Monometallic and bimetallic Cu-Ag MOF/MCM-41 composites: Structural characterization and catalytic activity

Article abstract of DOI:10.1039/c9ra03310f

Monometallic and bimetallic MOF/MCM-41 composites (Cu, Ag and Cu-Ag) were synthesized via a solvothermal method. The synthesized composites were characterized by XRD, FTIR, SEM, EDX and BET surface area measurements. The acidity was determined through two

Full text of DOI:10.1039/c9ra03310f

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Monometallic and bimetallic Cu–Ag MOF/MCM-41
composites: structural characterization and
catalytic activity
Cite this: RSC Adv., 2019, 9, 18803
W. S. Abo El-Yazeed * and Awad I. Ahmed
Monometallic and bimetallic MOF/MCM-41 composites (Cu, Ag and Cu–Ag) were synthesized via a solvothermal
method. The synthesized composites were characterized by XRD, FTIR, SEM, EDX and BET surface area
measurements. The acidity was determined through two techniques; potentiometric titration with n-butyl
amine for determining the strength and the total number of acid sites and FTIR spectra of chemisorbed
pyridine on the surface of MOFs for determining the type of acid sites (Brønsted and/or Lewis). All the
prepared MOFs showed Lewis-acid sites and the higher acidity was observed for the bimetallic Cu–Ag MOF/
MCM-41 composite. The catalytic activity was examined on the synthesis of 1-amidoalkyl-2-naphthol via the
reaction of benzaldehyde, 2-naphthol and benzamide. The best yield (92.86%) was obtained in the least time
Received 3rd May 2019
Accepted 7th June 2019
(
10 min) with a molar ratio 1.2 : 1.2 : 1.7 of benzaldehyde : b-naphthol : benzamide and 0.1 g bimetallic Cu–Ag
DOI: 10.1039/c9ra03310f
ꢀ
MOF/MCM-41 composite under solvent-free conditions at 130 C. Reuse of the catalysts showed that they
rsc.li/rsc-advances
could be used at least four times without any reduction in the catalytic activity.
2
5
26
27
reaction, oxidation, aza-Michael condensation and so on.
However, due to the low thermal stability and processability of
1
Introduction
28,29
Nanoporous metal–organic frameworks (MOFs) have received MOFs, the practical applications of them are limited.
Also,
more attention due to their attractive properties such as high the dispersive forces for some MOFs are weak due to the high
30
surface area, high porosity, low density and crystalline character amount of void spaces. To overcome these disadvantages,
1
–3
as well as their composition and chemical structure. There- composites have been prepared by combining MOFs with other
3
1,32
33
34
fore, MOFs used in various applications involving chemical substrates
as graphene, carbon nanotubes, activated
4
5
6
35
36
37
separation, gas adsorption and storage, drug delivery, lumi- carbon, metals and silica. Composites are considered as
nescence, biomedical imaging and used in many reactions as multicomponent materials which have special properties and
a catalyst. There is a strong host–guest interaction in the MOF many applications in the removal of pollutants and in the
between the metal nanoparticles and the framework via coor- catalysis eld. Zhou et al. prepared a composite from three
dination and p–p forces which depend on its electronic prop- different MOFs and SBA-15 which enhanced the thermal
erties and structure that in turn enhance the catalytic activity stability of MOFs and increased the decomposition temperature
7
8
9
38
10–12
ꢀ
39
and stability.
very high activity and selectivity, and can be separated easily
MOF catalysts are nontoxic, inexpensive, have from 318 to 350 C.
Hexagonal mesoporous MCM-41 materials has been
13
from the reaction mixture and reused. Nano MOFs oen discovered in 1992 as a member of the M41s family, family of
exhibit some additional chemical and physical properties, siliceous materials, which possess some properties as large pore
without changing the material composition, which differs from volume, large pore size (2–50 nm), controlled pore geometries,
usual inorganic metal oxides. Numerous methods have been well-dened structure, uniform size distribution and high
used to control the shape and the size of MOF crystals, such as surface area (up to 1000 m g ). Therefore, MCM-41 materials
applied in many elds as catalysts or catalyst supports.
microwave heating and reverse microemulsion. MOFs have integration of MOFs on mesoporous materials as MCM-41
been used as solid catalysts for some organic reactions as bio- would produce multiple interfaces, which created synergistic
14
2
ꢁ1 40
15
16
41,42
hydrothermal/solvothermal treatment, ultrasonic synthesis,
The
17
18
19
20
diesel production, cyanosilylation of aldehydes, synthesis of effects from multiple components by integration of more than
two active sites such as bimetallic or multimetallic catalysts
synthesis of indolizines through aldehyde–amine–alkyne which improve the catalytic activity.
21
22
coumarins,
catalytic degradation of o/m/p-nitrophenol,
43
23
24
couplings,
synthesis of 1,5-benzodiazepine,
Biginelli
Amidoalkyl naphthol derivatives are one of the multicom-
ponent reactions (MCRs) which have a great importance
nowadays because of their essential role in organic synthesis as
formation of desired products in a single synthetic process
Chemistry Department, Faculty of Science, Mansoura University, Mansoura, Egypt.
E-mail: dr_ws2008@mans.edu.eg; Tel: +201008282160
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without any separation problems which in role show high atom photoelectron spectroscopic (XPS) was collected on K-alpha
44
economy and high selectivity. Amidoalkyl naphthol derivatives (Thermo Fisher Scientic, USA) with monochromatic X-ray
have many biological applications such as bradycardiac, anti- Al K-alpha radiation (ꢁ10 to 1350 eV). The surface area of
4
5,46
bacterial and hypotensive activities.
the prepared catalysts was determined by nitrogen adsorp-
ꢀ
Herein, we prepared composites of monometallic and tion measurement apparatus at ꢁ196 C aer degassing at
ꢀ
ꢁ5
bimetallic MOFs with MCM-41 to combine both properties of 250 C for 4 h under a pressure of 10 torr.
metal–organic frameworks and mesoporous materials in these
3
composites. Also, we studied their role in the formation of 1-
amidoalkyl-2-naphthols.
