A novel nano-cotton-like bismuth oxyfluoride (NC-BiOF) and a novel nanosheet heterogeneous compound BiOF@ZIF-8 as catalyst for the selective and green oxidation of benzylic alcohols

Article abstract of DOI:10.1002/jccs.201800289

We describe here for the first time a new morphology of BiOF nanoparticles with a cotton-like structure, made using a hydrothermal synthesis method. We also prepared heterogeneous nanosheets of BiOF@ZIF-8 by a one-pot synthesis under hydrothermal conditions. We demonstrate that in this method the morphology of BiOF and one-pot synthesis conditions are the main factors for the preparation of the nanosheet BiOF@ZIF-8. Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), thermogravimetry-differential thermal analysis (TG-DTA), and BET surface area were used to characterize the samples prepared. XRD, SEM, and adsorption–desorption analysis showed that the structure of ZIF-8 and BiOF form intact only in one-pot synthesis of BiOF (with nano-cotton-like morphology) with Zn(NO₃)₃, while spectral techniques show the successful encapsulation of the sheet BiOF on ZIF-8. Nanosheet BiOF@ZIF-8 was found to be a highly efficient heterogeneous catalyst for the selective oxidation of alcohols. BiOF@ZIF-8 could be reused several times although it got less active with recycling.

Full text of DOI:10.1002/jccs.201800289

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Received: 24 July 2018
Revised: 28 September 2018
Accepted: 29 September 2018
DOI: 10.1002/jccs.201800289
A R T I C L E
A novel nano-cotton-like bismuth oxyfluoride (NC-BiOF) and a
novel nanosheet heterogeneous compound BiOF@ZIF-8 as
catalyst for the selective and green oxidation of benzylic alcohols
Narges Ghayoumian | Hamid Aliyan | Razieh Fazaeli
Department of Chemistry, Shahreza Branch,
We describe here for the first time a new morphology of BiOF nanoparticles with a
Islamic Azad University, Shahreza, Iran
cotton-like structure, made using a hydrothermal synthesis method. We also pre-
Correspondence
Razieh Fazaeli, Department of Chemistry,
pared heterogeneous nanosheets of BiOF@ZIF-8 by a one-pot synthesis under
hydrothermal conditions. We demonstrate that in this method the morphology of
BiOF and one-pot synthesis conditions are the main factors for the preparation of
Shahreza Branch, Islamic Azad University,
86145-311, Shahreza, Iran.
Email: raziehfazaeli@yahoo.com
the nanosheet BiOF@ZIF-8. Fourier transform infrared (FTIR), X-ray diffraction
Funding information
Shahreza Branch, Islamic Azad University
(XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX),
thermogravimetry-differential thermal analysis (TG-DTA), and BET surface area
were used to characterize the samples prepared. XRD, SEM, and adsorption–
desorption analysis showed that the structure of ZIF-8 and BiOF form intact only
in one-pot synthesis of BiOF (with nano-cotton-like morphology) with Zn(NO3)3,
while spectral techniques show the successful encapsulation of the sheet BiOF on
ZIF-8. Nanosheet BiOF@ZIF-8 was found to be a highly efficient heterogeneous
catalyst for the selective oxidation of alcohols. BiOF@ZIF-8 could be reused sev-
eral times although it got less active with recycling.
KEYWORDS
benzyl alcohol, nano-cotton-like morphology, nanosheet, oxidation, zeolite
imidazolate framework (ZIF-8)
most studied prototype of ZIFs, has well-known applications
in catalysis, separation, chemical sensing, and gas storage.[9]
1
| INTRODUCTION
Metal–organic frameworks (MOFs) have turned out be inter-
esting functional materials and organic coordination poly-
mers (CPs) because of their strong metal–ligand interactions,
organic functionality, tunable structures with high thermal,
hydrothermal, and chemical stability, large pore sizes, open
metal sites in the skeleton, and high surface area.[1–3] MOFs
are also interesting as designer matrices to support metal
nanoparticles (NPs) in composite materials of the type
“metals@MOFs” for use in gas storage, catalysis, and chem-
ical sensing.[4–6] Zeolite imidazolate frameworks (ZIFs) are
a new subclass of porous MOFs that frequently have
expanded zeolite topologies.[7,8] In particular, ZIF-8, as the
Some inorganic crystals have been focused on recently
in the development of the synthesis and fabrication methods
of various morphologies, such as zero-dimensional (0-D;
particles and polyhedra), one-dimensional (1-D; rods, wires,
belts, and tubes), two-dimensional (2-D; sheet, disks, and
plates), and three-dimensional (3-D; multi pods, snowflakes,
hyper branches, and dendrites) structures.[10–13]
Ternary bismuth oxyhalides are a family of important
functional materials with many potential applications
because of their unique electrical, magnetic, optical, and
luminescent properties, or even as oxidative catalysts.[14–16]
Ternary bismuth oxyhalides with the various morphologies
© 2018 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
J Chin Chem Soc. 2018;1–8.
http://www.jccs.wiley-vch.de
1

