Zeolite encapsulated Ni(ii) and Cu(ii) complexes with tetradentate N 2O2 Schiff base ligand: Catalytic activity towards oxidation of benzhydrol and degradation of rhodamine-B

Article abstract of DOI:10.1039/c4ta01869a

Nickel(ii) and copper(ii) complexes of the Schiff base ligand O,O′-trimethyl bis (salicylidene isonicotinylhydrazone) (H₂L) were synthesized and characterized. The encapsulation of these complexes in the cavities of the zeolite was achieved by

Full text of DOI:10.1039/c4ta01869a

Journal of
Materials Chemistry A
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Zeolite encapsulated Ni(II) and Cu(II) complexes
with tetradentate N2O2 Schiff base ligand: catalytic
activity towards oxidation of benzhydrol and
degradation of rhodamine-B†
Cite this: J. Mater. Chem. A, 2014, 2,
15598
a
a
b
*
G. Ramanjaneya Reddy, S. Balasubramanian and K. Chennakesavulu
Nickel(II) and copper(II) complexes of the Schiff base ligand O,O0-trimethyl bis (salicylidene
isonicotinylhydrazone) (H2L) were synthesized and characterized. The encapsulation of these
complexes in the cavities of the zeolite was achieved by a fixed ligand method (FLM). The free
complexes (FC) and the retention of the zeolite encapsulated metal complexes [ZEMC; i.e., Ni(II)L–Y,
Cu(II)L–Y] were investigated by several spectroscopic, thermal analysis, sorption and microscopic
techniques [i.e., FTIR, NMR, ESI-mass, conductivity, DRS/UV-Vis, EPR, XPS, AAS, TGA, XRD, nitrogen
isotherm, magnetic and (SEM/TEM)EDX]. This study reveals the formation and stability of the metal
complexes in the cavities of the zeolite. The catalytic activities of free complexes and encapsulated
complexes were studied in the liquid phase oxidation of benzhydrol/H2O2 and the photodegradation
of rhodamine-B (RhB) under UV/visible (H2O2) irradiation. The catalytic activities of benzhydrol (BH)
oxidation and RhB degradation were higher with free complexes and encapsulated complexes,
respectively. In most cases, the copper(II) [Cu(II)L$2ClO4, Cu(II)L–Y] complexes showed better activity
than the nickel(II) complexes [Ni(II)L$2ClO4, Ni(II)L–Y] in both BH and RhB degradation reactions. The
enhancement of Cu(II)L–Y activity was mainly due to the metal present in the cavities and on the
surface. Hence, in the case of FC, rate of the reaction (% of conversion) for the copper(II) complexes is
more than that for nickel(II) in BH oxidation, but, in the case of ZEMC, the photocatalytic activity and
rate of reaction (% of conversion) were more for Cu(II)L–Y than Ni(II)L–Y. These results show that both
the oxidation reactions follow pseudo first order kinetics. The catalytic activities of the recovered and
purified ZEMC were compared with the fresh catalyst.
Received 16th April 2014
Accepted 22nd July 2014
DOI: 10.1039/c4ta01869a
www.rsc.org/MaterialsA
research interest in the heterogeniation of homogenous catalyst
has increased.4,5 However, the enhancement of catalyst activity
1. Introduction
with nickel(II) and copper(II) based systems was an alternative to
highly expensive metals such as ruthenium and palladium.
Hence, impregnation of homogeneous transition metal
complexes into a solid support, such as a polymer, zeolite or
MCM41, was attempted.6 Zeolites are made up of aluminosili-
cates known as “solid acid” and are an alternative to commer-
cially available toxic acids such as sulphuric acid, potassium
dichromate, and nitric acid. The zeolite Na–Y is an interesting
material because of its low cost and an intracrystalline cavity,
which makes it suitable for transition metal ion exchange. The
exchange and encapsulation ability of metal complexes within
the cavities of supercages depends on Na+ ion and the size of the
zeolite host.7 Hence, the encapsulation (heterogeniation) of
metal complexes (homogeneous) within the supercages can be
used effectively in photo (chemical) oxidation reactions. The
modied catalyst has more advantages than its homogeneous
counter parts and can act as an effective ecofriendly catalyst to
convert high toxic pollutants to much less toxic minerals.
Transition metal complexes play a vital role in the eld of
catalysis and photocatalysis, i.e. liquid phase oxidation, reduc-
tion, polymerization, etc.1–3 The recovery and separation of
transition metals from products in homogeneous medium (e.g.
hydrocarbons, aliphatic alcohols, alkyl benzenes, amides,
amines, aliphatic carboxylic acids, thioethers, xanthene class of
dyes, etc.) are challenging tasks. To overcome this difficulty,
aDepartment of Inorganic Chemistry, School of Chemical Sciences, University of
Madras, Guindy Campus, Chennai-600 025, India
bDepartment of Chemistry and International Research Centre, Sathyabama University,
Jeppiaar Nagar, Chennai-600 119, India. E-mail: chennanml@yahoo.com;
gonturamunom@gmail.com; Tel: +91 9994228166; +044 22202794
† Electronic supplementary information (ESI) available: 1H and 13C-NMR spectra,
ESI-mass, FTIR, N1S, and O1S deconvoluted XPS spectral trace with survey graph
and M(II) 2P spectrum. N2 isotherms, UV-VIS spectral change, microscopic
analysis, percentages of the nickel, copper, silica and aluminium, the
DRS/UV-VIS spectra, PXRD and LC-MS for the recovered catalysts are given in
the electronic supplementary data. See DOI: 10.1039/c4ta01869a
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The modied zeolite can delocalise the band gap excited Perkin-Elmer 8300 spectrometer with a KBr disk, and the UV-
electrons of the HOMO and LUMO levels of metal complexes. visible diffuse reectance spectral (UV-Vis DRS) analyses were
Hence, they minimize the electron–hole recombination even carried on a Perkin-Elmer lambda-650 DRS UV-visible spectro-
though a relative number of active sites are present on the high photometer. UV-Vis absorption spectra were obtained using a
surface area solid supports. In addition, the ability of the Perkin Elmer Lambda-35 spectrophotometer operating in the
modied zeolite favours photo induced electron-transfer reac- range of 200–800 nm for liquid samples. Conductivity
tions and generates photoactive, powerful oxidative ion radical measurements were carried out in mmol solutions of the metal
species such as _OH, ꢀO2, and +_O2H. This modied zeolite with complexes in DMSO. The EPR spectrum of the copper(II)
the green oxidant, that is 30% H2O2, can enhance the photo- complex was recorded at LNT on a Varian E-4 X-band spec-
catalytic degradation of various dyes (RhB, methyl orange, trometer using TCNE as the g-marker (2.0023). XPS analyses
