Structuring Pd Nanoparticles on 2H-WS2 Nanosheets Induces Excellent Photocatalytic Activity for Cross-Coupling Reactions under Visible Light

Article abstract of DOI:10.1021/jacs.7b08619

Effective photocatalysts and their surface engineering are essential for the efficient conversion of solar energy into chemical energy in photocatalyzed organic transformations. Herein, we report an effective approach for structuring Pd nanoparticles (NPs) on exfoliated 2H-WS₂ nanosheets (WS₂/PdNPs), resulting in hybrids with extraordinary photocatalytic activity in Suzuki reactions under visible light. Pd NPs of different sizes and densities, which can modulate the photocatalytic activity of the as-prepared WS₂/PdNPs, were effectively structured on the basal plane of 2H-WS₂ nanosheets via a sonic wave-assisted nucleation method without any reductants at room temperature. As the size of Pd NPs on WS₂/PdNPs increased, their photocatalytic activity in Suzuki reactions at room temperature increased substantially. In addition, it was found that protic organic solvents play a crucial role in activating WS₂/PdNPs catalysts in photocatalyzed Suzuki reactions, although these solvents are generally considered much less effective than polar aprotic ones in the conventional Suzuki reactions promoted by heterogeneous Pd catalysts. A mechanistic investigation suggested that photogenerated holes are transferred to protic organic solvents, whereas photogenerated electrons are transferred to Pd NPs. This transfer makes the Pd NPs electron-rich and accelerates the rate-determining step, i.e., the oxidative addition of aryl halides under visible light. WS₂/PdNPs showed the highest turnover frequency (1244 h^-1) for photocatalyzed Suzuki reactions among previously reported photocatalysts.

Full text of DOI:10.1021/jacs.7b08619

Subscriber access provided by Gothenburg University Library
Article
Structuring Pd Nanoparticles on 2H-WS2 Nanosheets Induces Excellent
Photocatalytic Activity for Cross-Coupling Reactions under Visible Light
Faizan Raza, DaBin Yim, Jung Hyun Park, Hye-In Kim, Su-Ji Jeon, and Jong-Ho Kim
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b08619 • Publication Date (Web): 27 Sep 2017
Downloaded from http://pubs.acs.org on September 27, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Journal of the American Chemical Society is published by the American Chemical
Society. 1155 Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the
course of their duties.

Page 1 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Structuring Pd Nanoparticles on 2H-WS Nanosheets
2
Induces Excellent Photocatalytic Activity for Cross-
Coupling Reactions under Visible Light
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Faizan Raza, DaBin Yim, Jung Hyun Park, Hye-In Kim, Su-Ji Jeon, and Jong-Ho Kim*
Department of Chemical Engineering, Hanyang University, Ansan, 15588, Republic of
Korea.
KEYWORDS: C-C coupling, Pd/WS
visible light photocatalysis
2
hybrid, surface engineering, WS nanosheets, and
2
ABSTRACT
Effective photocatalysts and their surface engineering are essential for the efficient conversion
of solar energy into chemical energy in photocatalyzed organic transformations. Herein, we
report an effective approach for structuring Pd nanoparticles (NPs) on exfoliated 2H-WS
nanosheets (WS /PdNPs), resulting in hybrids with extraordinary photocatalytic activity in
Suzuki reactions under visible light. Pd NPs of different sizes and densities, which can
modulate the photocatalytic activity of the as-prepared WS /PdNPs, were effectively structured
on the basal plane of 2H-WS nanosheets via a sonic wave-assisted nucleation method without
any reductants at room temperature. As the size of Pd NPs on WS /PdNPs increased, their
photocatalytic activity in Suzuki reactions at room temperature increased substantially. In
addition, it was found that protic organic solvents play a crucial role in activating WS /PdNPs
2
2
2
2
2
2
catalysts in photocatalyzed Suzuki reactions, although these solvents are generally considered
much less effective than polar aprotic ones in the conventional Suzuki reactions promoted by
ACS Paragon Plus Environment
1

Journal of the American Chemical Society
Page 2 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
heterogeneous Pd catalysts. A mechanistic investigation suggested that photo-generated holes
are transferred to protic organic solvents, whereas photo-generated electrons are transferred to
Pd NPs. This transfer makes the Pd NPs electron-rich and accelerates the rate-determining step
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
i.e., the oxidative addition of aryl halides under visible light. WS /PdNPs showed the highest
2
‒
1
turnover frequency (1244 h ) for photocatalyzed Suzuki reactions among previously reported
photocatalysts.
INTRODUCTION
C-C coupling reactions are of great importance in various organic transformations and
polymer syntheses.1-3 C-C bonds can be formed via transition metal-catalyzed coupling
reactions, such as the Suzuki–Miyaura, Heck, and Sonogoshira reactions.4-10 These C-C
coupling reactions involve redox processes, including the oxidative addition of substances to
metal catalysts and the reductive elimination of the corresponding products.11-12 The redox
processes occur through electron transfer between transition metal catalysts and organic
substances, which typically requires elevated temperatures or sacrificial reagents. However,
electron transfer-mediated C-C coupling can also be triggered by visible light at room
temperature in the presence of photocatalysts.3, 13-15 Photoexcitation induces electron-hole
separation in the photocatalysts, followed by electron or hole transfer to substances for
initiating C-C coupling reactions. Two types of photocatalysts are widely employed in
photoredox reactions: organometallic compounds13-14 and semiconductors.16-20 In particular,
semiconductors are considered promising photocatalysts for organic transformations due to
effective absorption of visible light, good durability, capacity for multivalent binding to
substances, and cost-effectiveness. To improve the photocatalytic activity of semiconductor
photocatalysts in C-C coupling reactions, proper modification is required to adjust their redox
ACS Paragon Plus Environment
2

