A novel CoFe2O4?Cr-MIL-101/Y zeolite ternary nanocomposite as a magnetically separable sonocatalyst for efficient sonodegradation of organic dye contaminants from water

Article abstract of DOI:10.1039/d0ra00877j

In this research, a novel magnetic sonocatalyst nanocomposite, CoFe₂O₄?Cr-MIL-101/Y zeolite, has been successfully fabricated employing a simple hydrothermal method. The as-prepared catalyst was thoroughly identified using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), EDS elemental dot-mapping, transmission electron microscopy (TEM), atomic force microscopy (AFM), vibrating sample magnetometer (VSM), and nitrogen Brunauer-Emmett-Teller (N₂-BET) analyses. The procured CoFe₂O₄?Cr-MIL-101/Y nanocomposite was then assessed for the decomposition of three types of organic dyes namely methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) from water solution using ultrasound irradiation and subsequently monitored via UV-Vis absorption technique. The sonodecomposition reactions of organic dyes were accomplished in the presence of the H₂O₂ solution as a green oxidizing agent. Furthermore, the influence of various experimental independent factors such as irradiation time, process type, initial dye concentration, catalyst dosage, H₂O₂ concentration, scavenger type, and catalyst regeneration on the decomposition of MB, RhB and MO were surveyed. Additionally, a first order kinetic model was applied to investigate the sonodecomposition reactions of dye contaminants. The rate constant (k) and half-life (t_1/2) data were gained as 0.0675 min^-1 and 10.2666 min, respectively, for the decomposition of MB in the US/H₂O₂/CoFe₂O₄?Cr-MIL-101/Y system. Besides, evaluating the attained results, the distinctive performance of OH as the radical scavenger originating from H₂O₂ throughout the sonodecomposition process is vividly approved.

Full text of DOI:10.1039/d0ra00877j

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A novel CoFe2O4@Cr-MIL-101/Y zeolite ternary
nanocomposite as a magnetically separable
sonocatalyst for efficient sonodegradation of
organic dye contaminants from water†
Cite this: RSC Adv., 2020, 10, 10082
*
Meysam Sadeghi, Saeed Farhadi
and Abedin Zabardasti
In this research, a novel magnetic sonocatalyst nanocomposite, CoFe2O4@Cr-MIL-101/Y zeolite, has been
successfully fabricated employing a simple hydrothermal method. The as-prepared catalyst was thoroughly
identified using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission
scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), EDS elemental dot-
mapping, transmission electron microscopy (TEM), atomic force microscopy (AFM), vibrating sample
magnetometer (VSM), and nitrogen Brunauer–Emmett–Teller (N2-BET) analyses. The procured
CoFe2O4@Cr-MIL-101/Y nanocomposite was then assessed for the decomposition of three types of
organic dyes namely methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) from water
solution using ultrasound irradiation and subsequently monitored via UV-Vis absorption technique. The
sonodecomposition reactions of organic dyes were accomplished in the presence of the H2O2 solution
as a green oxidizing agent. Furthermore, the influence of various experimental independent factors such
as irradiation time, process type, initial dye concentration, catalyst dosage, H2O2 concentration,
scavenger type, and catalyst regeneration on the decomposition of MB, RhB and MO were surveyed.
Additionally, a first order kinetic model was applied to investigate the sonodecomposition reactions of
dye contaminants. The rate constant (k) and half-life (t1/2) data were gained as 0.0675 minꢀ1 and
10.2666 min, respectively, for the decomposition of MB in the US/H2O2/CoFe2O4@Cr-MIL-101/Y system.
Besides, evaluating the attained results, the distinctive performance of cOH as the radical scavenger
originating from H2O2 throughout the sonodecomposition process is vividly approved.
Received 29th January 2020
Accepted 4th March 2020
DOI: 10.1039/d0ra00877j
rsc.li/rsc-advances
supplies and the environment without any remediation can
cause serious and irreparable consequences for the human
1. Introduction
body and environmental species. The permanent exposure to
such organic dye contaminants even at low concentrations has
proven to be harmful owing to their bioaccumulation in living
tissues through skin, eyes, inhalation and unclean drinking
water.4 Therefore, these sorts of organic contaminants with
carcinogenic and mutagenic effects referred to the existence of
various aromatic compounds mostly naphthalene, benzidine
within their structures, should be scrupulously disposed or
removed from wastewater systems prior to their entrance into
the environment.5–7 From the other point of view, there are
diverse methodologies to eradicate contaminant dye molecules
from aqueous solutions such as ultrasonic degradation,8
adsorption,9,10 photocatalytic treatment,11 biodegradation,12
electrochemical oxidation,13 etc. Among them, the sonode-
composition reaction has been exerted as a signicant, effective
and environmentally friendly process to eliminate dye
contaminants through the formation of cOH (hydroxyl) and cH
(proton) radicals and a series of other species like HOOc (per-
hydroxyl) radicals, O2, etc.14 Furthermore, the versatile sorts of
In recent years, the numbers of major health and environ-
mental dilemmas have been growing from day to day due to the
release of tremendous amounts of chemicals into the environ-
mental zones like water, soil, air and so on.1 As industrial
activities are spreading all over the world, it will be much harder
to protect natural and environmental sources against drastic
quantities of chemicals which plummet from these units. Also,
it has been revealed that there are more than 10 000 different
kinds of dyes and pigments, approximately 700 000 tons of
which are produced yearly.2 On the other hand, more than
200 000 tons (about 10–15%) of residual synthetic dyes are
discarded from the textile mills dyeing processes and between 2
to 10% of them are directly evacuated into the sewage systems.3
The improper evacuation of organic dye sewages into water
Department of Chemistry, Lorestan University, Khorramabad, 68151-44316, Iran.
E-mail: farhadi.s@lu.ac.ir; sfarhadi1348@yahoo.com; Fax: +98 6633120618; Tel:
+98 6633120611
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra00877j
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catalysts, including CuFe2O4/MIL-101/Graphene,15 TiO2/mont- isopropyl alcohol (IPA, 99%), disodium ethylenediaminetetra-
morillonite,16 Yb,
CoFe2O4@ZnS,18
B
and Ga dopted Er3+:Y3Al5O12/TiO2,17 acetate (Na2-EDTA, 99%), methyl orange (MO, C14H14N3NaO3S,
Au/NiGa2O4–Au–Bi2O3,19 CoFe2O4/CdS,20 99%), rhodamine B (RhB, C28H31ClN2O3, 99%), and methylene
InVO4/TiO2,21 CeO2/TiO2,22 MgO,23 WO3,24 AgBr,25 and some blue (MB, C16H18ClN3S, 99%) were all purchased from Alfa
others, have been applied to remove dye contaminants through Aesar, Sigma-Aldrich and Merck companies.
