Intercalation of Azo Dyes in Ni-Al Layered Double Hydroxides

Abstract

Ni-Al layered double hydroxides were synthesized by hydrothermal process and intercalated with azo dyes viz. metanil yellow, sunset yellow and amaranth by anion exchange process. The resulting hybrid intercalated solid compounds were characterized by powder XRD, FTIR, DRS and TGA. The powder X-ray diffraction revealed the presence of supramolecular host-guest interaction between the host matrix and interlayer anionic dye guest with an expanded interlayer distance. The TGA studies showed that the dye-intercalated layered double hydroxides had higher thermal stability than the pristine dye. Moreover, there was no significant change in the UV-VIS/DR spectra of the dye-intercalated sample after heating up to 200 °C, indicating that the thermal stability of dye is markedly enhanced by the intercalation into the gallery domain of NiAl-LDH.

Full text

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
INTERCALATION OF [Fe (C2O4)3]3- AND [Cr (C2O4)3]3- IN NICKEL
ALUMINIUM CARBONATE LDH
Hemaprobha Saikia, Nabajit Sarmah and Jatindra Nath Ganguli*
Department of Chemistry, Gauhati University, Assam, India-781 014.
E-mail: jatin_ganguli_gu@yahoo.co.in
A Nickel Aluminum carbonate LDH was synthesized by hydrothermal process. The NiAl LDH was characterized by
XRD, FTIR, SEM, EDX, DRS and TGA. The PXRD study shows the basal spacing of NiAl LDH as 7.39Å. [Fe
(C2O4)3]3- and [Cr (C2O4)3]3- were intercalated in the NiAl LDH by anion exchange process. These intercalated
compounds were characterized by XRD, FTIR, SEM, EDX, DRS and TGA. The PXRD study shows that the basal
spacing of NiAl LDH on intercalation of [Fe (C2O4)3]3- and [Cr (C2O4)3]3- increases to 9.59 Å and to 9.4Å respectively.
The TGA study of NiAl LDH shows two weight losses in the temperature ranges 383K-513K and 513-910K but in
[Fe(C2O4)3]3- intercalated NiAl LDH four weight losses in the temperature ranges 383K-513K, 533K-623K, 653K-
670K and 673K-910K were observed. The SEM and TEM images show the morphology of the LDH. The EDX, IR and
TGA studies confirm intercalation of [Fe (C2O4)3]3- and [Cr (C2 O4 ) 3] 3- in NiAl LDH. Benzoylation of benzene using
intercalated trisoxalato ferrate (III) LDH and trisoxalato chromate (III) LDH as catalyst shows encouraging results.
Keywords: Ni-Al Carbonate LDH, Intercalation, [Fe (C2O4)3]3-, [Cr (C2O4)3]3-
Introduction
Hydrotalcite, a magnesium aluminum hydroxy carbonate was discovered in Sweden around 1842
[1]. It occurs in nature in foliated, contoured plates and fibrous masses. The electric charge of the
layers and interlayer ions is just the opposite of that found in smectite clays, and for this reason,
these materials are known as anionic clays. Like cationic clays, the interlayer anions in LDH are
easily exchanged and carbonate anions have been exchanged for different anions. The nature of the
layered cations can be varied. Although most of the studies reported in the literature refer to
systems with MII/MIII cations in the layers, others with MII/MIV or MI/ MIII are also known. The value
of the MII/ MIII ratio is limited if pure materials are desired, and such a ratio, in addition to being
important, also determines the concentration of interlayer anions. The general formula of the
hydrotalcite is [M1-xII MxIII (OH)2] Am-x/m.nH2O or shortened as MII, MIIIA- LDH. Many synthetic
LDH can be prepared by different combinations of MII, MIII and Am- components. Anions can be
simple ones as carbonate, nitrates, chloride etc. or bulk anions. The height of the interlayer space
depends both on the nature of the anion and on its orientations, if it is not spherical. An important
feature of these hydrotalcite is that they can be obtained by direct synthesis from soluble salt
precursors or by anionic exchange or by recovering the layered structure [2]. Once a hydrotalcite
has been calcined at moderate temperatures; it leads to mostly amorphous materials, which in
contact with solutions containing anions, recover the layered structure, hosting the anions in the
interlayer space. Interest in hydrotalcites and derived materials arises from the possibilities of their
wide use as: catalysts or catalyst supports, processing of selective chemical nanoreactors, separation
and membrane technology, filtration and controlled release of anions, electroactive and photoactive
materials [3-5].In this paper we report the synthesis of NiAl LDH, intercalation of [Fe (C2O4)3]3- and [Cr
(C2O4)3]3- in the interlayer space of NiAl LDH and characterization of the LDH composite. The NiAl LDH
and intercalated LDH were used as catalyst in the Benzoylation of benzene.
Experimental
Materials: The materials Aluminium nitrate and Nickel nitrate used were purchased from LOBA
CHEMIE, Benzoyl Chloride and Benzene from MERCK and Sodium Hydroxide and Sodium
carbonate were procured from Fine Chemicals Limited.
Synthesis of LDH
A mixture of Ni (NO3)2.6H2O and Al (NO3)3.9H2O was dissolved in 30 mL deionized water to form
a clear solution ([Ni2+] = 0.2M, [Al3+] = 0.1M). The salt solution was rapidly poured into a 30 mL
NaOH and Na2CO3 solution ([OH-] = 0.48M, [CO3]2-= 0.2 M) under vigorous stirring. The mixture
was further stirred for 20 minutes at room temperature. Subsequently, the suspension was
centrifuged, washed with water for 5 cycles to remove residue salts and redispersed in deionized
1

