Photocatalytic degradation of methylene blue in aqueous solution by magnetic ZnMn2O4@copper porphyrin nanocomposite

Article abstract of DOI:10.1007/s13738-021-02364-z

Magnetic photocatalyst [magnetic@silica@zinc manganate, Fe₃O₄@SiO₂@ZnMn₂O₄] (MZMO) and [magnetic@silica@zinc manganate@copper tetra hydroxyl phenyl porphyrin, Fe₃O₄@SiO₂

Full text of DOI:10.1007/s13738-021-02364-z

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-021-02364-z
ORIGINAL PAPER
Photocatalytic degradation of methylene blue in aqueous solution
by magnetic ZnMn2O4@copper porphyrin nanocomposite
Ensieh Gholamrezapor1 · Abbas Eslami1
Received: 10 December 2020 / Accepted: 27 July 2021
© Iranian Chemical Society 2021
Abstract
Magnetic photocatalyst [magnetic@silica@zinc manganate, Fe3O4@SiO2@ZnMn2O4] (MZMO) and [magnetic@silica@zinc
manganate@copper tetra hydroxyl phenyl porphyrin, Fe3O4@SiO2@ZnMn2O4@CuIITHPP] (MZMOCuP) nanocomposites
were prepared using green synthesis method and characterized by means of Fourier transform-infrared, scanning electron
microscope, energy-dispersive X-ray spectroscopy, X-ray difraction, vibrating sample magnetometer (VSM) and ultra-
violent-difuse refectance spectroscopy techniques. The magnetic properties of the synthesized samples were measured by
a VSM with maximum saturation magnetization values of 10 and 8 emu g−1 for MZMO and MZMOCuP nanocomposites,
respectively. UV-difuse refectance spectroscopy data of MZMOCuP indicate the red shift of the absorption edge and reduc-
tion of the band gap from 1.4 to 1.1 eV in comparison with MZMO. The nanocomposite of MZMOCuP showed excellent
photocatalytic activity for photodegradation of methylene blue (MB) in aqueous solution under visible-LED light irradiation.
The degradation of MB was monitored by UV–Vis spectrophotometer. Maximum degradation of 98% for MB was obtained
in the presence of MZMOCuP nanocomposite as the photocatalyst and under 180 min irradiation of 3 W blue LED light.
The recovery of the photocatalyst was easily performed by using an external magnetic feld.
Keywords Porphyrin · ZnMn2O4 · Methylene blue · LED light · Photocatalyst
Introduction
better method than previous ones [10]. Green synthesis pro-
cesses are known as eco-friendly method because of using
natural bio-reductants and stabilizers in the formation of
nanoparticles. Aloe vera includes peel and gel, which pre-
vious reports revealed that its leaf contains numerous vita-
mins, polysaccharides, proteins, phenolic compounds, ster-
ols, favonoids, enzymes and organic acids and has essential
role in the reduction of the metal ions to their elemental state
and forms their nanoparticles and increases stability of the
prepared nanoparticles [15, 16]. Magnetic nanoparticles of
Fe3O4 have been extensively investigated due to their super-
paramagnetic, high coercivity, low Curie temperature [17],
non-poison, large surface area to volume ratios [18], easy
functionalization[19], superparamagnetic property and for
various biological applications[20]. Recent reports show that
magnetic nanoparticles (MNPs) can facilitate the isolation
and recycling of expensive catalysts from the reaction media
[21, 22]. However, uncoated MNPs are easily aggregate due
to their interparticle interaction, and high specifc area which
limits their utilization [23]. Therefore, it is necessary to use
chemical stabilization of the uncoated magnetic nanoparti-
cles against aggregation over a long period. Generally, MNPs
The mixed valance metal oxides with spinel structure have
the formula AB2O4, where A and B are the di and trivalent
metal ions occupying tetrahedral and octahedral sites of the
cubic crystal structure, respectively [1–3]. Over recent dec-
ades, zinc manganate with spinel structure (ZnMn2O4) has
attracted much attention due to its new properties and broad
applications in diferent felds such as catalysis[4], solid
electrolytes [5], magnetic resonance imaging[6], lithium-ion
batteries [7] and photocatalysis [8]. The ZnMn2O4 nanopar-
ticles (NPs) have been prepared by sol–gel, co-precipitation,
hydrothermal and solvothermal processes [7, 9–13]. How-
ever, these processes are expensive and use toxic solvents
[14]. Therefore, using green technologies for the preparation
of ZnMn2O4 NPs (such as using plant extracts) would be a
* Abbas Eslami
eslami@umz.ac.ir; eslami_a@yahoo.co.uk
1
Department of Inorganic Chemistry, Faculty of Chemistry,
University of Mazandaran, P.O. Box 47416-95447, Babolsar,
Iran
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
can be chemically coated by an inert shell such as silica [24]
to prevent particle aggregation and surface functionalization
[25]. Fe3O4 acts as a semiconductor with a band gap about
3.0 eV which provides sufcient capability to perform elec-
tronic transfers in the UV range, but no performance was
observed at the visible light range [26]. ZnMn2O4 can also
be considered as a semiconductor with a band gap of 2.3 eV
[5]. A composite of these two semiconductors (Fe3O4 and
ZnMn2O4) can be an efcient photocatalyst at visible range.