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GHAYOUMIAN ET AL.
have been successfully prepared (e.g., nanobelts and nano-
tubes of ternary bismuth oxychlorides and oxybromides,[17,18]
BiOF nanosheets, and Bi26O38F2 nanorods).[19] The selective
oxidation of alcohols to carbonyl compounds without over-
oxidation to the corresponding carboxylic compounds is of
importance in the synthesis of natural products.[20] Different
reagents such as vanadium-catalyzed[21] polymer-supported
palladium catalyst,[22] undecamolybdophosphate,[23] tetra-
alkylpyridinium octamolybdate[24] and graphene oxide and
N-doped graphene[25] have been used for the oxidative trans-
formation of alkyl and benzyl alcohols to the corresponding
aldehydes and ketones. Although notable improvements in
terms of selectivity and performance have been achieved,
there is still a need to develop new recoverable palladium cat-
alysts able to work in “greener” reaction media.
(a)
(b)
Here we report a new morphology of nano-sized bismuth
oxyfluorides obtained using terephthalic acid and HF.
We were thus led to the choice of the microporous zeolite
imidazolate framework ZIF-8 (Zn(MeIM)2; MeIM = imida-
zolate-2-methyl; S(N2) = 1,373 m2/g) as the host for nano-
cotton-like BiOF.
20
40
60
80
2θ (°)
2
| RESULTS AND DISCUSSION
10
8
(c)
2.1 | Physicochemical characterization
The Fourier transform infrared (FTIR) spectrum of NC-BiOF
is shown in Figure 1a. It shows the expected Bi–O stretching
vibrations (~574 cm−1). This spectrum also shows broad
bands at 3,400 and 1,600 cm−1 corresponding to adsorbed
water. Figure 1b shows the X-ray diffraction (XRD) pattern
of NC-BiOF. The XRD pattern is suggestive of the tetragonal
phase of BiOF, consistent with the JCPDS file 73–1,595
(a = 3.746 Å, c = 6.626 Å) and is in good agreement with
that reported by Lee et al.[26] No other characteristic peaks
due to the impurities of Bi26O38F2 or Bi2O3 were detected.
Figure 1c shows the N2 adsorption–desorption isotherms of
NC-BiOF, which show the typical IV type isotherms corre-
sponding to nonporous behavior.
6
4
2
Ads
Des
0
0.0
0.2
0.4
0.6
0.8
1.0
p / po
(d)
The TEM images of the nano-cotton-like BiOF sample is
shown in Figure 1d. TEM image indicates that a cotton-like
material with poorly ordered morphology is obtained for BiOF.
The isolated primary 5–-7 nm nanoparticles of nanocotten-like
BiOF were also detected at TEM micrographs.
Figure 2 presents the FT-IR spectrum of the BiOF@ZIF-8
catalyst in the absorption region 400–4,000 cm−1. Several
bands are observed for BiOF@ZIF-8 in the FT-IR spectrum.
The absorption bands at 2,929 and 3,135 cm−1 are attributed
to the aromatic and aliphatic C–H stretch of the imidazole,
respectively. The band at 1,579 cm−1 could be assigned to the
C = N stretch. The absorption band at 420 cm−1 is due to the
Zn–N stretching mode, while those in the 1,100–1,400 cm−1
region are associated with the C–N stretch. The absorption
bands at 1,146 and 1,308 cm−1 are assigned to C–H
FIGURE 1 (a) FTIR spectra, (b) XRD pattern, (c) N2-adsorption–
desorption isotherms, and (d) TEM image of nano-cotton-like BiOF