Page 3 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
potentials and allow effective transfers of excited electrons or holes to substances under visible
light. Hence, developing facile and effective approaches for modulating the
photophysicochemical properties of semiconductor photocatalysts is of great interest in visible
light-driven photocatalysis.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Two-dimensional (2D) transition metal dichalcogenides (TMDs) have recently received
significant attention because of their intrinsic semiconducting properties and unique electronic
and optical characteristics.21-26 In particular, TMDs exhibit thickness-dependent electronic
structures; that is they have direct band gaps in the visible spectrum when their thickness
decreases to monolayer from a multi-layered bulk with indirect band gaps.27-29 Among TMDs,
exfoliated WS
2
nanosheets have a band gap (1.9 eV) and large absorption in the visible
spectrum and, thus, exhibit good performance in several photocatalytic reactions, including
3
0
31
32
degradation of dyes, H
2
evolution, reduction of nitrophenol, and the oxidative coupling of
amines. To extend the photocatalytic applicability of semiconducting (2H) WS nanosheets
to C-C coupling reactions, it is essential to modify their interfaces with organic molecules or
metals. However, the proper functionalization of semiconducting WS nanosheets able to
promote C-C coupling reactions under visible light has not been reported to date. Several
studies have demonstrated metallic (1T) WS nanosheets that were modified with metal
2
0
2
2
2
nanoparticles (NPs),33-37 but these materials are not suitable for visible light-driven
photocatalysis because they are metallic.
Herein, we report an effective approach for structuring Pd NPs on semiconducting (2H) WS
2
nanosheets, which induced outstanding photocatalytic activity in Suzuki cross-coupling
reactions at room temperature under visible light. A sonic wave-assisted reduction and
nucleation method without use of any reducing agents enabled to introduce Pd NPs with control
over their density and size on the basal plane of 2H-WS nanosheets under very mild conditions
2
ACS Paragon Plus Environment
3

Journal of the American Chemical Society
Page 4 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
25°C, 1.5 h). The as-prepared 2H-WS /PdNPs hybrids were then applied to photocatalyzed
2
Suzuki cross-coupling reactions under visible light, and the effects of the density and size of
the Pd NPs in the hybrids on their photocatalytic activity were investigated. In addition, the
reaction mechanism responsible for the photocatalyzed Suzuki reaction, in particular, the effect
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
of using a protic solvent on the photocatalytic activity of 2H-WS
investigated.
2
/PdNPs was also fully
RESULTS AND DISCUSSION
To prepare 2H-WS
bulk WS in N-methylpyrrolidone (NMP) using a modified liquid exfoliation method (see the
Supporting Information). Then, as-prepared 2H-WS nanosheets were mixed with Pd(OAc)
2
/PdNPs hybrids, a thin layer of 2H-WS nanosheets was exfoliated from
2
2
2
2
in ethylene glycol (EG) including poly(N-vinyl-2-pyrrolidone) (PVP), followed by sonication
at 25°C for 1.5 h (Figure 1). The mixture solution gradually turned black during sonication,
indicating the formation of Pd NPs. In conventional polyol methods, the reduction and
nucleation of metal ions for the formation of metal NPs require high temperatures (>100 °C)
3
8
39
at which EG was oxidized to either acetaldehyde or glycolaldehyde to provide electrons.
The sonic wave-assisted polyol method, however, allowed the rapid and effective formation of
Pd NPs on the basal plane of 2H-WS nanosheets at a low temperature (25°C) without the
2
addition of any reductant. Mild bath-sonication provided enough energy for EG to be rapidly
oxidized at a low temperature, leading to the effective formation of Pd NPs on the basal plane
of the 2H-WS nanosheets.
2
2
H-WS
2
/PdNPs hybrids were then analyzed by transmission electron microscopy (TEM).
nanosheets exfoliated in NMP had clear surface without
As shown in Figure 2a, the WS
2
noticeable particles, and their fast Fourier transformation (FFT) pattern revealed a
ACS Paragon Plus Environment
4

Page 5 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
semiconducting (2H) phase (inset). After sonication for 1.5 h at 25°C, the WS nanosheets were
2
densely and uniformly covered with Pd NPs of ca. 5.5 nm (Figure 2b). The Pd NPs formed on
the basal plane as well as at the edge. Figure 2c clearly shows the lattice fringes of Pd NPs with
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
a spacing of 0.22 nm and WS
atoms were distinctly observed in the atomic mapping images (Figure 2d-2f), showing that the
desired 2H-WS /PdNPs hybrids were synthesized successfully.
2
nanosheets with a spacing of 0.27 nm. In addition, W, S, and Pd
2
We then examined if the coverage of Pd NPs on the WS
by varying the molar ratio of Pd(OAc) to WS at a fixed concentration of PVP. As shown in
Figure 3a, the fractional coverage of Pd NPs in the as-synthesized 2H-WS /PdNPs hybrids was
2
nanosheets could be controlled
2
2
2
very low (15%) when the molar ratio was 0.5. However, the fractional coverage of Pd NPs
gradually increased as the molar ratio of the Pd precursor increased (Figure 3b and 3c), reaching
7
8% at a molar ratio of 1.25. These results indicated that the density of Pd NPs on 2H-WS
2
nanosheets was controllable.
Next, the effect of the ratio of PVP to Pd(OAc) on the size of the Pd NPs on the WS
2
2
nanosheets was investigated. The concentration of PVP is known to influence the size of NPs
in typical polyol methods. As shown in Figure S1a, in the absence of PVP, WS /PdNPs hybrids
2
were produced, but the Pd NPs on the surface of the hybrids were severely aggregated.
Therefore, PVP is required to introduce Pd NPs uniformly without aggregation on the surface
of 2H-WS
0, 20, and to 30 during a course of sonic wave-assisted reduction and nucleation. As shown
in Figure 4, the average size of the Pd NPs on the WS nanosheets was 2.9 nm at the ratio of 1.
2
nanosheets. Subsequently, the weight ratio of PVP to Pd(OAc)
2
was varied from 1,
1
2
When the ratio of PVP increased, the size of the Pd NPs also increased. The size of the Pd NPs
reached 5.5 nm when the ratio was 30. The dependence of the size of the Pd NPs in the hybrids
on the ratio of PVP is opposite to the behavior observed in typical polyol methods in which the
ACS Paragon Plus Environment
5

