Synthesis of polymer-supported Br?nsted acid-functionalized Zn–porphyrin complex, knotted with benzimidazolium moiety for photodegradation of azo dyes under visible-light irradiation

Article abstract of DOI:10.1007/s11164-019-03990-2

Abstract: A polymer-supported Br?nsted acid-functionalized Zn–porphyrin complex, knotted with benzimidazolium moiety (PSBAZnPP), has been synthesized and characterized by Fourier transform nuclear magnetic resonance (FT-NMR) and Fourier transform infrared spectroscopy (FTIR). The thermal stability was determined by thermogravimetric analysis (TGA), and surface morphology and elemental composition were investigated by scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDAX). The heterogeneous PSBAZnPP showed high efficacy as a photocatalyst for degradation of azo dyes, such as methyl red (MR), methyl orange (MO) and Congo red (CR), in the presence of visible-light irradiation at ambient condition using atmospheric air/H₂O₂. The concentration of the dyes was measured by UV–visible spectroscopy, and the degradation of the dyes was confirmed by GC–MS analysis. Further decolorization and degradation of MO were confirmed by using ultra-high-pressure liquid chromatography (UPLC). The optimum degradation was achieved by adding 10?mg catalyst for all azo dyes for 60?min in the presence of air. The effect of scavengers was studied to indicate the most active species generated during photocatalysis. PSBAZnPP furnished a good response toward the photodegradation of MR, MO and CR under optimized conditions. Finally, the mechanism of photocatalytic degradation process was suggested. Relevant active species produced in the PSBAZnPP/H₂O₂ or PSBAZnPP/air system under visible light were recognized by using different types of scavengers, viz. EDTA, p-benzoquinone (PBQ), terephthalic acid (TPA), sodium azide and sodium nitrate, for determination of formation of holes, O2·, OH ^·, ¹O ₂ and an aqueous electron (e^?), respectively. The comparative acidity of the synthesized PSBAZnPP catalyst was measured using UV–Vis and then equated to relations of the Hammett value (H₀). The efficiency of catalyst correlates with a considerable proton level required for degradation of organic dyes. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11164-019-03990-2

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03990-2
Synthesis of polymer‑supported Brønsted
acid‑functionalized Zn–porphyrin complex, knotted
with benzimidazolium moiety for photodegradation of azo
dyes under visible‑light irradiation
Vijay B. Khajone1 · Pundlik R. Bhagat1
Received: 25 July 2019 / Accepted: 18 September 2019
© Springer Nature B.V. 2019
Abstract
A polymer-supported Brønsted acid-functionalized Zn–porphyrin complex, knotted
with benzimidazolium moiety (PSBAZnPP), has been synthesized and characterized
by Fourier transform nuclear magnetic resonance (FT-NMR) and Fourier transform
infrared spectroscopy (FTIR). The thermal stability was determined by thermogravi-
metric analysis (TGA), and surface morphology and elemental composition were
investigated by scanning electron microscopy and energy-dispersive spectroscopy
(SEM/EDAX). The heterogeneous PSBAZnPP showed high efcacy as a photocat-
alyst for degradation of azo dyes, such as methyl red (MR), methyl orange (MO)
and Congo red (CR), in the presence of visible-light irradiation at ambient condition
using atmospheric air/H2O2. The concentration of the dyes was measured by UV–
visible spectroscopy, and the degradation of the dyes was confrmed by GC–MS
analysis. Further decolorization and degradation of MO were confrmed by using
ultra-high-pressure liquid chromatography (UPLC). The optimum degradation was
achieved by adding 10 mg catalyst for all azo dyes for 60 min in the presence of air.
The efect of scavengers was studied to indicate the most active species generated
during photocatalysis. PSBAZnPP furnished a good response toward the photodeg-
radation of MR, MO and CR under optimized conditions. Finally, the mechanism
of photocatalytic degradation process was suggested. Relevant active species pro-
duced in the PSBAZnPP/H2O2 or PSBAZnPP/air system under visible light were
recognized by using diferent types of scavengers, viz. EDTA, p-benzoquinone
(PBQ), terephthalic acid (TPA), sodium azide and sodium nitrate, for determina-
⋅
⋅
−
1
tion of formation of holes, O , OH , O2 and an aqueous electron (e ), respectively.
2
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-019-03990-2) contains supplementary material, which is available to authorized users.
*
Pundlik R. Bhagat
drprbhagat111@gmail.com
1
Department of Chemistry, School of Advanced Science, Vellore Institute of Technology,
Vellore, Tamil Nadu 632014, India
Vol.:(0123456789)
1 3

V. B. Khajone, P. R. Bhagat
The comparative acidity of the synthesized PSBAZnPP catalyst was measured using
UV–Vis and then equated to relations of the Hammett value (H0). The efciency
of catalyst correlates with a considerable proton level required for degradation of
organic dyes.
Graphic abstract
e -
Dye*
- Atm.