cango red) by the generation of an active radical (Eo ¼_OH) (Eo ¼ were carried out on a XM1000 Omicron nanotechnology XPS
2.8 V), which is more powerful than other oxidants.8 These system with Al-Ka monochromatic wavelength. The FC and
supported systems improve the rate of the reaction and catalytic ZEMC samples were prepared as pellets and were used as such
activity towards the decolourization of the carcinogenic for X-ray photoelectron spectroscopic (XPS) analysis. High
xanthene (azo) class of dyes and the oxidation of the aryl alco- resolution XPS traces were deconvoluted using the Gaussian
hols.9 Although the photodegradation of dyes is important, very and Lorentzian statistical analysis by Origin-7 soware. Crys-
few reports are available regarding the removal of the xanthene talline nature of FC and ZEMC was determined by powder X-ray
class of dyes using pure and supported Schiff base hydrazones diffraction using a Bruker D8 advance diffractometer with
complexes.10
monochromatic Cu-Ka1 radiation (l
¼
1.5418 A). Aer
˚
The metal complexes of aryl hydrazones have biological and completely destroying the zeolitic framework with hot HCl,
catalytic signicances because of the tetradentate (dioxa diaza) nickel and copper percentages were analyzed by atomic
moiety that gives them a chelating ability with the metal ions. absorption spectrophotometry (AAS, Perkin-Elmer 4100-1319),
The use of nickel(II) and copper(II) zeolite exchange complexes and SiO2 was determined by gravimetric analysis. TGA experi-
with aryl hydrazones have rarely been reported for liquid phase ments were performed using a Versa Therm Cahn thermo
oxidation reactions.11 The synthesis and extensive studies of balance TG-151 with a sensitivity of 10 mg. TGA experiments
acyclic tetradentate N2O2 Schiff base ligand O,O0-trimethyl bis were conducted in the temperature range of 300–1200 K with 20
(salicylidene isonicotinoyl hydrazone) with Ni(II) and Cu(II), its ꢁ 0.01 mg of the samples at a heating rate of 10 K minꢀ1 under a
corresponding encapsulated complexes formed by FLM in the static air atmosphere. N2 adsorption and desorption isotherms
cavities of the zeolite, and its application in BH oxidation and and Brunauer–Emmett–Teller (BET) specic surface area
degradation of RhB dyes have not been established.12
measurements were carried out at 77 K on a Micrometrics ASAP
In the present study, an attempt was made to synthesize the (Model 2020) surface area analyzer using nitrogen and helium
Schiff base ligand O,O0-trimethyl bis(salicylidene isonicotinoyl gases with a purity of 99.99%. The scanning electron micros-
hydrazone) (H2L) by condensation between 1,3-bis(2-carbox- copy (SEM) images were obtained using a HITACHI-S3690
yaldehydephenoxy)propane (SAL) and isonicotinyl hydrazine scanning electron microscope. HRTEM analysis was carried out
(INH) in the presence of Ni(II) and Cu(II) perchlorates. The metal using a FEI TECNAI G2 (T-30) transmission electron microscope
complexes were encapsulated in the cavities of the zeolite by with an accelerating voltage of 250 kV. The average particle size
FLM. The catalytic activity of the synthesised materials was was measured using the ImageJ soware tool. The products in
tested in the liquid phase oxidation of BH and the photo- one BH oxidation reaction were analyzed by LC-MS using Agi-
degradation of RhB. Spectrophotometry was used for the lent 6110 LC-MS ESI mode with carvacrol used as an internal
determination of the products and the catalytic activity of the standard.
composite materials.
2.3 Preparation of the 1,3-bis(2-carboxyaldehydephenoxy)
2. Experimental
propane (SAL)
2.1 Materials
Salicylaldehyde (0.61 g, 5 mmol) was dissolved in 20 mL DMF,
and potassium carbonate (1.73 g, 12.5 mmol) was added. The
mixture was stirred at room temperature, and then 1,3-dibro-
mopropane (0.51 g, 2.5 mmol) was added dropwise. Then, the
reaction mixture was stirred under reux for 6 h. The resulting
mixture was partitioned between water and ethyl acetate then
the ethyl acetate layer was collected, concentrated under
reduced pressure and then subjected to silica gel 100–200 mesh
column chromatography using 1 : 9 hexane–ethylacetate as the
Salicylaldehyde, 1,3 dibromo propane, isonicotinylhydrazide,
Zeolite-Y (Si/Al ¼ 2.7, Na52[(AlO2)52(SiO2)140)], benzhydrol,
hydrogen peroxide (30%) and rhodamine-B were obtained from
Sigma-Aldrich. Milli-Q water was used during the experimental
work.
2.2 Physicochemical measurements and characterization
NMR spectra were recorded on a Bruker Avance 400 MHz NMR eluent to afford compounds (1.07 g, 75%) in pure form. The
spectrometer, and ESI mass spectral data were obtained using puried SAL was characterized, and the results matched well
an ESI-MS Thermo Finnigan LCQ model advantage MAX with those of a previously reported method.13 (ESI: S35) 1H NMR
6000ESI spectrometer. FTIR spectra were recorded on a FTIR (CDCl3, 500 MHz): d 2.43 (2H, p, OCH2CH2CH2O), 4.33 (4H, t, J
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¼ 7.6 Hz, OCH2CH2CH2O), 7.03 (4H, m, Ar-H), 7.55 (2H, t,
J ¼ 7.7 Hz, Ar-H), 7.83 (2H, d, J ¼ 7.7 Hz, Ar-H), 10.49 (2H, s,
Aldehyde-H); 13C NMR (CDCl3, 125 MHz) (ESI: S36): d 29.2, 64.7,
112.5, 121.0, 124.9, 128.8, 136.2, 161.0, 189.6.
2.8 Preparation of the metal hydrazone Schiff base
complexes in the zeolite [M(II)L–Y] via FLM
Preparation of the Schiff base aryl hydrazone metal complexes
in the cavities of the zeolite was achieved by heating at 333 K in
DMF/methanolic solution of H2L with M(II)–Y for 8 h. The
resulting solids were washed with hot DMSO (10 mL) and water
and dried for 12 h. Then, the solids were Soxhlet extracted with
ethanol and acetonitrile/DMF aer 6 and 24 h, respectively, to
remove excess unreacted starting materials adsorbed onto the
external surface of the zeolite crystal. The resulting solids were
dried at 253 K under vacuum for 24 h. Yield: 0.3–0.34 g. Colour:
[Ni(II)L–Y] (pale yellow), [Cu(II)L–Y] (pale green).
2.4 Preparation of the O,O0-trimethyl bis (salicylidene
isonicotinoyl hydrazine) (H2L)
O,O0-Trimethyl bis (salicylidene isonicotinyl hydrazone) was
prepared by reuxing an aliquot of SAL (1.12 g, 2 mmol), iso-
nicotinyl hydrazide (1.8 g, 4 mmol), and two drops of glacial
acetic acid in absolute ethanol (40 mL) for 2 h. The resulting
white solid was washed with water, ethanol, chloroform, and
diethyl ether and then dried under vacuum. Yield: 0.68 g (80%).