2
.4. Acidity measurements
The total number of acid sites of the solid samples was deter-
mined by potentiometric titration. 0.03 g of the solid catalyst
activated at 120 C for 2 h under vacuum was suspended in
2
then titrated with (0.025 N) n-butyl amine in acetonitrile at
0
adding the n-butyl amine solution was measured with an Orion
49
ꢀ
2
2
Experimental
0 ml acetonitrile under stirring for 3 h. The suspension was
.1. Materials
Terephthalic acid (H
CHEMICA. Pure Cu(NO
mide (99.8%), tetra ethyl orthosilicate (TEOS), ammonium
hydroxide (28%), benzamide, acetonitrile, n-butyl amine, pyri-
dine, b-naphthol benzaldehyde and cethyltrimethylammonium-
bromide (CTAB) were provided from Merck.
2
BDC) (98%) was purchased from ALPHA
$3H O, AgNO , N,N-dimethylforma-
ꢁ
1
.005 ml min . The variation in the electrode potential aer
)
3 2
2
3
420 digital A model using a double-junction electrode.
FTIR spectra of adsorbed pyridine were used to determine
the Lewis and Brønsted acid sites on the surface of the exam-
50
ꢀ
ined catalysts. Firstly, the samples were heated at 150 C under
vacuum for 2 h. liquid pyridine was added quickly to minimize
the contact time with ambient atmosphere. The samples were
2
.2. Catalyst preparation
2
.2.1. Preparation of Cu-MOF/MCM-41 and Ag-MOF/MCM- maintained in contact with pyridine vapor, at room tempera-
4
1 composites. MCM-41 was prepared according to our ture, for 4 weeks, prior to analysis by FTIR. The excess pyridine
4
7
ꢀ
previous literature. Cu-MOF/MCM-41 and Ag-MOF/MCM-41 was removed by drying the samples at 120 C in an oven for 2 h.
4
8
composites were achieved by the solvothermal method as The FT-IR spectra of the pyridine-adsorbed on the samples were
following: 0.4832 g (2 mmol) of Cu(NO $3H
O or 0.3397 g (2 carried out using Thermo Scientic (Nicolet iS10) FTIR spec-
mmol) of AgNO
and 0.3323 g (2 mmol) of terephthalic acid trophotometer by mixing 0.01 g of the sample with 0.1 g KBr in
3
)
2
2
3
were dissolved in 40 ml of DMF solvent, then 10 ml distilled 30 mm diameter self-supporting discs.
water containing 0.05 g MCM-41 was added and the mixture
was stirred for 30 min. The two mixtures were transferred
into two autoclaves and heated at 140 C for 10 h. Aer
2.5. Catalytic activity
ꢀ
For synthesis of 1-amidoalkyl-2-naphthol, a mixture of benzal-
dehyde (1.2 mmol), b-naphthol (1.2 mmol), benzamide (1.7
mmol) and 0.1 g of the MOF were mixed in a 100 ml round
bottom ask and the subsequent mixture was stirred magneti-
cooling to room temperature, the precipitates were ltered
and washed several times with DMF followed by drying under
ꢀ
vacuum at 120 C for 6 h. Finally, the blue powder of Cu-MOF/
MCM-41 and gray powder of Ag-MOF/MCM-41 composites
were obtained.
ꢀ
cally under solvent-free condition at 130 C for the required
time. Aer completion the reaction (conrmed by TLC), the
reaction mixture was cooled to room temperature and washed
several times with 10 ml hot water with continuous stirring to
remove the unreacted starting materials. The product was
2.2.2. Preparation of bimetallic Cu–Ag MOF and Cu–Ag
MOF/MCM-41 composite. In the same procedures, Cu–Ag MOF
was prepared by mixing 0.2416 g (1 mmol) of Cu(NO ) $3H O,
3
2
2
0
.1699 g (1 mmol) of AgNO and 0.3323 g (2 mmol) of tereph-
3

ltered off and the separated catalyst was washed with ethanol
thalic acid and dissolved in 40 ml DMF solvent while Cu–Ag
MOF/MCM-41 composite was prepared by mixing the same
amounts with suspension of 0.05 g MCM-41.
ꢀ
and nally dried in an oven at 120 C for reuse. Amidoalkyl-2-
naphthol was collected from the ltrate and then recrystal-
lized from ethanol.
45,51
The product was characterized by its
ꢀ
melting point (235–237 C) and FT-IR. The % yield of 1-
2.3. Characterization techniques
amidoalkyl-2-naphthol can be calculated easily from the
FT-IR spectra were measured on the Thermo SCIENTIFIC following equation:
(
NICOLET iS10). The samples were mixed with dry KBr to be
obtained weight of product
ꢂ 100
thoretical weight of product
ꢁ1
analyzed and then scanned from 400 to 4000 cm . XRD
patterns were collected on a PW 150 (Philips) using Ni-
Yield ðwt%Þ ¼
˚
ꢀ

ltered Cu Ka radiation (l ¼ 1.540 A) from 2q of 4 to 80 at
4
0 kV. The morphology and the elements of the prepared
samples were examined via SEM (Scanning Electron Micros-
copy) and EDX (Energy-Dispersive X-ray Spectroscopy) anal-
ysis with the JEOL (Model JSM-6510LV SEM) scanning
3
Results and discussion
3.1. X-ray diffraction analysis
electron microscope. Before the analysis the samples were The low and high-angle XRD patterns of pure MCM-41 were
ꢀ
coated with gold. To study the binding energies, X-ray illustrated in Fig. 1a. At 2q ¼ 2.4, 4.0 and 4.6 , respectively, the
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Fig. 1 (a) Low and high-angle XRD of MCM-41 and (b) low-angle and (c) high-angle XRD for the prepared catalysts.
three characteristic peaks of the ordered hexagonal mesoporous MOF and Ag-MOF with a small shi of the peaks of Cu to
ꢀ
structure were observed, while at 2q ¼ 10–60 there is abroad lower 2q values supporting the successful preparation of
47
59,60
hump due to formation of an amorphous phase. Fig. 1b shows bimetallic MOF.