O2
Reducꢀon
e -
e -
1O2
e -
e -
-
O2
CB
VB
OH,
Reducꢀon
H2O2
OH⁻ + H⁺
Dye
h+
h+
H2O
+
Dye
PSBAZnPP
5W LED lamp
5W LED lamp
Keywords Zinc–porphyrin · Benzimidazolium · Azo dye degradation ·
Photocatalyst · Heterogeneous · Brønsted acid · Visible light · Hammett acidity
Introduction
The quantity of organic dye contaminants in wastewater has been increased radi-
cally in the last decades due to their extensive application in textile industry, in
leather and tanning industry, in paper production, in food technology, in agricultural
research, in light-harvesting arrays, in photoelectrochemical cells and in hair color-
ants [1–4]. Several techniques are available such as physical, biological and chemi-
cal methods to remove dyes from water. The physical methods such as adsorption,
ion exchange and fltration, the biological methods such as aerobic or anaerobic deg-
radation and the chemical methods including coagulation/focculation, Fenton rea-
gent technique, ozonization and photocatalytic methods played a vital role in the
removal of dyes. [5–9]. As physical methods often sufer from high costs and low
capability, for the chemical methods, the catalysts are generally difcult to recycle,
easy to aggregate and less efcient and may cause secondary pollutants. Therefore,
exploring new highly efcient visible-light-driven photocatalysts has been attract-
ing attention for the diminution of water pollution caused by dyes. Since the previ-
ous decade, photocatalytic degradation has been recognized to be an encouraging
technology for degrading organic pollutants because of its exploited solar energy
in resolving energy depletion and global ecological problems. The commercial
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
performance of the photocatalytic process is strongly reliant on the photosensitizer
materials. Till to date, inorganic semiconductors, such as TiO2, V2O5, ZnO, WO3,
CdS, ZrO2 and their saturated forms [10], have been verifed for their applications
in dye degradation. Conversely, the quick recombination of photogenerated elec-
tron–hole pairs and the incompetence to utilize visible light restrains their photo-
catalytic efciency and practical utility. Thus, evolving novel, highly efective visi-
ble-light-driven photocatalysts has been one of the most prominent topics to address
the exceeding problem [11]. Porphyrins and metalloporphyrins are functional mol-
ecules containing large p-conjugated organic molecules with very high extinction
coefcients in the visible-light region with potential photochemical electron transfer
ability. The photocatalyst has diverse applications such as luminant optoelectronic,
supramolecular self-assembly, solar energy-harvesting systems, photonic materi-
als and therapeutics [12–16] and acts as highly efcient photosensitizers for pho-
tocatalysts [17, 18]. As compared to the other techniques, photocatalysis is one of
the unique methods for resolving energy and environmental problems due to several
benefts such as low cost, facile process and high efectiveness. The photocatalysts
have the potential ability to remove the aromatic content such as phenolic pollutants
and benzene derivatives containing organic pollutant [19–25]. Among the photo-
catalysts, porphyrin (PP) and its derivatives are one of the best technologies for the
total removal of dyes from wastewater under visible light. The porphyrin (PP) ring
afords a vacant site at its center, perfectly suitable for metal combination. Moreo-
ver, porphyrins (PPs) possess a wide variety of photochemical and redox properties,
which can be easily modifed by peripheral substituent modifcations or metal com-
plexation. Hence, porphyrins have been usually considered as excellent photosen-
sitizers for photocatalysts. For example, TCPP/ZnFe2O4@ZnO nano-hollow sphere
composite has been reported for degradation of methylene blue and 4-nitrophe-
nol under visible light [26]. In short, a variety of processes are used to remove the
organic dyes, including electrochemical treatment, oxidation reduction, liquid–liquid
extraction, surface adsorption, etc. Photocatalytic removal is an efcient means to
decompose these pollutants [27]. Photocatalytic activity of a porphyrin/TiO2 com-
posite system has been designed and verifed to show improved visible-light photo-
catalytic activity in the photodegradation of famotidine under both visible-light and
solar light irradiation [28]. Subsequently, an enhancement of its photodegradation
of MB under visible-light irradiation was scrutinized by copper (II) meso-tetra(4-
carboxyphenyl) porphyrin (CuTCPP)-sensitized nano-TiO2 particles, CuTCPP–TiO2
[29]. Porphyrins (PPs) and their derivatives, as small molecules, are difcult to be
separated from wastewater after dyes decomposition, which supports in a secondary
pollution [30]. Thus, it is essential to develop heterogeneous and efcient photocat-
alysts in wastewater degradation system. Considering the remarkable feature, star-
shaped poly(N-isopropylacrylamide) (ZnTHPP-PAM) with zinc–porphyrins core
was synthesized [31] and investigated for the oxidative degradation of methylene
blue in aqueous medium. A novel silica microsphere functionalized with 5-(4-ally-
loxy) phenyl-10,15,20-tri(p-sulfonatophenyl) porphyrin (APTSPP), SiO2-S-APTSPP
and catalyst with high stability and reusability have been synthesized [32]. The het-
erogeneous catalyst demonstrated visible-light photocatalytic activity for the pho-
tooxidation of 1,5-dihydroxynaphthalene (DHN) in water. However, to the best
1 3

V. B. Khajone, P. R. Bhagat
of our knowledge, there are no reports concerning polymer-supported Brønsted
acid-functionalized Zn–porphyrin complex, knotted with benzimidazolium moiety
(PSBAZnPP) as heterogeneous photocatalyst in photodegradation of azo dyes from
the wastewater under visible light. Herein, for the frst time, we have designed and
synthesized polymer-supported Brønsted acid-functionalized Zn–porphyrin com-
plex, knotted with benzimidazolium moiety for photodegradation of azo dyes under
visible-light irradiation with excellent chemical and thermal stability.
Experimental details
Materials
Sodium chloride (98%) and propionic acid (97%) were purchased from Avra Pvt
Ltd. Hydrochloric acid (35.8–38.0%), sodium sulfate (99.5%) and methanol (99.9%)
were acquired from Fisher Scientifc. Formaldehyde solution (37–41% w/v AR)
and sodium hydride (60% dispersion in parafn oil) were purchased from SDFCL.
Zinc chloride anhydrous (97%), 4-vinylbenzyl chloride (90%), chloroform-d (99.8
atom % D for NMR spectroscopy), CDCl3 and 3-bromopropionic acid (97%) were
obtained from Sigma-Aldrich. Benzimidazole, pyrrole (99%), tetrahydrofuran
(99.5%), methyl red (98%), methyl orange (98%) and Congo red (98%) were sup-
plied by Spectrochem. Dimethyl sulfoxide-d6 (DMSO-d6, deuteration degree min
99.8% for NMR spectroscopy) and acetonitrile (99.8%) were received from Merck.
Chloroform, ethyl acetate (99%) and salicylaldehyde (99%) were obtained from
Sisco Research Laboratories Pvt. Ltd. α, α-Azoisobutyronitrile (98%) was purchased
from LOBA Chemie. All the reagents were used without further purifcation unless
otherwise noted. Crompton (B 22) 5 W LED lamp and aquarium air pump (AP-208)
(Venus Aqua) were obtained from the local shop.
Characterization techniques
1H NMR spectra were recorded on a Bruker spectrometer operating at 400 MHz at
ambient temperature, using DMSO-d6 and CDCl3 as solvent and TMS (δ=0.00) for
1H calibration. FTIR spectra were obtained from IR afnity Shimadzu FTIR spectro-
photometer using KBr pellet method. Surface morphology and the elemental com-
position of the complex were investigated by scanning electron microscope (SEM)
along with energy-dispersive X-ray (EDAX) spectroscopy (Carl Zeiss EVO/18SH,
UK). An accelerating voltage of 10 kV was applied to obtain SEM images. Thermal
stability of PSBAZnPP was confrmed using TGA thermoanalyzer SII, 7200 (Seiko,
Japan). A UV–Vis–NIR spectrophotometer (Jasco ISN-723, Sr. No. B 072061154,
made in Japan) was used to evaluate dye degradation, DRSs and Hammett acidity
of metal complex. The Sample Manager-FTN Acquity H UPLC Water (PDA eλ
detector) was used to analyze the colorants in dye samples, and GC–MS analysis
(by a Perkin Elmer Clarus 600 C mass spectrometer) was performed to confrm the
degradation. pH was measured using a pH meter supplied by a Digital pH meter
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
MK VI, and melting point was determined using an instrument supplied by Guna
Enterprises.
