Thermal and electrochemical studies of Fe(III) organophilic
montmorillonite

Bruno Trevizan Franzin1
• Caroline Polini Lupi1 • Lucas Alves Martins1

•

Filipe Corrêa Guizellini2 • Cecı́lia Cristina Marques dos Santos1,3
•

Iêda Aparecida Pastre1
• Fernando Luis Fertonani1

Received: 12 June 2016 / Accepted: 18 March 2017 / Published online: 3 April 2017

� Akadémiai Kiadó, Budapest, Hungary 2017

Abstract This study aimed at investigating the thermal

and electrochemical behavior of montmorillonite clay-8-

hydroxyquinoline (8-HQ) film in the absence and presence

of aqueous Fe(III) ions. The solid film characterization by

means of UV spectroscopy, thermal (TG/DTG and TG–

DTA, simultaneous) studies, SEM and optical images, and

XRD suggested the formation of the ternary complex type:

{Pt/[[Si–O]n[Fe(III)(OH2)3(8-HQ)k]}3-n-k, with thermal

stability up to 300 �C. The electrochemical study was

carried out on a platinum electrode modified by mechanical

deposition of a thin solid film of the binary composite

(SWy-1:8-HQ) from an aqueous suspension. The

mechanical stability of the film was followed by perform-

ing 80 cyclic voltammograms. The electrochemical

behavior of the modified electrode was investigated using

cyclic voltammetry (CV) at different ferric ions concen-

tration (CFe(III)), followed by a study of the effect of the

scan rate (v) with a fixed CFe(III) ions. In the CVs, two

independent pairs of current peaks, A/D and C/B, were

observed. For Fe(III) ions in solution, log ip versus log

v relationship shows a process controlled first by adsorption

(pair of peaks A/D) and then by diffusion control (pair of

peaks C/B). The current function ip/v1/2 versus v and ip
a/ip

c

versus v allowed a suggestion of two homogeneous coupled

chemical reactions associated with CE and EC mecha-

nisms, respectively, both with fast reversible chemical

reactions. The first investigation of a modified electrode

showed good sensitivity (S = 25.1 lA/lmol L-1) to low

concentrations of ferric ions and detection limit

[LOD = (2.4 ± 0.01) lmol L-1] and high sensitivity to

traces of O2, showing that this system has great analytical

potentials.

Keywords Organic montmorillonite � Electrochemistry �
Determination of Fe(III) ions � Pt-modified electrode � TG–

DTA � XRD

Introduction

The generation of large quantities of effluents with high

levels of undesirable organic compounds and toxic metal

ions is the result of several human activities. Among these

activities is the increased use of these compounds in dif-

ferent industrial processes and products by setting up a

legal and vital action for the removal and control of the

concentration of these ions in various matrices. The pres-

ence of metal ions (i.e.: Cu(II), Cd(II), Pb(II), Zn(II),

among others and organoleptic Fe(III) and Al(III), ions),

particularly in the environment, is responsible for the

contamination of drinking water sources and the organisms

living in this medium, representing a range of deleterious

effects to fauna, flora, and exposed human beings. How-

ever, even considering as toxic, metal ions are essential to

human life.

The iron ion plays a key role in living organisms; it is

used for oxygen transportation, for DNA synthesis and

energetic metabolism [1]. Its lack causes serious health

problems anemia being the most well known. However, an

excess is also harmful, since it increases the synthesis of

reactive oxygen species in cellular tissues, causing lesions

& Fernando Luis Fertonani

fertonan@ibilce.unesp.br

1 Departamento de Quı́mica e Ciências Ambientais, IBILCE/

Unesp, S. J. Rio Preto, SP, Brazil

2 Departamento de Quı́mica, Universidade Estadual de

Londrina – UEL, Londrina, PR, Brazil

3 Instituto Adolfo Lutz, São José do Rio Preto, SP, Brazil

123

J Therm Anal Calorim (2018) 131:713–723

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in the proteins, lipids, and DNA [1, 2]. Another harmful

aspect of the presence of iron is the possibility of causing

problems for the public water supply. When the iron ion is

present in a high concentration, it has organoleptic charac-

teristics such as a bitter taste and is yellow color and blurred,

causing stains on clothes and sanitary utensils. The devel-

opment of deposits of iron in plumbing and the overgrowth

of bacteria cause biological contamination of the water

distribution network. For these reasons, the iron ion con-

stitutes one of the legislated portability parameters [3].