Furthermore, metalloporphyrins are known as the most
promising sensitizers for the light trapping process. Metal-
loporphyrins are remarkable photosensitizers due to their
broad π- electron systems, and high absorptivity at Soret
band range (400–450 nm) and Q bands range (500–700 nm)
[27]. The porphyrins and metal oxides can be bonded with
some functional groups such as hydroxyl, carboxylic acids.
The porphyrins with hydroxyl group and metal oxides can be
connected by hydrogen bonding between OH in porphyrin
and O in surface of metal oxides [28]. Organic dyes used in
textile industries are important sources of the environmental
contaminations because of their non-bio degradability, and
high toxicity and dangerous efects on humans and animals.
Methylene blue (MB) is a chemical compound with IUPAC
name 3,7-bis(dimethylamino)-phenothiazin-5-ium chloride,
and the molecular formula C16H18N3SCl. At room tempera-
ture, it is a solid, and a dark green powder that gives a blue
solution when dissolved in water [29]. In this study, for the
frst time, we immobilized copper meso-tetrakis (4-hydroxy-
phenyl) porphyrin (CuIITHPP) (Scheme1) on the Fe3O4@
SiO2@ZnMn2O4 (MZMO) nanocomposite, and a photocata-
lyst was synthesized with efcient photocatalytic capabil-
ity for degradation of MB in the visible light range in the
presence of blue visible-LED lamps. Because of magnetic
property of this nanocomposite, it can be recovered from the
environment and reused.
Experimental
Chemicals and solutions
Zinc acetate (Zn(OCH2CH3)2.2H2O), manganese acetate
(Mn(OCH2CH3)2.2H2O), iron(II) chloride tetrahydrate
(FeCl2.4H2O), pyrrole, iron(III) chloride hexahydrate
(FeCl3.6H2O), NH4OH (25%w/w), tetraethyl orthosilicate
and solvents were purchased from Merck company; only pyr-
role was distilled before use. The leaves of Aloe vera were
collected from the local agricultural felds, Mazandaran,
Iran.
Preparation of the Fe3O4@SiO2@ZnMn2O4 (MZMO)
First, the Fe3O4 nanoparticles were synthesized via chemi-
cal precipitation [30]. A mixture of 8 g (30 mmol) of
FeCl3.6H2O and 2.9 g (15 mmol) of FeCl2.4H2O dissolved
in 80 ml deionized water was refuxed at 85 °C under argon
fow for 4 h. The pH of the solution was adjusted to 9 using
NH4OH (25% w/w) solution; then, the mixture was cooled
at room temperature, and solids were washed by deion-
ized water to pH 7. The silica flm was lied on Fe3O4 to
create SiO2@Fe3O4 by the sol–gel procedure [31]. The
magnetite nanoparticles (1.0 g) were dispersed in ethanol
(200 ml). Then, NH4OH (25% w/w) (6 ml) and tetraethyl
orthosilicate (TEOS) (2 ml) were added successively. After
stirring for 24 h, the black sediment was separated by an
external magnetic feld and washed up with ethanol three
times. The black sediment was dried and kept in a vacuum
oven at 60 °C. Then, ZnMn2O4 nanoparticles were lied
on a silica layer by green chemistry. Forty grams of thor-
oughly washed Aloe vera leaves were cut, and the obtained
gel was stirred in 150 ml of deionized water and stirred
and heated for 45 min at 60–80 °C to obtain a clear solu-
tion. The resulting extract was used as an Aloe vera plant
Scheme 1 The chemical struc-
tures of THPP and CuIITHPP
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extract. The mixture “A” was prepared by mixing 0.439 g
(2 mmol) (Zn(OCH2CH3)2.2H2O) and 0.835 g (1 mmol)
(Mn(OCH2CH3)2.2H2O) with 150 ml Aloe vera plant
extract. The mixture “B” was provided by mixing 0.583 g
of Fe3O4@SiO2 with 50 ml of diluted water. After 30 min
ultrasonic action on the mixture “B”, it was added to the
mixture “A,” and the new mixture was stirred for 3 h at room
temperature and then it was boiled until it turned to brown
paste and dried at 80 °C in an electric oven. The prepared
particles were heated at 800 °C and held for 2 h in air to get
Fe3O4@SiO2@ZnMn2O4 (MZMO) nanocomposite.