M.p. 521–523 K. ESI-mass: m/z 545.27 (M + Na). 1HNMR
(DMSO-d6, 400 MHz) ppm: 12.02 (s, 2H, amide NH), 9.01–8.42
(m, 6H, Ar-H and imine CH), 8.07–7.53 (m, 6H, Ar-H), 7.37 (s, 2H,
Ar-H), 7.11 (s, 2H, Ar-H), 6.98 (s, 2H, Ar-H), 4.27 (s, 4H, OCH2) and
2.26 (s, 2H, OCH2CH2CH2O); 13C NMR (DMSO-d6, 80 MHz) ppm:
162.08, 157.57, 150.77, 149.99, 144.91, 141.02, 132.37, 126.27,
123.60, 122.68, 122.03, 121.41, 113.26, 65.30 and 29.26. UV/Vis
(DMSO): lmax (3: cmꢀ1 molꢀ1 L) ¼ 272 (56 600), 288 (58 577) and
332 (6658).
2.9 Oxidation of BH by the FC and ZEMC composite
materials
A mixture of the M(II)L$2ClO4 (0.5 mg, 0.01 mmol; 100 mg in
case of ZEMC), 30% hydrogen peroxide (0.34 g, 1 mmol) and BH
(0.0184 g, 0.1 mmol) was added to a ask containing dry
acetonitrile (10 mL), and the reaction mixture was stirred for 7 h
at 333 K. The nal products were analysed under UV, and one of
the reaction products, benzophenone, was conrmed by LC-MS
analysis.
2.9.1 Photocatalytic degradation of RhB under UV and
visible light irradiation. The photo catalytic activities of the FC
and ZEMC were evaluated in the degradation of RhB under UV
as well as visible/H2O2 (1 mmol) in a cylindrical glass reactor
with a diameter of 66 ꢂ 98 mm that contains a water jacket at
room temperature. A mercury (Hg) lamp (100 W, 365 nm) was
used as a UV light source, and a 250 W tungsten lamp (Philips)
used as a visible light source equipped with a UV cut-off lter
was used to trigger photodecomposition reactions. The catalyst
0.06 mmol M(II)L$2ClO4 (0.05 g in case of ZEMC) was added to
0.01 mmol of 100 mL RhB aqueous solution, and the above-
mentioned catalysts were added separately for both UV(visible/
H2O2) irradiations. Aer optimising reaction conditions in the
dark at room temperature, the suspension was irradiated by the
light sources. 3 mL of the solution was collected for each pre-
determined time interval (30 min), and the consequent spectral
changes were monitored by UV-Vis spectra using a Perkin-Elmer
Lambda 35 spectrophotometer operating in the range of 200–
800 nm at 554 (ꢁ1) nm for 3 h. The percentage of conversion
and reaction rates in the photodegradation process were
formulated using the Lambert–Beer's correlation formulae.
2.5 Preparation of Ni(II)L$2ClO4
30 mL ethanolic solution of nickel perchlorate hexahydrate
(0.38 g, 0.5 mmol) was added to the DMF solution (5 mL) of
(H2L) (0.52 g, 1 mmol), and then heated at 353 K for 3 h. The
resulting lemon yellow solid was washed with hot water,
methanol, diethyl ether and dried under vacuum. Yield: 0.6 g
(72%), m.p. and decomposition > 543 K; ESI-mass m/z 579.2.
lmax ¼ 260 nm (3 ¼ 14 050 cmꢀ1 molꢀ1 L), 368 nm (3 ¼ 18 990
cmꢀ1 molꢀ1 L), 670 nm (3 ¼ 68 cmꢀ1 molꢀ1 Lꢀ1). Molar con-
ductivity (L) ¼ 14.5 mho cmꢀ2 molꢀ1
.
2.6 Preparation of Cu(II)L$2ClO4
30 mL ethanolic solution of copper perchlorate hexahydrate
(0.36 g, 0.5 mmol) was added to the DMF solution (5 mL) of
H2L (1.1 g, 0.5 mmol), and heated at 353 K for 3 h. The
resulting olive green solid was washed with hot water,
methanol, diethyl ether and dried under vacuum. Yield:
0.7 g (80%) m.p. and decomposition > 513 K; MS: m/z 585.
lmax ¼ 270 (3 ¼ 14 829 cmꢀ1 molꢀ1 L), 368 nm (3 ¼ 19 300 cmꢀ1
molꢀ1 L), 685 nm (3 ¼ 33 cmꢀ1 molꢀ1 L). Molar conductivity
A ¼ 3cl
(1)
where 3 ¼ molar extinction coefficient [Mꢀ1 cmꢀ1], c ¼ sample
concentration and l ¼ path length of the cuvette (1 cm).
(L) ¼ 11.8 mho cm2 molꢀ1
.
2.7 Preparation of metal exchanged zeolite, (M(II)–Y
[M ¼ Ni(II) and Cu(II)])
3. Results and discussion
3.1 Chemical and magnetic studies
Metal perchlorate [M(ClO4)$6H2O, 0.1 mmol] was added to
50 mL aqueous solution of 1 g Na–Y zeolite and stirred for Chemical analysis (AAS) results are given in Table A (ESI†). The
8 h at 368 K. The obtained solids were ltered, washed with parent zeolite unit cell formula was Na52[(AlO2)52(SiO2)140] with
100 mL of hot distilled water and dried under vacuum for 10 Si/Al ¼ ꢃ2.7. The silica to aluminium ratio (SAR) was the same
h at 353 K.
in all the exchange processes. The consistency of SAR suggested
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that the leaching of aluminium did not occur during the frequency around 1603 cmꢀ1 remains the same in all the
exchange processes. In addition, incomplete exchange of complexes, which shows that metal ions are not involved in
sodium metal ion with both copper(II) and nickel(II) was also coordination with pyridine nitrogen. The bands around 1378
found. The gradual decrease in the percentage of the metal from and 767 cmꢀ1 are because of the bending vibrations of the
M(II)-Y to ZEMC shows the formation and presence of the Schiff aromatic ring of C–H. At lower frequency region, the
base metal hydrazone complexes in the cavity of the zeolite. complexes exhibit medium intensity bands at around 414–
AAS, SEM/TEM(EDAX) and XPS analyses conrm the presence 490 cmꢀ1 and 518–580 cmꢀ1, corresponding to M–N and M–O
of nickel(II), copper(II), Si and Al. The simple Gouy balance vibration modes, respectively. From the ESI (Fig. S8 & S9†), a
technique was used for magnetic susceptibility studies. The broad signal appeared in the region of 1114 and 1084 cmꢀ1
results reveal a magnetic moment value of 1.78 BM for Cu(II) because of the antisymmetric stretching vibration of
L$2ClO4, and this value slightly changed to 1.92 BM for Cu(II)L–Y. perchlorate ions in complexes, and a medium band at about
The nickel(II) complex showed a diamagnetic nature. These 628 cmꢀ1 and 1000 cmꢀ1 because of the antisymmetric
values well matched with those of the earlier reports for mono bending and stretching vibrations of the metal coordinated
nuclear complexes.14
perchlorate moiety was conrmed.20
FTIR spectral data can give information regarding the crys-
tallinity of the zeolite and the encapsulation of complexes. The
FTIR studies of NaY ESI (Fig. S10†) and ZEMC (Fig. S11 & S12†)
show that the peak intensities are weak due to low concentra-
tion of the complexes in zeolite cavity. The NaY bands in the
range of 3600–3200 cmꢀ1 are attributed to the adsorbing
tendency of surface hydroxyl groups, and the bands at 1200–450
cmꢀ1 are because of lattice (Si/Al)O4 vibrations.21 The bands of
ZEMC and FC are exhibited in the region of 1615–1200 cmꢀ1
and were absent in NaY. The azomethine –C]N group
stretching frequency is observed around 1595 cmꢀ1, and the
pyridine –N]C group stretching frequency is observed as a
broad band around 1616 cmꢀ1 because of the bending
frequency of –OH groups of the ZEMC. C–O and N–N stretching
frequencies were merged with the O–Si–O and O–Al–O lattice
vibrations and all the other peaks corresponding to C–H, C–C,
and C]C band vibrations of ZEMC are almost similar to FC.
