Ruthenium Complex-Incorporated Two-Dimensional Metal-Organic Frameworks for Cocatalyst-Free Photocatalytic Proton Reduction from Water

Article abstract of DOI:10.1021/acs.inorgchem.9b03250

Ultrathin two-dimensional (2D) nanosheets with efficient light-driven proton reduction activity were obtained through the exfoliation of novel metal-organic frameworks (MOF), which were synthesized by using a bis(4′-carboxy-2,2′:6′,2″-terpyridine) ruthenium complex as a linker and 3d transition-metal (Mn, Co, Ni, and Zn) anions as nodes. The nanosheet of the Ni²⁺ node exhibits a photocatalytic hydrogen evolution rate of 923 ± 40 μmol g^-1 h^-1 at pH = 4.0, without the presence of any cocatalyst or cosensitizer. A combined experimental and theoretical study suggests a reductive quenched pathway for the photocatalytic hydrogen evolution by the nanosheet. The transition-metal nodes at the edge of the nanosheets are proposed as the active sites. Density functional theory (DFT) calculations attributed the different catalytic activities of the nanosheets to the discrepancy of H adsorption free energy at various transition-metal nodes.

Full text of DOI:10.1021/acs.inorgchem.9b03250

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Article
Ruthenium Complex-Incorporated Two-Dimensional Metal−Organic
Frameworks for Cocatalyst-Free Photocatalytic Proton Reduction
from Water
Debiao Huo, Feifei Lin, Shani Chen, Yueran Ni, Ranhao Wang, Hong Chen, Lele Duan, Yongfei Ji,*
Aiju Zhou,* and Lianpeng Tong*
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ABSTRACT: Ultrathin two-dimensional (2D) nanosheets with efficient light-driven proton reduction activity were obtained
through the exfoliation of novel metal−organic frameworks (MOF), which were synthesized by using a bis(4′-carboxy-2,2′:6′,2″-
terpyridine) ruthenium complex as a linker and 3d transition-metal (Mn, Co, Ni, and Zn) anions as nodes. The nanosheet of the
Ni2+ node exhibits a photocatalytic hydrogen evolution rate of 923 40 μmol g−1 h−1 at pH = 4.0, without the presence of any
cocatalyst or cosensitizer. A combined experimental and theoretical study suggests a reductive quenched pathway for the
photocatalytic hydrogen evolution by the nanosheet. The transition-metal nodes at the edge of the nanosheets are proposed as the
active sites. Density functional theory (DFT) calculations attributed the different catalytic activities of the nanosheets to the
discrepancy of H adsorption free energy at various transition-metal nodes.
solar light, transferring electrons, and converting the substrates
at the same time.20−24
INTRODUCTION
■
Hydrogen is a promising energy source as a sustainable
alternative to rapidly depleting fossil fuels.1 In the envisioned
hydrogen economy, hydrogen is generated from solar-light-
driven proton (water) reduction and then distributed to the
local storage infrastructure.2 Currently, one major challenge of
hydrogen energy utilization is the development of efficient
proton reduction photocatalysts.3
Recent advances in the field of metal−organic frameworks
(MOFs), also known as porous coordination polymers
(PCPs), have shown great potential in gas storage,4,5
separation,6,7 recognition,8,9 and catalysis.10−13 One advantage
of MOFs as heterogeneous catalysts is that their tunable
morphology at the molecular level allows the precise design of
active sites and spatial environment aiming to specific
substrates.14,15 Moreover, the components modulated in the
periodic lattice of a MOF structure are able to conduct
multiple functions simultaneously in a synergistic manner.16−19
The properties of MOFs, in particular, provide a new
perspective for the development of heterogeneous photo-
catalysts that possess the versatile capabilities of capturing the
Polypyridyl ruthenium complexes are classic photosensi-
tizers widely applied in photocatalysis because of their
convenient HOMO/LUMO levels and long-lived excited
states.25−27 Recently, MOFs that incorporate Ru-polypyridyl
complexes have been reported to promote the photochemical
hydrogen evolution reaction (HER).28,29 The presence of a
cocatalyst, however, is often required to facilitate the proton
reduction process (see examples in the Supporting Informa-
tion). On the other hand, MOFs with active catalytic
components usually have insufficient light absorption capa-
bility. Only under the assistance of a cosensitizer do these
MOFs catalyze photochemical hydrogen evolution with fast
rates (see examples in SI).30 This previous research naturally
Received: November 5, 2019
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Figure 1. (a) The chemical structure of [RuII(tpyCOO)2] and schematic synthetic routes to MOFs with different 3d transition-metal nodes. (b)
Crystal structure of Co-MOF-Ru(tpyCOO)2 (Co−Ru) showing packed layers viewed along the b-axis (solvent molecules and counterions are
omitted for clarity). (c) The sql network of Co−Ru, where the turquoise tetrahedra represents 4-connected cobalt nodes. (d) The theoretical
thickness of one coordination layer of Co−Ru. (e, f) The pore morphology and coordination environment of cobalt cations inthe crystal structure
of Co−Ru.