Journal of the American Chemical Society
Page 6 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
40
size of the NPs normally decreases as the amount of PVP is increased. We speculate that
increasing the amount of PVP could raise the local concentration of Pd(OAc) on the surface
of WS nanosheets and, thereby, accelerate the growth of Pd NPs. The obtained results suggest
that the size of the Pd NPs on the surface of the 2H-WS nanosheets was also controllable.
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
The chemical composition of the 2H-WS
2
/PdNPs was then investigated using X-ray
photoelectron spectroscopy (XPS). As shown in Figure 5a, the peaks appearing at 32.4 and
4+
3
4.6 eV originate from W , indicating that the WS
2
nanosheets have a semiconducting 2H
phase. The peak corresponding to oxidized W at 37.9 eV did not increase in the XPS
spectrum of 2H-WS /PdNPs, suggesting that the 2H-WS nanosheets remained stable during
the reduction of the Pd nucleation reaction. The XPS spectra of S2p3/2 and S2p1/2 also show the
characteristic peaks at 162.5 and 163.8 eV for 2H-WS nanosheets (Figure 5b). The slight shift
observed in the binding energy of S2p can be attribute to the growth of Pd NPs on the surface
2
0
6+
2
2
2
of WS
2
nanosheets. The deposition of Pd NPs on the WS nanosheets may change the electron
2
41
density of W-S bonds, causing the peak shift. In the XPS spectrum of Pd3d (Figure 5c), two
0
42
distinct and intense peaks corresponding to Pd appeared at 335.25 and 340.5 eV. In addition,
two more peaks with very low intensity were observed at 337.0 and 342.5 eV for divalent Pd
2+ 43
(
Pd ). This XPS analysis revealed that most Pd NPs on the WS /PdNPs hybrids consisted of
2
0
Pd , which is known to be an active species able to promote Suzuki coupling reactions
effectively.
The optical properties of the 2H-WS
generated peaks were detected in the absorption spectra of the 2H-WS
absorption of visible light from 300 to 700 nm increased significantly after the deposition of
2
/PdNPs hybrids were then measured. No newly
2
/PdNPs, but the
3
5
Pd NPs on the WS
2
surface (Figure S2a). The Raman spectrum of the WS /PdNPs hybrids
2
shows an increase in the distance between the two peaks of the E12g and A1g vibration modes
ACS Paragon Plus Environment
6

Page 7 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
as compared with that of WS
2
nanosheets (Figure S2b). The E12g peak was red-shifted by 1.83
-1
-1
cm , while the A1g peak was blue-shifted by 1.46 cm ; these changes are attributed to the
3
0
doping of the WS
2
nanosheets with Pd. Then, the fluorescence of the WS
2
/PdNPs hybrids
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
was measured. The fluorescence of the WS
2
/PdNPs hybrids was significantly quenched by the
deposition of Pd NPs, indicating that the oxidative quenching of the fluorescence occurs under
light irradiation (Figure S2c).44-46 The excited electrons of the WS
2
/PdNPs hybrids could be
transferred to metallic Pd NPs, preventing the electron-hole pairs from recombining for
fluorescence emission. We expect that this photo-induced electron transfer would make the Pd
NPs more electron-rich, accelerating the oxidative addition of Pd catalysts to aryl halides.
Next, the photocatalytic activity of the 2H-WS
cross-coupling reactions under visible light irradiation at room temperature, as shown in Table
. The WS /PdNPs (45% Pd coverage, 2.85 µg) were added to a EtOH/H O solution of 4-
bromotoluene (4-BT), phenylboronic acid (PBA), and K CO as a base. This mixture was then
2
/PdNPs hybrids was examined in Suzuki
1
2
2
2
3
stirred for 3 h under visible light irradiation using a white LED lamp (60 W). 4-BT was
converted into the corresponding product 4-methylbiphenyl at 92% yield (entry 1). In the
absence of the WS
addition, the reaction hardly proceeded without light irradiation, even when the WS
catalyst was present (entry 3). These results clearly indicate that the Suzuki cross-coupling
reaction of 4-BT is photocatalyzed by WS /PdNPs hybrids under visible light. For further
control experiments, either 2H-WS nanosheets or Pd NPs were added alone to the reaction
mixture, but no desired product was obtained (entry 5-6). Similarly, when the 2H-WS
2
/PdNPs catalyst, however, no desired product was obtained (entry 2). In
2
/PdNPs
2
2
2
nanosheets were physically mixed with Pd NPs that had been separately synthesized, as shown
in Figure S3, no product was produced by the reaction (entry 7). This result indicates that the
proper interfacial interaction of WS nanosheets with Pd NPs is crucial for the photocatalytic
2
activity of the WS
2
/PdNPs hybrids in Suzuki reactions.
ACS Paragon Plus Environment
7