This observation not only conrms the presence of a metal
complex in the zeolite, but also conrms no change in the
lattice nature of zeolite. All ZEMC showed peaks around 1121,
1020, 790 and 710 cmꢀ1 because of the zeolite,22 indicating no
changes in the zeolite cavities and de-alumination during
encapsulation. The new fairly less intense bands appearing at
the lower frequency region around 550 cmꢀ1 and 430 cmꢀ1 in
the encapsulated complexes originate from M–O and M–N
vibrations.23 These observations suggest that there is a very
weak involvement of metal ion in coordination with the zeolite.
FTIR spectral analysis provided evidence for the encapsulation
of metal complexes in the zeolite matrix and the crystallinity of
the host zeolite.
3.2 Infrared spectroscopy (FTIR)
The FTIR spectra of H2L, NaY, Ni(II)L$2ClO4, Cu(II)$2ClO4, Ni(II)–Y
and Cu(II)–Y are provided in ESI (Fig. S7–S12†). The shis in
bands and their peak assignments in wavenumber are listed in
Table 1. Fig. S7† shows the disappearance of aldehyde carbonyl
band. The bands in the FTIR spectra of ligand H2L, and the
appearance of three new bands at 1618 cmꢀ1, 1603 cmꢀ1 and
1660 cmꢀ1 are because of the stretching frequency of –C]N,
C]N (p) and –C]O groups, respectively.15,16 This clearly
indicates that the primary amino group of the isoniazid was
involved in the formation of the azomethine group in the
Schiff base ligand. The FTIR spectra of Ni(II)L$2ClO4 and
Cu(II)L$2ClO4 ESI (Fig. S7 & S8†) appear to have a band in the
region of 1505–1520 cmꢀ1 assigned to the valence vibrations
of n(O–C]N) because of the enolization of H2L during com-
plexation.17 The vibrations of the C]O group at 1660 cmꢀ1
disappeared for the complexes, and a new broad band
appeared at 1135–1150 cmꢀ1, which was assigned to the enol
form of deprotonated hydrazone (nC–Oꢀ).18 The azomethine
(N]C) group frequencies appeared at a lower region (1594–
1585 cmꢀ1) when compared with the ligand frequency at
1618 cmꢀ1 due to metal ion coordination.19 This observation
indicates that the M(II) ion coordinates with the dianionic
tetradentate N2O2 chelating ligand of the azomethine
nitrogen and enolic oxygen. Moreover, bands corresponding
to one of the N–H groups also disappear and new medium
bands appear around 1020 cmꢀ1, which correspond to the
N–N frequency. The pyridine (N]C) group stretching
Table 1 FTIR spectral values in cm ꢀ1 for FC and ZEMC
Wave number (cmꢀ1
)
Sample
n(C]O)
n(C]N)
n(C]N–N]C)
n(C–Oꢀ)
n(C–O–C)
n(N–N)
n(N–H)
n(M–O)
n(M–N)
SAL
H2L
Ni(II)L
Cu(II)L
Ni(II)L–Y
Cu(II)L–Y
1706
1661
—
—
—
—
—
1618
1583, 1504
1575, 1512
1598, 1518
1554, 1506
—
—
1147
1152
1155
1167
1230, 1307
1242, 1302
1244, 1301
1245, 1293
1245, 1306
1268, 1315
—
961
1024
1020
952–1000
947–1000
—
3034
—
—
—
—
—
582
540
530
579
—
—
444
492
430
463
1603
1602
1605
1612
1615
—
—
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3.3 Optical absorption spectra/DRS studies
3.4 EPR spectral studies
The UV-visible spectra were recorded for H2L, FC and ZEMC, The EPR spectra of Cu(II)L$2ClO4 and Cu(II)L–Y in liquid
and the corresponding spectra are given in Fig. 1(a–e). The nitrogen were recorded and are presented in Fig. 2(a & b). The g
absorption spectrum of H2L in the UV region exhibits three values are calculated relative to tetracyanoethylene g-marker
absorption bands at 272 nm (p / p*), 288 nm (p / p*) and (TCNE, g ¼ 2.0023.). The copper(II) (I ¼ 3/2) complex is typically
332 nm (n / p*). The spectrum of Ni(II)L$2ClO4 exhibit anisotropic in nature at LNT. Nitrogen hyperne splitting can
absorption bands at 258 nm and 352 nm because of the intra be clearly observed in the spectrum. The Cu(II)L$2ClO4 shows
ligand p / p* transitions and n / p* transitions of azome- g||, gt and gav values of 2.34, 2.079 and 2.16, respectively.