Figure 2. FE-SEM images of Co−Ru after drying treatment (a) and exfoliated Co−Ru nanosheets (b). (c) Co 2p XPS spectra of Co−Ru before
(black) and after (red) exfoliation.
leads us to attempts on manipulating the different components
of MOFs and fulfilling the light-harvesting and hydrogen-
evolving functions within one ordered frame, meanwhile taking
the advantage of ultrahigh surface area of the solid.
in the literature (details in SI). Solvothermal reactions of
[RuII(tpyCOOH)2]2+ with Mn(ClO4)2, Co(NO3)2, or Zn-
(NO3)2 afforded single crystals of Mn-MOF-Ru(tpyCOO)2
(Mn0.5[Ru(tpyCOO)2]ClO4, denoted as Mn−Ru), Co-MOF-
Ru(tpyCOO)2 (Co0.5[Ru(tpyCOO)2]PF6, Co−Ru), and Zn-
MOF-Ru(tpyCOO)2 (Zn0.5[Ru(tpyCOO)2]PF6, Zn−Ru)
(Figure 1a). Single-crystal X-ray diffraction identifies that all
three samples are crystallized in the isostructural geometry
(Figure 1, Tables S1−S9). Taking the Co−Ru compound as
an example, every cobalt cation coordinates with four
carboxylate groups from four ruthenium linkers in a distorted
tetrahedral geometry. Each ditopic [RuII(tpyCOO)2] linker
bridges two cobalt cation nodes via a carboxylate−metal
coordination bond, forming a 4-connected network with sql
topology (Figure 1c).36,37 The Co−O(carboxylate) bond
distance lies in the range from 1.947(7) to 1.990(7) Å. The
size of rhombohedral pores in Co−Ru is 16.62 × 26.87 Å,
corresponding to the in-plane Co−Co diagonals (Figure 1e).
In comparison, the Mn−O(carboxylate) and Zn−O-
(carboxylate) bond distances are 2.07−2.46 Å and 1.92−2.46
Å long, respectively. Diagonals of rhombohedral pores in the
Herein, novel MOFs composed of bis(4′-carboxy-2,2′:6′,2″-
terpyridine) ruthenium complex, [RuII(tpyCOOH)2]2+,31 as a
linker and 3d transition metals (Mn, Co, Ni, Zn) as nodes have
been successfully synthesized. These MOFs have a layered
morphology and are readily exfoliated into ultrathin 2D MOF
nanosheets, of which the Co- and Ni-containing ones
efficiently catalyze the photochemical HER in water without
the presence of any cocatalysts or cosensitizers. Regarding the
application of MOFs in photocatalytic reactions, 2D MOF
nanosheets exhibit certain superiority over the 3D MOFs
because the greater lateral dimension and larger surface area of
2D MOF nanosheets offer more accessible active sites for both
electron and proton transfer than the bulky 3D MOFs.32−35
RESULTS AND DISCUSSION
■
Synthesis and Characterization of MOFs. The complex
[RuII(tpyCOOH)2]2+ was prepared according to the protocols
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Figure 3. HRTEM images and FFT patterns (inset) of exfoliated Co−Ru (a) and Ni−Ru (b) nanosheets. (c) AFM image and corresponding
height profile diagrams of exfoliated Ni−Ru nanosheets.
n
Figure 4. (a) CV and DPV of [RuII(tpyCOOH)2](PF6)2, and CV of Co−Ru nanosheets in an acetonitrile solution of Bu4N(PF6) (0.1 M). (b)
CVs of Co−Ru nanosheets and [RuII(tpyCOOH)2](PF6)2 in phosphate buffer (pH = 3.11). The scan rate of CV is 100 mV/s (see the Supporting
Information for experimental details).
