ACS Catalysis
Research Article
Mn/tri-CN) were synthesized through a similar preparation
procedure except for a different magnesium precursor loading
(Mn 10 wt %).
Photoelectrochemical Tests. Photoelectrochemical tests
were conducted with a three-electrode system on a CHI 660
electrochemical workstation, using a Pt wire as the counter
electrode and an Ag/AgCl electrode as the reference electrode.
The working electrode was prepared with fluorine−tin oxide
(FTO) glass. A 5 mg sample was dispersed in 1 mL of ethanol
by sonication to form a slurry. The slurry was dropped on FTO
glass with an active area of 1 cm2. The working electrode was
dried in air at 60 °C and further dried at 120 °C for 2 h to
improve adhesion.
Characterizations. The as-obtained products were char-
acterized by X-ray diffraction (XRD) patterns on a Rigaku D/
MAX2500PC X-ray diffractometer with Cu Kα (λ= 1.5406 Å)
radiation at a voltage of 40 kV and 150 mA. XRD patterns were
scanned over the angular range of 10−90° (2θ) with a step size
of 0.02°. The metal loadings of samples were determined with
inductively coupled plasma atomic emission spectroscopy
(ICP-AES). The transmission electron microscopy (TEM)
images were measured with a JEOL Model JEM 2010 EX
instrument at an accelerating voltage of 200 kV. HAADF-
STEM characterization was conducted on a JEOL JEM-
ARM200F instrument . X-ray photoelectron spectroscopy
(XPS) measurements were performed on a Thermo ESCALAB
XI+ spectrometer. Electron paramagnetic resonance (EPR)
measurements were carried out a with Bruker Model A300
spectrometer.
Data Collection and Analysis for XAS Spectra. Mn K-
edge X-ray absorption spectra were acquired at room
temperature in fluorescence mode at the National Synchrotron
Radiation Research Center (NSRRC) using a Si (311) double-
crystal monochromator. The energy was calibrated using Mn
foil. The XAFS raw data were background-subtracted,
normalized, and Fourier-transformed by the standard proce-
dures with the Athena program (version 0.9.25). A least-
squares curve fitting analysis of the EXAFS χ(k) data was
carried out using the Artemis program (version 0.9.25) with
the theoretical scattering amplitudes, phase shifts, and the
photoelectron mean free path for all paths calculated by the ab
initio code FEFF8. The details of fitting parameters are
discussed in Table S4 in the Supporting Information.
Catalytic Reactions. The light-induced oxo-dehydrogen-
ation reactions were carried out in a quartz tube irradiated with
a photocatalytic reaction device (China Education Au-light
Company, CEL-PCRD300-12, 25 W). Under standard
conditions, the photocatalyst and 1,2,3,4-tetrahydroquinoline
(12.54 μL, 0.1 mmol) were dispersed in the reaction medium
(20 mL) in a quartz reactor. The reaction suspension was
connected with an atmosphere of air and stirred at room
temperature, and then the reaction was started under LED
light irradiation (455 nm). After the reaction, the suspension
was filtered through a porous membrane and the filtrate was
analyzed by GC-MS (Shimadzu QP2010 SE).
DFT Calculations. All of the first-principles calculations of
the study were performed using Dmol3. The exchange and
correlation terms were determined using the generalized
gradient approximation (GGA) in the form proposed by
Perdew, Burke, and Ernzerhof (PBE). For all elements, the all-
electron method was applied (the basis set as DNP with the
file is 4.4). Brillouin zone integration was performed using a 6
× 6 × 1 Monkhorst−Pack grid for a periodic slab with one
single-layer planar substrate sheet and a 24 Å vacuum between
the sheet and its periodic images. The cutoff was set as 4.5 Å,
and a 0.005 Ha smearing was used to facilitate the self-
consistent field (SCF) convergence. The thresholds of energy,
force, and displacement are 10−5 hartree, 2 × 10−3 hartree/
atom for the maximum force, and 5 × 10−3 Å for displacement.
The perfect conjugated tri-s-triazine framework consists of
one layer and was constructed in a periodic simulation lattice
built with three dimensions of x = 29.5 Å, y = 14.7 Å, and z =
10 Å. Subsequently, the Mn-N2 structure was obtained by
doping Mn atoms in the conjugated tri-s-triazine framework
system. Then types of optimized interaction patterns (top and
side views are shown in Figure S21 in the Supporting
Information) and adsorption energies of adsorbate molecules
(tetrahydroisoquinoline or O2) adsorbed on the conjugated tri-
s-triazine framework surface were designed and calculated.
The adsorption energy of an adsorbate molecule (tetrahy-
droisoquinoline or O2) on the substrate surface (ΔEads) was
calculated by eq 1
ΔEads = Esurf‐mol* − Esurf − Emol
(1)
where Esurf and Emol represent the energies of the substrate
surface and the adsorbate molecule, respectively. Esurf‑mol* is the
total energy of one of the adsorption configurations. A negative
value of Eads indicates that the process is an exothermic
reaction, and high negative value corresponds to a stronger
interaction, which indicates more heat release and a more
stable product.
Reactive Species Quenching Experiments and EPR
Trapping Tests. Under the optimal reaction conditions,
radical quenching experiments were performed through the
addition of different radical scavengers. Specifically, 5 mM
TRP (L-tryptophan) was chosen as the singlet oxygen (1O2)
scavenger, 5 mM TBA (tert-butanol) was chosen as the
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
hydroxyl radical (•OH) scavenger, and 5 mM pBQ (p-
Experimental section including the SEM, TEM, STEM,
XRD, HAADF-STEM results, nitrogen adsorption−
desorption isotherms, XPS survey spectra of the Mn1/
tri-CN catalyst and the tri-CN control sample, and
additional tables to support the results (PDF)
•−
benzoquinone) was chosen as the superoxide radical (O2
)
scavenger, respectively. For the EPR trapping test, 5,5-
dimethyl-1-proline N-oxide (DMPO) was used as the
superoxide radical (O2•−) trapping reagent. A 4 mg portion
of tri-CN or Mn1/tri-CN catalyst was dispersed into 2 mL of
methanol, forming a 2 mg/mL homogeneous suspension, and
then 50 μL of a methanol solution of DMPO was added to the
above suspension. After that, EPR signals were collected with a
Bruker Model A300 spectrometer under visible light irradiation
(λ > 400 nm) or in the dark.
AUTHOR INFORMATION
■
Corresponding Authors
Wengang Liu − College of Material Science and Engineering,
Qingdao University of Science and Technology, Qingdao
320
ACS Catal. 2021, 11, 313−322