performed on LEO-1455VP microscope (acceleration volt-
age 10 kV). FT-IR spectrum of the samples was recorded
by a FT-IR Bruker instrument. Difuse refectance UV-Vis
spectra (DRS-UV-Vis) were recorded on a Shimadzu (MPC-
2200) spectrophotometer. The X-ray diffraction (XRD)
measurement was carried out with a Bruker D8 difractome-
ter (Cu Kα irradiation) in the 2θ range 10–80°. The magnetic
properties of the samples were determined by the vibrating
sample magnetometer (VSM, Maghnatis Kavir Kashan Co,
Iran). A Bruker 400 MHz–Avance III spectrometer was used
for to obtain 1H NMR and 13C-NMR spectra.
Preparation of the Fe3O4@SiO2@ZnMn2O4@CuIITHPP
(MZMOCuP) nanocomposites
Investigation of photocatalytic activity
The photocatalytic activity of MZMO and MZMOCuP
nanocomposites (dosage=0.2 gL−1) in the degradation of
MB solution was investigated under visible light irradia-
tion. The light source used was four blue LED lamps (3 W)
(λ = 465 nm). The degradation of MB was performed at
room temperature and do not need cooling devices because
LED lamps do not produce heat. The oxygen was gently
bubbled into MB solution. Prior to irradiation, the MB solu-
tion was stirred in the dark for 30 min. After time interval,
1 ml MB solution was collected and separated with an exter-
nal magnetic feld (super magnet). The concentration of MB
was monitored by UV–Vis spectrophotometer.
The tetra hydroxyl phenyl porphyrin (THPP) was synthe-
sized according to the reported procedure previously [32].
The freshly distilled pyrrole and 4-hydroxybenzaldehyde
(7.5 mmol, 0.90 g) were refuxed in solvents of propionic
acid (80 ml), nitrobenzene (40 ml), glacial acetic acid
(40 ml) for 90 min at 150 °C. The copper metalloporphy-
rin (CuIITHPP) was prepared from refux of CuCl2·4H2O
and THPP in ethyl acetate according to the method of Adler
et al. [33]. The structure of THPP and CuIITHPP is shown
in Scheme 1. The mixture 1 was prepared by mixing 0.022 g
CuIITHPP in 20 ml absolute alcohol. The mixture 2 was pro-
vided by mixing 0.079 g MZMO in 25 ml absolute alcohol.
The amount of CuIITHPP used was adjusted to obtain a 0.3
wt% of CuIITHPP to MZMO. After 30 min ultrasonic action
on the mixture 1, it was added to the mixture 2. Then, the
resulted mixture was stirred for 24 h. After that, the solvent
was removed, and the sample washed several times with
deionized water in the presence an external magnetic feld
to separate the unreacted materials.