Journal of the American Chemical Society
Page 8 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
To elucidate the mechanism responsible for photocatalyzed Suzuki cross-coupling
reactions, p-benzoquinone (BQ) was added to the reaction of 4-BT with PBA as an electron
scavenger to trap the electrons transferred from Pd NPs to 4-BT.47-49 As shown in Table 1 (entry
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
8
), no desired product was produced in the presence of BQ. Furthermore,
diisopropylethylamine (DIPEA) was added as a hole scavenger to the reaction solution to block
hole transfer to the borate salt, which generally led to completely quenching the reaction in
other papers.50 The WS
/PdNPs hybrids, however, were still active to promote the
2
photocatalyzed Suzuki reaction in the presence of DIPEA although the reaction yield slightly
decreased to 79% (entry 9). We speculate that the decreased yield might be attributed to strong
chemisorption of basic DIPEA on the active sites of Pd NPs, preventing the oxidative addition
of 4-BT during the reaction. This result of the hole scavenger indicates that the photo-generated
holes on the WS /PdNPs hybrids would not transfer to the borate salt, and the different reaction
2
mechanism should exist in this photocatalyzed Suzuki reaction.
To better understand the reaction mechanism of photocatalyzed Suzuki reactions (Figure
6
a), the effects of different solvents were investigated, as shown in Figure 6b. The
photocatalyzed Suzuki reaction of 4-BT with PBA over WS /PdNPs hybrids (45% Pd coverage)
hardly proceeded in H O because of the poor solubility of 4-BT at room temperature. Hence,
mixture of polar protic or aprotic solvents with H O were examined. A mixture of aprotic N,N-
dimethylformamide (DMF) and H O (2:1) rarely produced the desired product in this
2
2
2
2
photocatalyzed Suzuki reaction, although all of the reagents were completely dissolved in the
solution. In addition, a mixture containing a polar aprotic solvent (dimethylsulfoxide [DMSO])
gave almost no product when the reaction was allowed to proceed at room temperature. This
result is very different from that observed in conventional Suzuki reactions catalyzed by
heterogeneous catalysts. Generally, polar DMF and DMSO are considered to be good solvents
for Suzuki reactions, leading to the generation of the desired products at high yields. However,
ACS Paragon Plus Environment
8

Page 9 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
this is not the case for photocatalyzed Suzuki reactions. A mixture of protic EtOH and H O,
2
however, gave the desired product at very high yield (92%) in a short period of time at room
temperature. In addition, other protic organic solvent mixtures involving MeOH or isopropyl
alcohol (IPA) gave moderate yields of the product in this photocatalyzed Suzuki reaction.
These results imply that protic organic solvents play an important role in photocatalyzed Suzuki
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
reactions over WS
2
/PdNP hybrids. We speculate that protic organic solvents may be oxidized
nanosheets of the hybrid catalysts.
more readily by photo-generated hole transfer from the WS
2
In contrast, aprotic organic solvents, such as DMF and DMSO could not be oxidized by this
hole transfer because they have higher oxidation potentials.51
Subsequently, we investigated the effects of bases on the photocatalyzed Suzuki reaction
catalyzed by WS
2
/PdNPs hybrids under visible light. Among the bases tested, K
2
CO was
3
found to be most effective in the photocatalyzed Suzuki reactions over WS
2
/PdNPs hybrids
(Figure 6c), whereas NaOH was found to be the least effective. This base effect on
photocatalysis is very similar to that observed in conventional Suzuki reactions.
Based on the above experimental results, we propose a mechanism responsible for
photocatalyzed Suzuki cross-coupling reactions catalyzed by WS
light, as shown in Figure 7. Upon visible light irradiation, the WS
electron-hole pairs within the 2H-WS nanosheets. Then, the photo-excited electrons are
2
/PdNPs hybrids under visible
2
/PdNPs hybrids generate
2
transferred to Pd NPs, and the photo-generated holes are transferred to a protic solvent, such
as EtOH. These electron-rich Pd NPs then undergo the oxidative addition of an aryl halide,
followed by trans-arylation of the borate salt. Finally, reductive elimination gives the desired
product, and the WS /PdNPs are regenerated for further reactions.
2
We then investigated the effects of the coverage and size of Pd NPs on the photocatalytic
activity of WS
2
/PdNPs hybrids in Suzuki reactions under visible light (Figure 6d and 6e). The
ACS Paragon Plus Environment
9

Journal of the American Chemical Society
Page 10 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
fractional coverage of Pd NPs on WS
2
nanosheets was controlled from 15% to 78% by varying
the precursor ratio of Pd and WS
2
. As shown in Figure 6d, the WS /PdNPs with 45% fractional
2
coverage gave the highest yield of the desired product, 4-methyl-1,1’-biphenyl. When the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
coverage of Pd NPs exceeded 45%, the product yields decreased because Pd NPs shield the
WS
nanosheets from being excited by visible light, which is a crucial step in photocatalyzed Suzuki
reactions. The effect of the size of the Pd NPs on WS /PdNPs hybrids on their photocatalytic
activity was also explored. As shown in Figure 4 and S1, the size of the Pd NPs on the
WS /PdNPs hybrids was effectively varied from 2.9 to 5.5 nm. Interestingly, the photocatalytic
activity of the WS /PdNPs hybrids increased as the size of the Pd NPs increased (Figure 6e).
2
nanosheets from visible light by absorbing it. This shielding effect prevents the WS
2
2
2
2
Generally, photocatalytic activity tends to increase as the particle size of the catalyst decreases
because of the increased number of active sites available on smaller catalysts. In order to
understand this discrepancy in the size effect, the oxidation states of the smaller size (2.9 nm)
and larger (5.5 nm) Pd NPs on the WS
2
/PdNPs hybrids were analyzed by XPS (Figure S4). As
0
the Pd NP size on the WS
2
/PdNPs increased, the proportion of active Pd species also increased
0
from 54% (2.9 nm) to 69% (5.5 nm). This higher proportion of active Pd species in larger Pd
NPs led to the enhanced photocatalytic activity of the resulting hybrids in Suzuki reactions.
Finally, 2H-WS /PdNPs hybrids were applied to the photocatalyzed Suzuki reactions of
2
various aryl halides and boronic acids at room temperature (Table 2). All aryl iodides were
converted to the corresponding products in high yields, regardless of whether electron-donating
or electron-withdrawing substituents were present (entry 1-5). However, the substituents on the
aromatic rings of aryl bromides were observed to exert an effect. The reaction yields for
bromoanisole (entry 6-7) and 4-bromophenol (entry 8) with electron-donating substituents
decreased slightly relative to those for aryl bromides bearing electron-withdrawing substituents,
such as 2- or 4-bromobenzonitrile and 4-bromobenzaldehyde. According to the experimental
ACS Paragon Plus Environment
1
0

