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UNIVERSITI PUTRA MALAYSIA
INTERCALATION AND ADSORPTION OF ORGANIC DYES ON LAYERED DOUBLE HYDROXIDES
AZIRA ABD AZIZ
FSAS 2003 29
INTERCALATION AND ADSORPTION OF ORGANIC DYES ON LA YERED DOUBLE HYDROXIDES
AZIRA ABD AZIZ
MASTER OF SCIEl'CE IJNIYERSITI PUTRA MALA YSIA
20U3
INTERCALATION AND ADSORPTION OF ORGANIC DYES ON LA YERED DOUBLE HYDROXIDES
By
AZIRA ABD AZIZ
Thesis Submitted to the School of Graduate Studies, Universiti Putra i\1alaysia, in Fulfilment of the Requirements for the Degree of ''laster
of Science
September 2003
11
Abstract of thesIs presented to Senate of UmversItI Putra MalaYSIa m fulfilinent of the reqUlrements for the degree of Master of SCIence
INTERCALATION AND ADSORPTION OF ORGANIC DYES ON LAYERED DOUBLE HYDROXIDES
By
AZIRA ABD AZIZ
September 2003
Chairman: Professor Mohd Zobir bin Hussein, Ph.D.
Faculty: Science and Environmental Study
Nanostructured matenal of layered orgamC-InorganIc hybnd nanocomposItes can be
generated by encapsulatIon of an orgamc mOIety mto an morgamc lamella m whIch
the open lamellar systems such as layered double hydrOXIdes (LDHs) can be used as
the host For thIS study, synthesIs of nanocomposIte matenals was carned out by
usmg Mg/Al LDH as a host of morgaruc layers and naphthol blue black (NEB), fast
green (FG) and methyl orange (MO), orgamc dyes, as a guest It was fOlmd that the
concentratIOns of the orgamc mOIety and pH are cntIcal for the formatIon of the well-
ordered nanolayered hybnd matenals The optImum concentratIon of NBB at 1 50 x
10-' M, FG of 250 x 10-2 M and 300 x 102 M of MO at pH 10 resulted a well-
ordered nanolayered orgamC-Inorgamc hybnd nanocomposItes FTIR spectmm of
each nanocomposItes resembled a mIxture of each spectrum of the organIc and
InOrganIC speCIes, Indlcatmg the presence of both In the resultIng matenals Surface
morphology of Mg/AI-LDH and ItS nanocomposltes show agglomerates of compact
llJ
and non-porou<; <;tructure, a typIcal surface morphology for LDH and Its
nanocomposlte<;
For the adsorptIon studIes, the hydrotalclte-hke compounds of Mg-Al-carbonate
system (MAC) \\ere prepared and theIr heat-treated products were obtamed by
calcmatton of MAC tmder atrnosphenc condItIon for 5 hours at 300 °C (MAC300)
and 500°C (MAC500), respectIvely Each of the matenals was used as an adsorbent
for color removal of naphthol blue black (NBB) Batch kmetIc study showed that
these matenals are efficIent adsorbents for the amomc dye The adsorptIOn data were
fitted to the LangmUIr adsorptlon Isothenn and the adsorptIon capaCIty of MAC500
and MAC300 \\ere found to be hIgher than MAC The adsorbent was subsequently
recovered and the resultIng propertIes were charactenzed There was no sIgmficant
dIfferences m FTIR and surface morphology between the adsorbents and theIr NBB
adsorbed speCIes, except for Powder X-Ray Dlffractogram m WhICh they resembled
the LDH dIffractogram mdlcatmg the memory effect property of the calcmed LDH
The formatlon of Mg! Al-FG (MAF) WIth and WIthout mIcrowave-assIsted agmg was
done and the propertIes of the resultmg matenal were compared For both methods,
the results showed that the FG anIon was successfully mtercalated mto the Mg! Al
layered double hydroxIde lamella However, the lllIcrowave-assIsted method dId not
accelerate the fonnatlon of MAF but the agmg penod played an lIllpOrtant role In the
productIon of better-ordered laver structure of MAF The PXRD pattern <;howed that
a<; the agmg tllJle tor the svnthesls of MAF mcrca<;ed the mtenslty of the (001) peak
IV
mcreased, indIcatmg a better order of the nanolayered structure of the ft'sultmg
material.