Comparing the pattern of Cu–Ag MOF with
that the MOF/MCM-41 composites still maintains the meso- that of Cu–Ag MOF/MCM-41, the intensities of the main
porous structure of MCM-41 by the appearance of the peak (100) diffraction peaks of Cu and Ag-MOF are decreased meaning that
ꢀ
at 2.4 . The XRD patterns of Cu-MOF/MCM-41, Ag-MOF/MCM- MCM-41 enhances the crystallinity of the MOF/MCM-41
41, Cu–Ag MOF/MCM-41 composites and Cu–Ag MOF are pre- composites.
sented in Fig. 1c. All the main diffraction peaks of the octahe-
dral Cu-MOF appeared in Cu-MOF/MCM-41 pattern at 2q ¼
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
9
4
(
.03 , 10.23 , 12.34 , 17.36 , 20.67 , 24.92 , 29.30 , 34.33 , 3.2. FT-IR spectroscopy
ꢀ
2.12 which assigned to (220), (222), (400), (440), (442), (731),
751), (951) and (971), respectively. These peaks are in a good
agreement with the patterns of Cu-MOF in the literature
indicating the successful preparation of the MOF. The peaks of
The FT-IR spectra of the prepared MOFs are shown in Fig. 2. The
spectra of pure MCM-41, Cu-MOF/MCM-41, Ag-MOF/MCM-41,
Cu–Ag-MOF/MCM-41 and Cu–Ag MOF exhibit clear absorption
spectra corresponding to metal–organic framework structure
5
2,53
ꢀ
ꢀ
Ag-MOF/MCM-41 composite appeared at 2q ¼ 13.27 , 16.74 ,
with a little shi in the wavelengths. The FT-IR spectra in the
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
1
8.93 , 28.51 , 30.88 , 38.11 , 44.37 , 64.46 , 77.35 in a good
ꢁ1
region 700–1200 cm
attributed to the ngerprint of tere-
54
ꢀ
agreement with the literature. The peaks at 2q ¼ 38.11 (111),
ꢁ1
phthalate compounds in which the absorption over 900 cm is
ꢀ ꢀ ꢀ
4
4.37 (200), 64.46 (220) and 77.35 (311) corresponds to a face
related to the bending aromatic C–H (in plane) and the
centered cubic of Ag species nanoparticles which may be
produced from the reduction of Ag to Ag metal with the aid of
DMF as reducing agent.
1 composite combines the characteristic peaks of both Cu-
ꢁ1
absorption lower than 900 cm
is related to the bending
+
55,61,62
aromatic C–H (out plane) of terephthalic acid linker.
The
55–58
The bimetallic Cu–Ag MOF/MCM-
stretching band of C–H groups related to linker is appeared at
4
ꢁ163
ꢁ1
2999 cm
Also, the peaks at 1621 and 1393 cm are related
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3
.3. SEM and EDX
The SEM and EDX images of Cu-MOF/MCM-41, Ag-MOF/MCM-
1, Cu–Ag MOF/MCM-41 composites and Cu–Ag MOF are pre-
sented in Fig. 3. The SEM image of Fig. 3a displays the disper-
4
64,69
sion of octahedral Cu structure on the surface of MCM-41,
while Fig. 3b shows the dispersed irregular spherical Ag parti-
70
cles with different sizes the surface of MCM-41. There is
a signicant difference in the surface morphology of the two
bimetallic MOFs, Cu–Ag MOF/MCM-41 composite and Cu–Ag
MOF (Fig. 3(c and d), respectively). The images show that the
agglomeration of irregular small Ag particles increased aer the
addition of MCM-41 which resulted in the appearance of more
dispersed blocks on its surface. This explains the signicant
effect of the incorporation of MCM-41 during the formation of
MOF and the high dispersion of the Cu–Ag MOF inside and
66,68,71
outside the pores of MCM-41.
The EDX spectra in Fig. 3(e
and f) reveal the contribution of C, O, Cu, Ag, and Si elements in
the Cu–Ag MOF/MCM-41 composite structure while C, O, Cu
and Ag elements in the Cu–Ag MOF structure.
Fig. 2 FTIR spectra of the prepared catalysts.
to the carboxylate ligands. The vibration absorption spectra of
the C–O group of free carboxylic acids are observed at 1666 and
3
.4. X-ray photoelectron spectroscopic (XPS)
ꢁ
1
64
ꢁ1
1470 cm
and the peaks at 575, 621 and 674 cm belongs to To determine the chemical composition of Cu–Ag MOF/MCM-
65,66
the stretching vibrations of the Cu–O.
appeared at 3456 cm in the FT-IR spectra of Cu-MOF/MCM-41 performed (Fig. 4.). As shown in the XPS survey scan (Fig. 4a.),
Also, the broad band 41 composite and the chemical state of its elements, XPS was
ꢁ
1
and Ag-MOF/MCM-41 composites attributes to the vibration of the Cu–Ag MOF/MCM-41 composite contains Cu, Ag, C, O and
6
7
coordinated water molecules.
MOF/MCM-41 composites Si elements which consisted with the EDX results. The C 1s XPS
ꢁ
1
exhibit bands of MCM-41 at 803, 959 and 1252 cm with a little spectrum (Fig. 4b.) reveals three peaks at 284.79, 286.35 and
shi which is good evidence on maintaining the mesoporous 288.62 eV which are attributed to C–C & C–H & C]C, C–O and
4
7,68
72
structure of MCM-41.
The disappearance of the broad O–C–O groups, respectively. O 1s emission spectrum (Fig. 4c.)