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
water. The resulting suspension was transferred into a 100 mL Teflon-lined stainless steel autoclave
and the volume of the suspension was made upto 70 mL with deionized water. The autoclave was
then tightly sealed and heated in an oven at 423 K for 10 hrs. The resulting bluish green suspension
was dried in an oven at 343 K.
Intercalation
4g of LDH was added to an aqueous solution of 2g of K3 [Fe (C2O4)3].3H2O in 100 mL of
decarbonated water. Then the solution was stirred for 72 hours. The solid was centrifuged, washed
and redispersed in deionized water. The light green solid was dried in an oven at 338 K. We have
also intercalated [Cr (C2O4)3]3- in NiAl LDH by the same process.
Characterization
Ni and Al were estimated by gravimetric Method [6], the C, H and N analysis was done with a
Perkin Elmer 2400 Analyzer. Powder X-ray diffraction (PXRD) patterns were collected on a
Brucker D8 Advance X-ray diffraction measurement system at USIC, GU. Fourier transform
infrared spectra (FT-IR) were recorded in a Perkin-Elmer Spectrum RX / FTIR system, TGA was
done in a Mettler Toledo instrument in nitrogen atmosphere at a heating rate of 100C/minute. The
diffuse reflectance spectra (DRS) of the samples were recorded in a HITACHI, U-4100
spectrophotometer. Specific surface area (BET) were measured with N2 adsorption/desorption in a
Micromeritic Triastar 3000 apparatus. The theoretical calculations were made using Gaussian 03
package program. HRTEM images were recorded in a Jeol Jem-2100 Electron Microscope.
Results and discussion
Composition
The composition of the LDH as found from elemental analysis were
[Ni0.68Al0.32 (OH) 2] (CO3)0.1(NO3)0.12 1/2 H20, for 1:0.5M LDH
[Ni0.70Al0.29 (OH) 2](CO3)0.1(NO3)0.09 1/2 H20, for 1:0.4M LDH
[Ni0.65Al0.35 (OH) 2](CO3)0.1751/2 H20, for 1:0.6M LDH
PXRD study
The pure LDH displays the characteristic diffraction peaks corresponds to hydrotalcite- like LDH
family. The (003), (006), (012), (110), and (113) reflections were recorded in Table 1. Fig.1 shows
the XRD of the NiAl LDH obtained after heating at different temperatures. The 003 and 006 peak
of LDH disappears on heating upto 673K, showing the collapse of LDH structure. The PXRD
shows mixed oxide reflections, which remains so even on heating upto 1173K. All calcined
products exhibit the diffractions of NiO- like Bunsenite phase, which can be easily indexed to cubic
NiO phase and existence of some amorphous products like alumina [5]. The reflections of LDH
were shifted slightly to lower values of θ indicating expansion of the layer structure on
intercalation. In case of trisoxalato ferrate (III) intercalated LDH, PXRD data shows an increase in
the basal spacing. In case of trisoxalato ferrate (III) intercalated LDH, PXRD data shows an
increase in the basal spacing (d003) of NiAl LDH from 7.3 Å to 9.59Å (Fig.2).
Table.1 XRD of NiAl LDH and intercalated Trisoxalato ferrate(III), Trisoxalato chromate(III)
NiAl
LDH
Intercalated
trisoxalato
ferrate(III)
LDH
Intercalated
trisoxalato
chromate(III)
LDH
d-
spacing
hkl d-spacing hkl d-spacing hkl
7.39 00
3
9.59 00
3
9.4 003
3.73 00
6
4.93 00
6
6.31 006
2.11 01
2
01
2
012
1.51 110 110 110
2