Results and discussion
Structural and morphology characteristics
FT-IR spectra of Fe3O4, Fe3O4@SiO2, CuIITHPP, MZMO
and MZMOCuP are shown in Fig. 1a–e. For all samples,
two peaks at 1640 and 3440 cm−1 are observed that related
to vibrations of adsorbed water molecules on the surface of
samples. In Fig. 1a, absorption peak at 570 and 452 cm−1
can be attributed to Fe–O stretching vibrations in Fe3O4
nanoparticles. For Fe3O4@SiO2 nanoparticles, the observed
two peaks at 810 and 1095 cm−1 can be related to stretching
vibrations of O–Si–O, and Si–O–H bonds (Fig. 1b). FT-IR
spectrum of CuIITHPP (Fig. 1c) shows absorption bands
at around 720, 796 and 1602 cm−1 related to porphyrin
skeletal and metal–ligand vibrations, also bands at 2850,
1640, 1550 and 1250 cm−1 can be related to C–H, O–H,
C=C and C–N stretching bands that are due to the pres-
ence of pyrrole and phenyl groups in this molecule. The
sharp peaks at about 400–500 cm−1 are related to the spinel
ZnMn2O4 and Fe–O that are the characteristic peaks of M–O
bonds (Fig. 1d). This result is good agreement with previous
studies [34]. The MZMOCuP nanocomposites have peaks
at around 462, 572, 510, 630,720, 796, 1250, 1550, 1600,
1640 cm−1 related to Fe–O, spinel ZnMn2O4 and porphyrin
1
THPP: HNMR (500 MHz, DMSO, δ/ppm, TMS ref-
erence): 7.989–8.010 (m, 8H, orto-H), 7.198–7.219 (m, 8
meta-H), 8.866 (s, 8 pyrrole-H), 9.983 (s, 4 OH), − 2.878
(br s, 2H, NH). 13CNMR (400 MHz, CDCl3, δ/ppm, TMS
reference): 114.383 (meso-C), 157.790 (α-C), 120.738 (β-
C), 132.237–136.070 (Aromatic carbons). Fourier trans-
form-infrared (FT-IR) (flm on KBr, ν/cm−1): 3426 (O–H),
3300 (N–H), 2923 (C–H), 1605 (C Aromatic), 1466 (C–N).
Visible (dichloromethane) λmax, (ꢀ = 3.2 × 105M−1cm−1):
Soret band (419 nm), Q band (645, 589,548 and 514 nm).
For CuIITHPP: FT-IR (flm on KBr, ν/cm−1): 3429(O–H),
2923(C–H), 1462 (C–N), 1605 (C Aromatic). Visible (chlo-
roform) λmax, (ꢀ = 3.2 × 105M−1cm−1): Soret band (414 nm),
Q band (538 nm).
Characterization
Scanning electron microscopy (SEM) analyses accompa-
nied by energy-dispersive X-ray spectrometry (EDS) were
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Fig. 1 FT-IR spectra of Fe3O4
(a) Fe3O4@SiO2 nanoparticles
(b) CuIITHPP (c) MZMO (d)
MZMOCuP nanocomposites (e)
skeletal vibrations, respectively (Fig. 1e). The XRD pat-
terns of prepared nanoparticles are shown in Fig. 2a–d. The
XRD pattern of Fe3O4 nanoparticles showed six character-
istic difraction peaks at 2θ of 30.2°, 35.5°, 43.2°, 53.6°,
57.1° and 62.7° corresponded to (220), (311), (400), (422),
(511) and (440) difraction plans, respectively, which are
in good agreement with the standard XRD data (JCPDS
No.19–0629). The mean crystallite size (D) of Fe3O4 nano-
particles is 20 nm that calculated from the half-width of the
(311) XRD peak using Debye–Scherrer formula D=0.89λ/β
cosθ, which λ is the wavelength of X-ray, θ is the difraction
angle of (311) peak, β is the half-width of the difraction
(311) peak. Silica-coated magnetite (Fe3O4@SiO2) shows
the same difraction peaks (Fig. 2b) of the pure magnetite
(Fe3O4) which indicated that the crystalline characteristic
of the magnetite is retained after the coating of the SiO2
layer. The XRD spectrum of MZMO is indicated in Fig. 2c,
which contains all difraction peaks of Fe3O4 and also there
Fig. 2 XRD pattern of Fe3O4
(a) Fe3O4@SiO2 (b) MZMO (c)
MZMOCuP nanocomposites (d)
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are other ten difraction peaks at 2θ of 29.3°, 31.2°, 33°,
36°, 38.9°, 50°, 52°, 59°, 61° and 65° which correspond to
(112), (200), (103),(211), (004), (204), (105), (321), (224)
and (400) difraction planes of cubic ZnMn2O4 with spinel
structure (JCPDS No. 24–1133). The mean crystallite size
(D) of ZnMn2O4 nanoparticles is 15 nm that calculated from
the half-width of the (211) XRD peak using Debye–Scherrer