the sonodecomposition activities. In addition to this, metal–
organic frameworks (MOFs) are introduced as one of the new
kind of organic–inorganic materials.26 Among all types of MOFs,
Cr-MIL-101 (with a band gap energy 2.06 eV)27 has attracted
special attention because of its prominent chemical and phys-
ical features.28,29 Moreover, as it has been lucratively applied in
different elds of research like gas sensing procedures, sepa-
ration and catalysis,30–32 it counts as a promising candidate for
the removal of organic dyes. It is also noticeable that the zeolites
are known as a subgroup of hydrated crystalline aluminosilicate
of alkali and alkaline-earth metals.33 Y zeolite displays the
Faujasite (FAU) framework which has a 3D porous structure is
known as one of the most accountable zeolites which has been
employed for numerous research purposes so far.33 Y zeolite
possesses distinctive features like high surface area, large pore
volume, high hydrothermal stability and biocompatibility
which is advantageous for its use in catalysis, development of
adsorbents, etc.34–36 Elsewhere, in recent years, the inorganic
spinel cobalt ferrite nanoparticles (CoFe2O4 NPs) with band gap
energy 1.76 eV have grabbed much attention referred to their
different properties such as coercivity, anisotropy, saturation,
magnetization, etc.37,38 Thereupon, these salient and applicable
features make magnetic CoFe2O4 NPs suitable for several elds
for instance drug delivery,39 magnetic uid hyperthermia,40
microwave devices,41 permanent magnets,42 catalysis,43 etc. The
incorporation of various sorts of magnetic NPs over the surface
of solid catalysts provides a high surface area to enhance the
efficiency of the catalytic processes.44 In this scientic research,
for the rst time, CoFe2O4@Cr-MIL-101/Y zeolite as a novel
magnetic catalyst nanocomposite was successfully fabricated
using hydrothermal route and subsequently identied by
several techniques including FTIR, XRD, FESEM, EDS, EDS dot-
mapping, TEM, AFM, VSM, and BET analyses. The foregoing
nanocomposite was then assessed for the sonodecomposition
of the cationic and anionic organic dyes of methylene blue
(MB), rhodamine B (RhB) and methyl orange (MO) in water
solution by employing H2O2 (hydrogen peroxide) as the hydroxyl
radicals (cOH) source. However, as far as we know, there are no
scientic researches reporting the sonodecomposition reac-
tions of organic dye contaminants using the CoFe2O4@Cr-MIL-
101/Y zeolite catalyst nanocomposite in any previous study.
2.2. Instrumentation
The morphological, structural and magnetic properties of the
as-prepared catalysts were evaluated using different analytical
instruments. In this respect, the Fourier transform infrared
(FTIR) was applied on a Schimadzu system spectrophotometer
8400S utilizing KBr disks in the wavelength between 400–
4000 cmꢀ1. The powder X-ray diffraction (XRD) patterns were
surveyed by type XPERT Poro panalytical diffractometer along
˚
with Ni-ltered CuKa radiation at l ¼ 1.5406 A (40 kV and 30
mA) and subsequently the related data were measured in the
variation range of 2q between 5ꢁ to 80ꢁ via a scanning speed of
2ꢁ minꢀ1. Elsewhere, a eld emission scanning electron
microscopy along with energy-dispersive X-ray spectroscopy
(FESEM-EDS) and X-ray dot-mapping (MIRA3 TESCAN) via an
operating voltage of 15 kV, were exerted to investigate the shape
and crystalline size of the understudy catalysts. Meantime, the
atomic force microscopy (AFM, Noncontact mode, Ara-AFM,
model Full plus) was operated and experiments were imple-
mented at 25 ꢂ 1 ꢁC. The transmission electron microscopy
(TEM) analysis was utilized to characterize the particles size and
morphology of the as-prepared catalyst nanocomposite with
type Philips CM120 electron microscope at an 80 kV voltage. For
the investigation of the magnetic properties of as-synthesized
catalysts, a vibrating sample magnetometer (VSM, Magnetic
Daghigh Kavir, MDKB model) was applied. The nitrogen Bru-
nauer–Emmett–Teller (N2-BET) with a PHSCHINA PHS1020
apparatus was used to study the specic surface area and pore
size distributions of the catalysts at 77 K. Moreover, an ultra-
sonic device (Sonic 6MX; 100W output acoustic power and
frequency of 37 kHz) was utilized to study all the sonode-
composition processes of organic dyes and the fabrication of
the catalysts. A double-beam ultraviolet-visible (UV-Vis) spec-
trophotometer (Cary 100, Varian Company) was employed to
evaluate the residual organic dyes concentrations from the
supernatant aqueous solutions before and aer the sonode-
composition reactions in the range wavelength between 200–
800 nm.
2.3. Synthesis of Y type zeolite
Typically, an adequate amount of NaOH (10 g) was poured into
the deionized water (10 mL). Aerwards, the value of Al(OH)3
(9.75 g) was transferꢁred into the NaOH solution and heated at
temperature of 100 C. Then, resultant suspension (10 g) was
2. Experimental
2.1. Materials
Cobalt(II) nitrate hexahydrate (Co(NO3)2$6H2O, 98%), iron(III) dissolved into the deionized water (61.2 mL) and subsequently
nitrate nonahydrate (Fe(NO3)3$9H2O, 98%), terephthalic acid NaOH (5.9 g) was added to this suspension until being dissolved
(H2BDC, 98%), chromium(III) nitrate nonahydrate (Cr(NO3)3- to prepare the solution A. Meanwhile, Na2SiO3 (22 g) was
$9H2O, 99%), aluminum hydroxide (Al(OH)3, 99%), sodium gradually poured into the prepared solution containing NaOH
hydroxide (NaOH, 98%), hydrogen peroxide (H2O2, 30%), (5.9 g) and deionized water (61.2 mL) until being dissolved to
sodium silicate (Na2SiO3, 98%), ethanol (C2H5OH, 96%), afford the solution B. The solution A was gently added to the
dimethyl formamide (DMF, 99%), benzoquinone (BQ, 98%), solution B and acquired mixture was stirred for 40 min. The
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molar composition of gel was 4.3Na2O : Al2O3 : 10SiO4- was moved to the UV-Vis spectrophotometer instrument at lmax
: 180H2O. The mixture was placed into a Teon-lined stainless of 663 nm to evaluate the residual MB dye. In addition, the
steel autoclave and heated at 90 ꢁC for 8 h. The product was inuence of several independent factors such as initial dye
ltered and washed by distilled water until the neutral pH was concentration (25, 35, 45 and 55 mg Lꢀ1), sonocatalyst kind (raw
achieved. Consequently, the nal product was dried at 100 ꢁC.45 CoFe2O4, Y, Cr-MIL-101, Cr-MIL-101/Y and CoFe2O4@Cr-MIL-
101/Y), sonocatalyst dosage (0.25, 0.5, 0.75 and 1 g Lꢀ1), initial
2.4. Synthesis of Cr-MIL-101/Y zeolite
H2O2 concentration (5, 10, 20, 30, 40 and 50 mmol Lꢀ1), and
irradiation time (5, 10, 20, 30, 40, 50, and 60 min) over the
sonodecomposition reactions of dyes were meticulously
surveyed. Besides, to study the sonocatalytic performance of the
CoFe2O4@Cr-MIL-101/Y nanocomposite to decompose and
decontaminate other organic dyes namely RhB and MO from
aqueous solution, the similar experimental conditions were
employed and the acquired data were reported in the present
research. The decomposition reaction efficiency% (DE%) was
also investigated through the equation below (1):
Firstly, as-prepared Y zeolite (0.2 g) was added into the deion-
ized water (30 mL) and subsequently was dispersed under
ultrasonic irradiation for 1 h. In the next step, the appropriate
values of H2BDC (0.5 g) and Cr(NO3)3$9H2O (1.2 g) as the
precursors were poured into the above specied solution and
the solution was then rigorously agitated for 30 min at 25 ꢂ
1 ꢁC. Subsequently, the resultant suspension was transferred to
a Teon-lined stainless steel autoclave and heated at 200 ꢁC
overnight. The gained product was then le to be cooled down
at 25 ꢂ 1 ꢁC. To achieve the extra puried sample, the resultant
mixture was rinsed several times sequentially using the DMF
and ethanol solvents to remove any possible impurities from
the unreacted H2BDC on its surface. Finally, the obtained
sample was dried at 150 ꢁC for 12 h to achieve the Cr-MIL-101/Y
zeolite composite.