thine (C]N) groups, respectively. It shows a broad visible band The g|| > gt > 2.0023 indicates the covalent environment of
1
1
centred at 650 nm, assigned to A1g to B1g transitions.24 In metal ion with the Schiff base. In addition, the A|| value at
addition, electronic spectral values in this region might suggest 148 T indicates that the coordinating metal environment
a slight distortion of the square planar geometry. The Ni(II) might have a square planar geometry and unpaired electrons
might have been surrounded by two imino nitrogen and two in the dx2–y2 orbital. Further, Cu(II)L$2ClO4 exhibits a G value
enolic form of oxygen atoms.25 Cu(II)L$2ClO4 in DMSO and [G ¼ (g|| ꢀ 2.0023)/(gt ꢀ 2.0023)] of 4.56, which is slightly
methanol also exhibits bands at 268 nm and 348 nm due to higher than 4, indicating no exchange interaction in the
p / p* and n / p* transitions, respectively. The square- (mono nuclear) copper(II) complex. It is evidenced that the
planar Cu(II) complex gives a broad absorption band between change of the geometry from octahedral to distorted square
600 and 700 nm by Jahn–Teller distortion. Because of the N2O2 planar with incipient axial coordination.29,30 The Cu(II)L–Y
moiety, the geometry of the copper complex might be distorted also exhibits the g tensor values of g|| (2.29) > gt (2.09) > gav
from octahedral to a tetragonal or planar geometry.26
(2.0023). This might be due to the hyperne coupling of
The DRS spectra of the ZEMC are shown in Fig. 1(d & e). Ni(II) copper(II) with tetradentate N2O2 with axial planar symmetry,
L–Y shows three characteristic bands at 223–269 and 334 nm and the peaks are well isolated with less intensity. The
due to p / p* and n / p* transitions, respectively, and a hyperne splitting factor (A||) at 160 T indicates the presence
broad band centred at 608 nm due to d–d transitions. Cu(II)L–Y of an unpaired electron in the dx2–y2 orbital with axial interaction
also shows corresponding peaks at 222–266 nm and 325 nm, leading to elongated tetragonal distorted octahedral geometry
and these are assigned to p / p* and n / p* transitions, with a square planar moiety.31 The Cu(II)L–Y exhibits a G value
respectively. The Cu(II)L–Y shows a broad peak at 650 nm due to (G ¼ (g|| ꢀ 2.0023)/(gt ꢀ 2.0023)) that is slightly higher than 4,
d–d transition.27,28 On comparing the ZEMC with FC, the peak indicating no copper(II) ion exchange interaction. It has been
shi indicates that the electronic transitions inuenced the reported that high g|| values are common to six coordinate Cu(II)
zeolite matrix and elongated the axial coordination of complexes with ligand containing hard donors such as nitrogen
complexes. This further gives an idea regarding all the and oxygen. The A|| value of the Cu(II) L–Y is larger than that of
complexes that do not undergo a similar kind of structural Cu(II)L$2ClO4, which might be either due to the electrostatic
change in zeolite-Y and (Si/Al)O4 groups might inuence a peak interaction of sodium ion or due to the silica skeleton. These
shi. However, the presence of similar electronic transitions in observations indicate that the geometry of the mononuclear
the ZEMC when compared with FC may indicate a greater copper complex in the free state and encapsulated state are
probability to form a stable planar geometry in the cavities of almost the same and even electronic studies also support this
the zeolite.
EPR observation.32
3.5 X-ray photoelectron spectroscopic analysis
The XPS spectra of ZEMC and FC are given in the ESI (Fig. S13a–
d†) and reveal the presence of C, N, O, Na, Si, Al, Ni(II) and Cu(II),
Fig. 2 Experimental (thick) line stemming (dash) line spectra X-band
EPR spectra of the (a) Cu(II)L$2ClO4 and (b) Cu(II)L–Y at LNT (the
spectrometer settings were a microwave power frequency of 9.43
Fig. 1 UV-Vis/DRS of (a) H2L, (b) Ni(II)L$2ClO4, (c) Cu(II)L$2ClO4, (d) GHz: microwave power of 13 mW: modulation frequency kHz;
Ni(II)L–Y and (e) Cu(II)L–Y.
modulation amplitude.2G).
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which conrms the respective surface chemical state of the
elements.33 These peaks are related to carbon in free and
encapsulated complexes, showing highly intense broad bands.
The C 1S, N 1S, O 1S and Cl 2P appear at 285.1, 400.0, 531.2 and
207 eV, respectively.34 From Fig. 3(a–e), the C 1S XPS traces can
be deconvoluted into ve peaks, and the corresponding values
284.6 eV, 285.1 eV, 286.4 eV, 286.9 eV and 288.8 eV are
attributed to the carbon sp2 (C]C), carbon sp3 (C–C), imine
C]N, aryl ether (C–O–C), and carbonyl (C]O), respectively.
The C]O group binding energy of 288.9 eV disappears for the
complexes and a new broad peak appears at 286.9 eV, which is
assigned to the enol form of deprotonated hydrazone (C–Oꢀ)
during complexation.35
The XPS studies of FC reveal the multiplicity of electrons,
valence states, magnetic states of metal ions and stereochem-
ical congurations. The phenomenon of shake-up satellite
peaks in the X-ray photoelectron spectra at the 2P level of
nickel(II) and copper(II) complexes are well documented.36 The
appearance of shake-up satellite lines behind the M(II) 2P core
lines of Ni(II) and Cu(II) showed the covalency, magnetic and
geometric properties of the compound. These XPS results
are match those of an earlier investigation.37 From Fig. 4 and
Fig. 4 M(II)2P3/2 XPS patterns of (a) Ni(II)L$2ClO4, (b) Ni(II)L–Y, (c) Cu(II)
L$2ClO4 and (d) Cu(II)L–Y.
Fig. 3 Deconvoluted XPS of the C1S region for (a) H2L, (b) Ni(II)L$2ClO4, (d) Cu(II)L$2ClO4, (c) Ni(II)L–Y and (e) Cu(II)L–Y.
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Table 2 Binding energy of the FC and ZEMC
Binding Energy (eV)
Compound
Si (2P)
Al (2P)
C (1S)
O (1S)
N (1S)
M(II) (2P)
D2P
Ni(II)L$2ClO4
Cu(II)L$2ClO4
Ni(II)L–Y
—
—
102.5
102.6
—
—
74.6
75.8
284.45
285.05
284.85
284.75
531.5
399.51
399.60
400.12
400.80
855.20, 873.13
934.12, 953.87
855.97, 875.10
934.90, 954.30
17.45
19.03
19.02
19.35
532.03
532.03
532.4
Cu(II)L–Y
Table 2, the traces of Ni(II)L$2ClO4 indicate that no shake-up
satellite peaks are observed behind the region of 878 eV for
Ni(II)(2P), and hence, it conrms the planar form and diamag-
netic nature of Ni(II).38,39 In the 2P level spectra of Ni(II)L–Y, D2P
(ca.1.73 eV) is more compared to that of Ni(II)L$2ClO4. This may
be because of the presence of intracrystalline hydroxyl groups
and electrostatic interactions with (Si/Al)O4 lattice.
From ESI (Fig. S14c & d†), copper(II) complexes were shown
to shake up satellites, whereas the diamagnetic Cu(I)(3d10
)
never gives any satellite peaks. Hence, the Cu(II)L$2ClO4 and
Cu(II)L–Y show a paramagnetic nature (3d9). These observations
conrm the presence of an unpaired electron in the dx2–y2
orbital, and the EPR spectral data also support the same
nding.40 The broadening of the Cu 2P3/2 satellite peak was
observed. It may be due to the distortion of the octahedral to
planar geometry. The Cu 2P peaks of Cu(II)L$2ClO4 appear at
binding energy values of 934.12 eV and 953.87 eV, but the Cu(II)
L–Y exhibits values at 934.90 eV and 954.30 eV for 2P3/2 and 2P1/
2, respectively. Cu(II)L–Y also exhibits the same peak position
similar to Cu(II)L$2CLO4 with a binding energy difference of
0.41 eV. From Fig. 4, the peak at 931.8 eV represents the
reduction of Cu(II) to Cu(I), which was caused by X-ray irradia-
tion during the acquisition time of XPS analysis. However, for
nickel proximity the reduction is less and XPS spectra show the
broadening of the 2P level peak.41 The deconvoluted N1S and
O1S XPS traces (ESI Fig. S15 & 16†) show that the binding energy
values also suggest that the M(II) ions are coordinated with
azomethine nitrogen and the enol form of deprotonated oxygen
in both FC and ZEMC.