The iron ion can be found in the environment as, for

example, in inorganic species of Fe(II) or Fe(III), as

organic complexes, in the form of oxyhydroxides in sedi-

ments and colloidal oxide [4, 5].

Several analytical methods have been used to determi-

nate iron, such as spectrofluorimetric [6, 7], spectrophoto-

metric [8, 9], atomic absorption spectrophotometer with

flame ionization [10], coupled plasma (ICP-OES) [11], and

electrothermal [12]. Accordingly, studies [13–17] have

suggested a simple and affordable method that can be used

for the determination of trace amounts of Fe(III) ions in

solution by an electrochemical method. Several studies

have shown the application of modified electrodes for

metal ions determination in aqueous solutions, some of

them using a modification process with clays and organ-

oclays [18–25].

Mineralogical clay materials have important character-

istics that facilitate its use as an alternative from the eco-

nomic and environmental viewpoint (low cost, abundance,

easy recovering to reuse, etc), coherent with the current

reality. These characteristics combined with the high sur-

face area and swelling capacity of smectite clays, used in

the present work, encourage significant investment in

research in order to enhance the applications conferred to

these materials. The use of an expansive 2:1 montmoril-

lonite clay (smectite class) in association with organic

molecules, such as 8-hydroxyquinoline (8-HQ) [26–28],

increases the stability of the new composite and improves

its adsorption capacity of inorganic ions (Mn?) [29, 30].

The occurrence of clays in the environment, their

interactions with natural organic substances, and the

retention of ionic species of different metallic ions (toxic or

not) on clay or its natural binary complexes are abundant in

nature. Recently, our team has been investigating

microstructured systems: binary, SWy-1-8-Hydroxyquino-

line, and ternaries SWy-1-8-hydroxyquinoline-Mn?

(Mn? = Cr to Zn, Ag, Cd, Pb, and Hg). These systems

have been studied using different spectral (UV–visible and

visible fluorescence), thermal, electrochemical, and surface

(SEM, XRD, and optical images) techniques to character-

ize them.

The studies, globally, aim to: 1) find out about the

special complexing capacity of 8-hydroxyquinoline,

adsorbed by the composite, against most elements of the

periodic table and 2) explore its physicochemical proper-

ties (complexation and acid–base), for the removal of toxic

and organoleptic metallic ions from the water used in urban

water supply and wastewater.

In this sense, the investigation of the electrochemical

properties of the ternary complexes becomes interesting

because it allows the elaboration of a physical system of

electrodes that makes possible: 1) the selective removal of

the metallic ions, using the physical–chemical and elec-

trochemical properties of ternary complexes and 2) the

recovery of the binary system for its reuse.

Thus, the main objective of this paper is to study: 1) the

behavior of the montmorillonite-8-hydroxyquinoline com-

posite (SWy-1:8-HQ) in the presence and the absence of the

organoleptic Fe(III) ions, by thermal, spectroscopic, SEM,

XRD, optical microscopy, and electrochemical techniques,

and 2) the elucidation of the global electrochemistry

mechanism of SWy-1:Fe(III)8-HQ ternary composite. Also,

the aim is to demonstrate: (1) the ease and speed of the

preparation of electrodes (repeatability); (2) the speed of the

experimental work development; (3) its mechanical and

thermal stability that allow its reuse; and (4) its low cost, in

relation to the chemicals compounds used (clay and 8HQ)

and its reuse. These features make possible future applica-

tions of the compound of montmorillonite-8-hydrox-

yquinoline (SWy-1:8-HQ) not just for global mechanism

studies but to future quantitative determination of electro-

chemical Fe(III) ions and indirect determination of trace

amounts of oxygen, and also as adsorbents for wastewater

and urban water purification process.