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
1.47 113 113 113
3

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
This
suggests that the interlayer distance of the LDH has increased to 4.82Å from 2.53 Å (given that the
original interlayer spacing of NiAl LDH is 2.53Å; calculated as: dLÅ=7.3-4.77). The trisoxalato
metal complexes may adopt different conformation depending on least energy for a particular
conformation. The least energy may be determined by the columbic forces and H-bonding between
the LDH layers and the anion. Therefore a theoretical calculations using Gaussian 3 was attempted.
The geometrical minima of the [Fe(C2O4)3]3- species were optimized with 6-31+g(d) basis set with
Becke three parameter exchange and Lee, Yang and Parr correlation functional, B3LYP [7] and was
confirmed by frequency calculations. Using theoretical calculation it has been found that the
minimum height of [Fe (C2O4)3]3- ion is 2.39 Å[8]. X-ray diffraction studies on the K3 [Fe
(C2O4)3].3H2O complex give the maximum recorded height as 5.32Å. Therefore the interlayer
spacing found from PXRD as 4.82Å is approximately equal to the expected value of the complex
[Fe (C2O4)3]3- without its three waters of crystallization. In case of [Cr (C2O4)3]3- intercalated NiAl
LDH, the reflections of 003 and 006 were shifted slightly to lower values of θ which may be due to
expansion of layer on intercalation of [Cr (C2O4)3]3- anion in the interlayer species of LDH on
exchange of CO32-. The basal spacing (d003) of NiAl LDH expanded from 7.3 Å to 9.4Å (Fig.3) in
4
Figure 2 PXRD of NiAl LDH at different temperatures (a) 373K, 473K, 573K and (b)
298K, 673K, 973K, 1173K
Figure 1 Schematic Diagram of Layered Double Hydroxides

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
case of trisoxalato chromate(III).
FT-IR
5
Figure 3 PXRD of NiAl LDH and intercalation of (a) trisoxalato ferrate(III), (b)
trisoxalato chromate(III) with NiAl LDH

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
The FT-IR spectra of pure LDH and intercalated LDH composite in the region between 4000 and
400 cm-1 are shown in Fig.4. For pure LDH, a broad absorption band around 3600-3200 cm-1
centered at 3441 cm-1 corresponds to the O-H stretching vibrations of hydroxyl groups of brucite
layers and interlayer water molecule. The bands at 1077 cm-1, 824 cm-1, 1514 cm-1, 1360 cm-1, were
attributed respectively to ν1, out of plane deformation (ν2), ν3, symmetric stretching vibrations of the
interlayer carbonate ions. The bands at 658 cm-1, 432 cm-1 were due to metal hydroxyl and metal
oxygen vibrations in the lattice of LDHs. In case of intercalated LDH, the bands appears at 1712
cm-1, 1387 cm-1, 885 cm-1, 797 cm-1, 580 cm-1, 528 cm-1 and 432 cm-1, which may be attributed to νa
(C=O) (ν7), νs (CO)+ν(CC) (ν2), νs (CO)+δ (O-C=O) (ν3), δ(O-C=O)+ν (MO) (ν9), crystal water, ν
(MO)+ ν(CC), metal oxygen (Ni-O) [9].
Morphology
SEM
The SEM images (Fig.5) clearly shows the layer structure of NiAl LDH and intercalated NiAl
LDH. The EDX also shows intercalation of tris oxalato ferrate (III) and tris oxalato chromate (III) into
NiAl LDH.
6
Figure 4 FT-IR of NiAl LDH and intercalation of (a) trisoxalato ferrate(III), (b)
trisoxalatochromate(III) with NiAl LDH

