was extensively characterized by several spectroscopic
techniques, such as UV–vis, FT-IR, Raman, as well as by theoretical
calculations [31–33,28,34–39]. It is accepted that interaction
between surface TiAOH groups and phenolic groups of the catechol
leads to the formation of catecholate species, which exhibit
absorption in the visible-light region. In particular, it was reported
that surface modification of nanocrystalline TiO2 particles with dif-
ferent catechol-type derivatives was found to alter optical proper-
ties [31].
However, the photocatalytic activities using TiO2 modified by
catechol and its derivatives as simple aromatic molecules have
not been systematically studied. Moreover, effects of phenyl ring
substitution with electron-withdrawing groups (EWG) and
⇑
Corresponding author. Fax: +81 6 6957 2135.
E-mail address: higashimoto@chem.oit.ac.jp (S. Higashimoto).
http://dx.doi.org/10.1016/j.jcat.2015.05.010
0021-9517/Ó 2015 Elsevier Inc. All rights reserved.

S. Higashimoto et al. / Journal of Catalysis 329 (2015) 286–290
287
electron-donating groups (EDG) on the optical properties of the ISC
have yet to be clarified. In this study, we investigated the photocat-
alytic activities for H2 evolution from aqueous TEA of TiO2 modified
by catechol and its derivatives substituted with EWG and EDG. In
particular, relationships between electronic structures of the ISC
and their photocatalytic activities have been clarified by the com-
bination of electrochemical measurements and DFT calculations.
H2PtCl6 (Pt/Ti: 0.1–2.0 atomic%) as co-catalyst was introduced into
a Pyrex cell under purging with N2. It was then irradiated by blue
LED lamps adjusted to 25,000 lux (kmax = 460 nm, ca. 10 mW/cm2).
The photoproduced H2 was quantitatively analyzed by GC-TCD
(Model 802, Ohkura; column: Molecular Sieve 5A).
To evaluate apparent quantum yields (AQY), photoirradiation
was carried out by a 100 W Xenon lamp (Lax Cute II, Asahi
Spectra Co., Ltd.) through several bandpath filters with a FWHM
of 10 2 nm (Asahi Spectra). The AQY at each centered wavelength
of light was calculated using the following Eq. (1):
2. Experimental
Catechol (referred to as CA) and its derivatives such as
ðamounts of H2 formedÞ ꢂ 2
AQY ð%Þ ¼
ꢂ 100
ð1Þ
4-tert-butylcatechol
(BC),
3-methoxycatechol
(MC),
2,3-
ðamounts of photons irradiatedÞ
dihydroxybenzoic acid (BA), 3,4-dihydroxybenzonitrile (BN) and
Tiron (TN), hydrogen hexachloroplatinate (IV) hexahydrate
(H2PtCl6ꢀ6H2O), acetonitrile, and triethanolamine (TEA) were
purchased from Wako Co., Ltd. The derivatives of catechols
were classified into two categories: BC and MC with substituted
EDG and BA, BN, and TN with substituted EWG as shown in
Fig. 1. Commercially available TiO2 (anatase, 320 m2 gꢁ1, ST-01,
Ishihara Co., Ltd.) was mainly used in this study. All chemicals were
used without further purification.
The flux of incident photons was measured by a power meter
(Ophir, ORION/PD), and photoirradiation was conducted in the
range of 7.24 ꢂ 1018–1.03 ꢂ 1019 photons hꢁ1
.