ꢁ
1
spectra at 3456 cm in the FT-IR spectra of Cu–Ag MOF/MCM- has two main peaks at 531.72 eV (characteristic of metal–oxygen
1 composite and Cu–Ag MOF indicates the removal of the bonds) and 533.17 eV (characteristic of the O–H groups). The
73
4
water during the formation of bimetallic MOF.
Si 2p emission spectrum shows only one peak at 103.52 eV
Fig. 3 SEM images of ((a) Cu-MOF/MCM-41, (b) Ag-MOF/MCM-41, (c) Cu–Ag MOF/MCM-41 and (d) Cu–Ag MOF) and EDX analysis of ((e) Cu-
MOF/MCM-41 and (f) Cu–Ag MOF).
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Fig. 4 XPS spectra of Cu–Ag MOF/MCM-41 composite: (a) the survey scan, (b) C 1s, (c) O 1s, (d) Si 2p, (e) Ag 3d and (f) Cu 2p.
(Fig. 4d.). Ag 3d XPS spectrum (Fig. 4e.) exhibits two main peaks that of MCM-41. This can be explained by the partial blocking of
at 368.21 eV (Ag 3d3/2) and 374.23 eV (Ag 3d5/2) which are the pores of MCM-41 through the dispersion of the MOF
ascribed to metallic Ag. The 6 eV spin-energy separation particles inside and/or outside them although the maintaining
between the two peaks of Ag 3d conrmed on the presence of of the mesostructure which is very important for catalysis
0
54,74
77,78
Ag in the Cu–Ag MOF/MCM-41 composite
that may be applications.
This was conrmed also by the decrease in the
+
produced from the reduction of Ag to Ag metal with the aid of pore volume. The increase in the surface area and pore volume
DMF as reducing agent as explained in XRD results. The high of the bimetallic Cu–Ag MOF compared with each mono-
resolution spectrum of Cu 2p exhibits ve peaks at 934.24, metallic MOF is observed that may be resulted from the creation
9
9
40.01, 944.08, 953.67 and 962.11 eV (Fig. 4f.). The peaks at of new micropores arises from two metals Cu and Ag in the
34.24 and 953.67 eV were assigned to Cu 2p3/2 and Cu 2p1/2 of bimetallic MOF. These values increases when the bimetallic
Cu–O. The presence of overlapping satellite peaks at 940.01 and MOF composited with MCM-41 as a result of presence of both
9
44.08 eV for Cu 2p3/2 and at 962.11 eV for Cu 2p1/2 indicated the meso and micropores. The pore size distribution curves
2
+
1+
presence of CuO (Cu ) or Cu
composite.
2
O (Cu ) species in the (Fig. 5b.) for all samples exhibit a narrow micropores peak
75,76
characteristic of the MOF centered at 1.27 nm. The MOF/MCM-
41 composites show also a mesoporous nature with two maxima
from 10 to 50 nm. Cu-MOF/MCM-41 and Cu–Ag MOF/MCM-41
composites reveals two peak centered at 14 and 33 nm while
Ag-MOF/MCM-41 composite reveal two peaks centered at 14
and 25 nm.
3
.5. Surface area measurements
The porosity of the prepared materials was characterized by N
2
ꢀ
adsorption–desorption isotherms at ꢁ196 C. As shown in
Fig. 5a., the Cu, Ag and Cu–Ag MOF/MCM-41 composites exhibit
type IV isotherm typical of mesoporous materials with H
3
3.6. Surface acidity
hysteresis loop. A linear increase in N adsorption at low relative
2
pressure is observed due to the formation of monolayer fol-
3.6.1. Nonaqueous potentiometric titration. To determine
lowed by the capillary condensation of N
pores. The Cu–Ag MOF exhibits type I isotherm indicating the surface, we used the potentiometric titration for the prepared
2
inside the meso- the strength and the total number of acid sites on the MOFs
63
79
3
microporous nature of the MOF with H hysteresis loop indi- MOFs with n-butyl amine and the curves are shown in Fig. 6.
71
cating the presence of cylindrical pores. The derived porosity The acid strength of these sites can be determined from the
parameters, surface area and pore volume, were calculated and value of the initial electrode potential (E ) and classied as
is increased than 100 mV, the sites are
as mentioned previously in our literature, while the pore classied as very strong acid sites,(ii) when E is between 0 and
i
2
ꢁ1
listed in Table 1. The surface area of MCM-41 was 1389.2 m g
follows: (i) when E
i
4
7
i
3
ꢁ1
volume was 3.63 cm g . Ag-MOF/MCM-41, Cu-MOF/MCM-41 100 mV, the sites are strong sites, (iii) when E is between ꢁ100
i
and Cu–Ag MOF/MCM-41 composites have a BET surface area and 0 mV, the sites are weak sites, and (iv) when E
i
is less than
2
ꢁ1
80
2
96.4, 545.2 and 594.8 m g , respectively which are lower than ꢁ100 mV, the sites are very weak sites. From Fig. 6 and Table 1,
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Fig. 6 Potentiometric titration curves of n-butyl amine in acetonitrile
for the prepared catalysts.
2
Fig. 5 (a) N adsorption–desorption isotherms and (b) pore size
distribution of the prepared composites.
the values of the initial electrode potential indicate that all the
prepared MOFs have very strong acid sites and Cu–Ag MOF/
MCM-41 composite has the highest number of total acid sites
and the highest E
i
value.
3.6.2. FTIR spectra of chemisorbed pyridine. The infrared
spectra of adsorbed pyridine on the surface of the MOFs were
used to determine the type of acid sites whether Brønsted or
Lewis as shown in Fig. 7. The spectra show two bands at 1507
Fig. 7 FTIR spectra of adsorbed pyridine on (a) Ag-MOF/MCM-41, (b)
Cu-MOF/MCM-41, (c) Cu–Ag MOF/MCM-41 and (d) Cu–Ag MOF.