Page 11 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
data shown in entry 6 and 9 of Table 2, the steric hindrance of aryl bromides rarely affects the
yields of the photocatalyzed Suzuki reactions. Based on the photocatalyzed Suzuki reaction of
iodotoluene with PBA, we calculated the turnover frequency (TOF) of the WS /PdNPs hybrids,
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
-
1
which was 1244 h . This TOF is higher than the values determined for previously reported
photocatalysts, as shown in Figure 8 and Table S1.46, 50, 52-63 Less-reactive aryl chlorides were
also subjected to photocatalyzed Suzuki reactions over WS
product was obtained.
2
/PdNPs hybrids, but no desired
As shown in Table 3, three different types of arylboronic acids bearing electron-donating
or electron-withdrawing substituents were exploited as starting compounds. p-Tolylboronic
acid containing an electron-donating group was converted to the corresponding biphenyl
product quantitatively (entry 1). However, the arylboronic acids with electron-withdrawing
groups showed decreased product yields and required longer reaction times (entry 2-3).
According to the experimental results, the substituent effect is more significant in arylboronic
acids than in aryl halides in photocatalyzed Suzuki reactions.
This synthetic approach for structuring NPs on the surface of TMDs can be extended to
various two-dimensional nanomaterials including transition metal oxides to induce outstanding
64
photocatalytic activity under visible light in various energy applications. In addition, 2H-
WS /PdNPs can be applied as an effective catalyst for other cross-coupling reactions such as
2
Heck and Sonogashira reactions.
CONCLUSION
We developed an effective approach to modulate the photocatalytic activity of 2H-WS
2
nanosheets via hybridization with Pd NPs under very mild conditions. The size and density of
ACS Paragon Plus Environment
1
1

Journal of the American Chemical Society
Page 12 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
the Pd NPs on as-prepared 2H-WS
process and were found to be crucial factors for modulating the photocatalytic activity of the
H-WS /PdNPs in Suzuki reactions under visible light. Moreover, the photocatalytic activity
of the 2H-WS /PdNPs hybrids for Suzuki reactions was extraordinarily enhanced in polar
protic solvents, whereas no photocatalytic activity was observed in polar aprotic solvents. 2H-
WS /PdNPs hybrids were successfully applied to the photocatalyzed Suzuki reactions of
various aryl halides with several aryl boronic acids at room temperature. The TOF value of 2H-
2
/PdNPs hybrids were readily controlled during the synthetic
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
2
‒1
WS /PdNPs hybrids for photocatalyzed Suzuki reactions (1244 h for) is the highest reported
2
for any previously investigated photocatalyst. We expect that this approach for modulating the
photocatalytic activity of catalysts will be applicable for diverse heterogeneous photocatalysts.
In addition, 2H-WS /PdNPs hybrids could potentially be employed as photocatalysts in other
2
C-C forming reactions, such as Sonogashira, Heck, and Stille reactions.
ASSOCIATED CONTENT
Supporting Information.
The supporting information is available free of charge on the ACS publication website at DOI:
http://pubs.acs.org. Materials; experimental produces for the synthesis of WS
2
nanosheets and
2
H-WS
2
/PdNPs hybrids, and Suzuki reactions under visible light; instrumentation; XPS; PL
1
and H-NMR data
AUTHOR INFORMATION
Corresponding Author
*
E-mail: kjh75@hanyang.ac.kr
ACS Paragon Plus Environment
1
2

Page 13 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
ACKNOWLEDGMENT
This work was supported by the Basic Science Research Program (2008-0061891, NRF-
014R1A2A1A11051877 and NRF-2017R1A2B2008455) through the National Research
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Foundation of Korea (NRF) funded by the Ministry of Science and ICT. Faizan Raza gratefully
acknowledges the scholarship support provided by the Higher Education Commission of
Pakistan (H.E.C) through its HRDI-UESTPS/UETS Faculty Development Program.
ACS Paragon Plus Environment
1
3

Journal of the American Chemical Society
Page 14 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 1. Schematic representation of the synthesis of 2H-WS /PdNPs hybrids.
2
ACS Paragon Plus Environment
1
4

Page 15 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Structural analysis of as-prepared 2H-WS
2
/PdNPs hybrids. TEM images of (a)
exfoliated 2H-WS
2
nanosheets (inset: FFT pattern), (b) 2H-WS /PdNPs, and (c) the lattice fringe
2
of W and Pd. (d)-(f) W, S and Pd elemental mapping images of 2H-WS /PdNPs.
2
ACS Paragon Plus Environment
1
5

Journal of the American Chemical Society
Page 16 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3. The effect of different Pd(OAc)
H-WS /PdNPs. TEM images of 2H-WS /PdNPs prepared at W/Pd ratios of (a) 4:1 and (b) 1:2.
c) A plot of the fractional coverage of Pd NPs on WS nanosheets against the Pd(OAc) /WS
ratios. The ratio of PVP to Pd(OAc) was fixed at 3.0.
2
/WS ratios on the fractional coverages of Pd NPs on
2
2
2
2
(
2
2
2
2
ACS Paragon Plus Environment
1
6