Photoelectrochemical measurements were carried out in a
three-electrode cell using a potentiostat/galvanostat (HABF5001,
HOKUTO DENKO). Photoirradiation was performed through a
low-cutoff filter (Y-45, Asahi Technoglass Co. Ltd.) transmitting light
with k > 420 nm. Aqueous LiClO4 (0.1 M) involving TEA (10 vol%)
was used as the electrolyte solution. The electrolyte was bubbled
vigorously with N2 for 30 min prior to measurements. TiO2 film
was used for the working electrode, Pt wires for the auxiliary
electrode, and Ag/AgCl for the reference electrode. The TiO2 film
was prepared as follows: 2.85 g of TiO2 powder (Degussa, P-25)
and 0.15 g of ST-01 was well dispersed in 5 mL of dilute HNO3 (pH
3) involving 0.3 g of polyethylene glycol (Hw = 20,000) and 0.3 mL
of Triton X-405. The paste was then spread onto transparent and
In a typical surface modification of TiO2, 1 g of TiO2 (ST-01) was
added to aqueous solutions (30 mL) involving CA and its deriva-
tives (40–200 lmol), and the suspension was stirred at 298 K for
3 h vigorously under N2 bubbling in the dark. To determine
amounts of modifiers loaded onto the TiO2, concentrations of the
modifiers in solutions were analyzed by HPLC (Shimadzu
LC10ATVP, UV–vis detector, column: Chemcopak, mobile phase: a
mixture of acetonitrile and 1.0 vol% aq. HCOOH in a volume ratio
of 3:7) after separation of the solids by a centrifuge. It was
observed that no surface modifiers remained in the solutions; i.e.,
all the modifiers were confirmed to anchor on the TiO2 surface. The
photocatalyst was referred to as x-XX/TiO2, where XX and x stand
conductive ITO-coated glass (10
X
cmꢁ2, Geomatec Co. Ltd.) by spin
coating, followed by heat treatment in air at 673 K for 1 h. This
process was repeated twice and the film thickness was adjusted to
ca. 15 lm. Then the BN/TiO2 and BC/TiO2 films were prepared by
immersing TiO2 films for 3 h in aqueous BN and BC (5 mM),
respectively.
for kinds of modifiers and amounts (
(1 g), respectively.
lmol) adsorbed onto TiO2
To determine the oxidative potentials (EA) of organic compounds,
cyclic voltammograms were obtained using three electrodes: a
glassy carbon electrode with active surface area of 7.1 mm2 (BAS
Inc.) for the working electrode, Pt wires for the auxiliary electrode,
and Ag/AgCl for the reference electrode.
UV–vis spectra were obtained by a diffuse reflection method
with a spectrometer (UV-3100PC, Shimadzu). The reflectance spec-
tra were converted into a Kubelka–Munk function. The IR spectra
of samples were measured with
Shimadzu) with MIRacle A (ZnSe ATR accessory) and measured
with 100 scans at resolution 4 cmꢁ1
a
FT-IR (IRPrestige-21,
.
Photocatalytic activities were evaluated by the evolution of H2
from aqueous TEA. The aqueous TEA (10 vol%, 10 mL) suspended
with photocatalyst (50 mg) and desired amounts of aqueous
3. Results and discussion
3.1. Surface characterization of TiO2 modified by catecholate-type
complexes
[Electron-donating groups (EDG)]
Fig. 2a and a0 shows FT-IR ATR spectra of free CA and
80-CA/TiO2, respectively. The CA exhibits IR bands at 1514 and
O
HO
HO
HO
HO
HO
1470 cmꢁ1 assigned to the stretching
v(CAC) or v(C@C) vibrations
of the aromatic ring, 1365 cmꢁ1 to the d(OAH), 1096 and
1040 cmꢁ1 to the bending d(CAH), and 1300–1150 cmꢁ1 to the
HO
catechol
(CA)
3-methoxy catechol
4-t-butyl catechol
stretching
the other hand, the 80-CA/TiO2 exhibits bands at ca. 1480 cmꢁ1
assigned to (CAC) or (CAO)
(C@C), and at ca. 1250 cmꢁ1 to
v(CAO) or bending d(CAO) vibrations [31,34,37,40]. On
(MC)
(BC)
v
v
v
[Electron-withdrawing groups (EWG)]
and/or d(CAO), while that at ca. 1365 cmꢁ1 assigned to d(OAH)
has completely disappeared. These results indicate that the cate-
cholate species is formed by linkage of the surface TiAOH groups
with CA. Moreover, the IR bands of 80-BC/TiO2 and 80-BN/TiO2
photocatalysts are also shown in Fig. 2. It was observed that the
characteristic bands at ca. 1365 cmꢁ1 due to the d(OAH) of free
BC and BN disappeared on 80-BC/TiO2 and 80-BN/TiO2, suggesting
that the linkage of the surface TiAOH groups with BC and BN forms
corresponding catecholate species [41].
SO3Na
HO
HO
HO
HO
HO
HO
SO3Na
N
O
HO
tiron
(TN)
3,4-dihydroxy benzonitrile
(BN)
2,3-dihydroxy benzoic acid
(BA)
TiO2 photocatalysts modified by CA and its derivatives (BC, MC,
BN, and TN) exhibit absorption with lower energy than 3 eV,
Fig. 1. Molecular structures of catechol and its derivatives with substituted EDG
and EWG.