formula. The XRD patterns of MZMOCuP nanocomposites
have all main peaks of Fe3O4 and ZnMn2O4 (Fig. 2d). This
result shows that the MZMO was coated with CuIITHPP, and
the presence of metalloporphyrin has no efect on the crys-
tal structure of MZMO nanocomposites. The morphology,
core–shell features and diameter of the prepared samples
were determined by SEM images (Fig. 3a–f). As shown in
Fig. 3a, Fe3O4 nanoparticles have spherical morphology and
diameter about 20–30 nm. The nanoparticles are relatively
well separated and show good homogeneity. The SEM imag-
ing of silica-coated magnetite (Fe3O4@SiO2) shows that
these nanoparticles are spherical and little agglomerated
with average size of 20–40 nm which is in good agreement
with the results of XRD analysis (Fig. 3b). The observed
few aggregates may be due to aggregation during the wash-
ing step. As shown in Fig. 3c, ZnMn2O4 nanoparticles lie
on silica-coated magnetic that their size is about 15 nm. It
can be seen from Fig. 3d that MZMOCuP is sphere-like and
minor-agglomerated with a size of 12 nm. Also, particle
size distribution of the samples (Fig. 4) was investigated
using ImageJ software which was in agreement with XRD
results. The elemental analysis of MZMO and MZMOCuP
nanocomposites was performed with EDS analysis that is
shown in Fig. 5a, b. This analysis revealed the presence of
the elements Fe, Si, O, Zn, Mn; and Fe, Si, O, Zn, Mn, C,
d, Cu in MZMO and MZMOCuP, respectively. The results
were clearly supported the loading of CuIITHPP on the sur-
face of the MZMO nanocomposites. The magnetic prop-
erties of prepared magnetic samples were measured by a
vibrating sample magnetometer (Fig. 6a–d). As shown in
Fig. 6, these hysteresis loops have a steep slope and do not
have remanence and coercivity, and therefore, all samples
indicate superparamagnetic behavior at room temperature.
The magnetic saturation value for Fe3O4 is 52 emug−1, and
after silica coating magnetic, magnetic saturation value for
Fe3O4@SiO2 is reduced to 39 emug−1. After ZnMn2O4 coat-
ing on Fe3O4@SiO2, magnetic saturation value is decreased
to 10 emug−1 and after CuIITHPP coating on MZMO nano-
composite is reduced to 8 emug−1. The UV–Vis-DRS spec-
tra of MZMO and MZMOCuP nanocomposites are shown in
Fig. 7A (a, b). The MZMO nanocomposite displayed absorb-
ance in the lower wavelength region than that in MZnCuP
nanocomposite which shows peak around 350 nm. Indeed, a
red shift of the absorption edge is observed for MZMOCuP
compare to MZMO nanocomposite. These changes can be
attributed to the presence of CuIITHPP in MZMOCuP which
Fig. 3 SEM images of Fe3O4 nanoparticles (a) Fe3O4@SiO2 (b)
MZMO (c) MZMOCuP nanocomposites (d)
causes a shift in optical absorbance edge from UV to UV-
Vis region. Figure 7B (a, b) depicts Tauc’s plot of MZMO
and MZMOCuP nanocomposites. The direct band gap is
calculated with following Tauc’s Eq. (1).
(
)
(ꢀ × hꢁ)n = A hꢁ − Eg
(1)
where hν and Eg are UV–Vis light photon energy and opti-
cal band gap of semiconductors. The power n signifes the
optional transition that can be 2 (indirect transition) or ½
(direct transition). Whereas ZnMn2O4 nanoparticles have
indirect transition, it was used from n = 2. Hence, this
result shows that MZMOCuP nanocomposite has more
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Fig. 4 Particle size distribu-
tion of Fe3O4 nanoparticles (a)
Fe3O4@SiO2 (b) MZMO (c)
MZMOCuP nanocomposites (d)
(a)
(b)
(c)
(d)
photocatalytic activity than MZMO nanocomposite under
light irradiation. Where α, h, ν, A and λ are absorption
coefcient, Plank’s constant, frequency of the photon, the
proportionality constant and wavelength, respectively. The
band gap energy of MZMO and MZMOCuP nanocompos-
ites was found 1.4 and 1.1 eV. The decrease in band gap
energy in MZMOCuP nanocomposite than MZMO nano-
composite can be the reason of the sensitizing efect of the
metalloporphyrin.