Synthesis and characterization of PSBAZnPP complex
Synthesis of intermediates 1-(sec-butyl)-4-(chloromethyl) benzene (PVBC) 1a,
1-(4-vinylbenzyl)-1H-benzimidazole (PVBIM) 1b, 5-(chloromethyl)-2-hydroxyben-
zaldehyde (CMSA) 1c and 5-(1-H-benzo[d]imidazole-1-yl) methyl)-2-hydroxyben-
zaldehyde (BMSA) 1e was successfully carried out by the methods adapted from
studies [33–36] and confrmed by the spectral analysis and was matched with those
of the literature report (Supporting Ref no. S3–S4 of 1a, S4–S6 of 1b, S8–S9 1c and
S12–S13 1e).
Synthesis of poly 1‑(4‑(sec‑butyl) benzyl)‑3‑(3‑formyl‑4‑hydroxybenzyl)‑1H‑benzo
[d] imidazol‑3‑ium chloride—1d
The mixture of poly 1-(4-s-butyl) benzyl)-1H-benzo[d]imidazole (5.284 g,
20 mmol) (1b) and 5-(chloromethyl)-2-hydroxybenzaldehyde (3.411 g, 20 mmol)
(1c) was transferred to a 100-mL round-bottom fask in acetonitrile medium. The
reaction mixture was kept at room temperature with controlled stirring for 24 h. The
precipitated compound was washed with diethyl ether (3×15 mL) to acquire white
powder of 1d [35]. Yield: 68.99%. M.P.=185–198 °C.
1H NMR (400 MHz, DMSO-d6): δ 0.52 (s, 1H), 0.74 (br. 1H), 1.08 (br. 1H),
1.29 (s, 1H), 1.92 (s, 1H), 5.65 (s, 4H), 7.36 (br. 6H), 7.73 (br. 1H), 10.13 (d, 2H,
J=8.97 Hz), 15.79 (br. 1H). 13C NMR (100 MHz, DMSO-d6): 190.77, 161.74,
159.18, 136.94, 135.46, 131.29, 129.18, 127.15, 122.94, 118.64, 114.49, 49.76.
FTIR—(KBr, v/cm−1): 3377.36, 3018.60, 2926.01, 1654.92, 1612.49, 1558.48,
1487.12, 1444.68, 1371.39, 1282.66, 1249.87, 1188.15, 1151.50, 1016.49,929.69,
842.89, 744.52, 698.23, 632.65, 540.07, 497.63, 424.34.
Synthesis of 3‑(2‑carboxyethyl)‑1‑(3‑formyl‑4‑hydroxybenzyl)‑1H‑benzo[d]
imidazol‑3‑ium bromide—1f
The synthesis of 3-(2-carboxyethyl)-1-(3-formyl-4-hydroxybenzyl)-1H-benzo[d]
imidazol-3-ium bromide was carried out according to [36] with slight modifcation.
The toluene solution (50 mL) of (1e) (7.56 g, 30 mmol) was stirred for 1 h at 60 °C.
To this, 3-bromopropionic acid (6.08 g, 40 mmol) in toluene was added dropwise for
30 min and continuously stirred for another 14 h at 85 °C. The desired whitish solid
product obtained was separated by decantation of toluene and washed with diethyl
ether (3×15 mL). Yield: 73.33%. M.P.=205 °C.
1H NMR (400 MHz, DMSO-d6): δ 2.63 (s, 2H), 4.33 (s, 2H), 5.35 (s, 2H), 6.67
(s, 1H),7.15 (s, 1H), 7.29 (s, 1H), 7.50 (d, 1H, J=19.52 Hz), 7.75 (s, 1H), 9.24 (s,
1H), 9.58 (s, 1H), 9.88 (s, 1H), 10.55 (s, 1H), 12.32 (1H, br), 15.58 (1H, br), 13C
NMR (100 MHz, DMSO-d6): 190.97, 172.31, 161.49, 161.32, 142.40, 142.57,
136.53, 129.55, 127.12, 126.01, 125.24, 122.90, 118.48, 116.31, 114.47, 114.34,
1 3

V. B. Khajone, P. R. Bhagat
113.51, 65.36, 49.56, 33.21, 15.63. FTIR—(KBr, v/cm−1): 3360, 3120, 1720, 1560,
1440, 1249, 1184, 1128, 989, 823, 744, 626, 495.
Synthesis of 1,1′1″‑(((20‑(5‑((3‑(4‑(sec‑butyl)benzyl)‑1H‑benzo[d]
imidazole‑3‑ium‑1‑yl)methyl)‑2‑hydroxyphenyl)porohyrin‑5,10,15‑triyl)
tris(4‑hydroxybenzene‑3,1‑diyl))tris (methylene)) tris(3‑(2‑carboxyethyl)‑1H‑benzo
[d]imidazole‑3‑ium) tribromide chloride (PSBAPP) ligand—1g
The mixture of 3-(2-carboxyethyl)-1-(3-formyl-4-hydroxybenzyl)-1H-benzo[d]
imidazol-3-ium bromide (1f) (3.039 g, 7.5 mmol) and 1-(4-(sec-butyl)benzyl)-3-
(3-formyl-4-hydroxybenzyl)-1H-benzo[d]imidazol-3-ium chloride (1d) (1.01 g,
2.5 mmol) was stirred in propionic acid (20 mL) at 60 °C for 30 min. To this mix-
ture, pyrrole (0.67 g, 10 mmol) in propionic acid (15 mL) was added dropwise for
30 min and continuously stirred for 45 min at 130–140 °C. The desired purple solid
product obtained was separated by the removal of two-thirds propionic acid using
a rotary evaporator and further more washed with methanol followed by diethyl
ether (3×15 mL) to achieve 1 g. Yield: 71.99%. M.P.=above 250 °C [38]. The NH
protons inside the ring of porphyrins acquire acidic character and therefore can get
deprotonated to provide porphyrin to ions [26].
1H NMR (400 MHz, DMSO-d6): δ -1.006 (s, 2H), 0.05 (t, 5H, J=7.62 Hz), 0.24
(s, 2H), 1.21(q, 3H, J=7.88 Hz), 1.54 (s, 3H), 1.99 (q, 2H, J=6.1 Hz), 3.74 (q, 3H,
J=7.21 Hz), 4.72 (brs, 5H), 6.17 (s, 7H), 6.57 (m, 9H), 6.69 (q, 4H, J=3.17 Hz),
6.84 (q, 7H, J=3.00 Hz), 6.98 (d, 4H, J=8.58 Hz), 7.07 (q, 4H, J=3.19 Hz), 7.10
(s, 5H), 8.49 (s, 6H), 8.86 (s, 2H), 12.21 (s, 2H). FTIR—(KBr, v/cm−1): 3026, 2929,
1712, 1610, 1560, 1502, 1438, 1330, 1255, 1182, 991, 827, 744, 601, 464.