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GHAYOUMIAN ET AL.
3
(a)
(b)
300
200
100
0
Ads: ZIF-8
Des: ZIF-8
Ads: BiOF@ZIF-8
Des: BiOF@ZIF-8
FIGURE 2 FTIR spectrum of nanosheet BiOF@ZIF-8
vibrations, while the peak at 1,384 cm−1 is attributed to C–C
stretching. The bands in the spectral regions 500–1,350 and
1,350–1,500 cm−1 are due to the bending and stretching
vibrations of the imidazole ring, respectively.
0.0
0.2
0.4
0.6
0.8
1.0
p/po
FIGURE 4 N2-adsorption–desorption isotherms of (a) ZIF-8 and
(b) BiOF@ZIF-8
Figure 2 presents the FT-IR spectrum of the BiOF@ZIF-
8 catalyst in the region 400–4,000 cm−1. Several bands can
be seen in the spectrum. The absorption bands at 2,929 and
3,135 cm−1 are attributed to the aromatic and aliphatic C–H
stretch of the imidazole, respectively. The band at
1,579 cm−1 can be assigned to the C=N stretching mode.
The absorption band at 420 cm−1 is due to the Zn–N stretch-
ing mode, while those in the 1,100–1,400 cm−1 region are
associated with the C–N stretch. The absorption bands at
1,146 and 1,308 cm−1 are assigned to C–H vibrations, while
the peak at 1,384 cm−1 is attributed to C–C stretching. The
bands in the spectral regions 500–1,350 and
1,350–1,500 cm−1 were due to the bending and stretching
vibrations of the imidazole ring, respectively.[27,28]
Figure 3a shows the XRD pattern of ZIF-8. The diffrac-
tion peaks of ZIF-8 correspond well in positions with those
of the standard pattern, indicating the phase purity of the
sample. The strong peaks (2θ) include 7.32ꢀ, 10.27ꢀ, 12.67ꢀ,
14.52ꢀ, 16.42ꢀ, and 17.92ꢀ, which correspond to the (110),
(002), (211), (220), (310), and (322) crystal planes. The
XRD pattern of the BiOF@ZIF-8 sample is shown in
Figure 3b. The sample shows good crystallinity. The main
sharp diffraction peak is at 2θ = 7.2ꢀ, and the relative dif-
fraction intensities of the prepared samples were found to be
the same as those of the standard data for ZIF-8.[28]
25000
20000
15000
10000
5000
0
20
40
60
80
2θ (°C)
(a)
The N2 adsorption–desorption isotherms of ZIF-8 and
BiOF@ZIF-8 catalysts are shown in Figure 4. In accordance
with the IUPAC nomenclature, both samples show typical
IV-type isotherms and H1-type hysteresis loop at high rela-
tive pressures.[28] However, compared with the parent ZIF-8,
the BiOF@ZIF-8 catalyst shows a slight decrease in the pore
volume (Table 1). This indicates that most of the BiOF
nanoparticles on BiOF@ZIF-8 catalysts may be located on
the exterior of ZIF-8. This speculation could be further
300
250
200
150
100
50
* BiOF
TABLE 1 Texture parameters of ZIF-8 and KNa/ZIF-8 samples
*
*
Texture parameters (N2 adsorption)
*
*
*
*
*
*
*
*
*
*
Surface area
(m2/g)
Pore volume
(cm3/g)a,b
Pore diameter
(nm)
0
Materials
ZIF-8
20
40
60
80
1,373
1,097
0.598
0.583
1.48
1.41
2θ (°)
BiOF@ZIF-8
a
(b)
Total pore volume measured at p/p0 = 0.99.
Pore volume and pore size (by BJH method) determined from N2 adsorption
at 77 K.
b
FIGURE 3 XRD patterns of (a) ZIF-8 and (b) BiOF@ZIF-8

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4
GHAYOUMIAN ET AL.
confirmed by the scanning electron microscopy (SEM)
images of the BiOF@ZIF-8 sample.
The SEM image of BiOF@ZIF-8 (Figure 5) shows that
BiOF@ZIF-8 consists of BiOF nanosheets that are clustered
together. The thickness of the nanosheet is about
48–143 nm. Smooth planes and well-defined edges are
observed for the pristine particles in Figure 5b–d. Alterna-
tively, fine and uniformly distributed BiOF particles are
(a)
(b)
(c)
(d)
ZnL
α
4000
3500
3000
2500
2000
1500
1000
500
C K
α
BiM
α
BiM
β
SiK
α
F K
α
α
N K
O K
α
AlK
α
ZnK
α
BiLl
ZnK
β
BiL
α
keV
0
0
5
10
(e)
FIGURE 5 (a–d) SEM images and (e) EDX results of nanosheet BiOF@ZIF-8