desorption equilibrium (2 h), MB solution was irradiated
by the blue LED light, and it was blowing by O2 until MB
dye degrades to smaller organic compounds, such as CO2
and H2O. The photocatalytic activity of synthesized nano-
composites for photodegradation of MB has been shown
with removal efciency diagram in Fig. 9 under dark and
blue Vis-LED light irradiation conditions. The dark condi-
tion was examined to estimate the adsorption properties
of synthesized photocatalysts. The results indicate that the
removal efciency of MB in the presence of Fe3O4@SiO2;
MZMO; and MZMOCuP was found to be 5% and 7%;
41%, and 72%; 50% and 98%, respectively, under dark and
blue Vis-LED light conditions. Figure 10 shows that after
complete establishment of adsorption–desorption equilib-
rium (120 min), no further decrease in absorbance was
seen, and then, the MB solutions were irradiated by visible
blue LED light with bubbling O2 until MB dye degrades.
The results show that MZMOCuP nanocomposite is more
efcient than MZMO nanocomposite. In fact, the results
revealed that irradiation of light, bubbling O2 and the pres-
ence of CuIITHPP are important parameters in enhancing
photodegradation of MB.
Catalytic activity
The photocatalytic activity of prepared nanocomposites
was examined for degradation of MB solution under the
blue Vis-LED lamps irradiation. In this study, several tests
have been conducted to determine the efective parameters
such as light, O2, concentration of the MB and the nature
of the catalyst on MB degradation. The time-dependent
UV–Vis spectra of MB photodegradation catalyzed by
prepared nanocomposites under blue Vis-LED light irra-
diation are exhibited in Fig. 8a and b. In these spectra,
frst bands are related to absorption of MB in the absence
of MZMO and MZMOCuP nanocomposites. The inten-
sity of frst bands is decreased in the presence of MZMO
and MZMOCuP nanocomposites in dark without oxygen
bubbling that it can be related to the adsorption of dye on
the nanocomposites. After establishment of adsorption/
As it can be seen, MZMOCuP nanocomposite showed
better photocatalytic activity with respect to MZMO and
pure Fe3O4@SiO2 nanoparticles. The removal efciency
of MB was calculated by Eq. (2):
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Journal of the Iranian Chemical Society
(a)
(b)
Fig. 5 EDS pattern of MZMO (a) MZMOCuP nanocomposites (b)
Fig. 7 (A) UV-DRS of the MZMO (a) MZMOCuP nanocom-
posites (b), (B) plot of (αhʋ)2 vs. photo energy (hʋ) of MZMO (a)
MZMOCuP (b) nanocomposites
A0 − Ai
Removal efficiency =
× 100%
(2)
A0
where A0 and Ai are the initial adsorption of MB in the
absence of photocatalyst and after degradation of MB in
the presence of photocatalyst and light irradiation at various
times, respectively. To indicate the advantage of this work in
comparison with recently reported photocatalysts, some of
the used photocatalysts in degradation of dyes are presented
in Table 1 [8, 34–38]. It is evident from Table 1 that the
present photocatalyst is superior to recently reported photo-
catalyst because of easy workup, recovery with an external
magnetic feld without fltering, mild condition reaction,
shorter time, visible light irradiation, elimination of homog-
enous photocatalyst. The prepared photocatalyst was stable,
recyclable, and indicated high yield of degradation.
Fig. 6 VSM curve of Fe3O4 (a) Fe3O4@SiO2 (b) MZMO (c)
MZMOCuP nanocomposites (d)
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(a)
(b)
Fig. 10 Photodegradation percent of dye solution MB using (a)
MZMOCuP catalyst in the presence of O2 and light (b) MZMOCuP
catalyst in the absence of O2 and light (c) MZMO catalyst in the pres-
ence of O2 and light (d) MST catalyst in the absence of O2 and light
(e) Only in the presence of O2 (no catalyst) (f) Only in the presence of
light (without catalyst and O2)
Mechanism
A possible mechanism of photodegradation of MB is indi-
cated in Scheme 2. It well known that the band gap value of
Fe3O4@SiO2 nanoparticles is in the range of UV light (about
3 eV) [26, 39]. Whereas the band gap value of ZnMn2O4
is in the range of visible light (about 2 eV) [5, 40]. The
band gap value was decreased to 1.1 eV in the presence of
copper porphyrin (CuIITHPP), and therefore, it can enhance
the absorption of visible light. As be shown in Scheme 2,
under irradiation of blue LED light, the electrons in val-
ance band (VB) of CuIITHPP are excited to the conduction
band (CB) and generate holes in VB. Because CB levels of
ZnMn2O4 and Fe3O4@SiO2 are lower than CB of CuIITHPP,
photoexcited electrons can be transferred to CB of ZnMn2O4
and Fe3O4@SiO2. The photoexcited electrons can reduce
Fig. 8 The absorbance changes vs. wavelength (nm) for MB (6 ppm)
on the surface of (A) MZMO, (B) MZMOCuP nanocomposites in the
absence of photocatalyst (a) in the presence of photocatalyst and dark
(b) in the presence of photocatalyst and blue Vis-LED light 90 min
(c) 180 min (d)
◦
−
molecular oxygen to superoxide radical (O2 ). The generated
radicals can degrade MB [41]. Important reactions involved
in photosensitization are listed in Eqs. (3)–(7)[42].