Synthesis of 1,1′1″‑(((19‑(5‑((3‑(4‑(sec‑butyl)benzyl)‑1H‑benzo[d]
imidazole‑3‑ium‑1‑yl)methyl)‑2‑hydroxyphenyl)‑12,13‑dihydro‑1
12H,32H‑11λ2‑1(12,3)‑1λ2‑5,8‑(azeno)pyrrolo[1,2‑b] [1] zinc [2, 11]
diazacycloundecina‑3(5,2)‑pyrrolacycloheptaphan‑5‑ene‑14,2,4‑triyl)tris
(4‑hydroxybenzene‑3,1‑diyl))tris(methylene))tris(3‑(2‑carboxyethyl)‑1H‑benzo[d]
imidazole‑3‑ium)tribromide chloride (PSBAZnPP) complex—1h
Polymer-supported Brønsted acid-functionalized Zn–porphyrin complex, knotted
with benzimidazolium moiety (PSBAZnPP) complex, was accomplished by slightly
modifying the method reported in the literature [42]. The PSBAPP ligand-1e
(0.903 g, 0.5 mmol) and ZnCl2 (0.097 g, 0.6 mmol) were added to a mixture of chlo-
roform and methanol (3:1), and the content was stirred initially for 30 min at room
temperature. The whole content was then refuxed at 75 °C for 5 h under nitrogen
atmosphere. The product was easily separated after the reaction by periodic washing
with methanol and dried in an oven at 80 °C for 2 h, to get purple color powder of
PSBAZnPP complex 1 h (Scheme 1). Yield: 79.93%. M. P.=above 250 °C.
FTIR—(KBr, v/cm−1): 3248, 1714, 1608, 1562, 1506, 1438, 1259, 1189, 1132,
993, 829, 746, 592, 505, 422.
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
Scheme 1 Synthesis of polymer-supported Brønsted acid-functionalized Zn–porphyrin complex, knotted
with benzimidazolium moiety
1 3

V. B. Khajone, P. R. Bhagat
Results and discussion
Catalyst characterization
As shown in Fig. 1a, FTIR spectra of ligand (PSBAPP) and Zn complex
(PSBAZnPP) were recorded in the range of 4000–400 cm−1. The spectra of
PSBAPP and PSBAZnPP were compared to confrm the coordination side
involved in the formation of the complex. The absorption band appearing in
the range 3600–2700 cm−1 in the spectrum of ligand corresponds to NH from
the porphyrin core and O–H of carboxylic acid. However, the slight change in
absorption band in metal complex of IR may be due to involvement of N–H from
the porphyrin core and the broad band due to free OH from carboxylic group is
not afected. The peak appearing in both ligand and metal complex in the range of
1700–1750 cm−1 belongs to C=O of carboxylic group.
(a)110
100
90
(b)
PSBAZnPP
PSBAPP
PSBAZnPP
1.0
0.9
0.8
0.7
0.6
0.5
- N
H
80
180
160
140
120
100
80
PSBAZnPP
70
60
-C=C
50
60
40
40
20
2.33 eV
0
30
-20
0
2
4
6
h
8
(eV)
10
12
14
20
-C=C
250
500
750
1000
1250
1500
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavelength (nm)
Wavenumber(cm
)
Element Weight% Atomic%
(d)100
C K
N K
O K
Br L
69.61
8.84
11.80
6.15
89.92
9.79
11.44
1.19
(c)
4.94%
at 29-223
Totals
100.00
90
80
70
60
50
40
II
I
Elemen Weight Atomic
t
%
%
C K
O K
Cl K
Zn L
69.07
16.73
5.47
81.29
14.78
2.18
53.28%
at 223-791
5.22
1.13
Totals
100.00
III
IV
0
100 200 300 400 500 600 700 800
Temperature (°C)
SEM-A (SAG-35)LIGAND, EDIX-B, SEM-C (SAG-36) METAL COMLEX, EDIX-D
Fig. 1 Characterization of the PSBAZnPP: a FTIR spectra of the PSBAPP and PSBAZnPP complex, b
UV–Vis and DRS of PSBAZnPP, c SEM/EDAX of the PSBAPP (I/II) and PSBAZnPP (III/IV) and d
thermogravimetric analysis of the PSBAZnPP
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
The optical properties of photocatalysts were examined by UV–Vis difuse refec-
tance spectra (DRSs) spectroscopy used as a solid sample in catalysis, and we have
calculated band gap of hole and electron 2.33 eV (Fig. 1b).
Surface morphology and the elemental composition of PSBAPP and PSBAZnPP
were studied by scanning electron microscope along with energy-dispersive X-ray
(SEM/EDAX) spectroscopy (Fig. 1c). The surface morphology of PSBAZnPP
as shown in Fig. 1c (III) compared with the ligand as shown in Fig. 1c (I) clearly
showed that the change in surface morphology may be due to formation of Zn–por-
phyrin complex. Moreover, the elemental data from EDAX displayed the presence
of Zn in PSBAZnPP as shown in Fig. 1c (IV) which is clearly shown in metal com-
plex present in zinc metal, compared with the ligand as shown in Fig. 1c (II). The
metal complex was found to have the small heterogeneous particles deposited all
over the surface.
The thermal stability of the PSBAZnPP was studied by thermogravimetric anal-
ysis (TGA), as illustrated in Fig. 1d. The TGA disclosed that the catalyst follows
three-step degradation patterns. The frst weight loss 4.94% below 223 °C may be
due to adsorbed solvent. The second weight loss (53.28%) in the range 223–791 °C
belongs to degradation of Zn–porphyrins core. Furthermore, the weight loss above
250 °C may be due to crumble of carboxylic benzimidazole and polymer-substituted
benzimidazole. The TGA results confrmed that the catalyst is stable up to 250 °C
and applicable for high-temperature reaction.
Photocatalytic degradation experiments
The dye concentration was prepared in ppm concentration tested by using UV–Vis
spectroscopy, the standard plot was drawn, and R-square value of dyes MR of 0.95
(Fig. 2a), MO of 0.97 (Fig. 2b) and CR of 0.95 (Fig. 2c) was analyzed.
Photocatalytic degradation of organic pollutants assisted by PSBAZnPP
The photodegradation of MR (3a), MO (3b) and CR (3c) (Fig. 3) under visible light
(5 W LED) and air/H2O2 at specifed pH was used as a probe to evaluate the per-
formance of photocatalyst PSBAZnPP (Fig. 4). PSBAZnPP-enhanced visible-light-
driven photocatalysis was assessed by studying various parameters with and without
0.18
0.16
0.14
0.12
0.10
0.08
0.06
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.055
0.050
0.045
0.040
0.035
0.030
0.025
0.020
y
= a + b*x
Equation
Weight
Residual Sum
of Squares
Congo Red
No Weighting
2.459E-4
Methyl Orenge
Methyl Red
Linear Fit of Sheet1 B
Linear Fit of Sheet1 B
Linear Fit of Sheet1 B
0.98133
0.95067
Pearson's
Adj. R-Square
r
Value
0.0353
0.01265
Standard Error
0.0095
0.00143
Intercept
Slope
B
B
R-Square = 0.9518
10
R-Square = 0.9790
10
R-Square = 0.9506
10
2
4
6
8
2
4
6
8
2
4
6
8
Concentration (ppm)
Concentration (ppm)
Concentration (ppm)
(a)
(b)
(c)
Fig. 2 R2 value of the methyl red (a), methyl orange (b) and Congo red (c)
1 3

V. B. Khajone, P. R. Bhagat
(a)
(b)
(c)
Fig. 3 Structure of the methyl red (a), methyl orange (b) and Congo red (c)
H2O2 and air at specifed pH. The light source 5 W LED lamp (Havells, White B22)
equipped with household table lamp was used to provide visible light (λ≥400 nm).