Abstrak teslS yang dlkemllkakan kepada Senat UmverSltl Putra Malaysia sebagm memenuhl keperluan untuk IJazah Ma�ter Sams
INTERKALASI DAN PENJERAPAN BAHA� PERWARNA ORGANIK KE AT AS LAPISAN BERGANDA HIDROKSIDA
Oleh
AZIRA ABD AZIZ
September 2003
Pengerusi: Professor Mohd Zobir bin Hussein, Ph.D.
Fakulti: Sains dan Pengajian Alam Sekitar
v
Bahan nanostruktur dan laplsan hlbnd organlk-tak organlk nanokomposlt boleh
dlhasIlkan dengan pengkapsulan bahan organlk ke dalam lamella tak organIk melalm
slstem terbuka lamella contohnya laplsan berganda hldrokslda Smthesls bahan
nanokomposlt Inl boleh dlhasIlkan dengan menggunakan Mg/ AI hldrokslda berlapIs
ganda sebagat laplsan tak organlk dlmana naphthol blue black (NBB), fast green (FG)
dan methyl orange (MO) bahan perwama organIk, tennterkalasl dl celahnya DldapatI
bahawa kepekatan bahan organIk serta pH adalah pentIng dalam pembentukan bahan
hIbnd nano laplsan yang sempurna Kepekatan NBB adalah 0 0015M, FG adalah
o 025M dan 0 03M bag! MO pada pH 10 menghasllkan bahan laplsan nanohlbnd
organlk-tak orgamk nanokomposlt yang sempurna Spektnl1TI FTIR bagl
nanokomposlt menyempat campuran setIap spektrum spes'es organIk dan tak organIk
menunJukkan kewuJudan kedua-dua bahan dl dalam bahan yang terhasIl Morpho]OgI
permukaan Mg/AI I11drokslda berlapls ganda dan nanokomposlt :yang lam
VI
memmJukkan penggumpalan seeara kelompok yang padat serta struktur tIdak
berlIang, struktur yang bJasa dtkaItkan dengan morpholog! pennukaan bahan
ll1droksJda berlapIs ganda serta nanokomposltnya
Selam dan ltu, kaJlan terhadap serapan Juga dlJalankan, dnnana bahan Mg-AI slstem
karbonat (MAC) dlSedtakan dan bahan terawat haba (MAC300 dan MAC500)
dlperolehl melalm pemanasan MAC dtbawah tekanan atmosfera selama 5 Jam pada
suhu 300 DC dan 500 DC Bahan yang terbentuk dtgunakan sebagaI penJerap dalam
proses penyahwama naphthol blue black (NBB) Keputusan kaJlan kmetIk
menunJukkan bahawa bahan mt merupakan penJerap yang efisen bag! pewarna
amomk Dl sampmg ItU, dtdapatI proses serapan mematuhl model lsotenna LangmUIr
dImana kapasltI Jerapan MAC500 dan MAC300 d]dapatl leblh tmgg! berbandmg
dengan MAC PenJerap yang telah d]gunakan dlproses semula dan proses peneman
dlJalankan terhadap bahan tersebut Tlada perbezaan ketara yang dapat d]hhat dan
bahan yang terJerap serta bahan yang menyerap dalam anahsls FTIR dan anallsls
mlkroskop pengJillbasan elektron, keeuah spektrum PXRD d]mana ]a menyerupm
spektrum laplsan htdrOkSlda berganda menunJukkan kesan memon ke atas bahan
lapIsan ludrokslda berganda terawat haba
Pembentukan MAF telah dtsmtesls dengan atau tanpa bantuan gelombang mtkro telah
dlkaJ] dt mana em-em bahan yang terbentuk dlbandmgkan Bag! kedua-dua kaedah,
dldapatI proses mterkalasl berlaku dlmana anIOn FG, rnasuk ke dalam lamella Mg/Al
lapIsan hldrokslda berganda T etapI bantuan gelombang mlkro tldak dapat
VlI
mempercepatkan proses pembentukan MAF Namun demlklan, proses penuan
memamkan peranan penhng dalam pembentukan struktur laplsan MAF yang
sempuma Spektra PXRD menunJukkan bahawa JIka proses penuan bagl MAF
menmgkat maka, keamatan puncak (003) Juga menmgkat, membukhkan kewuJudan
stmktur laplsan nano yang leblh balk
VIJI
ACKNOWLEDGEMENTS
Alhamduhllah, glory and praIse to Allah, the ahmghty for proVIdmg me
strength and dilIgence to complete despIte several obstacles encOlmtered throughout