Mn−Ru and Zn−Ru frameworks are 16.63 × 26.95 Å and
16.62 × 26.51 Å, respectively. The theoretical thickness of one
single coordination layer of Co−Ru is about 0.8 nm (Figure
1d), and adjacent lattice layers of the frameworks are primarily
stabilized via π−π interaction (centroid−centroid distance ≈
3.7 Å, Figure S4). The space between packed layers is occupied
by counterions and solvent molecules (mainly DMF), which
can be confirmed partially by refined crystal data of these
frameworks (Figures S5−S7). Regarding possible oxidation of
Co2+ and Mn2+ cations during the synthetic reaction, X-ray
photoelectron spectroscopy (XPS) was performed to probe the
covalence of these 3d transition-metal nodes in the MOFs. The
XPS spectrum of Co−Ru (Figure 2c) shows characteristic
2p3/2 and 2p1/2 satellite peaks of Co2+ species at ∼786 and
∼801 eV, respectively, and the XPS spectrum of Mn−Ru
(Figure S8) displays typical binding energy peaks of Mn2+
species at 641.2 and 642.7 eV. These results confirm the
divalent state of Co and Mn cations in the MOFs.
The powder X-ray diffraction (PXRD) profile of the as-
synthesized Co−Ru is consistent with the simulated pattern
against the single-crystal X-ray diffraction data (Figure S8).
After removing DMF molecules from the interplanar space of
Co−Ru under vacuum (80 °C), the prior diffraction peak at a
low 2θ angle around 6° disappeared. Meanwhile, shifts of
diffraction peaks at relatively low 2θ angles were observed in
the PXRD profile of Co−Ru, while the position and strength
of peaks at relatively high 2θ angle were maintained (Figure
S8). The PXRD patterns of Co−Ru, Mn−Ru, and Zn−Ru
after the drying treatment show identical diffraction peaks
(Figure S9). The field-emission scanning electron microscopy
(FE-SEM) image of Co−Ru (Figure 2a) indicates loss of
crystallinity after the drying treatment but maintenance of the
layered structure. Therefore, we propose that removal of
solvent molecules incorporated in the as-synthesized MOF
crystals leads to sliding of the organized 2D layers relative to
each other, due to lack of strong cohesive interaction between
the layers. The characteristic diffraction peaks in the resulting
PXRD patterns correspond to the structural features of the 2D
lattices.
Solvothermal reaction of [RuII(tpyCOOH)2]2+ with Ni-
(ClO4)2 yielded microcrystals of Ni-MOF-Ru(tpyCOO)2
(Ni0.5[Ru(tpyCOO)2]PF6, denoted as Ni−Ru). The PXRD
pattern of Ni−Ru is the same as the patterns of Co−Ru, Mn−
Ru, and Zn−Ru (Figure S9), indicating the isomorphous 2D
lattices of Ni−Ru with other frameworks discussed above.
Attempts to prepare single crystals of Ni−Ru suitable for X-ray
diffraction were not successful. The FE-SEM image of Ni−Ru
after drying treatment (Figure S11a) shows an evident layered
structure similar to that in the SEM image of dried Co−Ru.
The elemental analysis of these MOFs further confirms their
proposed formulas. Thermogravimetric analysis (TGA) reveals
that all MOF samples begin to lose solvents at about 100 °C
and decompose at about 300 °C under atmospheric pressure
(Figures S12−S15).