The distance between the sample and the lamp housing exit was 15 cm. The photo-
catalyst PSBAZnPP with MR, MO and CR was studied as the model system, and
10 mg catalyst was added to 25 mL MR, MO and CR 10 ppm solution (Table 1;
Fig. 4a). A certain amount of HCl (0.01%) was then added to the reaction mixture
maintaining the initial pH at 5, 6 and 7 (Figs. S23–S25). The same protocols were
used to evaluate catalyst loading. The efect of pH, air and H2O2 for the degradation
of all the dyes was investigated. Prior to irradiation, the photocatalyst/organics sus-
pension systems with or without air/H2O2 were stirred at 400 rpm in the dark for 1 h
to maintain adsorption/desorption equilibrium. At certain time intervals, a defnite
volume of the suspension sample was collected and centrifuged for the subsequent
analysis. The concentrations of MR and MO were analyzed at 465 nm and at CR
500 nm, using UV–Vis spectrophotometer. The optimization of photodegradation
was achieved by altering the process parameters. Photodegradation of dyes in simu-
lated sunlight was studied by varying a parameter and fxing another initial param-
eter value. After the accustomed parameter condition is attained, this parameter
value is used for the subsequent parameter study. Initially, to optimize the reaction
parameters such as air (Table 1, entries 1–17; Fig. 4a–c) and H2O2 (Table 2, entries
1–17; Fig. 4d–f), the photodegradation of MR, MO and CR in the presence of dif-
ferent quantities of catalyst at ambient temperature under simulated sunlight was
attempted. In the absence of catalyst, only 13.78% of MR, 7.09% of MO and 20.58%
of CR were degraded under air irradiation in 60 min (Table 1, entry 12; Fig. 4c).
The photodegradation of MR, MO and CR in the presence of variable catalyst load-
ing at ambient temperature under simulated visible light was carried out (Table 1,
entries 1–5; Fig. 4a). It was found that 88.88% of MR, 64.74% of MO and 74.11%
of CR removal were achieved with the addition of 5 mg PSBAZnPP (Table 1, entry
1; Fig. 4a). The further improvement was achieved 7.5 mg photocatalyst, where
94.93% of MR, 89.65% of MO and 79.41% of CR (Table 1, entry 2; Fig. 4a). Deg-
radation achieving the enhancement was more evident at higher catalyst concentra-
tions, where 95.07% of MR, 96.63% of MO and 94.11% of CR degraded with 10 mg
catalyst (Table 1, entry 3; Fig. 4a). However, the rate of degradation was improved
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
110
Air+MR+60 min
Air+MO+60 min
Air+CR+60 min
Air+MR+Cat.
Air+MO+Cat.
Air+CR+Cat.
100
90
80
70
60
50
105
100
95
90
85
80
75
70
65
60
4
6
8
10
12
14
16
5
10
15
20
25
30
Catalyst (mg)
Reaction time (min)
(a)
(b)
60
H2O2+MR+Cat.
H2O2+MO+Cat.
H2O2+CR+Cat.
Air+MR
Air+MO
Air+CR
110
100
90
50
40
30
20
10
0
80
70
-10
-20
-30
60
50
5
10
15
20
25
30
50
100
150
200
250
300
350
400
Reaction time (min)
Reaction time (min)
(c)
(d)
140
120
100
80
H2O2+MR+Cat.
H2O2+MO+Cat.
H2O2+CR+Cat.
H2O2+MR
H2O2+MO
H2O2+CR
70
60
50
40
30
20
10
0
60
40
e
l
c
y
C
-
20
4
0
20 40 60 80 100 120 140 160 180 200
Reaction time (min)
0-Cycle 1-Cycle 2-Cycle 3-Cycle 4-Cycle 5-Cycle
Recyclability
(e)
(f)
Fig. 4 Optimization of parameters for the degradation of methyl red, methyl orange and Congo red. a
Efect of catalyst loading MR, MO and CR, b efect of time with 10 mg catalyst and atmospheric air of
MR, MO and CR, c efect of time with atmospheric air MR, MO and CR, d efect of time with 10 mg
catalyst and 3% H2O2 (0.1 mL) in MR, MO and CR, e efect of time with 3% H2O2 (0.1 mL) for MR,
MO and CR, f recycling of catalyst for degradation of MR, MO and CR at (pH 5—MR, 6—MO and 7—
CR) in the presence of 5 W LED lamp
to 84.81% of MR, 93.62% of MO and 92.35% of CR for a higher loading of catalyst
12.5 mg (Table 1, entry 4; Fig. 4a), respectively, and the rate of degradation was
improved to 87.48% of MR, 94.58% of MO and 96.47% of CR for a higher load-
ing of catalyst 15 mg (Table 1, entry 5; Fig. 4a), respectively. However, the rate of
1 3

V. B. Khajone, P. R. Bhagat
Table 1 Total optimum condition of dye degradation in MR, MO and CR reaction condition: in the pres-
ence of atmospheric air, dyes 25 mL (10 ppm)
Entry Catalyst (mg) Atmospheric air Time (min) % Deg-
% Degradation MO % Degra-
dation CR
radation
MR
1
2
3
4
5
6
7
8
5
7.5
10
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
Atm.
60
60
60
60
60
3
88.88
94.93
95.07
84.81
87.48
85.37
88.32
84.52
84.24
85.09
92.4
13.78
34.17
33.61
36.56
43.88
46.13
64.74
89.65
96.63
93.62
94.58
49.69
68.23
83.87
93.98
96.14
99.03
7.09
1.2
2.16
−5.05
0.12
−31.52
74.11
79.41
94.11
92.35
96.47
64.7
12.5
15
10
10
10
10
10
10
6
9
77.64
90
9
12
15
18
60
120
180
240
300
360
82.94
84.11
84.11
20.58
21.76
25.88
27.05
41.17
45.29
10
11
12
13
14
15
16
17
improvement was less prominent at the loading of catalyst above 10 mg (Table 1,
entry 3; Fig. 4a), implying that the rate of production of photoinduced electrons and
holes is the rate-limiting factor at high catalyst concentrations. Hence, it was clear
that the photodegradation occurs well with 10 mg of photocatalyst. In advance, the
efect of reaction time at atmospheric air on the degradation was studied in the pres-
ence of optimized amount of catalyst, and the results are shown in Table 1, entries
6–11, and Fig. 4b. As it can be noticed from the fgures, increasing reaction time
with air increases the rate of degradation of MR, MO and CR from 3 to 18 min.
