Inorganic Chemistry
Article
n+
unstable structure and nonvacancy character of TBADT. The
only successful example is our recently reported carbon
quantum dot (CQD)-hybridized TBADT with a remarkably
Table 1. Metal Contents of M -TBADT Catalysts Measured
by ICP and Estimation of Their Molecular Formula
n+
Mn+
W (wt Mn+ content
26
M -
estimated molecular
enhanced visible-light catalytic performance.
a
b
TBADT (wt %)
%)
(mol %)
formula
Inspired by the above-mentioned research progress of metal-
hybridized POMs and CQD-hybridized TBADT, we would try
to develop a simple and productive HE strategy of TBADT by
transition metals here. A series of characterization and photo-
oxidation experiments support that the doping of some cheap
TBADT
54.80
56.8
3+
TBA3.865+Fe0.0453+W O
4−
4−
Fe -
TBADT
0.076
0.079
0.082
0.077
0.452
0.469
0.462
0.437
10 32
2+
TBA3.906+Fe0.0472+W O
Fe -
TBADT
57.51
55.24
58.4
10 32
3+
2+
2+
2+
n+
2+
TBA3.908+Co0.0462+W10
4−
3d transition metal ions Fe , Fe , Co , and Ni ions (M )
Co -
TBADT
O
32
can be directly achieved in the synthesis of TBADT, and the
2+
TBA3.912+Ni0.0442+W O
4−
n+
Ni -
TBADT
10
32
M
ion-doped TBADT catalysts obtained by this very simple
strategy have a more stable structure and stronger redox
capacity than pure TBADT. More importantly, their frontier
orbital energies, band gap energies, and photoexcited state
lifetimes can be fine-tuned at the molecular level by the metal
ion dopants, thus comprehensively resolving the above
inadequacies of TBADT and showing the remarkably
enhanced photocatalytic performance for the visible light-
driven selective oxidation of EB and other organic compounds
a
n+
The actual molar percentage of the doped M ions relative to W
b
n+
atoms. Molecular formula of M -TBADT was estimated based on
the following equation: the number of M in each W O
actual molar percentage/10, the number of TBA in each W O
n+
4−
= its
1
0
32
+
4−
=
1
0
32
n+
4−
(4 − n × the number of M in each W O ).
1
0
32
with O . This pioneering work not only provides an effective
efficiency. Powder X-ray diffraction (XRD) and transmission electron
microscopy (TEM) analyses of two typical samples TBADT and Ni -
TBADT indicated that the doping of Ni ions resulted in a sharp
2
2
+
HE strategy for the preparation of the metal ion-hybridized
TBADT photocatalysts but also opens up new voyages, using
inexpensive and readily available 3d transition metal ions to
fine-regulate the synthetic quality, redox ability, and photo-
physiochemical properties of TBADT at the molecular level.
2
+
2
+
attached energy dispersive spectroscopy (EDS) analysis (Table S1)
was equal to its theoretical value. Additionally, UV−vis spectra in
2
. EXPERIMENTAL SECTION
2+
Figure S3 showed that the synthetic quality of Ni -TBADT was
2
.1. Material and Sample Preparation. All chemicals were
affected by hydrothermal treatment temperature, and the best quality
could be obtained at 120 °C.
analytical grade and used without further purification. Sodium
tungstate (Na WO ·2H O), tetrabutylammonium bromide
TBABr), FeCl ·6H O, FeCl ·4H O, CoCl ·6H O, NiCl ·6H O,
2.3. Visible-Light-Catalytic Oxidation Experiments. Visible-
designed glass tube photoreactor (Figure S4, inner diameter, 1.7
cm, height, 15.5 cm) equipped with an ethanol (0−5 °C)-cooled
condenser and an oxygen storage vessel (1 atm). A 35 W tungsten−
2
4
2
(
3 2 2 2 2 2 2 2
concentrated hydrochloric acid (36% HCl), sulfuric acid (98%
H SO ), phosphoric acid (85% H PO ), benzenesulfonic acid
2
4
3
4
(
PhSO H), acetic acid (HAc) cyclohexane, toluene, ethylbenzene,
benzyl alcohol, and acetonitrile (MeCN) were purchased from
Sinopharm and used without further treatment. Distilled water was
3
2
bromine lamp (with an UV light filter, light intensity, 535 mW/cm ),
as a built-in light source, was built in a quartz glass tube (outer
diameter, 1.2 cm) and then immersed in a 5.5 mL MeCN solution
containing the catalyst and substrate. The whole lighting reaction was
operated in the closed reactor under normal temperature and pressure
and its specific operating conditions and analytical method for the
used throughout this experiment.