ꢀ
ꢁ
ꢀ
ꢁ
At
Ct
DE% ¼ 1 ꢀ
ꢃ 100 ¼ 1 ꢀ
ꢃ 100
(1)
A0
C0
In the aforementioned equation, A0 and C0, and also At and Ct
parameters in mg Lꢀ1 are ascribed to the absorbance and
concentration of decomposed MB dye at the initial and the
specied reaction time interval in min, respectively.
2.5. Synthesis of CoFe2O4@Cr-MIL-101/Y zeolite
3. Result and discussion
A hydrothermal approach was employed to synthesize the
magnetic CoFe2O4@Cr-MIL-101/Y zeolite catalyst nano- 3.1. FTIR analysis
composite as follows: the as-prepared Cr-MIL-101/Y composite
The Fourier transform infrared spectroscopy (FTIR) spectra of
(0.5 g) was appended into the deionized water (30 mL). Aer-
wards, the quantities of Fe(NO3)3$9H2O (1.32 g) and Co(NO3)2-
$6H2O (0.57 g) were added into the desired solution and
subsequently stirred for 1 h at 25 ꢂ 1 ꢁC. Thereaer, as-prepared
NaOH aqueous solution (1 mol Lꢀ1) was gradually added to the
above cited suspension to achieve pH of 11 while continuously
stirring for 1 h. Then, the immobilization reaction was ceased
and the mixture was calcined at 180 ꢁC for 12 h. Ultimately, the
attained precipitate was magnetically separated and thoroughly
rinsed using the deionized water and ethanol for multiple times
the as-prepared catalysts namely raw Y zeolite (Fig. 1a), Cr-MIL-
101/Y (Fig. 1b), CoFe2O4@Cr-MIL-101/Y (Fig. 1c), raw CoFe2O4
(Fig. 1d), and raw Cr-MIL-101 (Fig. 1e) have been exhibited in
Fig. 1. As demonstrated in Fig. 1a–c, the bands located at
459 cmꢀ1 and 578 cmꢀ1 are ascribed to the internal TO4 (T ¼ Al
and/or Si elements) tetrahedral units and bending vibrations of
the double six rings external linkage of Y zeolite, while the
specied absorption bands at 719 cmꢀ1 and 788 cmꢀ1 can be
assigned sequentially to the external linkage and vibrations
O–T–O internal tetrahedral symmetrical stretching. Moreover,
the observed bands near 1018 cmꢀ1 and 1135 cmꢀ1 are relevant
to the O–Al–O and/or O–Si–O external connection and internal
tetrahedral asymmetrical stretching vibrations of the Y zeolite.
ꢁ
and dried at 25 ꢂ 1 C.
2.6. Sonodecomposition experiments
To scrutinize the sonocatalytic decomposition reactions of The bands at 1631 cmꢀ1 and 3407 cmꢀ1 can be attributed to the
several organic cationic and anionic dyes including MB, RhB vibrations of hydroxyl groups and adsorbed H2O molecules
and MO over the desired catalysts from water solution, an bonds including O–H bonding and H–O–H bending sequen-
ultrasonic device was applied. Typically, the amount of tially in the structure of Y zeolite. Additionally, the bands at
magnetic CoFe2O4@Cr-MIL-101/Y catalyst (0.5 g Lꢀ1) was about 1512 cmꢀ1 and 1398 cmꢀ1 which have been indicated
transferred into the MB aqueous solution (25 mg Lꢀ1, 50 mL) from Fig. 1b and c, can be pertained to the C]C and carboxylate
and subsequently the resulting solution was shaken for 30 min (O–C–O) bonds in H2BDC which referred to the successful
in the darkness. This stirring step causes the formation an incorporation of Cr-MIL-101 in the structure of CoFe2O4@Cr-
adsorption–desorption equilibrium among the catalyst surface MIL-101/Y. On the other hand, the absorption bands affiliated
and organic dye. In the next step, the reaction was accom- to the M–O–Si and/or M–O–Al (M ¼ Co and/or Fe elements)
plished using the H2O2 (40 mmol Lꢀ1, 2 mL). Aer the desired from the incorporation of CoFe2O4 on the Cr-MIL-101/Y
time intervals, the reaction process was halted; the quantity of framework expected in the range of 400 to 1000 cmꢀ1, were
the aqueous solution (2 mL) was taken out and then the not illustrated because to the overlapping with the Y zeolite
CoFe2O4@Cr-MIL-101/Y nanocomposite was separated from the bands. The FTIR spectrum of the raw CoFe2O4 has been shown
supernatant solution using an external magnetic eld. At the in Fig. 1d. The bands at about 3450 cmꢀ1 and 1581 cmꢀ1 are
end, the transparent supernatant solution of the organic dye observed due to the adsorbed H2O molecules on the surface of
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CoFe2O4. The absorption bands between 400 cmꢀ1 to 600 cmꢀ1 can be revealed from Fig. 2a–c, the several intense peaks
were also recognized to the stretching vibrations of Co–O and belonged to the Y zeolite were determined at 2q angles
Fe–O bonds. Also, Fig. 1e reveals FTIR spectrum of the raw Cr- approximately 6.28ꢁ, 10.17ꢁ, 11.95ꢁ, 15.73ꢁ, 18.73ꢁ, 20.43ꢁ,
MIL-101. The absorption bands in the range of 748 cmꢀ1
,
23.71ꢁ, 27.13ꢁ, and 32.54ꢁ sequentially recognized to the
881 cmꢀ1, 1016 cmꢀ1, 1161 cmꢀ1, and 1508 cmꢀ1 are related to diffraction planes of (111), (220), (311), (331), (511), (440), (620),
the C–H and C]C bonds, respectively. The absorption bands (533), and (733), which have been crystallized in the cubic
around 1400 cmꢀ1 to 1662 cmꢀ1 are assigned sequentially to the structure with JCPDS card (41-0118). Besides, the main peaks of
asymmetric stretching vibrations and carboxylate (COO) raw Cr-MIL-101 phase were observed at 2q between 5ꢁ to 20ꢁ
symmetric stretching vibration from the H2BDC.