Experimental

Preparation of SWy-1 suspension

Montmorillonite SWy-1 (homoionic clay, Na-montmoril-

lonite) from Wyoming, USA, provided by the Clay Min-

erals Society, Source Clays Repository (Purdue University,

USA), was used in the studies. For electrochemical and

spectroscopic studies, an aqueous suspension of 0.11 g L-1

montmorillonite (SWy-1) was prepared by dispersion of

appropriated mass of SWy-1 in deionized water and

maintained under mechanical stirring for another 24 h.

Preparation of the SWy-1:8-HQ and SWy-1:8-HQ-

Fe(III) composites

For electrochemical and spectroscopic studies, an aqueous

suspension of SWy-1 was previously prepared and pure

solid 8-hydroxyquinoline (8-HQ) was added in a proportion

of 10% mass and maintained under mechanical stirring for

714 B. T. Franzin et al.

123



24 h, generating the binary composite, SWy-1:8-HQ. For

the studies in solid state, a methanolic suspension of SWy-

1:8-HQ was likewise prepared for the aqueous suspension

described above. In one portion of suspension of SWy-1:8-

HQ, Fe(III) ions were added from a stock solution of

Fe(NO3)�9H2O with a concentration 5.38 9 10-2 mol L-1

and maintained under mechanical stirring for another 24 h,

generating the ternary composite, SWy-1:8-HQ-Fe(III).

Then, the resulting suspensions were dried under a labora-

tory fume exhaust hood for 24 h, producing the solid binary

and ternary composites. Thermal analysis (TG/DTG and

TG–DTA), XRD, SEM, and optical images were performed

on these samples.

Electrode surface modification

The suspension SWy-1:8-HQ prepared as described in the

previous item was re-suspended by stirring it for 12 h. To

prepare the SWy-1:8-HQ film electrode: SWy-1:8-HQ

suspension increments of 0.5 lL were applied on the top of

the platinum disk in order to cover the entire surface with a

single drop. The solvent was evaporated in a forced cir-

culation air stove at 50 �C for 20 min. The procedure was

repeated five times to obtain a suitable film thickness.

Study of the electrochemical behavior of SWy-1:8-

HQ composite film

Cyclic voltammetric experiments were performed by

applying the following potential program: Estart =

Eend = -0.7 V and Einv. = ? 0.5 V, scan rate

(25 B v B 200) mV s-1 using 0.1 mol L-1KCl as sup-

porting electrolyte, deaerated with N2, in the absence and

presence of 2.40 9 10-6 mol L-1 of Fe(III) ions. Cyclic

voltammograms were obtained in a Microquı́mica poten-

tiostat model MPQG-01. A three-electrode electrochemical

cell of 10 mL was used for the CVs measurements: a Pt

working electrode with geometric area, Ageom = 0.0314 cm2,

modified with SWy-1:8-HQ composite; a reference electrode

Ag|AgCl|KNO3(sat.) (E = 0.465 V/ERH); and an Ir foil as

counter electrode (Ageom. = 1.025 cm2).

Study of the spectrophotometric behavior (UV)

of the composites

UV–Vis spectra of the SWy-1:8-HQ suspensions were

obtained in the absence and presence of different concen-

trations of Fe(III) ions (0.1\CFe(III)\ 1.61) 9 10-5

mol L-1 in order to study the possible formation of com-

plex species, such as Fe(III)-8-HQ adsorbed into the SWy-1,

originating the named ternary composite (SWy-1:Fe(III)-8-

HQ) and their effect on the spectra, using an UV–Vis

Cary 1 E (Varian) and a quartz cell with 1.00 cm of

optical path.