288
S. Higashimoto et al. / Journal of Catalysis 329 (2015) 286–290
1480
1250
1096
1365
1367
1514
1470
1040
(a’)
(b’)
1494
1490
1267
(a)
1120
1520
1288
1091
1435
(b)
(c’)
0.025
1520
1116
1446
1361
0.005
(c)
1500
1400
1300
1200
1100
1000
1500
1400
1300
1200
1100
-1
1000
-1
Wavenumber /cm
Wavenumber /cm
Fig. 2. FT-IR ATR spectra of free (a) CA, (b) BC, (c) BN and (a0) 80-CA/TiO2, (b0) 80-BC/TiO2 and (c0) 80-BN/TiO2.
although TiO2 by itself exhibits little absorption in the visible-light
regions, as shown in Fig. 3. It should be noted that the modifiers in
aqueous solutions showed absorption in the UV region with energy
According to the previous report, the ISC is likely to form
through bidentate binuclear (bridging) complexes being more
energetically favorable than five-membered ring coordination
[31,35]. Such coordination bonds help to induce intramolecular
ligand-to-titanium charge transfer transitions within the ISC [36].
DFT calculations for ISC with different substituted groups clearly
demonstrated that the donor levels in the TiO2 midband are mainly
constructed by the orbitals of the catecholate species hybridized
with lattice oxygen. The donor levels and energy gaps obtained
higher than 4 eV, as shown in Fig. SI
1 in the Supporting
Information. These results indicate that the interactions of
colorless catechol and its derivatives with the TiO2 surface exhibit
strong visible-light absorption, which originates with the
electronic transitions in the ISC [32,36]. Furthermore, the energy
gaps were determined from UV–vis spectra, and results are listed
in Table 1. It was observed that BC/TiO2 (2.28 eV) and MC/TiO2
(2.32 eV) with substituted EDG exhibit smaller energy gaps than
CA/TiO2 (2.40 eV), while BN/TiO2 (2.52 eV) and TN/TiO2 (2.57 eV)
with substituted EWG exhibit larger energy gaps. That is, the
energy gaps of the ISC enlarged as the electron-withdrawing ability
in the substituted groups increased.
Table 1
Energy gaps of TiO2 modified with catechol and its derivatives estimated by UV–vis
spectroscopy and DFT calculations.
Photocatalyst
Energy gaps (eV)a
Energy gaps (eV)b
Donor level (eV)c
The oxidative potentials (EA) of CA, its derivatives (BC, MC, BA,
BN, TN), and TEA were determined from the cyclic voltammogram
and results are listed in Table 2. It was found that the EA increases
as follows: BC ꢃ MC < (TEA) < CA < BA < BN < TN. From these
results, it was clearly indicated that the EA of BC and MC with sub-
stituted EDG are more cathodic than that of TEA, while those of CA
and BA, BN, and TN with substituted EWG are more anodic.
BC/TiO2
MC/TiO2
CA/TiO2
BN/TiO2
TN/TiO2
2.28
2.32
2.40
2.52
2.57
2.39
2.43
2.48
2.51
–
0.43
0.37
0.33
0.31
–
a
Energy gaps were estimated by UV–vis spectroscopy.
Details in computational methods and Figs. SI 2–7 are shown in the Supporting
Information. Energy gaps were determined from the differences between the donor
level and conduction band minimum of TiO2 by DFT calculations.
b
c
Donor level indicates the difference above the valence band maximum of TiO2
by DFT calculations.
1
(d)
0.8
0.6
0.4
Table 2
Oxidative potentials (EA) of organic compounds.a
(b)
(e)
(f)
Organic compounds
EA (V) vs. Ag/AgCl
BC
1.08
1.12
1.18
1.36
1.44
1.47
1.14
MC
CA
BA
BN
TN
TEA
(c)
0.2
(a)
0
2
2.2
2.4
2.6
2.8
3
Energy / eV
a
EA was determined from an anodic peak in the voltammogram of the organic
Fig. 3. UV–vis spectra of (a) TiO2, (b) 80-BC/TiO2, (c) 80-MC/TiO2, (d) 80-CA/TiO2,
(e) 80-BN/TiO2, and (f) 80-TN/TiO2.
compounds (5 mM, 0.1 M aqueous LiClO4). Details are shown in Fig. SI 10 in the
Supporting Information.