ꢁ
1
and 1421 cm on Ag-MOF/MCM-41 composite and four bands
in the samples Cu-MOF/MCM-41, Cu–Ag MOF/MCM-41
composites and Cu–Ag MOF at 1449, 1487, 1507 and
optimize various reaction parameters, we performed some trials
for the synthesis of 1-amidoalkyl-2-naphthol as a model reac-
tion on MOF catalyst; the conditions of a MOF amount and the
ꢁ
1
1
620 cm which are assigned to the adsorbed pyridine on
81–83
Lewis acidic sites.
ꢀ
reactants molar ratio under solvent free condition at 130 C are
3.7. Catalytic activity (synthesis of 1-amidoalkyl-2-naphthol)
examined.
The catalytic activity was examined by synthesis of pharma-
3.7.1. Effect of the MOF amount. The effect of Cu–Ag MOF/
ceutically important 1-amidoalkyl-2-naphthol. Firstly, to MCM-41 composite amount on the synthesis of 1-amidoalkyl-2-
Table 1 Surface and acidic properties of the prepared catalysts
2
ꢁ1
3
ꢁ1
No. of acid sites/g ꢂ 10ꢁ20
Catalyst
S
BET (m g
)
V
t
(cm g
)
i
E (mV)
Cu-MOF/MCM-41
Ag-MOF/MCM-41
Cu–Ag MOF/MCM-41
Cu–Ag MOF
545.2
296.4
594.8
551.3
0.32
0.18
0.37
0.34
225.1
128.2
369.9
276.2
1.64
1.34
2.46
2.03
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ꢀ
Table 2 Synthesis of 1-amidoalkyl-2-naphthol under solvent free conditions at 130 C
Molar ratio benzaldehyde : b-
naphthol : benzamide
Apparent rate
(min )
ꢁ
1
Catalyst
Catalyst weight (g)
Time (min)
Yield (%)
Cu-MOF/MCM-41
Ag-MOF/MCM-41
Cu–Ag MOF/MCM-41
Cu–Ag MOF
Cu–Ag MOF/MCM-41
Cu–Ag MOF/MCM-41
Cu–Ag MOF/MCM-41
Cu–Ag MOF/MCM-41
Cu–Ag MOF/MCM-41
Cu–Ag MOF/MCM-41
Cu–Ag MOF/MCM-41
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.03
0.05
0.08
0.13
1.2 : 1.2 : 1.7
1.2 : 1.2 : 1.7
1.2 : 1.2 : 1.7
1.2 : 1.2 : 1.7
1.2 : 1.2 : 1.2
1.2 : 1.2 : 1.5
1.2 : 1.2 : 1.9
1.2 : 1.2 : 1.7
1.2 : 1.2 : 1.7
1.2 : 1.2 : 1.7
1.2 : 1.2 : 1.7
20
25
10
12
60
20
30
60
25
13
10
80.2
65.1
0.401
0.260
0.929
0.728
0.067
0.438
0.265
0.339
0.648
0.870
0.715
92.86
87.38
40.23
87.62
79.52
60.97
80.95
90.48
92.91
naphthol was planned using 1.2 : 1.2 : 1.7 benzaldehyde : b- prepared bimetallic catalysts is increased compared with
ꢀ
naphthol : benzamide under solvent free condition at 130 C. that of the monometallic catalyst which could be attributed
Initially, the reaction was carried out without MOF catalyst to the presence of two different metals Cu and Ag and/or
under similar condition, but no yield was formed even aer changing the active sites dispersion on the MOF surface in
5
,12,84–86
1
2 h. Increasing the amount of MOF from 0.03 to 0.1 g led to the bimetallic catalyst.
increase the yield of 1-amidoalkyl-2-naphthol from 60.97% to Table 2 illustrate that Cu–Ag MOF/MCM-41 composite is the
2.86% and the time was decreased from 60 min to 10 min best catalyst with respect to reaction times (10 min) and
The results in Fig. 10 and
9
indicating that 0.1 g of the catalyst was the best percentage of yields (92.86%) of the products. The enhancement in the
the yield aer 10 min. On increasing the amount of the catalyst catalytic activity of this composite may be due to the
to 0.13 g, there is no improvement of the yield of 1-amidoalkyl-2- following four factors: (i) the various active sites on the MOF
naphthol as illustrated in Table 2 and Fig. 8.
surface with higher strength and acidity especially Lewis
3.7.2. Effect of the molar ratio of the reactants. The reac- acid sites, (ii) the high surface area (iii) the presence of both
tion was performed on 0.1 g Cu–Ag MOF/MCM-41 composite meso and micropores and (iv) the presence of both Cu and
ꢀ
under solvent free condition at 130 C by using different molar Ag metals.
ratio of the reactants. The best yield was obtained with a molar
In comparison with other literatures; 1-amido alkyl-2-
ratio 1.2 : 1.2 : 1.7 of benzaldehyde : b-naphthol : benzamide naphthol was obtained under solvent free conditions with
aer 10 min as shown in Table 2 and Fig. 9.
a yield of 88% aer 20 min using graphene oxide as a cata-
ꢀ
3.7.3. Effect of MOF type. The synthesis of 1-amidoalkyl- lyst at 120 C, 86% aer 75 min using Ba
3
(PO
4
)
2
catalyst at
ꢀ
2
-naphthol reaction was carried out using 0.1 g of different 100 C and 90% aer 25 min using sulfonated poly-
ꢀ
45,87,88
MOFs (Cu-MOF/MCM-41, Ag-MOF/MCM-41, Cu–Ag MOF/ naphthalene at 80 C.
MCM-41 composites and Cu–Ag MOF) using 1.2 : 1.2 : 1.7 A possible mechanism for the synthesis of 1-amidoalkyl-2-
benzaldehyde : b-naphthol : benzamide molar ratio under naphthol was suggested in Scheme 1, based on the litera-
ꢀ
89
solvent free condition at 130 C. The catalytic activity of the ture. The reaction of benzaldehyde with b-naphthol in the
Fig. 8 Effect of the MOF weight on the synthesis of 1-amidoalkyl-2- Fig. 9 Effect of the molar ratio of reactants on the synthesis of 1-
naphthol.
amidoalkyl-2-naphthol.