Thermal characterization and X-ray diffraction

of composites

The thermal study of composite SWy-1:8-HQ-Fe(III) was

made for samples prepared in the previous item (preparation

of the SWy-1:8-HQ and SWy-1:8-HQ-Fe(III) composites)

employing a sample mass of 7 mg. The mass samples were

subjected to a heating rate of b = 20 �C min-1 in an air

and/or nitrogen (N2) dynamic atmosphere, with a flow rate

of 50 mL min-1 using an alumina crucible. The TG–DTA

simultaneous curves were obtained in the temperature range

from 30 up to 720 �C, using the TA Instruments SDT 2960,

and a crucible of a-Al2O3.

XRD analyses were carried out using a diffractometer

Mini Flex II X-ray diffractometer—Rigaku�, Cu Ka =

1.54184 Å, (3 B 2h B 40�), step = 0.05�, an accelerating

voltage of 40 kV, and a beam current of 15 mA.

SEM and optical images

The solid samples prepared as described above, pure clay

SWy-1, composites SWy-1:8-HQ and SWy-1:8-HQ-

Fe(III), were investigated with a scanning electron micro-

scope (SEM), Top Con—SM 300 Instrument. The solid

sample was placed onto a carbon tape and covered with a

conductive gold coating. SEM images were taken with

secondary electrons and 10 kV, magnification of 30009.

The optical images were obtained with a digital micro-

scope—Dino Lite Plus AM—313, magnification of 2009.

Results and discussion

Thermal and X-ray diffraction (XRD) studies

of the {[>Si–O]n[Fe(III)(OH2)3:(8-HQ)k]}32n2k

composite or [SWy-1:Fe(III)(OH2)3-8HQ]

Thermal analyses (Fig. 1, simultaneous TG/DTG–DTA),

were used to investigate the {[[Si–O]n[Fe(III)(OH2)3:(8-

HQ)k]}3-n-k ternary composite in two different atmo-

spheres: oxidizing air atmosphere and inert (N2). XRD data

(Table 1) were used combined with TG, SEM and optical

images, UV spectroscopy, and cyclic voltammetry (CV)

allowing the possible structure of the ternary clay complex

to be proposed. UV spectroscopy and cyclic voltammetry

results will be discussed later.

Figure 1 shows that volatile species were removed from

the surface of the ternary composite and it was possible to

identify the stages of the composite degradation as a

Thermal and electrochemical studies of Fe(III) organophilic montmorillonite 715

123



function of the increasing of TG temperature. XRD anal-

yses, TG/DTG–DTA data, and SEM images allowed the

evaluation of the changes in the opening of the interlayer

spaces (d001) and the surface structural rearrangement

caused by the complex formation between aqueous Fe(III)

ions and 8-HQ molecules from the original binary com-

posite, SWy-1:8-HQ [26].

Curves a and b (Fig. 1) represent the simultaneous

DTG–DTA curves in an air oxidizing atmosphere. The

profile of the curve a shows that the mass loss occurs in

four steps, as follows: The first step was attributed to the

elimination of solvent molecules adsorbed in the clay

system, in an endothermic process (Tmax = 84.5 �C)

occurring in the temperature range between 35 and 130 �C;

the second step was attributed to the endothermic elimi-

nation of three water molecules (Tpeak = 180 �C), previ-

ously coordinated with Fe(III) ions in the ternary complex.

This step occurs in the temperature range from 135 to

270 �C; the third step, attributed to the oxidation of

the ternary complex, is an exothermic process

(Tpeak = 400 �C) with elimination of only one molecule of

8-HQ, which is coordinated with the Fe(III) ion as quino-

lone N-oxide (O/:8-HQ) product [31] and occurring in the

temperature range from 290 to 520 �C; and the fourth

stage, collapse of the lamellar structure, with simultaneous

water (dihydroxylation–endothermic process) [32] and

CO2 and H2O elimination from residues of 8-HQ mole-

cules (exothermic process) trapped in the interlayer spaces

(Tpeak = 630 �C) [26].

Curve d (Fig. 1) shows DTG obtained after a pretreat-

ment to water removal from the sample, by applying

isothermal heating at Tiso = 270 �C during a hold time of

t = 5 min. After the previous treatment, a new DTG curve

was run in the same experimental conditions as the curve a.