Exfoliation of the bulk MOF solids in an ultrasonic bath at 0
°C generates 2D MOF nanosheets. Concerning further
application of these 2D materials in an aqueous environment,
we used protic solvents in the exfoliation experiments. The FE-
SEM images of exfoliated Co−Ru (Figure 2b) and Ni−Ru
(Figure S11 b and c) demonstrate the morphology of
nanosheets consisting of several lattice layers. High-resolution
transmission electron microscopy (HRTEM) images and fast
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Figure 5. (a) Plots of photocatalytic hydrogen production versus time under visible-light irradiation (>420 nm) from ascorbic acid solution (0.5 M,
pH = 4.0) containing different 2D MOF nanosheets. (b) Initial rates (μmol g−1 h−1) of photocatalytic hydrogen evolution for different 2D MOF
nanosheets and control experiments.
Fourier transform (FFT) patterns of Co−Ru (Figure 3a) and
Ni−Ru (Figure 3b) nanosheets confirm the rhombohedral
topology of their 2D networks. The distance of lattice fringes
in the HRTEM image of Co−Ru nanosheetsis measured to be
0.37 nm (Figure 3a). Additionally, the HRTEM image of Ni−
Ru nanosheetsdisplays lattice fringes with d = 0.31 nm (Figure
3b). The similar HRTEM lattice fringes between Co−Ru and
Ni−Ru nanosheets reflect their structural similarity. Atomic
force microscopy (AFM) characterization of the ultrasonicated
Co−Ru suspension (Figures S16 and S17) shows the thickness
of exfoliated nanosheets to be ∼2.8 nm and the average lateral
size to be 230 nm. In contrast, the thickness of exfoliated Ni−
Ru nanosheets ranges from 3.9 to 5.7 nm (Figure 3c); the
lateral size of the nanosheets distributes from 20 to 160 nm,
with an average value of 85 nm (Figure S16). Taking the one-
layer thickness of 0.8 nm (Figure 1d) into account, the
exfoliated Co−Ru nanosheets are comprised of 3−4 layers of
2D lattices, whereas the exfoliated Ni−Ru nanosheets account
for 5−7 layers. The PXRD patterns of Co−Ru or Ni−Ru
nanosheets persist all characteristic diffraction peaks of the
frameworks prior to the exfoliation (Figure S19), indicating the
intact 2D lattices during the exfoliation process. The XPS
spectrum of Co−Ru nanosheets (Figure 2c) shows character-
istic binding energy peaks of Co2+ species very similar to the
XPS spectrum of Co−Ru before exfoliation, ruling out
oxidation of Co2+ nodes during exfoliation.
Cyclic voltammograms (CVs) of Co−Ru nanosheets in
organic electrolyte show one redox wave at 0.99 V and another
three redox waves in the range from −1.6 to −2.1 V versus
ferrocenium/ferrocene (Fc+/0, Figure 4a). The potentials of all
four redox events are close to the redox potentials of
[RuII(tpyCOOH)2](PF6)2 complex, and therefore, the redox
events of Co−Ru nanosheets are supposed to occur mainly at
the [RuII(tpyCOO)2] linker part. CVs of Ni−Ru, Mn−Ru, and
Zn−Ru nanosheets in organic electrolyte display similar redox
features with those of Co−Ru (Figure S20). In acidic aqueous
buffer (pH = 3.11), Co−Ru nanosheets undergo the RuIII/RuII
redox process at 1.5 V versus the reversible hydrogen electrode
(RHE, Figure 4b). Meanwhile, an irreversible reduction wave
appears at about −0.72 V vs. RHE in the CV of Co−Ru
nanosheets, concurrent with a salient current enhancement.
Likewise, the CV of Ni−Ru nanosheets in the acidic buffer
shows a ruthenium-centered redox wave at 1.5 V and an
irreversible wave at −0.75 V vs. RHE (Figure S21).
Comparison of CVs of [RuII(tpyCOOH)2]2+ and 2D MOF
nanosheets manifests that deprotonation and coordination of
the Ru complex incorporated in the MOF structure do not
change its electrochemical behavior significantly. Under acidic
or neutral conditions, the ruthenium linker at its one-electron
reduction state assigned as a formal [RuI(tpyCOO)2]− species
can thermodynamically drive the proton to hydrogen half-
reaction, for which the potential is 0 V vs. RHE (Figure S24).