S. Higashimoto et al. / Journal of Catalysis 329 (2015) 286–290
289
35
30
25
20
15
10
5
0.8
0.6
0.4
0.2
0
40
30
[I]
(b)
(d)
(f)
20
(a)
(e)
10
(c)
(a, b)
0
0
400
0
2
4
6
450
500
550
600
Time / h
Wavelength / nm
40
30
20
10
0
Fig. 6. AQY (a) for H2 evolution from aqueous TEA (10 vol%) and (b) absorption
spectrum of 80-BN/TiO2.
Evacuation
Evacuation
[II]
on the 80-BN/TiO2 (Pt/Ti: 0.5 atomic%) exhibited
a turnover
number (TON), i.e., a total number of the photoformed H2 per
BN-complex, of ca. 15 for 5 h, indicating that this reaction proceeds
photocatalytically. The photocatalytic performance of 80-BN/TiO2
(Pt/Ti: 0.5 atomic%) was repeatedly evaluated to confirm the stabil-
ity of the ISC in this reaction. This photocatalyst was recyclable at
least three times without drastic decrease of H2 evolution after
consecutive evacuations (see Fig. 4[II]).
Fig. 5 shows activity for H2 evolution on several ISC photocata-
lysts as a function of EA of corresponding modifiers. It was observed
that the BC-TiO2 and MC-TiO2 with substituted EDG exhibited little
activity (Fig. 5a and b), while CA-TiO2; BA-TiO2, BN-TiO2, and
TN-TiO2 with substituted EWG exhibit photocatalytic activities
(Fig. 5c–f). It was confirmed that the more anodic the EA of cate-
chols with substituted groups are, the higher the activities of the
ISC photocatalyst become. Furthermore, photocatalytic activities
can be explained by the correlation of oxidative potentials of mod-
ifiers with that of TEA. Meanwhile, when methanol was employed
instead of TEA as a sacrificial hole scavenger, the photocatalytic
reaction did not proceed on the BN/TiO2. This result suggests that
the photoinduced hole on the BN/TiO2 do not have enough oxidiz-
ability of methanol.
0
5
10
15
Time / h
Fig. 4. Photocatalytic H2 evolution [I] from aqueous TEA (10 vol%) on (a) 80-BC/
TiO2, (b) 80-MC/TiO2, (c) 80-CA/TiO2, (d) 80-BA/TiO2, (e) 80-BN/TiO2, and (f) 80-TN/
TiO2; catalytic recycling property [II] on the 80-BN/TiO2.
8
(f)
(e)
6
4
(d)
2
(c)
(b)
(a)
0
1.0
To clarify photoresponsive sites, the apparent quantum yields
(AQY) on the 80-BN/TiO2 were measured, and results are shown
in Fig. 6. The AQY for H2 evolution was estimated to be 0.8% under
monochromatic photoirradiation at 510 nm, 12.5% at 450 nm, and
32% at 420 nm; i.e., the action spectrum that is formed by the AQY
plots fits the absorption of 80-BN/TiO2. These results suggest that
the photoexcitation of the ISC plays a significant role in the
photocatalytic reaction.
1.1
1.2
1.3
1.4
1.5
EA / V vs. Ag/AgCl
Fig. 5. Photocatalytic activity of (a) 80-BC/TiO2, (b) 80-MC/TiO2, (c) 80-CA/TiO2, (d)
80-BA/TiO2, (e) 80-BN/TiO2 and (f) 80-TN/TiO2 as a function of the EA of each
modifier. The arrow represents the EA of TEA.
from DFT calculations are listed in Table 2. It was observed that an
increase of electron-withdrawing ability of the substituted groups
induces anodic shift of the donor levels, accompanied by an
enlargement of the energy gaps. These results correspond to
energy gaps measured by UV–vis spectroscopy (see Table 2) and
clearly demonstrate the electronic effects due to the substituted
groups.