Page 17 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. The effect of PVP/Pd(OAc)
2
ratios on the size of the Pd NPs on 2H-WS
2
nanosheets. TEM images and size distributions of 2H-WS
2
/PdNPs prepared at ratios of
(
a)-(b) 1, (c)-(d) 10, and (e)-(f) 30. (g) A plot of the size of the Pd NPs on 2H-
WS /PdNPs against the PVP/Pd(OAc) ratios. The ratio of Pd(OAc) to WS nanosheets
was fixed at 0.75.
2
2
2
2
ACS Paragon Plus Environment
1
7

Journal of the American Chemical Society
Page 18 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
a)
W4f7/2
W4f
W4f5/2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
W5p3/2
4
0
38 36 34 32
(b)
S2pS2p3/2
S2p1/3
1
65 164 163 162 161 160
(c)
Pd 3d
0
Pd 3d5
/2
0
Pd 3d3
/2
2+
Pd 3d
2
+
5/2
Pd 3d
3/2
3
44
340
336
332
Binding Energy (eV)
Figure 5. XPS analysis of 2H-WS
and (c) Pd3d for the 2H-WS
PVP/Pd(OAc) = 30.0, and Pd(OAc)
2
/PdNPs. High resolution spectra of (a) W4f, (b) S2p,
2
/PdNPs synthesized under the following conditions:
/WS = 0.75.
2
2
2
ACS Paragon Plus Environment
1
8

Page 19 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Table 1. Photocatalytic Suzuki Cross Coupling Reaction over 2H-WS
2
/PdNPsa
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Entry
1
2
3
4
5
6
7c
8d
9e
2
H-WS2/
2H-
WS2
Pd
NPs
+
̶
+
̶
+
+
+
PdNPs
hν
+
+
̶
̶
+
+
+
+
+
Yield (%)b
92 n.r 25 n.r n.r
n.r n.r n.r 79
a
Reaction conditions: 4-bromotoluene (0.1 mmol), phenylboronic acid (1.2
equiv.), 2H-WS /PdNPs (Pd 2.85 µg), K CO (5 equiv.), EtOH/H O (2:1), a
2
2
3
2
b
6
0W white LED lamp, r.t. Determined by gas chromatography (GC) using
c
toluene as an internal standard. WS nanosheets were mixed with Pd NPs in
2
d
ethe reaction. 0.1 mmol of p-benzoquinone (electron scavenger) was added.
.5 mmol of diisopropylethylamine (hole scavenger) was added. (n.r = no
reaction)
0
ACS Paragon Plus Environment
1
9

Journal of the American Chemical Society
Page 20 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 6. Photocatalytic activity of 2H-WS
2
/PdNPs under various conditions. (a) Reaction
scheme for the photocatalyzed Suzuki cross-coupling reaction of 4-bromotoluene. Effects of
(b) solvents and (c) bases on the photocatalytic activity of 2H-WS
2
/PdNPs. (d) Effect of the
/PdNPs. (e) Effect
fractional coverage of the Pd NPs on the photocatalytic activity of 2H-WS
2
of the size of the Pd NPs on the photocatalytic activity of 2H-WS /PdNPs.
2
ACS Paragon Plus Environment
2
0

Page 21 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 7. Proposed mechanism responsible for photocatalytic Suzuki cross- coupling reactions
over 2H-WS /PdNPs.
2
ACS Paragon Plus Environment
2
1

Journal of the American Chemical Society
Page 22 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table 2. Photocatalyzed Suzuki Cross-coupling Reactions of Various Aryl
a
Halides by 2H-WS /PdNPs
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Time
(h)
Yield
(%)b
Entry
Aryl halides
Product
1
2
3
4
5
3
3
4
4
4
100
98
99
96
98
6
7
8
4
6
6
82
81
88
9
6
99
1
1
0
1
6
6
98
98
aReaction conditions: Aryl halide (0.1 mmol), phenylboronic
acid (1.2 equiv.), 2H-WS /PdNPs (Pd 2.85 µg), K CO (5
equiv.), EtOH/H O (2:1), a 60W white LED lamp, r.t.
2
2
3
2
b
Determined by GC using toluene as an internal standard.
ACS Paragon Plus Environment
2
2

Page 23 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 8. Comparison of the TOF value of 2H-WS /PdNPs with those of previously reported
2
photocatalysts for photocatalyzed Suzuki reactions
ACS Paragon Plus Environment
2
3

Journal of the American Chemical Society
Page 24 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Table 3. Photocatalyzed Suzuki Cross-coupling Reactions of Several
Arylboronic Acids with 4-bromotoluene by 2H-WS
/PdNPsa
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Arylboronic
Time Yield
(h)
Entry
1
Product
(%)b
acid
4
90
2
3
6
6
71
75
aReaction conditions: 4-bromotoluene (0.1 mmol),
arylboronic acid (1.2 equiv.), 2H-WS /PdNPs (Pd 2.85 µg),
CO (5 equiv.), EtOH/H O (2:1), a 60 W white LED
2
K
2
3
2
b
lamp, r.t. Determined by GC using toluene as an internal
standard.
ACS Paragon Plus Environment
2
4