Scheme 1 The proposed reaction mechanism of Ni(II) and Cu(II)
complexes with a tetradentate N2O2 Schiff base moiety.
NMR, ESI-mass and the above mentioned spectral studies
conrm the possible proposed structure of the complexes in the
free and encapsulated systems, as given in Scheme 1 & 2.
Scheme 2 The proposed reaction mechanism and framework struc-
ture of zeolite with encapsulated metal aryl hydrazone complexes of
Ni(II) and Cu(II).
3.6 Powder X-ray diffraction
The XRD patterns of the NaY, Ni(II)L–Y, Cu(II)L–Y, NI(II)L$2ClO4
and Cu(II)L$2ClO4 were recorded at room temperature, as
shown in Fig. 5(a–c). The XRD patterns of Ni(II)L–Y and Cu(II)L–
Y are comparable with that of Na–Y, although a slight change The Ni(II)L–Y shows three new peaks at 2q values of 12.9ꢄ, 27.1ꢄ
was observed in the peak intensity. The relative peak intensities and 40.37ꢄ, and Cu(II)L–Y also shows new peaks at 18.2ꢄ and
of the 220, 311, and 331 reections for ZEMC slightly decreased 42.6ꢄ. These new peaks suggest the allocation and formation of
when compared with the parent zeolite reections, and this can metal complexes in the cavity of zeolite. In another manner, FC
be attributed to a change in sodium ion exchange by metal causes the surface reduction of Na–Y during encapsulation,
moieties. NaY shows a peak intensity of I331 > I220 > I311, but in and hence, the observed peak intensity was low. (Asterisks
the case of the Ni(II)L–Y and Cu(II)L–Y, the corresponding peak Fig. 5).43 The crystalline nature of NaY does not change during
intensities I331 > I311 ¼ I220 and I331 [ I311 > I220 are observed.42 impregnation.
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Fig. 5 XRD spectra of (a) NaY, (b) Ni(II)L–Y and (c) Cu(II)L–Y (stick
diagram shows the XRD patterns of (b) Ni(II)L$2ClO4 and (c) Cu(II)
L$2ClO4). (Asterisks indicate the presence of metal complexes in the
cavity of the zeolite.)
3.7 BET analysis
The results of the Brunauer–Emmett–Teller (BET), N2 adsorp-
tion/desorption isotherms, surface area and the pore volume
studies for NaY, Ni(II)L–Y and Cu(II)L–Y are shown in ESI
(Fig. S17a–c†). The pore size distribution curves of the samples
were evaluated from the adsorption branches of isotherms
(stick diagrams) using the BJH method, and these composites
had type IV isotherms initially up to at p/p0 ¼ 0.35 with a steep
increase at p/p0 ¼ 0.35–0.7, reecting their narrow pore size
distribution because of the capillary condensation of pores, i.e.,
the presence of guest molecules in the pores of zeolite.44,45 The
surface area of zeolite was observed to be 600 m2 gꢀ1. However,
in the case of ZEMC, the surface area was drastically reduced to
305 m2 gꢀ1 and 230 m2 gꢀ1 respectively. The average pore size of
free zeolite was 0.62 nm and it reduced to 0.26 and 0.17 nm on
Ni(II) and Cu(II) respectively, possibly due to the presence of
metal complexes in the pores of zeolite. This clearly suggests
that the FC was encapsulated in the cavities of zeolite. The
surface analysis reveals the ZEMC based on metal loading;
hence, the copper(II) complex may show more reactive sites than
nickel(II) complex.
3.8 Thermal analysis
The TG/DTG curves of FC and ZEMC were obtained in a static
air atmosphere, and are shown in Fig. 6(a–e). In the case of
ZEMC, the TG curve shows a residual mass of around 85%,
clearly suggesting and showing the thermal stability of the
composites. The DTG curves of FC and ZEMC clearly show
multi-step decomposition. In the case of Ni(II)L$2ClO4, the rst
step between 303–423 K corresponds to the loss of coordinated
counter ions with a mass loss of 8%. In the second step, the
continuous loss of the ligand molecules of the complex was
observed in the temperature range of up to 731 K with a mass
loss of 79%. The residual mass of 12% corresponds to the
formation of nickel oxide. In the case of Cu(II)L$2ClO4, the mass
loss of 17% lattice water and perchlorate molecules occurred
Fig.
6
TG-DTG curves of (a) Ni(II)L$2ClO4, (b) Cu(II)L$2ClO4, (c)
Ni(II)L–Y, (d) Cu(II)L–Y and (e) Na–Y.
below 513 K. A further step corresponds to the degradation of temperature of ZEMC was higher when compared with the peak
Cu(II)–ligand moiety between 523–773 K with a mass loss of temperatures of the FC. This clearly suggests that the metal free
70%. The residual mass of 11% indicates the formation of complexes were strongly included in the cavities of zeolite.
CuO.46 From Fig. 6c & d, DTG analysis showed that the peak From Fig. 7(e), the NaY weight loss (15%) occurred sharply in
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Fig. S25†), Ni(II)L–Y and Cu(II)L–Y 98 nm, which have corre-
sponding average sizes of around 145 nm, 165 nm and 180 nm,
respectively.47,48
The TEM photographs of the parent NaY and ZEMC are
shown in Fig. 8(a–c). These reveal that the structure of the
solid supports was rectangular spheroid (tablet shape) and
that its channels were well ordered. The encapsulated
complexes Ni(II)L–Y and Cu(II)L–Y also show an opaque
nature and well ordered shape but a slight change at the
surface edges. In addition, negligible agglomeration is
observed when compared to parent zeolite. The morphology
and the SAED patterns of the Ni(II)L–Y and Cu(II)L–Y show a
crystalline nature even aer the encapsulation of complex
moiety in the cavities of the zeolite.48 The bright eld images
of Na–Y and ZEMC show the absence of metal complex traces
on the surface.