(Fig. 2d), which conrms the excellent crystalline framework of
the fabricated sample. Also, by supporting of Cr-MIL-101 and
CoFe2O4 subsequently over the Y zeolite surface to form the
CoFe2O4@Cr-MIL-101/Y nanocomposite, no signicant change
was found in its crystalline structure. In this respect, the peaks
attributed to the Cr-MIL-101 were demonstrated at scattering
3.2. XRD analysis
Fig. 2 elucidates the X-ray diffraction (XRD) patterns of the raw Y
zeolite (Fig. 2a), Cr-MIL-101/Y (Fig. 2b), CoFe2O4@Cr-MIL-101/Y
(Fig. 2c), raw CoFe2O4 (Fig. 2d), and raw Cr-MIL-101 (Fig. 2e). As
Fig. 1 FTIR spectra of the as-synthesized (a) raw Y zeolite, (b) Cr-MIL- Fig. 2 XRD patterns of the as-synthesized (a) raw Y zeolite, (b) Cr-MIL-
101/Y, (c) CoFe2O4@Cr-MIL-101/Y, (d) raw CoFe2O4, and (e) raw Cr- 101/Y, (c) CoFe2O4@Cr-MIL-101/Y, (d) raw CoFe2O4, and (e) raw Cr-
MIL-101.
MIL-101.
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angles (2q) approximately 8.62, 9.18ꢁ, 11.45ꢁ and 16.60ꢁ, zeolite, the octahedral framework of the Cr-MIL-101 and also
respectively. Moreover, several new peaks affiliated to the the quasi-spherical shape of the CoFe2O4 were displayed from
presence of CoFe2O4 throughout the fabrication process of the the FESEM images. Based on the attained data, it can be
nanocomposite were located at 2q of 30.34ꢁ, 35.67ꢁ, 37.12ꢁ, inferred that by supporting the Cr-MIL-101 and CoFe2O4
43.29ꢁ, 53.65ꢁ, 57.20ꢁ, 62.82ꢁ, 71.25ꢁ, 74.23ꢁ and 78.97ꢁ corre- subsequently over the surface of the Y zeolite, its morphology
sponded to the (220), (311), (222), (400), (422), (511), (440), (620), and framework remained intact. Moreover, the average particles
(533), and (444) (JCPDS card: 01-1121). The average crystalline size of the CoFe2O4 NPs as the guest molecules within the
size (dc) of the CoFe2O4 NPs over the Cr-MIL-101/Y was CoFe2O4@Cr-MIL-101/Y catalyst were found to be about 12 nm.
measured approximately 12 nm using the Debye–Scherrer eqn
(2):
3.4. EDS and EDS elemental dot-mapping analyses
ð0:9Þl
dc ¼
(2)
The energy dispersive X-ray (EDS) was operated to fully clarify
the elemental composition of the as-fabricated catalysts. Fig. 4
represents the EDS analysis of the raw Y zeolite (Fig. 4a),
CoFe2O4@Cr-MIL-101/Y (Fig. 4b), raw CoFe2O4 (Fig. 4c), and
raw Cr-MIL-101 (Fig. 4d), respectively. The acquired data from
the analysis elucidates the existence of the four main elements
of Si, O, Al and Na in all of the samples including raw Y zeolite
b cos q
herein, l factor is the wavelength of X-ray, b shows the full width
at half maximum (FWHM) of the desired diffraction pattern and
q is also recognized as the Bragg angle.
3.3. FESEM analysis
To survey the structure, morphology and size of the as-prepared and CoFe2O4@Cr-MIL-101/Y. Also, Fig. 4b displays the presence
samples, eld emission scanning electron microscopy of a series of other elements such as Co, Fe and O related to the
a
(FESEM) analysis was applied. The FESEM images of the raw Y CoFe2O4 NPs, and plus Cr, C and O corresponded to the Cr-MIL-
zeolite (Fig. 3a and b), Cr-MIL-101/Y (Fig. 3c and d), CoFe2- 101 within the framework of the CoFe2O4@Cr-MIL-101/Y
O4@Cr-MIL-101/Y (Fig. 3e and f), raw CoFe2O4 (Fig. 3g), and raw ternary nanocomposite, which affirms the formation of the
Cr-MIL-101 (Fig. 3h and i) with different resolutions were all CoFe2O4 and Cr-MIL-101 over the Y zeolite (see Table 1). Also, as
respectively indicated in Fig. 3. The cubic crystals of the Y can be seen from Fig. 4b and d, composition analyses of the C
Fig. 3 FESEM images of the as-synthesized (a and b) raw Y zeolite, (c and d) Cr-MIL-101/Y, (e and f) CoFe2O4@Cr-MIL-101/Y, (g) raw CoFe2O4, (h
and i) raw Cr-MIL-101 with different resolutions.
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and O elements clearly approved the presence of carboxylate
within the Cr-MIL-101 frameworks. Further, the FESEM image
affiliated to the EDS elemental dot-mappings of the CoFe2-
O4@Cr-MIL-101/Y were depicted in Fig. 4e. Evaluating the
elemental mappings analysis represented in Fig. 4e, the
uniform distribution of Si, O, Al, Na, Co, Fe, Cr and C elements
on the nanocomposite is clearly veried.
3.5. TEM analysis
The TEM analysis was applied to further warrant the particle
size and morphology of the as-prepared CoFe2O4@Cr-MIL-101/
Y nanocomposite. The TEM images of CoFe2O4@Cr-MIL-101/Y
with different resolutions are shown in Fig. 5a–c. Regarding
the TEM images, it can be deduced that the both Cr-MIL-101
Fig. 4 EDS analyses of the as-synthesized (a) raw Y zeolite, (b) CoFe2O4@Cr-MIL-101/Y, (c) raw CoFe2O4, (d) raw Cr-MIL-101, and (e) FESEM
image affiliated to the EDS dot-mappings of the as-synthesized CoFe2O4@Cr-MIL-101/Y.
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Table 1 The quantitative results of the elemental composition of the
the successful synthesis of the aforementioned guest molecules
within the host framework. Besides, mean size of the composed
CoFe2O4 NPs in the CoFe2O4@Cr-MIL-101/Y catalyst were
approximately about 12.8 nm, which acquired data from this
analysis are in good consistency with the FESEM, TEM and
XRD.
as-synthesized
nanocomposite
CoFe2O4@Cr-MIL-101/Y
zeolite
catalyst
Element type
Line
Weight%
Atomic%
C
O
Ka
Ka
Ka
Ka
Ka
Ka
Ka
Ka
47.77
33.43
1.51
0.97
2.03
0.88
8.81
4.60
61.25
32.17
1.01
0.55
1.11
0.26
2.43
1.20
Na
Al
Si
Cr
Fe
Co
3.7. VSM analysis
The vibrating sample magnetometer (VSM) analysis was utilized
to thoroughly investigate the magnetic properties of the as-
prepared samples at 25 ꢂ 1 ꢁC. Fig. 6 reveals the hysteresis
loops of the raw CoFe2O4 NPs (Fig. 6a) and CoFe2O4@Cr-MIL-
101/Y (Fig. 6b). Both raw CoFe2O4 NPs and CoFe2O4@Cr-MIL-
101/Y illustrate the ferromagnetic features due to the exis-
tence of three parameters namely coercive force (Hc), remnant
magnetization (Mr) and saturation magnetization (Ms). In this
respect, the values of the Hc, Mr and Ms parameters of the raw
CoFe2O4 NPs were determined approximately at about 1500 Oe,
33.94 emu gꢀ1 and 63.46 emu gꢀ1, whereas by supporting of the
CoFe2O4 NPs on the surface of the Cr-MIL-101/Y, the above-
mentioned values decreased to 2500 Oe, 15.10 emu gꢀ1 and
26.10 emu gꢀ1, respectively. Consequently, it is deduced that
the CoFe2O4@Cr-MIL-101/Y nanocomposite can be separated
from the reaction solution in the shortest possible time using
a simple external magnetic eld.
and CoFe2O4 NPs as the guest molecules were successfully
incorporated over the Y zeolite structure. The mediocre particle
diameter about 12 nm and plus the narrow particle size distri-
bution between 8 to 16 nm were clearly identied using the TEM
images. The abovementioned results were in good agreement
with the mediocre particle diameter attained via the FESEM and
XRD analyses.