The DTG profile shows an increase in the Tpeak, observed

at Tpeak = 396 �C, of DT * 30 �C for the removal of the

8-HQ molecules, after eliminating the total of water

molecules (absence of the peak on Tpeak = 180 �C). In this

way, this increase in the Tpeak value was ascribed to the

close down of the interlayer, which is in agreement with

XRD (Table 1).

The thermal experiments conducted under different

experimental conditions aim to differentiate the thermal

process of 8-HQ removal from the ternary complex. Thus,

in N2 atmosphere, the curve c in Fig. 1 showed an

endothermic process with slow kinetic, with Tpeak = 430 �C

20 120 220 320 420 520 620 720
–0.2

–0.1

0.00.16

0.11

0.06

0.01

Temperature/°C

dm
/d

t/%
 °

C
–1

dt
/d

m
/°

C
 m

g–
1

Endo
84.50 °C

a
b

d

180.69 °C

396.35 °C

628.90 °C 

c

Fig. 1 DTG–DTA

simultaneous curves for the

ternary solid complex. {[[Si–

O]n[Fe(III)(OH2)3:(8-

HQ)k]}3-n-k—DTG curve:

a oxidizing atmosphere, and

DTA curves: b (solid line)

oxidizing atmosphere;

c (continuous line) inert

atmosphere of N2; d as in

a previously heated to 270 �C
and holding by t = 5 min and

after reheated ramp of

temperature T = 30–720 �C.

msample = 7.0 mg;

b = 20 �C min-1; synthetic air

flow = 50 mL min-1

Table 1 d001 XRD data obtained for different clay composites

Composite d001/Å Dd001/Åa Remarks

SWy-1 12.17 – H2Ointerlayer

[SWy-1:8-HQ] 13.45 1.28 8-HQinterlayer not in excess

[SWy-1:8-HQ]-Fe(III) 16.99 3.54 Complexinterlayeranhydrous

[SWy-1:8-HQ]-Fe(III)(OH2)3 18.22 4.77 Complexinterlayerhydated

a Dd001 = (d001 composite - d001 [SWy-1])—all composites were prepared by the same method

716 B. T. Franzin et al.

123



and occurring from 380 to 460 �C, which was ascribed to the

removal of 8-HQ molecules complexed (distillation process,

see arrow).

In an oxidizing atmosphere, the curve b in Fig. 1 showed an

opposite behavior in comparison to the curve obtained in N2

atmosphere. From curve b, we observed a peak

Tmax = 400 �C, which is exothermic in contrast to the

endothermic peak observed at Tpeak = 430 �C; curve b still

shows a rapid kinetic process. This thermal behavior is pos-

sibly caused by the exothermic oxidation process involving

the species present on the surface with the consequent for-

mation of 8-HQ-N-oxide (O/:8-HQ) species [31].

Once the apparent stoichiometry of the ternary complex

{[[Si–O]n[Fe(III)(OH2)3:(8-HQ)k]}3-n-k has been sug-

gested, the next step was to investigate the apparent geom-

etry of the system. Thus, XRD data were obtained for the

different systems: a) pure clay (SWy-1) represented as a

silanol group [[Si–O] in the binary and ternary composite; b)

binary composite ({[[Si–O]n:(8-HQ)k]}
n-k = SWy-1:8-HQ); c)

anhydrous ternary composite ({[[Si–O]n[Fe(III):(8-HQ)k]}
3-n =

[SWy-1:8-HQ]-Fe(III)); and d) hydrated ternary compos-

ite ({[[Si–O]n[Fe(III)(OH2)3:(8-HQ)k]}
3-n = [SWy-1:8-HQ]-

Fe(III)(OH2)3; all composites were prepared in the same way

(Table 1).

The data shown in Table 1 demonstrated that the

interlayer space opening increased steadily in the transition

from pure clay (SWy-1) to the binary composite, by the

intercalation of 8-HQ molecules into SWy-1 and later with

the complexation of Fe(III) ions by the 8-HQ molecules.

So, the maximum aperture of the interlayer spaces occurs

due to the complexation of Fe(III) ions by 8-HQ molecules.