Page 25 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
REFERENCES
1
2.
.
Hussain, I.; Capricho, J.; Yawer, M. A., Adv. Synth. Catal. 2016, 358, 3907-3907.
Schmidt, N. G.; Eger, E.; Kroutil, W., ACS Catal. 2016, 6, 4286-4311.
3
6
4
.
Corrigan, N.; Shanmugam, S.; Xu, J. T.; Boyer, C., Chem. Soc. Rev. 2016, 45, 6165-
212.
.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Johansson Seechurn, C. C. C.; Kitching, M. O.; Colacot, T. J.; Snieckus, V., Angew.
Chem. Int. Ed. 2012, 51, 5062-5085.
5.
Hartings, M., Nat. Chem. 2012, 4, 764-764.
6
7
6
8
9
.
.
Stahl, S. S., Science 2005, 309, 1824-1826.
Kim, J. H.; Kim, J. W.; Shokouhimehr, M.; Lee, Y. S., J. Org. Chem. 2005, 70, 6714-
720.
.
.
Kim, J. H.; Lee, D. H.; Jun, B. H.; Lee, Y. S., Tetrahedron Lett. 2007, 48, 7079-7084.
Shokouhimehr, M.; Kim, J. H.; Lee, Y. S., Synlett. 2006, 618-620.
10.
Park, J. H.; Raza, F.; Jeon, S. J.; Kim, H. I.; Kang, T. W.; Yim, D.; Kim, J. H.,
Tetrahedron Lett. 2014, 55, 3426-3430.
1
1
1
1.
2.
3.
Miyaura, N.; Suzuki, A., Chem. Rev. 1995, 95, 2457-2483.
Miyaura, N.; Yamada, K.; Suzuki, A., Tetrahedron Lett. 1979, 20, 3437-3440.
Prier, C. K.; Rankic, D. A.; MacMillan, D. W. C., Chem. Rev. 2013, 113, 5322-5363.
Skubi, K. L.; Blum, T. R.; Yoon, T. P., Chem. Rev. 2016, 116, 10035-10074.
Karkas, M. D.; Porco, J. A.; Stephenson, C. R. J., Chem. Rev. 2016, 116, 9683-9747.
Serpone, N.; Emeline, A. V., J. Phys. Chem. Lett. 2012, 3, 673-677.
Kisch, H., Angew. Chem. Int. Ed. 2013, 52, 812-847.
14.
1
1
1
1
5.
6.
7.
8.
Zhang, Z. Y.; Edme, K.; Lian, S.; Weiss, E. A., J. Am. Chem. Soc. 2017, 139, 4246-
4249.
19.
Jeon, S. J.; Kang, T. W.; Ju, J. M.; Kim, M. J.; Park, J. H.; Raza, F.; Han, J.; Lee, H. R.;
Kim, J. H., Adv. Funct. Mater. 2016, 26, 8211-8219.
2
6
2
0.
, 2754-2759.
1. Li, H.; Wu, J.; Yin, Z.; Zhang, H., Acc. Chem. Res. 2014, 47, 1067-1075.
Raza, F.; Park, J. H.; Lee, H.-R.; Kim, H.-I.; Jeon, S.-J.; Kim, J.-H., ACS Catal. 2016,
22.
Xu, M.; Liang, T.; Shi, M.; Chen, H., Chem. Rev. 2013, 113, 3766-3798.
Huang, X.; Zeng, Z.; Zhang, H., Chem. Soc. Rev. 2013, 42, 1934-1946.
Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H., Nat. Chem. 2013,
2
2
5
2
3.
4.
, 263-275.
5. Wang, Q. H.; Kalantar-Zadeh, K.; Kis, A.; Coleman, J. N.; Strano, M. S., Nat.
Nanotechnol. 2012, 7, 699-712.
26. Coleman, J. N.; Lotya, M.; O’Neill, A.; Bergin, S. D.; King, P. J.; Khan, U.; Young, K.;
Gaucher, A.; De, S.; Smith, R. J.; Shvets, I. V.; Arora, S. K.; Stanton, G.; Kim, H.-Y.; Lee, K.;
Kim, G. T.; Duesberg, G. S.; Hallam, T.; Boland, J. J.; Wang, J. J.; Donegan, J. F.; Grunlan, J.
C.; Moriarty, G.; Shmeliov, A.; Nicholls, R. J.; Perkins, J. M.; Grieveson, E. M.; Theuwissen,
K.; McComb, D. W.; Nellist, P. D.; Nicolosi, V., Science 2011, 331, 568-571.
27.
Zhao, W.; Ghorannevis, Z.; Chu, L.; Toh, M.; Kloc, C.; Tan, P.-H.; Eda, G., ACS Nano
2
2
2
013, 7, 791-797.
8.
9.
Kang, J.; Tongay, S.; Zhou, J.; Li, J.; Wu, J., Appl. Phys. Lett. 2013, 102, 012111.
Kim, H.-C.; Kim, H.; Lee, J.-U.; Lee, H.-B.; Choi, D.-H.; Lee, J.-H.; Lee, W. H.; Jhang,
S. H.; Park, B. H.; Cheong, H.; Lee, S.-W.; Chung, H.-J., ACS Nano 2015, 9, 6854-6860.
30. Atkin, P.; Daeneke, T.; Wang, Y.; Carey, B. J.; Berean, K. J.; Clark, R. M.; Ou, J. Z.;
Trinchi, A.; Cole, I. S.; J. Mater. Chem. A 2016, 4, 13563-13571.
3
1
1.
4127.
Mahler, B.; Hoepfner, V.; Liao, K.; Ozin, G. A., J. Am. Chem. Soc. 2014, 136, 14121-
ACS Paragon Plus Environment
2
5