3.6. AFM analysis
The atomic force microscopy (AFM) is recognized as a suitable
analytical method to study several important properties of the
as-obtained catalysts such as surface roughness, size and
topography. Fig. S1† represents AFM 2-dimensional (2D) and 3-
dimensional (3D) images ascribed to the raw Y zeolite (Fig. S1a
and b†), Cr-MIL-101/Y (Fig. S1c and d†) and CoFe2O4@Cr-MIL-
101/Y (Fig. S1e and f†), respectively. By comparing the images, it
is brightly indicated that the surface of the Y zeolite was mainly
covered via the Cr-MIL-101 and CoFe2O4 NPs, which refers to
3.8. BET analysis
To meticulously unveil the structural outstanding of the as-
prepared catalysts, BET analysis was utilized. Fig. 7 demon-
strates the N2 adsorption–desorption isotherms and pore size
distributions of raw Y zeolite (Fig. 7a) and CoFe2O4@Cr-MIL-
101/Y (Fig. 7b), respectively. Pursuant to the acquired plot of
isotherms of the understudy catalysts, it is obviously known that
these plots can be assorted to type-IV isotherm with a H3
hysteresis loops (as per IUPAC recommendation), which
affirmed the presence of mesoporous structure of the catalysts.
The values of BET specic surface area for raw Y zeolite and
CoFe2O4@Cr-MIL-101/Y were also measured about 494 and 222
m2 gꢀ1 respectively and reected in Table 2. As can be seen in
Fig. 5 TEM images of the as-synthesized (a–c) CoFe2O4@Cr-MIL- Fig. 6 VSM curves of the as-synthesized (a) raw CoFe2O4 and (b)
101/Y with different resolutions.
CoFe2O4@Cr-MIL-101/Y.
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Fig. 7 BET analyses, BJH and t plots of the as-synthesized (a) and (b) raw Y zeolite, (c) and (d) CoFe2O4@Cr-MIL-101/Y.
Table 2, the acquired specic surface area, pore size distribu- spectra of the MB aqueous media in the reaction with the
tions, Vme and Vmi of CoFe2O4@Cr-MIL-101/Y decreases in CoFe2O4@Cr-MIL-101/Y zeolite catalyst indicates the prom-
comparison with raw Y zeolite, which conrms the formation of inent role of the shaking time. Based on the observations on the
the Cr-MIL-101 and CoFe2O4 on the Y zeolite framework.
attained spectra it becomes crystal clear that the stringency of
the punctuated peak assigned to MB (emerged at 663 nm) is
directly affected by the time intervals. As time goes on, the
intensity of the specied peak diminishes ceaselessly till the
point of 60 min at which it becomes almost hard to be spotted
which is connoting the high yield decomposition of MB
(98.9%). According to the implemented sonocatalytic experi-
ments and evaluated results on decomposition of MB dye, the
particular visible light sono decomposition role of the CoFe2-
O4@Cr-MIL-101/Y zeolite nanocomposite is vividly conrmed.
As it has been displayed in Fig. 8c, plotting ln initial dye
concentration versus contact time (min) results in some curves
which are of great signicance for the investigation of the
sonodecomposition reaction kinetics. Elsewhere, the decom-
position rate constant symbolized as k (minꢀ1), was calculated
using the rst order equation of
3.9. Sonodecomposition processes investigation
3.9.1. The inuence of the irradiation time. The irradiation
time is an effective factor for the investigation of the cationic
and anionic dyes sonodecomposition reactions using the
CoFe2O4@Cr-MIL-101/Y zeolite catalyst. To meticulously eval-
uate these reactions, a period of time intervals was considered
and the gained data studied to survey for all of the sonocatalytic
experiments. Investigating the acquired results from the
experiments clearly approved the remarkable dependency
between the decomposition percentage and different reaction
times. Thus, the sonodecomposition processes were done using
the determined absorption bands ascribed to the MB organic
dye at lmax about 663 nm. At rst, the intended amount of
CoFe2O4@Cr-MIL-101/Y zeolite catalyst (0.5 g Lꢀ1) was trans-
ferred into the MB aqueous media (50 mL, 25 mg Lꢀ1) and the
resulted suspension was exposed to the US irradiation along
with H2O2 (40 mmol Lꢀ1). As can be observed in Fig. 8a and b,
the tangible differences between the gained UV-Vis analysis
ln(Co/Ct) ¼ kt.
(3)
In the represented equation, Co is dened as the initial
concentration of the understudy dye, Ct represents the dye
Table 2 The acquired data from the N2-BET, BJH and t plots corresponded to the as-synthesized catalysts at 77 K
Total pore volume
[cm3 gꢀ1
Average pore
diameter [nm]
Sample
as, BET [m2 gꢀ1
]
Vme [cm3(STP) gꢀ1
]
Vmi [cm3(STP) gꢀ1
]
]
Y zeolite
CoFe2O4@Cr-MIL-101/Y
494
222
113
51.06
0.10
0.02
1.50
0.34
12.44
6.11
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concentration at time interval of t and k symbolizes the CoFe2O4@Cr-MIL-101/Y (48.1%) > US/H2O2/CoFe2O4 (41.5%) >
decomposition rate constant. Meanwhile, the half-life (t1/2
)
US/CoFe2O4@Y (37.56%)
>
H2O2/CoFe2O4@Cr-MIL-101/Y
amount was also computed employing the equation of
(34.38%) > US/H2O2/Cr-MIL-101 (23%) > US/H2O2/Y (19.1%) >
US/H2O2 (9.55%) > US (only), with respective constant values of
0.0675, 0.0114, 0.0109, 0.0083, 0.0072, 0.0071, 0.0042, 0.0034,
0.0016, and 0.0000 minꢀ1 (see Table 3). Pursuant to the analysis
outcomes, US/H2O2/CoFe2O4@Cr-MIL-101/Y was recognized as
the most operative system for the decomposition of MB which is
related to the impeding of the electron–hole incorporation by
the linkage among Y zeolite, Cr-MIL-101 and CoFe2O4. The
obtained data illuminates that reaction components including
CoFe2O4@Cr-MIL-101/Y, US and H2O2 undoubtedly exhibit
great performance for the decomposition process of MB dye in
aqueous solutions. Additionally, applying US along with H2O2
method, intensies the emission of hydroxyl radicals leading to
the effectively much higher decomposition efficiency of the
desired dye. Also, this decomposition efficiency can be
explained as the generation of more oxidizing radicals in the
presence of a higher concentration of H2O2. On the other hand,
it should be noted that the sonocatalytic decomposition process
in the absence of H2O2 (here focusing on US/CoFe2O4@Cr-MIL-
101/Y) occurs most probably via the formation of cOH radicals
t1/2 ¼ ln(2)/k.