The redox reaction of transition-metal nodes of Co−Ru and
Ni−Ru was not distinguished during the potential sweep
process, probably because of sluggish electron transfer rate
from the node to the electrode or interference of the electron
transfer process by the MOF structure.38
Photocatalytic Hydrogen Evolution. The solid-state
UV−vis absorption spectra of these 2D MOFs all exhibit a
strong absorbance band at about 480 nm, which is attributed
to the metal-to-ligand charge transfer (MLCT) of
[RuII(tpyCOO)2] linkers in the framework (Figure S22).
The oxidation potential of the ruthenium linker at its excited
state, E(RuIII/RuII*), is estimated to be −0.35 V vs. RHE (pH
= 3.11), according to its maximum emission at 670 nm (1.85
eV, Figure S22) and its RuIII/RuII redox potential (1.5 V vs.
RHE) at the ground state. Therefore, electron transferring
from the excited Ru linkers to protons, reducing protons, and
evolving hydrogen are thermodynamically favored under acidic
and neutral conditions (Figure S24).
Photocatalytic HER activity of exfoliated 2D nanosheets was
investigated in water containing ascorbic acid as a sacrificial
electron donor. Under the irradiation of visible light (λ > 420
nm), both Co−Ru and Ni−Ru nanosheets effectively evolved
hydrogen in the tested pH range from 3 to 5, without the
presence of any cocatalyst or cosensitizer (Figures S25−S27).
In contrast, neither Mn−Ru nor Zn−Ru nanosheets displays
substantial catalytic activity toward light-driven HER in the
photocatalytic experiments of this pH range. At pH = 4.0, Co−
Ru and Ni−Ru nanosheets achieved photocatalytic HER rates
of 589 19 and 923 40 μmol g−1 h−1 (Figure 5a). After an 8
h photocatalysis, an overall amount of 2545 400 and 3734
280 μmol H2 was produced per gram of Co−Ru and Ni−Ru
nanosheets as catalysts, respectively (Figure S28). Never-
theless, Mn−Ru and Zn−Ru nanosheets only generated a
trivial amount of hydrogen under the same photocatalytic
conditions. At pH = 3.0 or 5.0, the photocatalytic HER rates of
Co−Ru and Ni−Ru nanosheets declined in comparison with
their rates at pH = 4.0. This is because the pH value does not
only manifest the proton concentration of the medium but also
affects the electron-donating ability of ascorbic acid.39 The
control photocatalysis experiments using stoichiometric Co-
(NO3)2 or Ni(ClO4)2 coupled with the [RuII(tpyCOOH)2]-
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Figure 6. (a) The photoluminescent decay traces of solid Ni−Ru (blue dots) and [RuII(tpyCOOH)2](PF6)2 (black dots) during the initial 50 ns
period (λex = 339 nm). (b, c) The iso-electron density of LUMO and LUMO+1 orbitals of Ni−Ru nanosheets.
Figure 7. (a) Free energy landscapes for hydrogen evolution at the metal sites of Ni−Ru and Mn−Ru, on the (100) surface and at the edge. The
optimized structures of H* at the metal sites on the (100) surface (b) and at the edge (c). (d) Proposed photocatalytic mechanism of hydrogen
evolution by Ni−Ru nanosheets.
(PF6)2 complex, instead of the 2D MOF nanosheets, did not
show effective hydrogen evolution (Figure 5b).
electron transfer rates of Ni−Ru and [RuII(tpyCOOH)2]-
(PF6)2 are 1.49 and 1.78 ns (Table S11), estimated by fitting
the photoluminescent decay trace with a biexponential
function. The quite close photoluminescent decay rates
imply that the excited [RuII(tpyCOO)2] linkers of Ni−Ru
do not transfer electrons to the coordinated nickel nodes. The
photocatalytic hydrogen evolution by Ni−Ru proceeds in a
reductive quench pathway.
The electron density of the orbitals of Ni−Ru at the bottom
of the conduction band was calculated with density functional
theory (DFT). As shown in Figure 6b and c (Figure S30), the
iso-electron density of LUMO and LUMO+1 orbitals of Ni−
Ru nanosheets is primarily located over the terpyridine
moieties. This calculated electron density distribution confirms
our experimental observation that under light illumination the
electron transfer happens basically within the
[RuII(tpyCOO)2] linker of Ni−Ru nanosheets from the Ru
center to the 4′-carboxy-2,2′:6′,2″-terpyridine ligand and not
to the Ni nodes.