the progress of thIS study, WhiCh at tImes seemed msurmountable
FIrst and foremost, I would hke to express my deepest appreCiatIOn to my
supefVlsor, Prof Mohd Zoblr bm Hussem for hIS gUidance, mvaluable aSSistance
constructIve cntIcism throughout the duratIon of thIS project 1 would hke to express
my smcere thanks to Assoc Prof Dr Zulkarnam Zamal and Dr Asmah HJ Yahaya
for theIr mvaluable aSSistance and advlces as well as theIr kmdness and WIllmgness to
help
Smcere thank to all the staff m the ChemiStry Department of UPM and staffs
from Electron Microscopy Umt, UPM and the sponsorship of P ASCA scheme of
UPM
Deepest affectIon to my beloved mummy, Ba, Belboy and my Sisters for theIr
love, canng and understandmg for all these whIle Last but not least, to my dearest
husband Tengku Nash, for the support and love, and my close friend, NaI, not
forgettmg all the postgraduate students m Lab 2, Kak Zaemah, Kak DIla, Kak Ida and
WeI Long for all theIr help and co-operatIOn dunng the research \\orh
IX
I certIf\ that an ExammatIOn CommIttee met on 23 SeptemJber 2003 to conduct the final e'CammatIOn of AzIra Abd AzIZ on her Master of SCIence thesIs entitled "IntercalatIOn and AdsorptIon of Orgamc Dyes on Layered Double HydroXIdes" m accordance WIth UmversItI Pertaman MalaYSIa (HIgher Degree) Act 1980 and UmversItl Pertaman MalaYSIa (HIgher Det,Yfee) Regulations 1981 The CommIttee recommends that the candIdate be awarded the relevant degree Members of the Exammatton CommIttee are as fol1o\\s
Mohd Zaizi Desa, Ph.D. AssocIate Professor Faculty of SCIence and EnVlfonmental StudIes UmversItI Putra MalaYSIa (Chalf1l1an)
Mohd Shamsu) Hairi Mohd Salleh, Ph.D. Faculty of SCIence and EnVIronmental StudIes, UmversllI Putra MalaYSIa (Member)
Mohamed Ibrahim Mohamed Tahir, Ph.D. Faculty of SCIence and EnvIronmental StudIes Umversltl Putra MalaYSIa (Member)
Mohd Ambar Yarmo, Ph.D. AssocIate Professor Pusat PengaJIan Sams Kuma dan TeknologI Makanan FakUltI Sams dan TeknologI UmversItl Kebangsaan MalaysIa (Member)
ProfessorlDeputy ean School of Graduate StudIes UmversIlI Putra MalaYSIa
Date q :fAt4 �4
ThIS thesIs submItted to the Senate ofUmversItI Putra Malays13 and has been accepted as the fulfihnent of the requrrements for the degree of Master of SCIence The members of the SupefVlsory CommIttee are as follows
MOHO. ZOBIR BIN HUSSEIN, Ph.D. Professor Faculty of SCIence and EnVIronmental StudIes
UmversItI Putra MalaYSIa (Chamnan)
ZULKARNAIN ZAINAL, Ph.D. AssocIate Professor, Faculty of SCIence and EnVIronmental StudIes Umversltl Putra MalaysIa (Member)
ASMAH Y A HA Y A, Ph.D. Faculty of SCIence and EnVIronmental StudIes UmversltI Putra MalaysIa (Member)
� -. /- . ..J AINI IDERIS, Ph.D. Professor / Dean
x
School of Graduate StudIes Umversltl Putra MalaysIa
Date 3 0 JAN 2004
XI
DECLARA TION
I hereby declare that the thesIs IS based on my ongtnal work except for quotations and citatIOns which have been duly acknowledged I also declare that It has not been prevIOusly or concurrently subnutted for any other degree at UPM or other mstItutlOns
AZIRA ABD AZIZ
Date t 3� �4
XII
TABLE OF CONTENTS
Page ABSTRACT 11 ABSTRAK v ACKNOWLEDGEMENTS Vln DECLARATION Xl LIST OF TABLES xv LIST OF FIGURES XVl LIST OF ABBREVIA nONS XIX
CHAPTER I INTRODUCTION
Nanocomposlte Matenals 1 Layered Double HydroxIde (LDH) 3