(4)
To specify the mentioned adsorption kinetics, the value of 0.5 g
L
ꢀ1 of CoFe2O4@Cr-MIL-101/Y zeolite was introduced to several
containers each comprising 25 mg Lꢀ1 of the considered dye at
certain time periods and the subsequent relevant outcomes
were demonstrated in Table 3. To provide an overview on the
potentials and workability of each participant component in the
decomposition reaction of MB dye, several systems of US, US/
H2O2, US/H2O2/Y, US/H2O2/Cr-MIL-101, US/H2O2/CoFe2O4, US/
CoFe2O4@Y, US/H2O2/Cr-MIL-101/Y, H2O2/CoFe2O4@Cr-MIL-
101/Y, US/CoFe2O4@Cr-MIL-101/Y, and US/H2O2/CoFe2O4@Cr-
MIL-101/Y were designed and employed as the relevant results
have been represented in Fig. 8a–c. In addition, the value of
25 mg Lꢀ1 as the initial concentration of MB dye was appointed
for all of those specied experiments. In brief, the collected
information from the implemented experiments revealed
a decomposition sequence consisting of US/H2O2/CoFe2O4@Cr-
MIL-101/Y (98.9%) > US/H2O2/Cr-MIL-101/Y (54.5%) > US/
Fig. 8 UV-Vis absorption spectra of the sonodecomposition process of MB dye over the CoFe2O4@Cr-MIL-101/Y catalyst nanocomposite as
a function of the irradiation time (a and b), the first order kinetic plot (ln(C0/Ct)) against the irradiation time (c) (optimized experimental conditions;
[MB dye]o: 25 mg Lꢀ1 (50 mL), [H2O2]: 40 mmol Lꢀ1 (2 mL), [catalyst dosage]: 0.5 g Lꢀ1, pH: 7 and temperature: 25 ꢂ 1 ꢁC).
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using the degradation of H2O molecules. In contrast, when meaningfully concluded that the reduced decomposition effi-
H2O2 as oxidizing agent was appended to the understudy ciency is dependent to the sudden and consecutive increase in
systems, the generation of cOH radicals were considerably dosage of the organic dye and plus the constant quantities of
accelerated related to the degradation of H2O2 via the generated the synthesized nanocomposite, H2O2 and its related to cOH
electrons on the catalysts surface. According to what specied (hydroxyl radicals) at denite irradiation time. Ultimately, the
above, it is deduced that US/H2O2/CoFe2O4@Cr-MIL-101/Y, US/ lack of proportionate recipient sites along with the loss of the
CoFe2O4@Cr-MIL-101/Y and H2O2/CoFe2O4@Cr-MIL-101/Y hydroxyl radicals originated from H2O2 negatively affected the
systems have the same mechanism for the degradation of dyes. decomposition process.
3.9.2. The inuence of the organic dye type. To survey the
3.9.4. The inuence of the H2O2 concentration. Hydrogen
potential of the sonodecomposition processes using the peroxide and its subsequent affiliated hydroxyl radicals perform
CoFe2O4@Cr-MIL-101/Y zeolite catalyst, the reactions were a particular role in the entire decomposition process which
performed in the presence of RhB and MO dyes from water should not be supercially handled. From this point of view, to
solution. According to the acquired data from Fig. 9a–c, the explore all aspects of the reaction and to pick up the most
sonodecomposition yields of MO and RhB dyes at lmax about relevant concentration of hydrogen peroxide as the main spring
554 nm and 463 nm were determined more than 94% and 82% of hydroxyl radicals is of undeniable importance. According to
at time intervals of 60 min and 70 min, respectively. Conse- that, six separated experiments were precisely designed and
quently, the results showed that several factors for example pursuantly performed to nd out the optimized dosage of the
electric charges, molecule sizes, chemical compositions and so hydrogen peroxide ranging from 5–50 mmol Lꢀ1 prior to the
on, can cause differences in the potentials and applications of decomposition of MB dye in CoFe2O4@Cr-MIL-101/Y nano-
the as-fabricated CoFe2O4@Cr-MIL-101/Y zeolite catalyst in the composite catalyst. Looking crossly to the results as have been
sonodecomposition reactions.
represented in Fig. S3,† it is observed that in concentrations of 5
3.9.3. The inuence of the initial dye concentration. To and 10 mmol Lꢀ1 of H2O2, the decomposition efficiencies of
investigate and characterize the performance of the initial MB 54.5% and 69.7% in 60 min were respectively attained. Addi-
dye concentration and its pursuant inuence on the sonode- tionally, further increase in concentration of H2O2 (20 to
composition process is of great signicance. It provides an 40 mmol Lꢀ1) led to a considerable enhancement of the
evaluating ground which elucidates the operable strength of decomposition efficiencies from 81.1% to 98.9% in 60 min
a denite value of the CoFe2O4@Cr-MIL-101/Y zeolite catalyst respectively. This phenomenon affirms the undeniable coher-
nanocomposite toward the continuous increase in the concen- ency between the dosage of hydrogen peroxide and its subse-
tration of the organic dye. In this regard, a series of experiments quent off shoot hydroxyl radicals with the nal decomposition
were meticulously designed and implemented at which the efficiency. On the other hand, further intensication in
value of CoFe2O4@Cr-MIL-101/Y zeolite remained unchanged concentration of hydrogen peroxide beyond 40 mmol Lꢀ1
while the concentration of the organic dye enhanced consecu- caused a consecutive decreasing order which is referred to the
tively. From the Fig. S2,† it can be obviously comprehended that additional amounts of H2O2 functioning as cOH scavenger to
as the concentration of the dye rises from 25 to 55 mg Lꢀ1, the generate perhydroxyl (HOOc) radicals with lower oxidation
decomposition efficiency drops tangibly from 98.9% to 45.6%. sufficiency. Thereupon, the concentration of 40 mmol Lꢀ1 was
This observed phenomenon is attributed to unbalanced values considered and applied as the optimized value of H2O2 for
of the synthesized nanocomposite against the increased pursuant decomposition reactions.
concentration of dye molecules. Hence, it is inferred that the
3.9.5. The inuence of the catalyst dosage. It has always
higher the concentration of the target dye molecules, the more been an ideal horizon to use the least amount possible of an
the number of occupied active sites on the nanocomposite adsorbent to reach the highest efficiency of adsorption or
catalyst. In addition to what illustrated above, it can be decomposition. From this point of view, to indicate the most
Table 3 The attained data for the MB sonodecomposition reactions via different processes (optimized experimental conditions; irradiation time:
60 min, [MB]o: 25 mg Lꢀ1 (50 mL), [H2O2]: 40 mmol Lꢀ1 (2 mL), [catalyst dosage]: 0.5 g Lꢀ1, pH: 7 and temperature: 25 ꢂ 1 ꢁC)
Rate constant
Half-life (t1/2,
min)
Process type
(k, minꢀ1
)
Kinetic equation [ln Co/Ct ¼ at + b]
US only
US/H2O2
US/H2O2/Y
US/H2O2/Cr-MIL-101
US/H2O2/CoFe2O4
US/CoFe2O4@Y
US/H2O2/Cr-MIL-101/Y
H2O2/CoFe2O4@Cr-MIL-101/Y
US/CoFe2O4@Cr-MIL-101/Y
US/H2O2/CoFe2O4@Cr-MIL-101/Y
0.0000
0.0016
0.0034
0.0042
0.0071
0.0072
0.0114
0.0083
0.0109
0.0675
0.0000
433.1250
203.8235
165.0000
97.6056
96.2500
60.7894
83.4939
63.5779
10.2666
y ¼ 0.0000
y ¼ 0.0016x + 0.0112
y ¼ 0.0034x + 0.0076
y ¼ 0.0042x + 0.0145
y ¼ 0.0071x + 0.0090
y ¼ 0.0072x + 0.0486
y ¼ 0.0114x + 0.0525
y ¼ 0.0083x + 0.0451
y ¼ 0.0109x + 0.0378
y ¼ 0.0675x ꢀ 0.2700
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applying concentration of the sonocatalyst for the decomposi- waves transmittal into the working solution which weakens the
tion of considered organic dye, multiple experiments each ultrasonic scattering procedure. According to what explained
representing different values of CoFe2O4@Cr-MIL-101/Y zeolite above, the concentration of 0.5 g Lꢀ1 was assigned as the opti-
(ranging from 0.25 to 1 g Lꢀ1) were dened and carried out and mized value of the synthesized sonocatalyst for the ulterior
the affiliated results were demonstrated in Fig. S4.† It is also designed experiments.