Journal of the American Chemical Society
Page 26 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
2.
Lee, H. R.; Park, J. H.; Raza, F.; Yim, D.; Jeon, S. J.; Kim, H. I.; Bong, K. W.; Kim, J.
H., Chem. Commun. 2016, 52, 6150-6153.
3. Su, S.; Zhang, C.; Yuwen, L.; Chao, J.; Zuo, X.; Liu, X.; Song, C.; Fan, C.; Wang, L.,
ACS Appl. Mater. Interfaces 2014, 6, 18735-18741.
3
3
1
3
4.
232.
5.
Kim, J.; Byun, S.; Smith, A. J.; Yu, J.; Huang, J., J. Phys. Chem. Lett. 2013, 4, 1227-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Yuwen, L.; Xu, F.; Xue, B.; Luo, Z.; Zhang, Q.; Bao, B.; Su, S.; Weng, L.; Huang, W.;
Wang, L., Nanoscale 2014, 6, 5762-5769.
36.
Sun, Z.; Zhao, Q.; Zhang, G.; Li, Y.; Zhang, G.; Zhang, F.; Fan, X., RSC Adv. 2015, 5,
Shi, Y.; Huang, J.-K.; Jin, L.; Hsu, Y.-T.; Yu, S. F.; Li, L.-J.; Yang, H. Y., Sci.Rep.2013,
1
3
3
3
3
0352-10357.
7.
, 1839.
8.
Fievet, F.; Lagier, J. P.; Blin, B.; Beaudoin, B.; Figlarz, M., Solid State Ionics 1989,
2–33, 198-205.
39.
Skrabalak, S. E.; Wiley, B. J.; Kim, M.; Formo, E. V.; Xia, Y., Nano Lett. 2008, 8,
2
4
4
077-2081.
0.
1.
Teranishi, T.; Miyake, M., Chem. Mater. 1998, 10, 594-600.
Guardia, L.; Paredes, J. I.; Rozada, R.; Villar-Rodil, S.; Martinez-Alonso, A.; Tascon,
J. M. D., RSC Adv. 2014, 4, 14115-14127.
42. Kumar, G.; Blackburn, J. R.; Albridge, R. G.; Moddeman, W. E.; Jones, M. M., Inorg.
Chem. 1972, 11, 296-300.
4
3
4
Technol. 2014, 4, 2494-2498.
45. Linsebigler, A. L.; Lu, G.; Yates, J. T., Chem. Rev. 1995, 95, 735-758.
4
4
8
4
3.
92-396.
4. Jiao, Z.-F.; Guo, X.-N.; Zhai, Z.-Y.; Jin, G.-Q.; Wang, X.-M.; Guo, X.-Y., Catal. Sci.
Zhao, X.; Zhu, J.; Liang, L.; Liu, C.; Liao, J.; Xing, W., J. Power Sources 2012, 210,
6.
7.
Jiao, Z.; Zhai, Z.; Guo, X.; Guo, X.-Y., J. Phys. Chem. C 2015, 119, 3238-3243.
Zhang, Y.; Li, D.; Zhang, Y.; Zhou, X.; Guo, S.; Yang, L., J. Mater. Chem. A 2014, 2,
273-8280.
8. Yuan, L.; Yang, M.-Q.; Xu, Y.-J., Nanoscale 2014, 6, 6335-6345.
49.
Yang, M.-Q.; Zhang, Y.; Zhang, N.; Tang, Z.-R.; Xu, Y.-J., Sci. Rep. 2013, 3, 3314.
Wang, Z. J.; Ghasimi, S.; Landfester, K.; Zhang, K. A. I., Chem. Mater. 2015, 27, 1921-
5
1
5
0.
924.
1.
Luca, O. R.; Gustafson, J. L.; Maddox, S. M.; Fenwick, A. Q.; Smith, D. C., Org. Chem.
Front. 2015, 2, 823-848.
52.
190, 1-11.
5
2
5
6
Li, Y.; Zhang, Z.; Pei, L.; Li, X.; Fan, T.; Ji, J.; Shen, J.; Ye, M., Appl. Catal. B 2016,
3.
Xiao, Q.; Sarina, S.; Jaatinen, E.; Jia, J.; Arnold, D. P.; Liu, H.; Zhu, H., Green Chem.
014, 16, 4272-4285.
4.
, 1764-1771.
Xie, A.; Zhang, K.; Wu, F.; Wang, N.; Wang, Y.; Wang, M., Catal. Sci. Technol. 2016,
55.
6.
Singh, G.; Kumar, M.; Sharma, K.; Bhalla, V., Green Chem. 2016, 18, 3278-3285.
Cui, J.; Li, Y.; Liu, L.; Chen, L.; Xu, J.; Ma, J.; Fang, G.; Zhu, E.; Wu, H.; Zhao, L.;
5
Wang, L.; Huang, Y., Nano Lett. 2015, 15, 6295-6301.
5
1
58.
59.
6
6
7.
8897.
Verma, P.; Kuwahara, Y.; Mori, K.; Yamashita, H., J. Mater. Chem. A 2015, 3, 18889-
Li, X.-H.; Baar, M.; Blechert, S.; Antonietti, M., Sci. Rep. 2013, 3, 1743.
Zhang, S.; Chang, C.; Huang, Z.; Ma, Y.; Gao, W.; Li, J.; Qu, Y., ACS Catal. 2015, 5,
481-6488.
0.
Sharma, K.; Kumar, M.; Bhalla, V., Chem. Commun. 2015, 51, 12529-12532.
ACS Paragon Plus Environment
2
6

Page 27 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
6
6
1.
2.
Mori, K.; Kawashima, M.; Yamashita, H., Chem, Commun. 2014, 50, 14501-14503.
Wang, F.; Li, C.; Chen, H.; Jiang, R.; Sun, L.-D.; Li, Q.; Wang, J.; Yu, J. C.; Yan, C.-
H., J. Am. Chem. Soc. 2013, 135, 5588-5601.
63.
4.
Gao, S.; Shang, N.; Feng, C.; Wang, C.; Wang, Z., RSC Adv. 2014, 4, 39242-39247.
Kalantar-zadeh, K.; Ou, J. Z.; Daeneke, T.; Mitchell, A.; Sasaki, T.; Fuhrer, M. S.,
6
Appl. Mater. Today 2016, 5, 73-89.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment
2
7

Journal of the American Chemical Society
Page 28 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
TOC
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ACS Paragon Plus Environment
2
8

Page 29 of 37
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 1. Schematic representation for the synthesis of 2H-WS2 /Pd NPs hybrid.
1
98x65mm (300 x 300 DPI)
ACS Paragon Plus Environment