Structure Of LDHs 5 Calcmed LDHs 8 IntercalatIon ReactIon 10
ApphcatIon OfLDHs 18 Wastewater Treatment In TextIle Industry 19
SynthetIc Orgarnc Dyestuff 21 ClassrficatIon Of Dye In TextIle 23 Naphthol Blue Black (NBB) 24 Fast Green (FG) 25 Methyl Orange (MO) 26
MIcrowave 27 Fundamentals Of MIcrowave 29
The AdsorptIon Process 30 AdsorptIon KmetIcs 32
AdsorptIon Isotherms 32 LangmuIr Isotherm 35 Fretmdhch Isotherm 36 Brunner, Emmet and Teller (BET) Isotherm 37
The Pores System 39 ObjectIves Of The Study 40
II METH ODOLOGY Apparatus 41 Matenals 41
2 PreparatIon Of Mg/ AI-C03 -LDH 42 IntercalatIon OfNBB, FG And MO Into Mg/Al-LDH 42
ConventIOnal OIl Bath Method 42 MIcrowave-ASSIsted Method 41
CharactenzatlOns 44 Po\\der X-Ray DlftractlOn (PXRO) 44
III
IV
V
Founer Transform-Infrared (FTIR) ThermograVImetnc (TGA) and DdferentJal Thermo GraVImetry (DTG) Analyses
Scanmng Electron MIcroscope (SEM) Surface Area And POroSIty Analyses
AdsorptIOn StudIes AdsorptIOn Properties
Ultra-VIOlet (UV -VIsIble) Spectroscopy Effect Of Contact Tune Effect Of Adsorbent Dosage Effect Of pH
RESULT AND DISCUSSIONS I:
XlII
44
45
45 45 46 46 47 47 48 48
PHYSICO-CHEMICAL PROPERTIES OF MgJAI-LDH, Mg/AINBB, Mg/Al-FG, MgJAI-MO, Zn/AI-MO And Cu/AI-MO
PhYSIcal Aspects 49 Powder X-Ray DIffractIOn (PXRD) 50 Founer Transform-Infrared (FTIR) 57 Thermal Analyses 67 Surface Morphology 78
RESULT AND DISCUSSIONS II: ADSORPTION PkOPERTIES Removal ofNBB from standard solutIon
Effect of contact tIme Effect of adsorbent dosage Effect of pH AdsorptIon ofNBB and ItS calcmed product
CharactenzatIon of the Adsorbent Matenals Powder X-Ray DIffractIon (PXRD) Founer Transform-Infrared (FTIR) Surface Property Pore SIZe DIstnbutIOn Surface Morphology
RESULT AND DISCUSSIONS III: MICROWAVE-ASSISTED SYNTHESIS OF Mg/AI-FG Powder X-Ray DIffractIon (PXRD) FOllner Transfonn-Infrared (FTIR) Thermal Analyses Surface MorphoJog\
82 82 84 86 88 92 92 96 99 102 103
105 109 I 14 118
VI CONCLUSIONS
VII RECOMMENDATIONS
REFERENCES
A PPENDICES A
B
C
D
VITA
Poster presented at the RegIOnal Conference for Young ChemIst (RCYC), 3-4 Apnl2001 at USM Conference Hall,
Umversitl Sruns MalaysIa, Penang
Paper presented at the FIfth InternatIOnal Conference on Matenal Chenustry 24-27 July 2001, UmversIty of Wales Bangor, Umted Kmgdom
Paper publIshed ill proceedIngs of the RegIOnal Conference for Young Chenust 2001
Paper publIshed ill Matenal SCIence and Engmeenng Journal by ElseVIer SCIence on 26 October 2001
XIV
120
123
124
132 132
133
134
140
145
xv
LIST OF TABLES
Table Page
1 1 Factors mfluencmg the synthesIs of hydrota1clte 4
1 2 RelatIOnshIp of colors observed to wavelength of lIght adsorbed 22
1 3 SolubIhsmg groups used m dye molecules 23
1 4 The electromagnenc spectrum 29
1 5 Frequency bands 29
I 6 ClasslilcatIOn of accordmg to theIr wIdth 39
3 1 Basal spacmg for the LDH, nanocomposItes and theIr color 50
32 Percent weIght loss for the nanocomposItes 71
4 1 AdsorptIon capacIty of NBB on MAC, MAC300 and MAC500 and 89 surface propertIes
5 1 Percentage weIght loss for MAF and MAF60mm 115
XVI
LIST OF FIGURES
Figure Page
1 1 Structure of Mg/ A l- CO,2 layered double hydroxIde 7
1 2 IntercalatIOn process of LDR for the formatIon of nanocomposIte 12
1 3 Structure of Mg/Al-MO nanocomposlte mtercalated Wlth MO anIOn 13