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Fig. 11 Reuse of the Cu–Ag MOF/MCM-41 composite.
Fig. 10 Effect of the MOF type on the synthesis of 1-amidoalkyl-2-
naphthol.
3.7.4. Reusability of the catalyst. The reusability is one of
the most important characteristics of any catalyst. The recy-
cling experiment was carried out with benzaldehyde, b-
naphthol and benzamide under the same conditions as
described above for the Cu–Ag MOF/MCM-41 composite
catalyst. To maintain constant catalyst weight (0.1 g) during
reusability experiments, we performed each experiment four
times using the Cu–Ag MOF/MCM-41 composite in the same
time and the second, third and fourth recycles are carried out
by the same catalyst and constant weights. We found that Cu–
Ag MOF/MCM-41 composite can be used four times without
presence of MOF catalyst produces ortho-quinone methides
(
o-QMs) which reacted with benzamide via conjugated addi-
tion on the a,b-unsaturated carbonyl group to yield 1-
amidoalkyl-2-naphthol. It was found that using benzalde-
hyde as aromatic aldehyde is better than aliphatic aldehyde
9
0,91
which gave low yield in previous reports,
this can be
attributed to an o-QMs intermediate produced from aliphatic
aldehydes is less stable than that with aromatic aldehyde.
Scheme 1 A possible mechanism for the synthesis of 1-amidoalkyl-2-naphthol.
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Fig. 12 (a) XRD, (b) FTIR and (c) SEM analysis of reused Cu–Ag MOF/MCM-41 composite after catalytic reaction.
any reduction in the catalytic activity (Fig. 11.). The FTIR,
XRD and SEM analysis were determined for the fresh and
reused Cu–Ag MOF/MCM-41 composite as shown in Fig. 12.
3 Q.-L. Zhu and Q. Xu, Chem. Soc. Rev., 2014, 43, 5468–5512.
4 J.-R. Li, R. J. Kuppler and H.-C. Zhou, Chem. Soc. Rev., 2009,
38, 1477–1504.
5
X. Yang and Q. Xu, Cryst. Growth Des., 2017, 17(4), 1450–
455.
1
4
Conclusion
6
J. An, S. J. Geib and N. L. Rosi, J. Am. Chem. Soc., 2009, 131,
8376–8377.
We found that MCM-41 enhanced the crystallinity and the
catalytic activity of the prepared MOFs. The bimetallic Cu–Ag
MOF/MCM-41 composite in comparing with other MOFs has
the highest Lewis acidity and gave the best yield (92.86%) of 1-
amidoalkyl-2-naphthol in 10 min. The enhancement in the
catalytic activity of this bimetallic MOF/MCM-41 composite
7 M. D. Allendorf, C. A. Bauer, R. K. Bhakta and R. J. Houk,
Chem. Soc. Rev., 2009, 38, 1330–1352.
8 X. Lian and B. Yan, RSC Adv., 2016, 6, 11570–11576.
9 J. Xiao, Y. Wu, M. Li, B. Y. Liu, X. C. Huang and D. Li, Chem.–
Eur. J., 2013, 19, 1891–1895.
could be attributed to its well acidity, its high surface area, the 10 Q. Yuan, D. Zhang, L. V. Haandel, F. Ye, T. Xue, E. J. M
presence of both meso and micropores and the presence of both
Cu and Ag metals.
Hensen and Y. Guan, J. Mol. Catal. A: Chem., 2015, 406,
58–64.
1
1
1
1
1
1 D. Zhang, Y. Guan, E. J. M. Hensen, T. Xue and Y. Wang,
Catal. Sci. Technol., 2014, 4, 795–802.
2 B. Xia, C. Liu, H. Wu, W. Luo and G. Cheng, Int. J. Hydrogen
Energy, 2015, 40, 16391–16397.
3 P. Puthiaraj, A. Ramu and K. Pitchumani, Asian J. Org. Chem.,
Conflicts of interest
There are no conicts to declare.
2
014, 3, 784–791.
4 M. Y. Masoomi and A. Morsali, RSC Adv., 2013, 3, 19191–
9218.
References
1
1
J. Zhao, Y. Wang, J. Zhou, P. Qi, S. Li, K. Zhang, X. Feng,
B. Wang and C. Hu, J. Mater. Chem. A, 2016, 4, 7174–7177.
S.-J. Lee, K. C. Kim, T.-U. Yoon, M.-B. Kim and Y.-S. Bae,
Microporous Mesoporous Mater., 2016, 236, 284–291.
5 X. Cheng, A. Zhang, K. Hou, M. Liu, Y. Wang, C. Song,
G. Zhang and X. Guo, Dalton Trans., 2013, 42, 13698–13705.
2
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 18803–18813 | 18811

View Article Online
RSC Advances
Paper
1
1
1
1
2
2
2
2
2
2
6 Z.-Q. Li, L.-G. Qiu, T. Xu, Y. Wu, W. Wang, Z.-Y. Wu and 44 A. Chinnappan, A. H. Jadhav, W.-J. Chung and H. Kim, J.
X. Jiang, Mater. Lett., 2009, 63, 78–80. Mol. Liq., 2015, 212, 413–417.
7 J. Klinowski, F. A. A. Paz, P. Silva and J. Rocha, Dalton Trans., 45 S. A. Pourmousavi, P. Moghimi, F. Ghorbani and M. Zamani,
011, 40, 321–330. J. Mol. Struct., 2017, 1144, 87–102.
8 W. J. Rieter, K. M. L. Taylor, H. An, W. Lin and W. Lin, J. Am. 46 M. N-Esfahani, M. Montazerozohori and M. Taei, C. R.
Chem. Soc., 2006, 128, 9024–9025. Chim., 2016, 19, 986–994.