The infuence on the photodegradation using photocatalyst has been further con-
frmed by performing degradation only in air (Table 1, entries 12–17; Fig. 4c). The
results clearly demonstrated that 10 mg PSBAZnPP was efective photocatalyst in
the presence of air under simulated sunlight. Since air alone without photocatalyst
does not show appreciable degradation of MR, MO and CR in 1 h under visible light
(Table 1 entry 12; Fig. 4c), it is confrmed that PSBAZnPP involved in the photo-
catalytic degradation process.
Afterward, the efect of reaction time and H2O2 on the degradation was studied
and the results are shown in Table 2, entries 1–6; Fig. 4d, and entries 7–12; Fig. 4e).
As it can be noticed from the fgures, increasing reaction time and H2O2 increases
the rate of degradation of MR, MO and CR from 5 to 30 min. Conversely, the pres-
ence of minute quantity (3%, 0.1 mL) of H2O2 leads to increased radical oxygen
concentration and consequently to increased conversion, resulting in the enhanced
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
Table 2 Total optimum condition of dye degradation in MR, MO and CR reaction condition: in the pres-
ence of (3%) H2O2 in (0.1 mL), dyes 25 mL (10 ppm)
Entry
Catalyst (mg)
H2O2 (3%) mL
Time (min)
% Degrada- % Degrada- % Degra-
tion MR
tion MO
dation CR
1
2
3
4
5
6
7
8
10
10
10
10
10
10
–
–
–
–
–
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.1
5
10
15
20
25
30
30
60
90
120
150
180
30
30
30
52.6
76.29
77.61
84.35
83.03
97.71
97.71
10.22
6.61
7.58
7.94
4.81
5.53
98.43
98.31
97.35
96.14
95.02
88.23
97.05
92.35
99.41
95.29
94.11
32.35
47.64
46.47
54.7
57.64
61.17
96.47
95.29
94.7
49.64
59.35
61.04
65.82
90.01
45.36
48.27
53.72
45
57.89
58.20
92.96
91.66
90.15
88.34
87.52
9
10
11
12
13
14
15
16
17
–
10
10
10
10
10
30
30
94.11
93.52
rate of degradation to 90.01% in 30 min of MR (Table 2, entry 6-MR; Fig. 4d),
97.71% in 25 min for MO (Table 2, entry 5-MO; Fig. 4d) and 99.41% in 20 min
for CR. (Table 2, entry 4-CR; Fig. 4d). The infuence of H2O2 on the photodeg-
radation using PSBAZnPP has been further confrmed by performing degradation
only in H2O2 (Table 2, entries 7–12; Fig. 4e). The results clearly demonstrated that
10 mg PSBAZnPP was efective photocatalyst in the presence of H2O2 under simu-
lated sunlight. Since H2O2 alone without photocatalyst does not show appreciable
degradation of MR, MO and CR in 1 h under simulated sunlight (Table 2 entry 8;
Fig. 4e), it is confrmed that PSBAZnPP involved in the photocatalytic degradation
process. Above percentage of the decolorization and degradation reaction kinetics
was studied by varying diferent parameters such as catalyst amount, initial concen-
tration of dye (C0) and concentration of dye at (Ct) at time t. Degradation rate was
calculated using the following equation:
C0 − Ct
(%) Decolorization and degradation of dye =
× 100
(1)
C0
Detection of active species
Relevant active species produced in the PSBAZnPP/H2O2 or PSBAZnPP/air system
under simulated light were recognized by adding diferent types of scavengers. In
this study, EDTA, p-benzoquinone (PBQ), terephthalic acid (TPA), sodium azide and
1 3

V. B. Khajone, P. R. Bhagat
100
100
100
Methyl Red (10 ppm)
Methyl Orange (10 ppm)
Congo red (10 ppm)
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
0
80.79
74.45
68.17
67.93
62.75
59.34
58.73
58.3
57.09
46.87
44.98
•OH
TPA
42.13
38.1
37.08
36.84
•O
1
Hole
Hole
•OH
TPA
O
2
•O
e
1
2
Hole
EDTA
OH
O2
1
O
2
e
O
2
2
e
dye
EDTA
PBQ
NaN3 NaNO2
dye
TPA
PBQ
NaN3 NaNO2
dye
EDTA
PBQ
NaN3 NaNO2
Type of scavengers
Type of scavengers
Type of Scavengers
(a)
(b)
(c)
Fig. 5 Detection of active species: a methyl red, b methyl orange and c Congo red
e -
Dye*
- Atm.
O2
Reducꢀon
e -
e -
1O2
e -
e -
-
O2
CB
VB
OH,
Reducꢀon
H2O2
OH⁻ + H⁺
Dye
h+
h+
H2O
+
Dye
PSBAZnPP
5W LED lamp
5W LED lamp
Fig. 6 Probable mechanism for dye degradation by PSBAZnPP
⋅
⋅
1
sodium nitrate were used for detection of holes, O2, OH , O2 and an aqueous elec-
tron (e−), respectively. It is concluded that methyl red was degraded due to formation
⋅
⋅
of O2 and OH radical compared to other active species. Similarly, methyl orange was
⋅
degraded due to formation of O2 radical and hole and Congo red due to formation of
hole compared to other active species (Fig. 5).
The possible mechanism of the dye degradation by PSBAZnPP is shown in Fig. 6.
When exposing with simulated sunlight, the photogenerated holes could oxidize OH−
⋅
to OH and electrons could reduce O2 to O−⋅ radicals. The generation of more radicals
2
occurred due to the higher electron–hole pair separation efciency of photocatalyst.
−⋅
⋅
1
These radicals comprising O2 , OH and O2 were responsible for the degradation of
dyes. The details of radical’s formation are illustrated in Eqs. (2–10).
PSBAZnPP + hꢀ → e−cb + hV+B
(2)
⋅
e−cb + O2 → O2
(3)
h+VB + H2O → H+ + OH−
(4)
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
O−2 + H+ → O2H
⋅
(5)
(6)
O2H + h+VB → O2 + OH
⋅
1
⋅
O2H + e−cb + H+ → H2O2
⋅
(7)
(8)
⋅
H2O2 + O−2 → OH + O2 + OH−
H2O2 + e− → OH + OH−
⋅
(9)
⋅
Dye + OH → Degraded product
(10)
Hammett acidity of PSBAZnPP
The comparative acidity of the synthesized PSBAZnPP catalyst was measured
using UV–Vis and then equated in terms of the Hammett value (H0). As depicted
in Fig. 7, the absorbance of a deprotonated form of the indicator was decreased with
the addition of PSBAZnPP. Calculations suggest that the Hammett acidity (H0) of
PSBAZnPP follows the order in Eq. 11 and found H0 is equal to 1.55 at 380 nm.