n+
2
.2. Synthesis of Transition Metal Ions (M )-doped TBADT
2+ 2+ 2+ 3+
Catalysts. The 3d transition metal ion Ni , Co , Fe , and Fe -
n+
doped TBADT catalysts (tagged M -TBADT) were synthesized via a
27
hydrothermal reaction. Typically, 6.4 g (19.4 mmol) of Na WO ·
oxygenated products could be found in our recent publication.
2
4
2
1
H O was dissolved with 40 mL of water, followed by the addition of
Here, each photoreaction was repeated in duplicate, and the obtained
data between two parallel experiments differed by less than
approximately 2%. The average results of the two parallel experiments
were used in this study.
2
n+
3.4 mL of 3 M HCl solution containing 0.1 mmol of M ; the
acidified solution was heated to boiling for 5−10 min to obtain a
decatungstate acid solution. Next, 6 M TBABr solution (20 mmol)
was added to the decatungstate acid solution at 100 °C under
continuous stirring, and the white solid was gradually precipitated
from the reaction solution. Then, the obtained precipitate and
reaction solution were transferred to a 100 mL Teflon-lined autoclave
and treated at 120 °C for 12 h under autogenous pressure (about 0.19
MPa). The obtained precipitate was filtered, repeatedly washed with
water and ethanol, and then dried under a vacuum at 60 °C for 24 h
to yield the goal products (M -TBADT, here, the theoretical content
of the doped M ions was ca. 0.5 mol % relative to W atoms). In
order to prevent Fe oxidation to Fe the preparation of Fe -
TBADT was carried out under high pure N protection. The metal
2.4. Characterization. X-ray photoelectron spectroscopy (XPS)
of the samples was measured on a VG Multi Lab 2000 system with a
monochromatic Mg Kα source operated at 20 kV. Powder X-ray
diffraction (XRD) of the samples was conducted on a Rigaku 2550 X-
ray diffractometer using Cu Kα radiation (λ = 0.15406 nm) and a
graphite monochromator. Transmission electron microscopy (TEM)
images of the samples were obtained from a JEOL JEM-2100
transmission electron microscope at an accelerating voltage of 200 kV.
Liquid UV−vis spectra of the samples in MeCN were recorded from
200 to 800 nm on a UV-2450 spectrophotometer (Shimadzu, Japan),
and their UV/vis diffuse reflectance spectra (DRS) were recorded on
a U-3310 spectrophotometer (HITACHI). Their transmission FT-IR
n+
n+
2
+
3+
2+
,
2
n+
contents of TBADT and M -TBADT catalysts were measured by the
−
1
ICP method, and the measured data are listed in Table 1. It can be
seen from Table 1 that the actual W content of TBADT measured by
ICP-AES analysis was 54.80 wt % and slightly lower than the
theoretical W content (55.40 wt %) estimated from the molecular
formula (nBu N) W O . And the actual W contents of most of the
spectra were recorded from 400 to 4000 cm on a Nicolet Nexus 510
P FT-IR spectroscopy using a KBr disk. Photoluminescence (PL)
measurements of the samples in MeCN were carried out on a
fluorescence spectrophotometer (HITACHI F-7000) at room
temperature. The metal contents of these samples were measured
by inductively coupled plasma-optical emission spectroscopy (ICP-
OES) on Optima 5300DV. Cyclic voltammetric (CV) experiments of
the samples in MeCN were measured with an electrochemical
analyzer (CHI 650e Chenhua Instrument Company).
4
4
10 32
n+
M -TBADT catalysts were obviously higher than the theoretical
+
value, which should be due to the partial replacement of TBA by
n+
M . The actual doping amount of these metal ions is about 90% of
their theoretical doping amount, indicating their high doping
B
Inorg. Chem. XXXX, XXX, XXX−XXX
Chen, Mengke