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
HRTEM
The HRTEM shows the layer lattice structure of NiAl LDH. Fig.6 shows the morphology of the tris
oxalato ferrate and Tris oxalato chromate (III) intercalated NiAl LDH. The TEM image shows rod like
layers for NiAl LDH and honey-comb structures for the intercalated LDH.
Diffuse reflectance spectra
The DRS spectra were shown in fig.7. The three bands in the spectra of the NiAl LDH at 373 nm,
650 nm and 1101 nm may be assigned to respectively 3A2g 3T2g, 3A2g 3T1g(F), 3A2g 3T1g (P)
transitions of octahedral Ni- hydroxo complex in the LDH and the band at 195nm may be due to
charge transfer from oxygen to aluminum atoms. Close inspection of the middle bands of Ni shows
the splitting due to spin-orbit coupling between the 3T1g (F) and the 1Eg states, because of close
energy at the Δ o value given by 6(OH) groups. The Tris-oxalatoferrate(III) complex shows four
bands, spin forbidden transitions 6A1 4T1, 6A1 4T2 (G) 6A1 4A, 4E and 6A1 4E (D) at 1448nm,
950nm, 659nm and 369nm. The intercalated DRS clearly shows the 1448 nm and the 400nm
transitions of Fe (III) but the middle transitions of Fe (III) and Ni (II) overlaps in the spectra of the
7
Figure 5 SEM and EDX of (a) NiAl LDH and (b) Intercalation of trisoxalato ferrate(III)
with NiAl LDH
Figure 6 HRTEM of (a) NiAl LDH and (b) Intercalation of trisoxalato chromate(III) with
NiAl LDH

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
complex.The intercalated NiAl LDH clearly shows the NIR band iron-oxalate complex at 1448nm,
while 950nm of iron complex and 1101nm band of Ni-LDH appears as broad band in the
intercalated complex. Same was the case for 650 nm of Ni and 659nm of iron complex as broad
band in the intercalated LDH. The 195nm and 373 nm band of LDH is unaffected in the intercalated
complex and were clearly visible in both neat and intercalated complex. In case of trisoxalato
chromate(III) intercalated NiAl LDH, there are broad bands around 300 nm, 580 nm and 680 nm may
be due to 4A2g 4T2g, 4A2g 4T1g(F), 4A2g 4T1g(P) . The DRS of NiAl LDH at different
temperatures, around 473K a sharp peak obtained at 300 nm and it may be due to Al to Oxygen
charge transfer in alumina formed from decomposition of LDH.
Surface Area
The N2 adsorption/desorption isotherm and the particle size distribution of the LDH and the
intercalated LDH were shown in fig.8.The surface area calculated by BET method from N2
adsorption/desorption isotherm was 106m2/g for NiAl LDH, 146 m2/g for intercalated tris oxalato
ferrate(III) and 138 m2/g for intercalated trisoxalato chromate(III) LDH. The micropore volume
determined by BJH method was 0.044cm3/g for LDH and 0.088cm3/g for intercalated LDH. The
slight increase of surface area and pore volume on intercalations of larger [Fe (C2O4)3]3- anion in
place of carbonate supports conclusion obtained from the PXRD that expansion due to intercalation
takes place.
8
Figure 7 DRS of NiAl LDH and intercalation of (a) trisoxalato ferrate(III) and (b)
trisoxalato chromate(III) with NiAl LDH
Figure 8 Surface Area of NiAl LDH and intercalation of (A) trisoxalato ferrate(III), (B)
trisoxalato chromate(III) with NiAl LDH

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
Thermal decomposition
Fig.9. shows the thermal decomposition of NiAl LDH, intercalated NiAl LDH with trisoxalato
ferrate(III) and Trisoxalato chromate(III). There were two weight losses in NiAl LDH. The first weight
loss at 383K was due to loss of interlayer water and second weight losses at 533K were due to
decarboxylation and dehydroxylation. There were four weight losses in the intercalated NiAl LDH.
The first weight loss was due to dehydration of water and rest weight losses were due to
decomposition of trisoxalato ferrate anion. In case of potassium trisoxalato ferrate, there were four
weight losses, in the first step, it was due to loss of hydrated water, in the second step, it was due to
loss of CO2 from the complex , third step, it was due to loss of CO2 and CO with complete
breakdown of the complex. The fourth step was the reduction of Fe3O4 by carbon [10-21]. This
decomposition also occurs at the intercalated LDH. In case of intercalated [Cr (C2O4)3]3- four weight
losses were found in the TG analysis.
Figure 9 TGA of NiAl LDH and intercalation of (A) trisoxalato ferrate(III), (B) trisoxalato
chromate(III) with NiAl LDH
Benzoylation of Benzene
6.15g of Benzene and 2.48g of Benzoyl chloride was stirred with 0.05g of trisoxalato ferrate (III)
intercalated NiAl LDH in a 50 mL round bottom flask at room temperature and atmospheric
pressure. After stirring for 3hrs the catalysts was removed by centrifugation and the solid product
was isolated by evaporation of the solvent from the reaction mixture in a rotatory evaporator. The
solid product was recrystallised and identified as benzophenone from NMR. [Proton NMR (300
MHz, CDCl3), δ ppm 8.152 (4H, doublet) 8.127 (2H, triplet) 7.725 (4H, triplet) and 13C NMR (75
MHz CDCl3) δ ppm (135.29, 131.35, 128.43, 128.26),]. The isolated product yield was about 72.1%
when trisoxalato ferrate(III) intercalated NiAl LDH was used as catalyst but when the same reaction
was performed using neat LDH as catalyst, the product yield was only 40%. Trisoxalato
chromate(III) intercalated NiAl LDH was also used as catalyst for the same reaction. The isolated
product yield was about 71.8%. The results show enhanced catalytic activity of LDH when metal
ion complexes are intercalated in it.
9