H0 = pk(I)(aq) + log(I∕IH+)
(11)
Detection of degradation products by GC–MS and UPLC
The degradation of azo dye was further supported by GC–MS and UPLC. The deg-
radation of MO was further confrmed by the formation of intermediates in GC–MS
analysis. The fast degradation of azo dyes may be ascribed to the terminal acid and
azo groups that assist incoming O−2 ⋅ anion radicals to attack. The likely interaction
Fig. 7 Absorbance spectra of
4NA
ZnPP
4-nitroaniline after addition of
PSBAZnPP in water at 25 °C
1.2
0.8
0.4
0.0
-0.4
350
360
370
380
390
400
410
420
Wavelength (nm)
1 3

V. B. Khajone, P. R. Bhagat
sites in azo dyes are the carbon-bearing –N=N– groups and the carbon with the ter-
minal acid groups (Supporting information Figs. S26–S44).
The degradation of MO was further confrmed by UPLC using a mixture of ace-
tonitrile and water (20: 80 v/v) as a mobile phase at pH 5 maintained by (0.01 M)
phosphoric acid. Sample Manager-FTN ACQUITY H-CLASS (PDA eλ detector)
Water, ultra-high-pressure liquid chromatography (UPLC) technique was used to
analyze the colorants in dye samples. This UPLC system consisted of a quaternary
pump (H-CLASS), automatic injector and a degasser PDA eλ detector (H-CLASS)
which was controlled by Waters Empower software. Chromatographic parameters
(pH, fow rate, mobile-phase composition and gradient programmed) were stud-
ied and adjusted through X-Bridge Columns Waters (made in Ireland) BEH C-18
column [2.1×100 mm Column XP (id), 2.5 µm particle size] (part no. 186006031,
serial no. 01683804418426) (100 Ǻ pore size) ftted with a 2.1×100 mm column
id, guard column containing the same stationary phase; to achieve good and quick
separation, gradient elution programmed was employed. Mobile phase A was made
up of a mixture of acetonitrile and water (20:80 v/v) at required pH. The mobile-
phase fow rate was maintained at 3 µL/min through the BEH C-18 column, which
was operated at ambient temperature. The automatic injection volume varied from
2.5 to 10 µL, depending on the level of analyte, and run time was to 20 min. Using
Processed channel Descr. PDA spectrum max plot 190.0–800.0 nm. A signifcant
escalation in UPLC removal was detected by the decreasing MO concentration with
time (Supporting information Fig. S45).
Comparative analysis
A comparison of the outcomes of the present study against recently reported stud-
ies is presented in Table 3: 1(MR), 2(MO), 3(CR). It is clear from the table that the
developed heterogeneous photocatalyst (PSBAZnPP) resulted in the efective deg-
radation of the dyes (i.e., MR, MO and CR) using just 5 W LED in the presence/
absence of H2O2/air. The complete photocatalytic degradation of the MR, MO and
CR was achieved with 10 mg catalyst for 60 min under atmospheric air (Table 1
entry 3; Fig. 4a), respectively,
Recyclability of PSBAZnPP
The stability and reusability of PSBAZnPP were studied and presented by perform-
ing several irradiation cycles under simulated sunlight. It was assessed by additional
experiments to degrade MR, MO and CR under simulated sunlight irradiation cycled
for fve times (Fig. 4f). It can be observed that PSBAZnPP has good stability for the
degradation of MR, MO and CR under irradiation during fve cycles. In each cycle,
simulated light was irradiated for 60 min at ambient temperature (Fig. 4f). Promi-
nently, PSBAZnPP could retain a better photocatalytic performance with the deg-
radation more than fve photocatalytic cycles. After the ffth photocatalytic recycle
was completed, the photodegradation of PSBAZnPP reduced to about 87.52% MR,
95.02% MO and 93.52% CR (Table 2 entry 17; Fig. 4f) under simulated sunlight
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
1 3

V. B. Khajone, P. R. Bhagat
120
110
100
90
ILPPSSBZAnPZPnPP
R-PSBAZnPP
R-ILPSZnPP
80
70
60
50
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 8 Spectrum of the fresh and recycled PSBAZnPP catalyst
using 5 W LED lamp at optimized conditions. As shown in Fig. 4f, the results of
the FTIR after ffth recycle of PSBAZnPP were noticeably same from those of
PSBAZnPP before being used for photocatalytic degradation, which exemplifed the
stability of catalyst. Moreover, stability of the PSBAZnPP was confrmed by using
FTIR spectroscopy (Fig. 8). The spectrum of the fresh and recycled PSBAZnPP cat-
alyst was compared and inferred that there was no alternation in the structure. This
result confrmed the catalyst structure is intact during the photodegradation reaction.
Conclusions
In summary, we have successfully synthesized a polymer supported Brønsted acid
functionalized Zn–porphyrin complex, (PSBAZnPP) heterogeneous photocatalysts
and characterized by (FT-IR) and (FT-NMR), thermal stability was confrmed by
TGA and the energy band gap measured from DRS-spectra. The photocatalytic
activity of the heterogeneous PSBAZnPP catalyst was assessed for the degrada-
tion of the methyl red, methyl orange and Congo red using simulated sunlight (5 W
LED) in the presence and absence of H2O2/air at specifed pH. The concentration
of the dyes was studied by UV–visible spectroscopy, and the degradation dye was
confrmed by GC–MS and UPLC. The complete photocatalytic degradation of the
methyl red, methyl orange and Congo red was achieved with 10 mg catalyst for
30 min under atmospheric air, respectively. The highly recyclable catalyst showed
its excellent activity in the absence of any additives such as ZnO/TiO2. Therefore,
this protocol is suitable for the degradation of organic pollutant from the water. A
possible mechanism for the generation of various radical species was suggested in
this study. In simulated visible-light system, the substantial enhancement of the
photocatalytic activity of PSBAZnPP with porphyrin sensitizer acquired an admi-
rable efciency toward the degradation of MR (92.96%), MO (98.43%) and CR
(96.47%) under simulated visible-light irradiation. Moreover, long-term stability
1 3

Synthesis of polymer-supported Brønsted acid-functionalized…
and recyclability up to fve times without signifcant deactivation established a pro-
tocol with a bright prospect, especially for wastewater treatment.
Acknowledgements The authors gratefully acknowledge VIT-SIF SAS and the SEM Facility at SBST
VIT, Vellore, for instrumentation facilities. The authors also thank VIT for providing ‘VIT SEED
GRANT’ for carrying out this research work. We kindly acknowledge VIT Management, Department
of Chemistry (SAS), “Smart Materials Laboratory for Biosensing and Catalysis.” We would also like to
extend our thanks to Mr. Sagar Krushnarao Datir for his valuable advice and suggestions.