120
(a)
off light on
100
80
3.2. H2 evolution from aqueous TEA on several ISC photocatalysts
under visible-light irradiation
50 μA
60
40
60 s
The activities on several ISC photocatalysts were evaluated by
H2 evolution from aqueous TEA through in situ photodeposition
of Pt under visible-light irradiation. As shown in Fig. 4[I], the
photocatalytic activity strongly depends on the substituted
20
(b)
-0.5
0
-1
-0.9
-0.8
-0.7
-0.6
groups:
80-BC/TiO2 ꢃ 80-MC/TiO2 < 80-CA/TiO2 ꢄ 80-BA/TiO2 <
E / V vs. Ag/AgCl
80-BN/TiO2 ꢃ 80-TN/TiO2. By optimizing amounts of the modifier
and Pt co-catalyst loaded, the preferable photocatalyst was
80-BN/TiO2 (Pt/Ti: 0.50 atomic%) (details are shown in Figs. SI 8
and 9 in the Supporting Information). The photocatalytic activity
Fig. 7. Iph–E curve on (a) BN/TiO2 and (b) BC/TiO2 electrodes, and (inset) typical
photoresponse on BN/TiO2 in aqueous LiClO4 (0.1 M) involving TEA (10 vol%) at
ꢁ0.6 V vs. Ag/AgCl under visible-light illumination (k > 420 nm).

290
S. Higashimoto et al. / Journal of Catalysis 329 (2015) 286–290
its derivatives. TiO2 with such modifiers as BN and TN with EWG
E / V vs. Ag/AgCl (pH 10)
was found to exhibit high photocatalytic activity, while BC and
MC with EDG do not induce activity. The photocatalytic activity
is significantly influenced by the electronic structures of the substi-
tuted groups, which can tune the donor levels. Understanding the
electronic effects of the substituted groups in the aromatics helps
us to further design new photocatalytic systems.
e-
Pt
CB
H2
Efb
-0.94
E(H+/H2)
2 H+
-080
Visible-light
(λ > 400 nm)
Appendix A. Supplementary material
TEA/TEA
Donor level
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jcat.2015.05.010.
h+
+1.58
+2.26
O
O
O
Ti
Ti
O
O
0.68 eV
VB
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3.3. Understanding reaction mechanisms in the photocatalytic system
Fig. 7 (inset) shows a stable and photosensitive current at
ꢁ0.6 V vs. Ag/AgCl (pH 10). The photocurrent (Iph)–voltage (E)
characteristics of the BN/TiO2 film under visible-light irradiation
(k > 420 nm) are shown in Fig. 7a. As the cathodic bias is applied
to the BN/TiO2 photoelectrode, the photocurrent gradually
decreases, and the onset potential was estimated to be ꢁ0.94 V
vs. Ag/AgCl. On the other hand, the BC/TiO2 exhibited little
photocurrent (see Fig. 7b). These results indicate that the TEA
can be oxidized by the photoinduced holes on the BN/TiO2, not
on the BC/TiO2, since the EA of BN is more anodic and that of BC
is more cathodic than that of TEA, as shown in Table 1. It was thus
confirmed that the influence of the electronic structures of the ISC
with EWG and EDG on the photocurrent efficiency has been clearly
demonstrated by the combination of the photo-electrochemical
properties.
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Fig. 8 shows the reaction mechanism for photocatalytic H2
production from aqueous TEA on BN/TiO2 under visible-light
irradiation. From the results of the energy gap and onset potential
for the photoresponse on BN/TiO2, the donor level is determined to
be located at 0.68 eV above the valence band of TiO2. The donor
levels can be tuned by the electronic effects of the substituted
groups. The photocatalytic activity strongly depends on the
relationships between the donor levels and oxidative potentials
of the TEA. Visible-light irradiation of the BN/TiO2 photocatalyst
induces the charge carrier (hole and electron) separation. The
photoinduced holes localized in the ISC can oxidize the TEA. On
the other hand, the photoexcited electrons participate in the
reduction of protons to form H2 on the conduction band through
the Pt co-catalyst, since the onset potential at ꢁ0.94 V is more
cathodic than the redox potential E(H+/H2) at ꢁ0.80 V.
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[41] The role of surface TiAOH was demonstrated by the surface treatment with
HF. Details are shown in Figs. SI 11 and 12.
A visible-light-sensitive photocatalyst for H2 evolution from
aqueous TEA in the presence of Pt co-catalyst was successfully
designed by surface modification of the TiO2 with catechol and