Intercalation of ….…. By H Saikia et al., Bulltin of the Catalysis Society of India, 11 (2012) 1-8
+
COCl
C
O
0.25g Catalyst
Conclusion
In this work we have demonstrated that anionic complex-LDH hybrid could be prepared by simple
ion exchange process. The intercalation of anionic complex in the LDH increases its thermal
stability. Such intercalated anionic complex LDH may serve as precursors for preparation of mix
metal oxide used in catalysis, magnetic materials, photoactive oxide and superconductors.
Acknowledgement
The authors are thankful to UGC for providing research fellowship under RFSMS scheme for
financial support. The authors are also grateful to IITG, USIC, GU and IASST, for providing
instrument facilities.
References
[1] R. Vicente, Marı´a Angeles Ulibarri b Coordination Chemistry Reviews 181 (1999) 61-120.
[2] S. Carlino, M. J. Hudson, Solid State Ionics. 4 (1994) 99-104.
[3] F. Kooli, V Rives, A. M. Ulibarri, Inorg. Chem. 34 (1995) 5114-5121.
[4] F. Kooli, V Rives, A. M. Ulibarri, Inorg. Chem. 34 (1995) 5122-5128.
[5] Zhonghao Li, jianling Zhang, Tiancheng Mu, Jimin Du, Zhimin Liu, Buxing Han*, Jing. Chen
Colloids and Surfaces A: Physicochem. Eng. 243 (2004) 63–66.
[6] A.I. Vogel, Vogels Textbook Of Macro And Semimicro Qualitative Inorganic Analysis, Fifth
Addition, 1979 London and New York.
[7] (a) A.D. Becke, J. Chem. Phys. 98 (1993) 5648-52. (b) C. Lee, W. Yang, R.G. Parr, Phys. Rev.
B, 37 (1988) 785-89.
[8] M.A. Drezdon, Inorg Chem. 27 (1998) 4628-4632.
[9] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds, 4th Ed.
New York: Wiley-interscience 245, 1997.
[10] J. Schmelz, T. Miyazawa, I.S. Mizushima, J.T. Lane, V.J. Quagliano, Spectrochim. Acta 9
(1957) 51.
[11] S. Carlino, Solid State Ionics. 98 (1997) 73-84.
[12] S. Carlino, M. J. Hudson. Solid State Ionics 110 (1998) 153-161.
[13] D. Broadbent, D.Dollimore, J.Dollimore, J.Chem.Soc.A 1 (1967) 451-454.
[14] S. Carlino, M. J. Hudson, Solid State Ionics. 5 (1995) 1433-1442.
[15] S. Carlino, M. J. Hudson, S.W.Hussain, J.A.Knowles, Solid State Ionics. 84 (1996) 117-129.
[16] G.M. Bancroft, K.G. Dharmawardena, A.G. Maddoch, Inorganic Chem. 9 (1970) 223-226.
[17] M. Del Arco, S Gutirrez, C Martin, V Rives, J Rocha, J.Solid State Chem. 151 (2000) 272-280.
[18] J. Fujita, L A Martell, K Nakamoto, J. Chem. Phys. 36 (1962) 324-331.
[19] T. Kwon, J .T Pinnavaia, Chem. Mater. 1 (1989) 381-383.
[20] P. Z. Xu, S.G. Stevenson, Q C. Lu, Q. G. Lu, F. P. Bartlett, P. P. Gray , J. Am. Chem. Soc.
128 (2006) 36-44.
[21] K.El Malki, M.Guenane. C.Forano, A.De Roy, J.P.Besse, Materials Sci. Forum 171 (1992) 91-
93.
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