References
1. Y. Yuan, H. Lu, Z. Ji, J. Zhong, M. Ding, D. Chen, Y. Li, W. Tu, D. Cao, Z. Yu, Z. Zou, Chem. Eng.
J. 275, 8 (2015)
2. S. Xu, Y. Lv, X. Zeng, D. Cao, Chem. Eng. J. 323, 502 (2017)
3. Y. Pi, X. Li, Q. Xia, J. Wu, Y. Li, J. Xiao, Z. Li, Chem. Eng. J. 337, 351 (2018)
4. Y. Wei, Y. Zhu, Y. Jiang, Chem. Eng. J. 356, 915 (2019)
5. S. Pirillo, E.H. Rueda, M.L. Ferreira, Chem. Eng. J. 204–205, 65 (2012)
6. M. Gmurek, J.S. Miller, S. Ledakowicz, Chem. Eng. J. 210, 417 (2012)
7. J. Zhang, M. Feng, Y. Jiang, M. Hu, S. Li, Q. Zhai, Chem. Eng. J. 191, 236 (2012)
8. H. Ghafuri, Z. Movahedinia, R. Rahimi, H.R.E. Zand, RSC Adv. 5, 60172 (2015)
9. R.V. Kandisa, K.V.N. Saibaba, J. Bioremediation Biodegrad. 07 (2016)
10. J.M. Dąbrowski, B. Pucelik, M.M. Pereira, L.G. Arnaut, W. MacYk, G. Stochel, RSC Adv. 5, 93252
(2015)
11. H. Xu, J.X. Xiang, P. Wu, Y.F. Lu, S. Zhang, Z.Y. Xie, Z.Z. Gu, RSC Adv. 6, 45617 (2016)
12. M.O. Ansari, M.M. Khan, S.A. Ansari, M.H. Cho, New J. Chem. 39, 8381 (2015)
13. J.H. Castillo-Ledezma, J.L.S. Salas, A. López-Malo, E.R. Bandala, Eur. Food Res. Technol. 233,
825 (2011)
14. G. Cernuto, N. Masciocchi, A. Cervellino, G.M. Colonna, A. Guagliardi, J. Am. Chem. Soc. 133,
3114 (2011)
15. D. Chatterjee, S. Dasgupta, J. Photochem. Photobiol. C Photochem. Rev. 6, 186 (2005)
16. Y.I. Choi, S. Lee, S.K. Kim, Y. Il Kim, D.W. Cho, M.M. Khan, Y. Sohn, J. Alloys Compd. 675, 46
(2016)
17. M. Fujitsuka, T. Majima, J. Photochem. Photobiol. C Photochem. Rev. 35, 38 (2018)
18. M. Silva, M.E. Azenha, M.M. Pereira, H.D. Burrows, M. Sarakha, C. Forano, M.F. Ribeiro, A. Fer-
nandes, Appl. Catal. B Environ. 100, 1 (2010)
19. Q. Wu, X. Hao, X. Feng, Y. Wang, Y. Li, E. Wang, X. Zhu, X. Pan, Inorg. Chem. Commun. 22, 137
(2012)
20. M. Cheng, W. Ma, C. Chen, J. Yao, J. Zhao, Appl. Catal. B Environ. 65, 217 (2006)
21. B. Li, L. Shao, B. Zhang, R. Wang, M. Zhu, X. Gu, J. Colloid Interface Sci. 505, 653 (2017)
22. B. Li, Y. Hao, X. Shao, H. Tang, T. Wang, J. Zhu, S. Yan, J. Catal. 329, 368 (2015)
23. B. Li, R. Wang, X. Shao, L. Shaob, B. Zhang, Inorg. Chem. Front. 4, 2088 (2017)
24. B. Li, Y. Hao, B. Zhang, X. Shao, L. Hu, Applied Catal. A Gen. 531, 1 (2017)
25. Y. Xiao, X. Tao, G. Qiu, Z. Dai, P. Gao, B. Li, J. Colloid Interface Sci. 550, 99 (2019)
26. M. Rabbani, M. Heidari-Golafzani, R. Rahimi, Mater. Chem. Phys. 179, 35 (2016)
27. Z. Zhang, H. Liu, J. Xu, N. Zhang, Photochem. Photobiol. Sci. 16, 1194 (2017)
28. S. Murphy, C. Saurel, A. Morrissey, J. Tobin, M. Oelgemöller, K. Nolan, Appl. Catal. B Environ.
119–120, 156 (2012)
29. H. Wang, D. Zhou, S. Shen, J. Wan, X. Zheng, L. Yu, D.L. Phillips, RSC Adv. 4, 28978 (2014)
30. Y. Li, Q. Duan, H. Wang, B. Gao, N. Qiu, Y. Li, J. Photochem. Photobiol. A Chem. 356, 370 (2018)
31. N. Qiu, Y. Li, S. Han, G. Cui, T. Satoh, T. Kakuchi, Q. Duan, J. Photochem. Photobiol. A Chem.
283, 38 (2014)
32. J.H. Cai, J.W. Huang, H.C. Yu, L.N. Ji, J. Taiwan Inst. Chem. Eng. 43, 958 (2012)
33. A.G. Khiratkar, P.N. Muskawar, P.R. Bhagat, RSC Adv. 6, 105087 (2016)
34. K.R. Balinge, A.G. Khiratkar, P.R. Bhagat, J. Mol. Liq. 242, 1085 (2017)
1 3

V. B. Khajone, P. R. Bhagat
35. K.R. Balinge, A.G. Khiratkar, P.N. Muskawar, K. Thenmozhi, P.R. Bhagat, Res. Chem. Intermed.
44, 2075 (2018)
36. P.N. Muskawar, S. Senthil Kumar, P.R. Bhagat, J. Mol. Catal. A Chem. 380, 112 (2013)
37. R. Rahimi, M.M. Moghaddas, S. Zargari, J. Sol–Gel. Sci. Technol. 65, 420 (2013)
38. H. Lv, X. Zhao, H. Niu, S. He, Z. Tang, F. Wu, J.P. Giesy, J. Hazard. Mater. 369, 494 (2019)
39. K.S. Min, R.S. Kumar, J.H. Lee, K.S. Kim, S.G. Lee, Y.A. Son, Dye. Pigment. 160, 37 (2019)
40. Q. Li, T. Zhao, M. Li, W. Li, B. Yang, D. Qin, K. Lv, X. Wang, L. Wu, X. Wu, J. Sun, Appl. Catal.
B Environ. 249, 1 (2019)
41. Z. Feng, J. Yu, J. Kong, T. Wang, Chem. Eng. J. 294, 236 (2016)
42. P. Kharazi, R. Rahimi, M. Rabbani, Mater. Res. Bull. 103, 133 (2018)
Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional afliations.
1 3