1 4 The molecular structure ofNBB 24
1 5 The molecular structure of F CF 25
1 6 The molecular structure of MO 26
3 ] PXRD patterns for NBB, MAC and MAN 52
32 PXRD patterns for FG and Its nanocomposIte synthesIZed at different 53 con centratIOn
33 PXRD patterns for MAC, MO and ItS nanocomposlte, synthesIzed at 54 dIfferent concentratIOn
34 PXRD patterns for ZAM synthesIZed at VarIOUS concentratIon 55
35 PXRD patterns for CAM synthesIzed at vanous concentratIOn 56
36 FTIR spectra for MAC, NBB and ItS nanocomposlte, MAN 62
3 7 FTIR spectra for FG and ItS nanocomposlte, MAF 63
38 FTIR spectra for MO and ItS nanocomposlte, MAM 64
39 FTIR spectra for MO and ItS nanocomposlte, ZAM 65
3 10 FTIR spectra for MO and ItS nanocomposIte, CA M 66
3 11(a)TGA and DTG thermograms for MAC 72
, 11(b)TGA and DTG thennogram� for MAN n
3 1 1 (C) TGA and DTG thennograms for MAF
3 11(d)TGA and DTG thennograms for MAM
3 1 I ( e) TGA and DTG thennograms for ZAM
3 I I (f) TGA and DTG thennograms for C AM
3 12(a) SEM mIcrograph for MAC
3 12(b) SEM micrograph for MAN
3 12( c) SEM micrograph for MAF
3 12( d) SEM micrograph for MAM
3 12( e) SEM mIcrograph for ZAM
3 12( f) SEM mIcrograph for CAM
4 I The effect of contact orne on the percentage uptake ofNBB (60ppm) on MAC, MAC300 and MAC500
XVlI
7 4
75
76
77
79
79
80
80
8 1
81
83
4 2 The effect of adsorbent dosage on the percentage uptake ofNBB (60ppm) 85 on MAC, MAC300 and MAC500
4 3 Percent uptake ofNBB (60 ppm) at vanous pHs for MAC, MAC300 and 87 MAC500
4 4 LangmUIr adsorptIOn Isothenn ofNBB on MAC, MAC300 and MAC500 90
45 FreundlIch adsorption ofNBB on MAC, MAC100 and MAC500 91
4 6(a) X-ray dIffraction patterns of (a) MAC, (b) MAC300 and (c) MAC500 94
4 6(b) X-ray dlffractlOn patterns of (a) AMAC, (b) AMAC300 and 95 (c) AMAC500
4 7(a) FTIR spectra for (a) MAC, (b) MAC300 and (c) MAC500 97
4 7(b) FTIR spectra for (a) AMAC, (b) AMAC300 and (c) AMAC500 98
48 NItrogen ad�orptlOn-desorptlOn for MAC MAC300 dnd MAC500 (a), and AMA C AMAC�OO and AMAC500 (b)
10 1
XVIll
49 BJH pore SIze dlstnbutlOn for MAC, ,MAC300 and MAC500 (a), 102 and AMAC, AMAC300 and AMAC500, (b)
49 Surface morphology for (a) MAC (b) MAC300 (c) MAC500, ]04 (d) AMAC, (e) AMAC300 and (f) AMAC500
5 1 PXRD patterns for MAF prepared by conventIonal 011 bath 107
52 PXRD patterns for MA F prepared by mIcrowave-assIsted method 108 under varIOUS agmg tIme
5 3 FTIR spectra for FG and Its nanocomposlte, MAF 11 2
5 4 FTIR spectra for FG and MAF60mm 113
5 5(a) TGAlDTG curve for MAF 116
5 5(b) TGAlDTG curve for 1'v1AF 60mm 117
5 6(a) SEM mIcrograph for MA F 119
56(b) SEM mIcrograph for MAF60mm 119
LIST OF ABBREVIATIONS
AMAC adsorbed matenal with NBB solution for MAC
AMAC300 adsorbed matenal wIth NBB solutIOn for MAC300
AMAC500 adsorbed matenal wIth NBB solutIon for MAC500
A SA P Accelerated Surface Area and Porosimetry
BET Brenauer, Emmett and Teller
CAM Cu/AJ-MO
FG F ast Green
LDH Layered Double HydroXIde
MAC Mg/AJ-LDH
MAF Mg/Al-FG
MAF60mm Mg/Al-FG (60mm)
MAM M glAl-M O
MAN MglAl-NBB
MO Methyl Orange
NBB Naphthol Blue Black
NC Nanocomposlte
PXRD Powder X-Ray DIffractIOn
R RatIO of M l+ to AI'+
SEM Scanmng Electron MICroSCOpy
XIX
xx
TGAlDTG Thennogravimetric (TGA) and Differential Thenno Gravimetry
(DTG) Analyse
ZAM Zn! AJ-MO
CHAPTER 1
INTRODUCTION
Nanocomposite Materials