4 Catalytic studies
4.1 Interaction of the Ni(II)L$2ClO4 and Cu(II)L$2ClO4 with
hydrogen peroxide
The effect of hydrogen peroxide in the presence of the Ni(II)
L$2ClO4 and Cu(II)L$2ClO4 was recorded with the UV-Vis spectra
shown in the ESI (Fig. S25a & b†) with a 2 : 1 molar ratio of H2O2
and metal complexes. The decrease in optical density for the d–
d transition peak value was observed, and new peaks around
450 and 470 nm and colourless solid particles indicate the
existence of metal activated oxygen radicals like superoxo or
oxodimer species. The same phenomenon may be expected for
the ZEMC in the formation of the new intermediates adduct and
it can improve the substrates rate of the reaction rate and
selectivity. It was observed that copper has a higher tendency for
the formation of the reactive intermediates than nickel. ZEMC
is less likely to form dimerised oxo and polymeric species with
metal(II) centres. This improves the product formation in liquid
phase oxidation reactions.49
Fig. 7 SEM images of (a) NaY, (b) Ni(II)L–Y and (c) Ni(II)L–Y.
4.2 Catalytic activity and kinetic parameters of ZEMC and FC
in BH oxidation
one step due to the presence of water molecules, and a
comparison of these observations also suggested the presence
of metal complexes in the zeolite cavities.
The catalytic activity of the FC and ZEMC was investigated in the
liquid phase (mild) oxidation reaction of BH, while using H2O2
as an oxidant. In general, the metal complex oxidation reaction
depends on the formation of perhydroxy and hydroxyl radicals
3.9 FESEM/HRTEM analysis
Typical scanning electron micrographs obtained for the parent in the presence of oxidants. The polymeric nature of free
NaY and ZEMC are shown in Fig. 7(a–c). The NaY has a cubic complexes might show less activity even with H2O2. In the
angular shape. The SEM analysis of the ZEMC shows that the absence of H2O2, BH oxidation does not occur, and the metal
crystalline nature of Na–Y remains almost the same even aer active centre plays a crucial role in BH oxidation. In the pres-
complexation occurs in the cavities of zeolite. From the ESI ence of FC, an optimum conversion was observed with H2O2
(Fig. S18–21†), EDAX spectra of ZEMC show that each element is because of the formation of [M(II)(L)]$H2O2 adduct as an inter-
present in the cavity of zeolite. SEM image elemental mapping mediate. The adduct can generate _OOH and _OH intermediates
indicates a uniform distribution of elements in the cavities of with nickel(II) and copper(II). From Section 4.1, the decrease in
zeolite. Elemental mapping clearly suggests that particle surface the peak intensity of charge transfer and d–d transitions of FC
boundaries do not have surface complexes. Using ImageJ and simultaneous formation of radical intermediates were
analysis soware, a histogram was plotted for the ZEMC. The observed around 450 and 470 nm.50 The BH oxidation reaction
average size of the ZEMC particles was calculated based on the was monitored by the absorption spectra. The aliquot samples
Gaussian t of the size distribution histogram of NaY (ESI were collected from the reaction mixture aer every 60 min, and
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Fig. 8 HRTEM images of the (a) NaY, (b) Ni(II)L–Y and (c) Cu(II)L–Y and corresponding SAED pattern (d) NaY, (e) Ni(II)L–Y and (f) Cu(II)L–Y.
absorbance values were recorded at 223 (ꢁ2) nm. From ESI and ZEMC. Copper has a greater tendency to form hydroperoxy
(Fig. S26a–e†), the progressive decrement of the absorption intermediates with H2O2 in acetonitrile medium than nickel.
bands were recorded at 250 and 340 nm every 60 min.51 From Cu(II) is a 15-electron species and participates actively in this
Fig. 9(a), the percentages of conversion for NaY, Ni(II)L$2ClO4, electron back-donation process; hence, it shows a higher cata-
Cu(II)L$2ClO4, Ni(II)L–Y and Cu(II)L–Y are 18%, 56%, 96%, 65% lytic activity in comparison to the corresponding 16-electron
and 85%, respectively (no signicance difference in conversion Ni(II) complex. Kinetic parameters in BH oxidation also follow
was observed even at 12 h). The copper complex was shown to the pattern of the conversion percentage. From Fig. 9(b), the
have a higher conversion percentage than nickel in both the FC kinetic plot between ln(Ct/C0) vs. time shows a negative slope
Fig. 9 (a) & (b) Graphs of time vs. % conversion, and (c) & (d) kinetic plots for FC and ZEMC.
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and the reaction follows pseudo rst order kinetics. All the O2_ꢀand _OH radicals are very reactive and quickly oxidise
kinetic reactions show the same phenomenon. This may be due organic species at the surface of the zeolite. Hydroxyl radi-
to the usage of H2O2 and a constant BH concentration. The rate cals (_OH) are considered to be the most powerful oxidant
of the reaction follows the rst order rate equation:
(Eo ¼ 2.8 V) among other oxidants.55 Even an acidic nature
can enhance the formation of the active radical and limit
degradation time. During metal reduction from M(II) to M(I),
the generation of _OH radical is greater in the presence of
H2O2.56 Even the uniform distribution of metal in the zeolite
cavity leads to a fast photogeneration of hydroxyl radical
(eqn (3)). Therefore, catalytic activity depends on the
percentage of metal, which results in more unsaturated
surface coordination sites.
ꢀ
ꢁ
Ct
ln
¼ ꢀkappt
(2)
C0
where Ct is the concentration of BH at different time, C0 is
the initial concentration, t is the time and k is the reaction
rate constant in minꢀ1. From Fig. 9(b), the values of the rate
constant for NaY, Ni(II)L$2ClO4, Cu(II)L$2ClO4, Ni(II)L–Y and
Cu(II)L–Y catalysts are 0.000375 minꢀ1, 0.00202 minꢀ1
,
0.00491 minꢀ1, 0.00181 minꢀ1 and 0.00468 minꢀ1, respec-
tively. The Cu(II)L–Y shows a higher rate than Ni(II)L–Y,
which may result from the increased generation of OHꢀ
ion with the copper(II) centres compared to the nickel(II)
centres. Cu(II)L–Y has a smaller surface area than Ni(II)L–Y
and Na–Y, but still shows higher activity.52 Hence, copper
and nickel enhance the host–guest interaction, which
leads to the avoidance of the formation of polymeric metal
species and enhances the catalytic activity of the reaction.53
hv
ƒƒƒƒƒ!