9 A. Nikseresht, A. Daniyali, M. A. Mohammadi, A. Afzalinia 47 A. I. Ahmed, S. E. Samra, S. A. El-Hakam, A. S. Khder, H. Z. El-
2
and A. Mirzaie, Ultrason. Sonochem., 2017, 37, 203–207.
0 I.-H. Choi, Y. Kim, D. N. Lee and S. Huh, Polyhedron, 2016,
Shenawy and W. S. Abo El-Yazeed, Appl. Surf. Sci., 2013, 282,
217–225.
1
05, 96–103.
48 T. Han, C. Li, X. Guo, H. Huang, D. Liu and C. Zhong, Appl.
Surf. Sci., 2016, 390, 506–512.
1 T. N. Lieu, K. D. Nguyen, D. T. Le, T. Truong and
N. T. S. Phan, Catal. Sci. Technol., 2016, 6, 5916–5926.
2 X.-Q. Wu, G.-X. Wen, Y.-P. Wu, W.-W. Dong, J. Zhao and
D.-S. Li, J. Solid State Chem., 2016, 42, 243–247.
3 G. H. Dang, H. Q. Lam, A. T. Nguyen, D. T. Le, T. Truong and
N. T. S. Phan, J. Catal., 2016, 337, 167–176.
4 T. D. Le, K. D. Nguyen, V. T. Nguyen, T. Truong and
N. T. S. Phan, J. Catal., 2016, 333, 94–101.
5 P. Li, S. Regati, R. J. Butcher, H. D. Arman, Z. Chen, S. Xiang,
49 A. I. Ahmed, S. A. El-Hakam, A. S. Khder and W. S. Abo El-
Yazeed, J. Mol. Catal. A: Chem., 2013, 366, 99–108.
50 A. I. Ahmed, S. A. El-Hakam, M. A. Abd Elghany and
W. S. Abo El-Yazeed, Appl. Catal., A, 2011, 407, 40–48.
51 A. Davoodnia, R. Mahjoobin and N. Tavakoli-Hoseini, Chin.
J. Catal., 2014, 35, 490–495.
52 S. Rostamnia, H. Alamgholiloo and X. Liu, J. Colloid Interface
Sci., 2016, 469, 310–317.
B. Chen and C.-G. Zhao, Tetrahedron Lett., 2011, 52, 6220– 53 A. R. Abbasi, M. Karimi and K. Daasbjerg, Ultrason.
222. Sonochem., 2017, 37, 182–191.
6 G. Chen, S. Wu, H. Liu, H. Jiang and Y. Li, Green Chem., 2013, 54 H. Guo, Y. Zhang, Z. Zheng, H. Lin and Y. Zhang, Talanta,
5, 230–235. 2017, 170, 146–151.
7 L. T. L. Nguyen, T. T. Nguyen, K. D. Nguyen and N. T. S. Phan, 55 D. K. Yadav, V. Ganesan, F. Marken, R. Gupta and
Appl. Catal., A, 2012, 425/426, 44–52. P. K. Sonkar, Electrochim. Acta, 2016, 219, 482–491.
8 M. Ghorbanloo, V. Safarifard and A. Morsali, New J. Chem., 56 R. Gupta and V. Ganesan, Sens. Actuators, B, 2015, 219, 139–
6
2
2
2
1
2017, 41, 3957–3965.
145.
2
3
9 S. Li and F. Huo, Nanoscale, 2015, 7, 7482–7501.
0 L. Li, X. L. Liu, H. Y. Geng, B. Hu, G. W. Song and Z. S. Xu, J.
Mater. Chem. A, 2013, 1, 10292–10299.
1 T. Han, Y. Xiao, M. Tong, H. Huang, D. Liu, L. Wang and
C. Zhong, Chem. Eng. J., 2015, 275, 134–141.
2 T. Wehner, K. Mandel, M. Schneider, G. Sextl and K. M u¨ ller-
Buschbaum, ACS Appl. Mater. Interfaces, 2016, 8, 5445–5452. 60 Z. Zhou, L. Mei, C. Ma, F. Xu, J. Xiao, Q. Xia and Z. Li, Chem.
3 B. Szcz ˛e ´s niak, J. Choma and M. Jaroniec, Microporous
Mesoporous Mater., 2019, 279, 387–394.
4 F. Wang, X. Chen, L. Chen, J. Yang and Q. Wang, Mater. Sci.
Eng., C, 2019, 96, 41–50.
57 P. K. Sonkar and V. Ganesan, J. Solid State Electrochem., 2015,
19, 2107–2115.
58 P. K. Rastogi, V. Ganesan and S. A. Krishnamoorthi, J. Mater.
Chem. A, 2013, 2, 933–943.
59 J. Yang, C. Zheng, P. Xiong, Y. Li and M. Wei, J. Mater. Chem.
A, 2014, 2, 19005–19010.
3
3
3
3
3
3
3
Eng. Sci., 2016, 147, 109–117.
61 S. R. Thakare and S. M. Ramteke, Catal. Commun., 2017, 102,
21–25.
62 N. Iswarya, M. G. Kumar, K. S. Rajan and R. J. B. Balaguru,
Asian J. Sci. Res., 2012, 5, 247–254.
63 N. E. Tari, A. Tadjarodi, J. Tamnanloo and S. Fatemim, J. CO2
Util., 2016, 14, 126–134.
5 Y. Liu, P. Ghimire and M. Jaroniec, J. Colloid Interface Sci.,
2
019, 535, 122–132.
6 Y. Han, H. Xu, Y. Su, Z.-l. Xu, K. Wang and W. Wang, J. Catal.,
019, 370, 70–78.
7 R. Ameloot, A. Liekens, L. Alaerts, M. Maes, A. Galarneau,
2
64 S. Mosleh, M. R. Rahimi, M. Ghaedi, K. Dashtian and
S. Hajati, RSC Adv., 2016, 6, 17204–17214.
B. Coq, G. Desmet, B. F. Sels, J. F. M. Denayer and D. E. De 65 J. Zhou, X. Li, L. Yang, S. Yan, M. Wang, D. Cheng, Q. Chen,
Vos, Eur. J. Inorg. Chem., 2010, 24, 3735–3738.