(
)
CuIITHPP + hꢀ → CuIITHPP1∗ → CuIITHPP3∗ e− + h+
CB
VB
(3)
(4)
(
)
◦
CuIITHPP3∗ + 3O2 e−CB → CuIITHPP+ + O2
−
H2O + h+VB → OH◦ + H+
(5)
(6)
◦
−
MB + O2 → Degradation products
Fig. 9 Photodegradation percentage of MB removal in the presence
of Fe3O4@SiO2 nanoparticles, MZMO and MZMOCuP nanocompos-
ites under dark and Vis-LED light conditions
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Table 1 Comparison of prepared photocatalyst with the other photocatalysts
Entry Pollutant
Catalyst system
ZnMn2O4
Reaction condition
Yield (%) Refs.
1
2
Rhodamine B
500 W high pressure xenon lamp, dose catalyst=1000 mg/L, 92
3 h
[8]
Methyl orange
TiO2 +ZnMn2O4
Medium pressure mercury lamp, dose cata-
65
[34]
lyst=900 mg/L,180 min
3
4
RY 86 dye
Rhodamine B
ZnFe2O4
Under UV light, H2O2, 50 min, dose catalyst=2 g/L, pH=4 94
[35]
[36]
ZnO/TAPPI–CoTPPS 1000 W halogen–tungsten lamp, dose catalyst 2 g/L,
98
120 min, pH=7
5
6
Rhodamine B
CuPp–ZnO
400 W halogen lamp, 200 mg/L, 200 min, H2O2
92
[37]
[38]
MB, 4-nitrophenol (4-NP) TCPP/ZnFe2O4@ZnO 5 W LED lamps, 200 mg/L (MB), 50 mg/L(4-NP), 3 h, H2O2 98
67
7
MB
Fe3O4@SiO2@
ZnMn2O4@CuI-
ITHPP
3 W Vis-LED lamp, 180 min, bubbling O2, catalyst
dose=100 mg/L
98
This work
Scheme 2 The suggested
mechanism of photodegradation
of MB by MZMOCuP nano-
composite
MB + OH◦ → Degradation products
Conclusion
(7)
Fe3O4@SiO2@ZnMn2O4@CuIITHPP (MZMOCuP) nano-
composite with improved photocatalytic activity was suc-
cessfully synthesized using mixing of Fe3O4@SiO2, zinc
acetate and manganese acetate with Aloe vera extract solu-
tion to form Fe3O4@SiO2@ZnMn2O4 (MZMO) and then
immobilization of copper porphyrin (CuIITHPP) on its
The studied nanocomposites in this work were easily recov-
ered due to their magnetic behavior at room temperature.
The removal efciency of MB for frst, second, third and
fourth runs were 98, 87, 79, 75% for MZMOCuP and 72,
68, 65, 63% for MZMO nanocomposites, respectively. These
results showed that removal ability of MZMOCuP is rela-
tively higher than that of MZMO.
1 3

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to be active for degradation of MB under irradiation of
blue Vis-LED light and in the presence of O2 at neutral
pH. MZMO and MZMOCuP nanocomposites showed the
band gaps of 1.4 eV and 1.1 eV. The presence of copper
porphyrin in MZMOCuP nanocomposite increases photo-
catalytic activity for MB degradation. MB degraded 98%
on MZMOCuP after 180 min blue LED light irradiation.
The photocatalysts were easily separated from solution
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