MðIIÞ þ eꢀ
MðIÞ
:
OHꢀ þ hþ/ OH
:
O2 þ Hþ/O2
ꢀ
(3)
:
:
O2 ꢀ þ Hþ/HO2 þ O2
:
2HO2 /H2O2 þ O2
:
H2O2 þ eꢀ/ OHþꢀOH
From the ESI Fig. S28†, the decrease in wavelength of 5 nm
from 554 nm is due to either the electrostatic interactions of
hydroxyl groups present on the surface, or formation of the de-
ethylated species of the dye molecule during degradation.57 The
photogenerated electrons increase the efficiency towards hole
formation and minimize band gap energy; meanwhile, the
4.3 Mechanistic issues for photochemical performance
The photocatalytic degradation of RhB with NaY, Ni(II)L–Y,
Cu(II)L–Y, Ni(II)L$2ClO4 and Cu(II)L$2ClO4 under UV/visible irra-
diation has been investigated. The percentage of degradation
and kinetic parameter were calculated based on Lambert–Beer's
law (3 ¼ 103 930 molꢀ1 cmꢀ1 L) (A ¼ 3cl).
formation of _OH, _O2H and ꢀO2 radicals starts a cascade of
+
oxidation reactions that can completely convert organic matter
in solution into water, carbon dioxide and inorganic
compounds.58,59 From the ESI (Fig. S38†), the change in hyp-
sochromic shi was around 25 nm, which caused the detach-
ment of the chromophoric group present in the dye molecule
and the formation of the de-ethylated intermediates of RhB
molecules.60
The degradation efficiency was calculated by the optical
absorption spectral analysis. The aliquot samples of reac-
tion medium were collected, and the resulting absorption
changes were recorded at 554 ꢁ 1 nm. The spectral changes
are given in ESI (Fig. S27 & S28†). ZEMC has greater degra-
dation performance when compared to FC and NaY zeolite.
In both the probe reactions, the removal percentages are
15%, 88%, 100%, 55% and 50% (26%, 73%, 78%, 44% and
63% in the case of visible light) for NaY, Ni(II)L–Y, Cu(II)L–Y,
Ni(II)L$2ClO4 and Cu(II)L$2ClO4, respectively. The metal
enhances the acidity of the zeolite during the exchange
process, and due to this photocatalytic performance,
the rate of reaction and removal efficiency of RhB also
increases.54 ZEMC could decrease the recombination of
electron–hole pairs and enhance the photocatalytic perfor-
mance. The apparent rate constant (kapp) values at xed
concentration of the H2O2 concludes rst order reaction.
Fig. 9 reveals the negative slope in both the cases. The rate
constants for Na–Y, Ni(II)L–Y, Cu(II)L–Y, Ni(II)L$2ClO4 and
Cu(II)L$2ClO4 in UV-light were 0.00128, 0.375, 0.0279, 0.0115
and 0.0285 minꢀ1 and in visible light were 0.0018, 0.00653,
0.00704, 0.00274 and 0.00866 minꢀ1 respectively. The ZEMC
shows higher activity because of its metal loading efficiency
(from Table A†), which enhances photogenerated electron
pairs (eꢀ and h+). Photogenerated holes and electrons
may react with surface hydroxyl groups that are adsorbed
water or O2 to generate the active oxidative ionic radicals
4.4 Recycle tests, metal leaching tests and catalytic activity
The stable (Si/Al)O4 moiety of the zeolite does not allow metal
ion leaching. Because of the higher cross-sectional area of RhB,
it is not possible for RhB to enter the cavities of the zeolite.
While using H2O2 negligible metal leaching was observed. The
approximate cross-sectional area of the metal hydrazone
2
2
˚
˚
complexes is 162 A and 164 A (measured using the chem
sketch soware tool). It can be t to the zeolite unit cell
Fig. 10 The overall percentage of conversion of BH oxidation (bar
diagram) and dye degradation (line diagram) in the three cycles for the
(O2_ꢀ, ꢀOOH) and _OH) from the reaction medium. The recovered ZEMC.
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dimensions, and in the liquid phase encapsulation, the free
complexes form. Hence, FC can be impregnated in the cavity of
the zeolite and stabilised by (Si/Al)O4 moieties. Thus, metal ion
leaching is very difficult aer impregnation (Table A†). Aer
completing the reaction, ZEMC was recovered by nano-ltration
and washed with a mixture of water, dilute HCl, acetonitrile and
methanol. The resulting coloured solid was dried at 353 K for 6
h and the catalytic activity of each composite was investigated.
The overall percentages are provided in Fig. 10.
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inuence the rate of reaction and conversion percentage. The
optical spectral data and LC-MS data have shown benzophe-
none fragments in the BH oxidation. In the photocatalytic
S. Rachinski, C. B. Pinheiro, R. B. Faria, A. Casellato,
S. P. Machado, A. S. Mangrich and M. Scarpellini, J. Braz.
Chem. Soc., 2010, 21, 1218.
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generated oxidants like ꢀOH, +_O2H, ꢀO2 interacting with metal
D. R. Richardson, JBIC, J. Biol. Inorg. Chem., 2003, 8, 866.
species, thus starting a cascade of oxidation reactions that can 17 A. Cukurovali, I. Yalmaz and S. Kirbag, Transition Met.
convert the organic matter in solution completely into water, Chem., 2006, 31, 207.
carbon dioxide, and inorganic compounds. In the dye removal 18 S. Sujatha, S. Balasubramanian, H. K. Fun and
and BH oxidation, the apparent rate constant (kapp) represented K. Chinnakali, Polyhedron, 2008, 27, 1925.
the pseudo rst order reaction in all cases. Here the percentage 19 M. R. Maurya, S. J. J. Titinchi and S. Chand, J. Mol. Catal. A:
of the conversion was more for the copper complexes than for
Chem., 2003, 201, 119.
nickel complexes. Hence, the surface active species accelerates 20 L. L. Sheu, H. Knozinger and W. M. H. Sachtler, J. Mol. Catal.,
the rate of the reaction in both the cases. The surface area and 1989, 57, 61.
the percentage of copper (Table A ESI†) might inuence the 21 S. M. Emam, F. A. E. Saied, S. A. E. Enein and H. A. E. Shater,
rate of the reaction rather than average particle size and
crystalline nature.
Spectrochim. Acta, Part A, 2009, 72, 291.
22 M. S. Niasari, F. Davar and K. Saberyan, Polyhedron, 2010, 29,
2149.
23 M. S. Niasari and A. Sobhani, J. Mol. Catal. A: Chem., 2008,
285, 58.
Acknowledgements
One of the authors G. Ramanjaneya Reddy is grateful to the 24 A. B. P. Lever, Inorganic electronic spectroscopy, Elsevier,
University Grants Commission (UGC), New Delhi, India for Amsterdam, Netherlands, 1984.
nancial support. The authors are thankful to the Centre for 25 S. Yadav, M. Ahmad and K. S. Siddiqi, Spectrochim. Acta, Part
Nanoscience and Nanotechnology, University of Madras, A, 2012, 98, 240.
Chennai, India for their support during the characterization. 26 M. M. A. Neaimi and M. M. A. Khuder, Spectrochim. Acta, Part
The authors are grateful to Dr G. Bhaskar Raju, Scientist-in- A, 2013, 105, 365.
Charge, NML-CSIR Madras Complex, Chennai for support 27 M. V. Angelusiu, G. L. Almsjan, D. C. Ilies, T. Rou and
during the experimental work.
M. Negoiu, Chem. Bull. Politehnica, 2008, 53, 1.
28 V. P. Singh, A. Katiyar and S. Singh, BioMetals., 2008, 21, 491.
29 S. Sujatha, S. Balasubramanian and B. Varghese, Polyhedron,
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