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was initiated by adding H2O2 aqueous solution (0.1 mL, 30 wt%).
During the reaction, aliquots (5.0 mL) of the reaction mixture were
taken out at certain time intervals (10 min) and centrifuged before
measuring the fluorescence with a spectrophotometer. A peak at
the wavelength of about 425 nm (2-hydroxyterephthalic acid) by
excitation with the wavelength of 315 nm was achieved. The pro-
of the nanosheets also plays a great role in their catalytic prop-
erties. The increased delocalization in the nanosheets and the
reduction of FeIII (FeIII!FeII) in the nanosheets promote the
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generation of OH radicals. The investigation of FeOCl nano-
sheets provides an opportunity to gain significant fundamental
insights into catalytic processes. These results may shed new
light on such catalytic processes and could be extrapolated to
benefit other 2D nanosheets for use as Fenton reagents.
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duction of OH radicals on FeOCl plates with the same weight and
surface area compared with the nanosheets was also measured by
using the above method for comparison.
Characterization
Experimental Section
The phase structure of the product was identified by using XRD
(scan rate=28minÀ1; scan step=0.068) with a Rigaku D/Max 2200-
PC diffractometer with the tube electric voltage and current of
40 kV and 35 mA for CuKa radiation (l=0.15418 nm) and a graphite
monochromator at ambient temperature. The shape and size of
the samples were characterized by TEM (JEM-100CXII) with an ac-
celerating voltage of 80 kV. The Fourier transform infrared (FTIR)
spectra were measured with a Nicolet 5DX-FTIR spectrometer by
using the KBr pellet method in the range 400–4000 cmÀ1. The Bru-
nauer–Emmett–Teller (BET) surface area (SBET) was measured by N2
adsorption at 77 K by using a QuadraSorb SI surface area analyzer.
The scanning electron microscopy (SEM) images were obtained
with a Field Emission-SEM ZEISS system. Qualitative chemical analy-
ses were performed by using energy-dispersive X-ray spectrometry
(EDS) at 15 kV. The UV/Vis absorption spectra were collected with
a UV/Vis spectrophotometer (Lambda-35, PerkinElmer). Atomic
force microscopy (AFM, multimode 8, Bruker) was applied to mea-
sure the thickness of the FeOCl nanosheets. Fluorescence was ana-
lyzed on a Cary Eclipse fluorescence spectrophotometer. X-ray pho-
toelectron spectra (XPS) were acquired on a PerkinElmer PHI-5300
ESCA. The binding energies obtained in the XPS analysis were cor-
rected for specimen charging by referencing C1s to 284.6 eV. The
products of the degradation of phenol were measured by HPLC-
MS (Agilent 6510). The leaching of Fe after reaction was analyzed
by using an ICP-MS (Nu ATTOM).
All of the chemicals were purchased from Sinopharm Chemical Re-
agent Co., Ltd., and were of analytical grade and used without any
further purification.
Exfoliation of FeOCl plates into bilayer nanosheets
We used a solid-phase method to synthesize FeOCl plates.[26] Exfoli-
ation of the FeOCl plates was performed by dispersing the FeOCl
plates (0.05 g) in acetonitrile (5 mL). The suspensions were treated
for 30 min at ambient temperature with 250 W ultrasonication. To
remove any non-exfoliated particles, the suspension was kept with-
out disturbance for 24 h and subjected to 10 min of centrifugation
at 10000 rpm. The supernatant was then centrifuged at 13000 rpm
for 30 min. The final exfoliated nanosheets were obtained and
then dried at 908C in a vacuum oven for 12 h.
Catalytic activity measurements of FeOCl plates and bilayer
nanosheets
The Fenton catalytic performance of FeOCl nanosheets was tested
by the degradation of phenol with H2O2 at pH 7 (initial pH value of
phenol solution) under sunlight and at room temperature. In a typi-
cal experiment, FeOCl nanosheets (10 mg) were added to a phenol
solution (100 mL, 100 mgLÀ1) and stirred for 60 min to reach the
adsorption equilibrium. The reaction was initiated by adding H2O2
aqueous solution (0.1 mL, 30 wt%). During the reaction, aliquots
(5 mL) of the reaction mixture were taken out at certain time inter-
vals (2 min) and centrifuged before measuring the UV/Vis absorp-
tion spectra. In addition, the Fenton reaction using FeOCl plates
with the same weight (10 mg) was carried out as a comparison.
The degradation of phenol was monitored by the changes in the
phenol absorption peak at 270 nm in the UV/Vis spectra. To study
the surface effect after exfoliation, the catalytic activity of the
FeOCl plates with the same surface area compared to the nano-
sheets was also determined.
Theoretical methods and models
To give an insight into the exfoliation process, first-principle calcu-
lations were performed with the Vienna ab initio simulation pack-
age (VASP).[59] The exchange-correlation functional was constructed
by the generalized gradient approximation (GGA)[60] and ion–elec-
tron interactions were described by the projector-augmented wave
(PAW) potential[61] with the cutoff energy at 500 eV whereas van
der Waals contributions were evaluated with the Grimme-D2 ap-
proach included for surface molecular adsorption.[62] The Brillouin
zone was sampled by a G-centered grid,[63] and k-points mesh 10
512 for bulk and 441 for (010) and (101) surface geometry
optimization calculations were used, respectively. In addition, a 2
2 supercell was constructed for surface molecular adsorption calcu-
lations. Both the lattice constant and the positions of all atoms
were relaxed until the convergence criteria reached 110À5 eV for
the total energy and 0.02 eVÀ1, respectively.
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The production of OH radicals on FeOCl plates and bilayer
nanosheets
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The formation of OH radicals on FeOCl plates and nanosheets sur-
face was determined by fluorescence techniques using terephthalic
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acid as a trapping agent, which can be reacted with OH radicals to
produce highly fluorescent product (2-hydroxyterephthalic
acid).[56] The intensity of the fluorescent peak (2-hydroxyterephthal-
a
As shown in Figure S1, a typical crystal structure of FeOCl has a la-
mellar structure. The adjacent layers are bonded in the b-direction
across the chlorine atom planes by van der Waals interactions. Ad-
mittedly, iron-based composites exhibit ferromagnetic properties
because of the non-half or fulfilled 3d electrons.[64] Herein, our cal-
culations also show that the antiferromagnetic structure of FeOCl
is the most stable structure (Table S1). Therefore, all of our calcula-
tions are based on the antiferromagnetic structure. The DFT+U
method was used to calculate the electronic density of states
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ic acid) was known to be proportional to the amount of OH radi-
cals.[57] The concentration of the terephthalic acid solution was 5
10À4 m in a diluted NaOH aqueous solution (210À3 m); it has been
proved that the hydroxylation reaction of terephthalic acid pro-
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ceeds mainly by OH radicals under the present experimental con-
ditions.[58] FeOCl nanosheets (10.0 mg) were added to terephthalic
acid solution (100 mL) and stirred for 30 min. Then, the reaction
Chem. Eur. J. 2016, 22, 9321 – 9329
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