The free energy of H adsorption, ΔG(H*), has been
frequently used as a descriptor to evaluate the activity of the
heterogeneous HER catalysts.41 To investigate the different
catalytic efficiency of MOFs with various transition-metal
nodes, we calculated ΔG(H*) of the transition-metal nodes
residing in the (100) surface and at the edge of the MOFs.
Since both Co−Ru and Ni−Ru nanosheets are significant
more efficient toward light-driven hydrogen evolution than
their Zn−Ru and Mn−Ru counterparts, we only performed
calculations upon the Ni−Ru and Mn−Ru nanosheets in
The relatively long-term (8 h) photocatalytic HER experi-
ment at pH = 4.0 shows a tendency toward a diminished
hydrogen evolution rate versus reaction time for Co−Ru and
Ni−Ru (Figure S28). As the light-driven HER proceeds, the
nanosheet catalysts decompose into Ru complexes and
transition-metal cations and “dissolve” in the aqueous solution.
The decomposition of the Ni−Ru nanosheet can be followed
by monitoring the absorbance argument of the aqueous
solution at a wavelength of 480 nm (Figure S29), which is the
absorbance feature of the dissociated [RuII(tpyCOOH)2]2+
linkers. On the contrary, if the acidic solution containing Ni−
Ru nanosheet was kept in the dark, little decomposition of the
nanosheet was observed over 8 h (Figure S29). Clearly, the
visible-light irradiation triggered and boosted the decom-
position of the nanosheets under the catalytic conditions.
Photocatalytic Mechanism. In general, the photocatalytic
hydrogen evolution reaction can undergo either a reductive
quench pathway, where the excited sensitizer is first reduced by
the sacrificial donor and then transfers one electron to the
catalyst, or a oxidative quench pathway, where the excited
sensitizer transfers an electron to the catalyst first and oxidizes
the sacrificial donor afterward.40 In order to probe the
photocatalytic pathway of Ni−Ru, we measured the transient
emission decay traces of solid Ni−Ru and [RuII(tpyCOOH)2]-
(PF6)2 complex samples. As shown in Figure 6a, the MLCT
emission of pristine [RuII(tpyCOOH)2](PF6)2 complex is not
quenched by the coordinating Ni2+ cations in the MOF. The
E
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parallel and tried to acquire mechanism insights by comparing
these two materials. The free energy surfaces (FES) and the
optimized structures of the intermediates are displayed in
Figure 7a−c. According to the FES, both the Mn and Ni metal
sites at the edge show smaller ΔG(H*) than the metal sites in
the (100) surface. This suggests that the metal nodes at the
edge of nanosheets are more kinetically favored than those in
the surface to reduce protons. Therefore, the metal nodes at
the edge of the ultrathin 2D nanosheets are proposed as the
major active sites for catalytic hydrogen evolution. The
unsaturated coordination sphere of the metal sites at the
edge may enhance their affinity to protons by providing a
vacant chelating space. Importantly, the ΔG(H*) value (0.57
eV) of Ni sites at the edge is significantly smaller than the
ΔG(H*) value (0.66 eV) of Mn sites at the edge. The smaller
ΔG(H*) of Ni sites agrees with the photocatalytic HER
assessment of more catalytically efficient Ni−Ru nanosheets
than Mn−Ru nanosheets.
The photocatalytic hydrogen evolution cycle (Figure 7d) by
Ni−Ru nanosheets is proposed on the basis of the combined
experimental and theoretical results above. The hydrogen
evolution reaction is initiated by excitation of the ruthenium
linkers of the 2D MOF nanosheets. The excited Ru linker is
quenched by ascorbic acid,39 generating a formal monovalent
RuI species. The Ni node at the edge of Ni−Ru nanosheets
consequently accepts one electron from the adjacent
monovalent Ru linker and reduces a proton by forming a
tentative metal-hydride bond. Hydrogen evolves in the
following one-electron, one-proton process mediated by the
metal-hydride, and the overall catalytic cycle is complete.