emphasized that the quantities of other participant species of
3.9.6. The inuence of the scavenger type. To provide an
the reaction including the understudy hydrogen peroxide explicit perception of the inuential species and to indicate
(40 mmol Lꢀ1) and organic dye (25 mg Lꢀ1) kept unchanged their function as practical active oxidants through the decom-
throughout the assigned experiments. In consequence, as the position reactions, several experiments were organized and
concentration of the nanocomposite sonocatalyst was sequentially implemented. In this regard, delving into Fig. S5†
enhanced, the better results for the decomposition process were leads to a substantial deduction. It claries when 5 mmol Lꢀ1 of
recorded. Nevertheless, this gradual ascendant procedure was isopropyl alcohol (IPA) performing as cOH scavenger was
substituted by a diminution sequence at concentrations higher poured into the solution comprising 0.5 g Lꢀ1 of the catalyst
than 0.5 g Lꢀ1. As a matter of fact, it is inferred that continuous nanocomposite and 25 mg Lꢀ1 of MB, the decomposition effi-
increase in catalyst dosage provides much more active sites ciency phenomenally dropped to 32% aer 60 min of irradia-
accompanied by hydroxyl radicals on the CoFe2O4@Cr-MIL-101/ tion. Based on the described observation, the essentiality of
Y zeolite which counts as the major reason for the increase of existence and the irrefutable role of hydroxyl radicals as
the decomposition efficiency. Moreover, the reported incessant oxidants in the sonocatalytic process can be strongly empha-
decrease aer the concentration of 0.5 g Lꢀ1 is assigned to the sized. On the other hand, the addition of disodium ethylene-
aggregation of the present nanoparticles related to the sono- diaminetetraacetate (Na2-EDTA) and benzoquinone (BQ) as
catalyst as it is likely for them to detrimentally affect the hole (h+) and superoxide (cO2ꢀ) scavengers to the above cited
decomposition process by reducing the number and dispensa- solution caused an inconspicuous decrease in the decomposi-
tion of the active sites and further suppressing the ultrasonic tion efficiency of MB dye. Considering the gathered results from
Fig. 9 UV-Vis absorption spectra of (a) RhB and (b) MO. (c) Decomposition efficiency% of MO and RhB dyes as a function of the irradiation time
over the CoFe2O4@Cr-MIL-101/Y catalyst nanocomposite (optimized experimental conditions; [dye]o: 25 mg Lꢀ1 (50 mL), [H2O2]: 40 mmol Lꢀ1 (2
mL), [catalyst dosage]: 0.5 g Lꢀ1, pH: 7, and temperature: 25 ꢂ 1 ꢁC).
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Fig. 10 (a) The regeneration plot, (b) XRD (c) FESEM, and (d) EDS analyses of the recovered CoFe2O4/Y@Cr-MIL-101 on the sonodecomposition
process of MB after four runs (optimized experimental conditions; irradiation time: 60 min, [MB]o: 25 mg Lꢀ1 (50 mL), [H2O2]: 40 mmol Lꢀ1 (2 mL),
[catalyst dosage]: 0.5 g Lꢀ1, pH: 7 and temperature: 25 ꢂ 1 ꢁC).
those above specied experiments, it is perceived that the noted 101/Y was spotted aer the rst run. However, the high
holes and superoxides display auxiliary roles either as cOH decomposition efficiency results recorded for those assigned
origins or oxidizing agents.
frequent runs verify the signicant potentials and reliability of
3.9.7. Regeneration and stability of the CoFe2O4@Cr-MIL- the synthesized catalyst nanocomposite in diverse decomposi-
101/Y zeolite. In order to investigate the applicable potentials tion runs. As it can be observed in Fig. 10a, the regeneration
and the regeneration of the synthesized sonocatalyst, the spent phase was renewed four times and applying the regenerated
CoFe2O4@Cr-MIL-101/Y zeolite was submerged in a solution of catalyst nanocomposite led to the decomposition efficiencies of
ethanol–deionized water. The implemented washing procedure higher than 93% for all of those cited runs. Additionally, XRD,
leads to the segregation of the MB molecules from the CoFe2- FESEM and EDS techniques were all utilized to provide a better
O4@Cr-MIL-101/Y zeolite sonocatalyst nanocomposite. Aer- understanding of the regenerated and fresh CoFe2O4@Cr-MIL-
wards, the recovered sonocatalyst was dried and repeatedly 101/Y and plus to identify any possible characteristic conver-
exerted for some several continual decomposition runs. In fact, sion or disguration. Fig. 10b–d display the outcomes gathered
a negligible decline in the regeneration of CoFe2O4@Cr-MIL- from those above specied techniques. The XRD results showed
Table 4 A comparison between the CoFe2O4@Cr-MIL-101/Y and several reported catalysts
[Catalyst]
No Catalyst type
Irradiation type Dye type [H2O2]o (mmol Lꢀ1
)
[Dye]o (mg Lꢀ1
)
(g Lꢀ1
)
Time (min) Eff.% Ref.
1
2
3
4
5
6
7
8
9
Cr-MIL-101@NiO/13X
Cr-MIL-101@NiO/13X
TiO2@CNTs/AgNPs/C10 Visible light
Ultrasonic
Ultrasonic
MB
RhB
MB
RhB
RhB
MB
RhB
MB
40
40
25
25
20
0.02
40
25
25
25
25
0.5
0.5
0.5
0.5
0.5
1
1
0.5
0.5
80
80
120
60
300
20
20
60
60
97.2
94.3
100
90
95
83
20
98.9
94.6
26
26
46
47
48
49
49
0.782 mol Lꢀ1
Fe3O4
Ultrasonic
Visible light
Ultrasonic
Ultrasonic
40
50
4 vol%
4 vol%
40
Fe3O4/Al-B
SCN/CoFe2O4
SCN/CoFe2O4
CoFe2O4@Cr-MIL-101/Y Ultrasonic
CoFe2O4@Cr-MIL-101/Y Ultrasonic
This work
This work
RhB
40
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no considerable variation between the fresh and the regen- the excited holes to be appeared. To calculate the absorption
erated CoFe2O4@Cr-MIL-101/Y aer the fourth run (Fig. 10b). band energy (Eg) of the as-prepared catalysts according to the
Besides, the FESEM technique (Fig. 10c) proved that there was available literatures,27,38 the following equation can be used
no sensible transguration or deleterious alteration in the (5):50
framework of CoFe2O4@Cr-MIL-101/Y aer the fourth run
(ahv)2 ¼ A(hv ꢀ Eg)
(5)
compared to the fresh nanocomposite catalyst. Elsewhere, as it
has been depicted in Fig. 10d, the EDS analysis exposed some
substantial characteristic peaks of Si, O, Al, Na, Co, Fe, Cr and C
affiliated to the regenerated CoFe2O4@Cr-MIL-101/Y aer the
fourth run of handling.