Y. Dong, P. Liu, W. Cai and C. Zhang, Anal. Chim. Acta, 2015,
3
3
4
4
4
4
8 M. Florent and T. Bendosz, Microporous Mesoporous Mater.,
899, 57–65.
2015, 204, 8–14.
66 Q. Chen, X. Li, X. Min, D. Cheng, J. Zhou, Y. Li, Z. Xie, P. Liu,
W. Cai and C. Zhang, J. Electroanal. Chem., 2017, 789, 114–
122.
9 L. B. Sun, J. R. Li, W. Lu, Z. Y. Gu, Z. Luo and H. C. Zhou, J.
Am. Chem. Soc., 2012, 134(38), 15923–15928.
0 S. K. Sharma, K. Sudarshan, D. Sen and P. K. Pujari, J. Solid 67 S. Aryanejad, G. Bagherzade and A. Farrokhi, Inorg. Chem.
State Chem., 2019, 279, 10–17. Commun., 2017, 81, 37–42.
1 N. Cakiryilmaz, H. Arbag, N. Oktar, G. Dogu and T. Dogu, 68 S. W. Li, R. M. Gao, R. L. Zhang and J. S. Zhao, Fuel, 2016,
Catal. Today, 2019, 323, 191–199. 184, 18–27.
2 Y. Chi, J. Xue, J. Zhuo, D. Zhang, M. Liu and Q. Yao, Sci. Total 69 J. B. Raoof, S. R. Hosseini, R. Ojani and S. Mandegarzad,
Environ., 2018, 633, 1105–1113. Energy, 2015, 90, 1075–1081.
3 G. Zhan and H. C. Zeng, Coord. Chem. Rev., 2016, 320–321, 70 L. Ai, X. Liu and J. Jiang, J. Alloys Compd., 2015, 625, 164–170.
81–192.
1
18812 | RSC Adv., 2019, 9, 18803–18813
This journal is © The Royal Society of Chemistry 2019

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Paper
RSC Advances
7
1 S. W. Li, J. R. Li, Q. P. Jin, Z. Yang, R. L. Zhang, R. M. Gao and 80 L. R. Pizzio, P. G. V ´a squez, C. V. C ´a ceres and M. N. Blanco,
J. S. Zhao, J. Hazard. Mater., 2017, 337, 208–216. Appl. Catal., A, 2003, 256, 125–139.
72 M.-J. Tian, F. Liao, Q.-F. Ke, Y.-J. Guo and Y.-P. Guo, Chem. - 81 P. Carnitia, A. Gervasinia, F. Bossolab and V. D. Santo, Appl.
Eur. J., 2017, 328, 962–976. Catal., B, 2016, 193, 93–102.
73 D. Chen, C. Chen, W. Shen, H. Quan, S. Chen, S. Xie, X. Luo 82 C. R. Reddy, G. Nagendrappa and B. S. Jai Prakash, Catal.
and L. Guo, Adv. Powder Technol., 2017, 28, 1769–1779. Commun., 2007, 8, 241–246.
74 J. H. Cui, C. F. Hu, Y. H. Yang, Y. J. Wu, L. F. Yang, 83 M. N. Alaya and M. A. Rabah, J. Alloys Compd., 2013, 575,
Y. L. Wang, Y. L. Liu and Z. Y. Jiang, J. Mater. Chem., 2012,
2, 8121–8126.
5 X. Xiao, S. Peng, C. Wang, D. Cheng, N. Li, Y. Dong, Q. Li,
D. Wei, P. Liu, Z. Xie, D. Qu and X. Li, J. Electroanal. 85 Y. Miao, S. Li, L. Gao and G. Xiao, Mol. Catal., 2017, 436, 128–
Chem., 2019, 841, 94–100. 137.
6 T. Aydan, C. Yang, Y. Xu, T. Yuan, M. Zhang, H. Li, X. Liu, 86 H. Liu, R. Fang, Z. Li and Y. Li, Chem. Eng. Sci., 2015, 122,
285–291.
2
84 W. Yu, Y. P. Hsu and C. S. Tan, Appl. Catal., B, 2016, 196,
185–192.
7
7
X. Su and J. Wang, Inorg. Chem. Commun., 2019, 102, 162–
70.
7 N. E. Tari, A. Tadjarodi, J. Tamnanloo and S. Fatemi,
Microporous Mesoporous Mater., 2016, 231, 154–162.
350–359.
1
87 A. Gupta, D. Kour, V. K. Gupta and K. K. Kapoor, Tetrahedron
Lett., 2016, 57, 4869–4872.
88 H. Taghrir, M. Ghashang and M. N. Biregan, Chin. Chem.
Lett., 2016, 27, 119–126.
7
7
8 J. Ying, Z.-Y. Hu, X.-Y. Yang, H. Wei, Y.-X. Xiao, C. Janiak,
S.-C. Mu, G. Tian, M. Pan, Gu. V. Tendeloob and B.-L. Su, 89 S. A. R. Mulla, T. A. Salama, M. Y. Pathan, S. M. Inamdar and
Chem. Commun., 2016, 52, 8219–8222. S. S. Chavan, Tetrahedron Lett., 2013, 54, 672–675.
9 L. R. Pizzo, P. G. V ´a squez, C. V. C ´a ceres and C. V. Blanco, 90 Z. K-Jaberi and H. Fakhraei, Bull. Chem. Soc. Ethiop., 2012,
7
Proceedings of the 17th Symposium Iberoam, Catalysts,
000, 1, 563.
26, 473–478.
2
91 A. R. Supale and G. S. Gokavi, J. Chem. Sci., 2010, 122, 189–
192.
This journal is © The Royal Society of Chemistry 2019
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