Nanosized and/or nanostructured materials have dimensions, as their names imply, in
the scale range of 1 - 100 nanometer ( l nm = 10-9 m, i.e., one billionth of a meter)
thick layers (sheets) range.
Nanostructured materials are becoming of major significance and the technology of
the production is rapidly growing into a powerful industry. These fascinating
materials inc1ude nanofilms, nanocrystal, nanopartic1e, nanotubes, alloys,
nanocomposite and semiconductors. Exploitation of the nanopartic1es or
nanostructured materials is expected to lead to 'breakthrough in areas such as
materials and manufacturing, nanoelectronics, medicine and environment' (Fendler,
2001).
The syntheses of organlc-morgarnc hybrid materials, especially in the area of
composite in a nanoscale regime, or the so-called nanocomposite materials have
received considerable attention lately. Nanocomposite are particularly of interest
2
because the electrical, mechanical, optical, and other physicochemical properties of
the materials can be favorably modified due to nanometer level interphase
interactions and quantum effects (Komarneni, 1992; Ozin 1992).
Layered double hydroxide commonly used for the formation of nanocomposite
material with their crystal lattice consists of two-dimensional layers where a central
octahedral sheets of alumina or magnesia is fused to external layer of tetrahedron by
tips so that the oxygen ions of the octahedral sheets also belong to the tetrahedral
sheets. These layers organize themselves to form stacks with a regular Van der Waals
gap in between them called the interlayer gallery. Morphological descriptors such as
intercalation and exfoliation are commonly used to describe the state of aggregation
of the individual sheets of the layer. A variety of anionic species can be inserted as
guests into the interlayer spaces of the LDH, resulting in an expansion of the
interlayer distance to a nanometer sized dimension to form a new nanocomposite
material (Moore and Reynold, 1997).
3
Layered Double Hydroxides (LDHs)
In recent years, research on layered double hydroxides (LDHs) also known as anionic
clays has become an active field in material research in layered solids. Among these
interesting layered materials, hydrotalcite-like compounds (HTlcs), in particular have
attracted great attention because of th�ir intercalation ability and other important
physiochemical properties for technological applications (Xu and Zeng, 200 I, Carja
et al., 2001 and Olanrewaju et al., 2000)
The structure of most of them corresponds to that of hydrotalcite, a natural
magnesium-aluminium hydroxycarbonate, discovered in Sweden around 1842, which
occurs in nature in foliated and contomed plates and/or fibrous masses. Its formula is
M�A2(OH)16C03.4H20, although due to the relationship between the structure and
that of brucite, Mg(OH)2, it IS usually formulated as
[Mgo7sA1o2S(OH)2](C03)o02S.0.5H20. Brucite shows the well known Cdh-type
structure, i.e. an hexagonal close-packing of hydroxy ions, with all octahedral sites
every two interlayers occupied by Mg2+ ions. Partial substitution of Mg2+ / Al3+ gives
rise to positively charged layers, thus leading to location of anions in the unoccupied
interlayers. In natural hydrotalcite these interlayer anions are carbonate, and water
molecules also exist in the interlayer space (Rives et aI., 1999)