While the driving force of photocatalytic hydrogen evolution
by these 2D nanosheets originates from the reduced ruthenium
linker, formally [RuI(tpyCOO)2]−, the hydrogen evolution
kinetics of different 2D nanosheets relies on how effective their
transition-metal nodes adsorb and activate protons. The H
absorption energy of the metal nodes at the edge is less
demanding than that of the metal nodes in the surface.
Notably, these 2D nanosheets carry positive charges after
dissociation of their counteranions and therefore attract
ascorbate anions in the aqueous solution. The static interaction
between the positively charged nanosheet and anionic
ascorbates is expected to facilitate the intermolecular electron
transfer under the photocatalytic HER conditions.
photocatalytic oxidation and reduction reactions, besides
proton reduction, are under investigation. We believe that
there is a great potential to employ these 2D MOFs in the
construction of versatile photocatalytic platforms.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.9b03250.
Synthesis procedures, crystallographic structure details,
characterization data of MOF materials, electrochemis-
try, photocatalytic experiments, and theoretical study
(PDF)
Accession Codes
CCDC 1914911−1914913 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
AUTHOR INFORMATION
■
Corresponding Authors
Yongfei Ji − School of Chemistry and Chemical Engineering/
Institute of Clean Energy and Materials, Guangzhou University,
Guangzhou 510006, P. R. China; Email: yongfeiji2018@
gzhu.edu.cn
Aiju Zhou − School of Chemistry and Chemical Engineering/
Institute of Clean Energy and Materials, Guangzhou University,
Guangzhou 510006, P. R. China; Email: ahcfzhouaiju@
163.com
Lianpeng Tong − School of Chemistry and Chemical
Engineering/Institute of Clean Energy and Materials,
Guangzhou University, Guangzhou 510006, P. R. China;
orcid.org/0000-0002-7977-7941; Email: ltong@
gzhu.edu.cn
Authors
Debiao Huo − School of Chemistry and Chemical Engineering/
Institute of Clean Energy and Materials, Guangzhou University,
Guangzhou 510006, P. R. China
Feifei Lin − School of Chemistry and Chemical Engineering/
Institute of Clean Energy and Materials, Guangzhou University,
Guangzhou 510006, P. R. China
Shani Chen − School of Chemistry and Chemical Engineering/
Institute of Clean Energy and Materials, Guangzhou University,
Guangzhou 510006, P. R. China
Yueran Ni − School of Environmental Science and Technology,
Southern University of Science and Technology, Shenzhen
518055, P. R. China
Ranhao Wang − School of Environmental Science and
Technology, Southern University of Science and Technology,
Shenzhen 518055, P. R. China
Hong Chen − School of Environmental Science and Technology,
Southern University of Science and Technology, Shenzhen
518055, P. R. China; orcid.org/0000-0003-4053-7147
Lele Duan − Department of Chemistry, Southern University of
Science and Technology, Shenzhen 518055, P. R. China;
orcid.org/0000-0003-1662-5817
CONCLUSION
■
In summary, we have prepared a family of isostructural
ruthenium sensitizer-incorprated MOF crystals with various
nodes of 3d transition-metal cations. They are readily
exfoliated into ultrathin 2D MOF nanosheets several nano-
meters thick, which are able to catalyze the visible light-driven
hydrogen evolution from aqueous solution without the need
for any cocatalysts or cosensitizers. The 2D nanosheets
containing Ni2+ and Co2+ nodes represent outstanding efficient
catalysts among MOF-based composites for photocatalytic
hydrogen evolution (Table S10). At pH = 4.0, Ni−Ru
nanosheets achieved a light-driven HER rate of 923 40 μmol
g−1 h−1. The photocatalytic reaction is proposed to undergo a
reductive quench pathway involving electron transfer from the
reduced Ru photosensitizer linkers to the catalytic Ni nodes.
DFT calculation relates H absorption energy to the type and
coordination environment of transition-metal nodes and
assigns the metal nodes at the edge of the nanosheets as the
active sites. The application of these 2D MOFs in other
Complete contact information is available at:
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (21701036 and 21777045). We also
thank the Natural Science Foundation of Guangdong Province
(2016A030313619) for support.
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