3.9.8. Comparison of CoFe2O4@Cr-MIL-101/Y zeolite with
other research works. To precisely appraise the performance of
the as-fabricated CoFe2O4@Cr-MIL-101/Y zeolite, the decom-
position efficiency of this nanocomposite against several other
catalysts was compared (see Table 4).26,46–49 The represented
results from several designed experiments and also character-
ization studies along with the comparison with other research
works in the same eld, all conrm the superiority of the newly
introduced catalyst nanocomposite versus the others.
in the above noted equation, a, h, v, Eg and A parameters are the
optical absorption coefficient, Plank constant, light frequency,
absorption band gape energy, and a constant corresponded to
the as-fabricated catalysts, respectively. Based on the afore-
mentioned equation, the energy band gap (Eg) of CoFe2O4 and
Cr-MIL-101 were estimated to be about 1.76 and 2.06 eV,
respectively. Moreover, the amounts of CB and VB of CoFe2O4
and Cr-MIL-101 can be calculated utilizing the atom's Mulliken
electronegativity denition according to the following equa-
tions (eqn (6) and (7)):
1
EVB ¼ c ꢀ Ee þ Eg
(6)
(7)
2
3.9.9. Plausible mechanism of the dyes sonodecomposi-
tion process. It is explicitly known that the high temperature
and pressure affiliated light and hot spots are formed by the
ECB ¼ EVB ꢀ Eg
ultrasonic cavitation. Thereupon, these two particular parame- here EVB and ECB parameters are the VB and the CB potentials
ters can be used to provide a relevant explanation for the respectively, Ee is the energy of free electrons on the hydrogen
sonocatalytic decomposition of the understudy organic dyes. scale (4.5 eV) and c parameters is the absolute electronegativity
Meanwhile, the pyrolysis of the H2O molecules under specic of the desired semiconductors. Based on the above mentioned
situation originates hydroxyl radicals. In addition to this, equations, the EVB and ECB amounts of Cr-MIL-101 were esti-
sonoluminescence which is known as a phenomenon assigned mated to be +0.49 eV and ꢀ1.57 eV (ref. 27) and in contrast, the
to the ultrasonic cavitation, causes the creation of the light with potentials for CoFe2O4 were calculated to be +1.9 eV and
a wide wavelength extent. Meeting the relevant wavelength of +0.14 eV (ref. 38), respectively. It is notable that the mentioned
the emerged light with the Cr-MIL-101 and CoFe2O4 makes exited electrons situated at the conductions band (CB) of Cr-
them exited and also causes the sonogenerated electrons and MIL-101 (ꢀ1.57 eV)27 are capable to transfer straightly to the
Fig. 11 A plausible mechanism for the sonodecomposition process of dye contaminants utilizing the US/H2O2/CoFe2O4@Cr-MIL-101/Y system
from water solution.
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CB of CoFe2O4 (+0.14 eV).38 In contrast, the above underlined
sonogenerated holes which are existent at the valence band (VB)
of CoFe2O4 (+1.9 eV)38 easily transfer to the VB of Cr-MIL-101
(+0.49 eV).27 As a matter of fact, these perpetual migrations of
the sonogenerated holes and electrons alleviate the probable
aggregation and moreover enhance the charge segregation rate
leading to substantially higher sonocatalytic efficiency. Besides,
there is an inuential phenomenon of the sonogenerated elec-
trons migration to the surface of the CoFe2O4@Cr-MIL-101/Y
zeolite nanocomposite in which the particular electron recep-
tors are present. Considering another advantageous aspect of
the synthesized catalyst nanocomposite, it is noteworthy that
the zeolites26 (in this case focusing on Y type zeolite) generally
are non-absorber of light in UV-Vis extent which makes them
operative supports for sonocatalysis purposes. Pursuant to the
above provided illustrations, the continuous motions of the
sonogenerated electrons of Cr-MIL-101 and CoFe2O4 nally
conduct them toward the Y type zeolite. The accommodated
electrons on the surface of Y zeolite interact with H2O2 and O2
from the working solution so that the resultant hydroxyl (cOH)
and superoxide (cO2ꢀ) radicals appear, respectively. Addition-
ally, more reactive hydroxyl radicals (cOH) are likely to be
produced when H2O2 molecules inaugurate scavenging the
specied holes (H2O/OHꢀ). In consequence, the originated
oxidizers respond to the involved organic dye molecules over
the CoFe2O4@Cr-MIL-101/Y. This phenomenon which is
attributed to the electrostatic forces triggers the creation of
H2O, CO2 and extra salts namely NO3ꢀ, SO42ꢀ, etc. as the non-
toxic products of sonodecomposition reactions (eqn (8)–
(16)).15,18,27,51,52 A comprehensive plausible schematic mecha-
nism of the entire above demonstrated process has been briey
depicted in Fig. 11.
4. Conclusion
For the very rst time, we report a simple hydrothermal route to
prepare the CoFe2O4@Cr-MIL-101/Y zeolite as a new magnetic
catalyst nanocomposite. The morphological, structural and
magnetic properties of the as-fabricated catalyst was charac-
terized by several different techniques including FTIR, XRD,
FESEM, EDS, EDS dot-mapping, TEM, AFM, VSM, and BET. The
sonocatalytic decomposition experiments of cationic and
anionic organic dyes contaminants from water solution over the
CoFe2O4@Cr-MIL-101/Y were accomplished in the presence of
H2O2 as the hydroxyl radial (cOH) origin. The inuence of
various parameters like irradiation time, initial dye concentra-
tion, catalyst dosage, H2O2 concentration, scavenger type,
process type, and catalyst regeneration over the decomposition
of MB, RhB and MO were evaluated. The experiments data from
UV-Vis analysis showed the maximum sonodecomposition
efficiency of 98.9%, 94.6% and 82% for MB, RhB and MO in the
presence of US/H2O2/CoFe2O4@Cr-MIL-101/Y system, respec-
tively. Besides, the reaction kinetics study of MB was fullled
based on the rst order model. The values of rate constant (k)
and half-life (t1/2) were determined as 0.0675 minꢀ1 and
10.2666 min, respectively. In consequence, it is deduced that
the CoFe2O4@Cr-MIL-101/Y exhibits particular and superior
functionality to decompose the organic dyes compared to other
catalysts such as Cr-MIL-101/Y, Y zeolite, Cr-MIL-101 and
CoFe2O4.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
US irradiation / heat–light (ref. 18)
(8)
The authors sincerely acknowledge all of the supports from
Lorestan University, Khorramabad, Iran.
CoFe2O4/Cr-MIL-101 + heat or light /
(CoFe2O4/Cr-MIL-101)* (ref. 27)
(9)
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