The major interlayer opening value (Dd001 = 4.77 Å),

observed for the ternary composite, is greater than the

opening obtained for the binary composite, prepared in an

excess of 8-HQ molecules (Dd001 = 4.15 Å) [26, 28]. On

the other hand, when the binary composite was prepared

with a low amount of 8-HQ molecules, the interlayer

opening value is Dd001 = 1.28 Å [26]. By this way, the

binary composites formed showed, respectively, an angular

package arrangement (Dd001 = 4.15 Å) and a flat arrange-

ment (Dd001 = 1.28 Å) for the 8-HQ molecules [26].

The presence of water molecules in the ternary complex,

removed at Tpeak = 180 �C, according to the DTG–DTA

curve profile, was attributed to [Fe(OH2)3]3? aqueous ions,

due to the strong Lewis acid character of Fe(III) ions. Thus,

Fe(III) ions carry with them coordinating water molecules

retained, at least partially, during the formation of the

ternary composite (Fig. 1, curve a). So, when these water

molecules were totally removed, at Tiso = 270 �C/5 min

(Fig. 1, curve d), the ternary complex interlayer is closed

by Dd001 = 1.23 Å. This interlayer closing traps the 8-HQ

molecules hindering the 8-HQ removal from the ternary

complex, shifting its decomposition peak temperature of a

DT = 35 �C (Tpeak = 430 �C; Fig. 1, curve d).

The XRD behavior of these different composites with

the thermal water removal reflects and corroborates the

proposed stoichiometry for the ternary composite.

Clay binary film investigation

To verify the mechanical stability of the thin solid film of

SWy-1:8-HQ, mechanically deposited on Pt disk electrode

surface of the geometric area, Ageom = 0.0314 cm2, 80

consecutive cyclic voltammetric cycles and at different

scan rate values (25 B v B 200) mV s-1 were obtained.

Figure 2 shows the profile of the last CV cycle for the

different v values and evidences the absence of a significant

difference among them. The CV profiles show two peaks,

one in the cathodic branch, peak A, E = -0.395 V, and

the other in the anodic branch of low intensity, peak B,

E = 0 V. With the increase in v, the current of peak A was

intensified. At the same time, the anodic peak, B, although

with lower current intensity was also intensified slightly

with the increase in v values. The electrochemical process

for peak A was investigated and the relation ip
A versus

v [33] shows to be linear. This behavior suggests that 8-HQ

species are adsorbed into the clay surface, according to UV

spectra obtained for the same binary composite in a water

suspension system.

Figure 3 shows the UV spectra obtained for binary and

ternary aqueous suspensions systems prepared in the same

experimental way that samples used for obtaining the

simultaneously TG–DTA curves and XRD patterns. The

spectra are from an aqueous suspension of the binary

–5.0

–2.5

0.0

2.5

–0.6 0.0 0.6

E/mV

i/A

B

A

25 mV s–1

50
75
100
125
150
175
200

Fig. 2 Last cycles of CVs obtained for SWy-1:8-HQ-modified

electrode, (25 B v B 200) mV s-1 in 0.100 mol L-1 KCl. Estart =

Eend = -0.7 V and Einv. = 0.5 V; T = (25 ± 2) �C;

Ageom = 0.0314 cm2; n = 10

Thermal and electrochemical studies of Fe(III) organophilic montmorillonite 717

123



composite SWy-1:8-HQ in the presence of different

Fe(III) ion concentrations, (1.0\CFe(III)\ 16.1) 9 10-6

mol L-1 (Fig. 3I, curves a–i) and in the absence of Fe(III)

ions (Fig. 3II). Figure 3 II shows spectra of a freshly re-

suspended SWy-1:8-HQ binary composite. This UV spectra

shows a peak at k = 239 nm (peak a) attributed to a

hydrophobic dimeric species, (8-HQ)2, which is of a

maximum intensity, and a peak of lower intensity near

k = 252 nm attributed to a monomeric species, 8-HQ

adsorbed into the clay [27], according to the equation:

2 8-HQð Þ� 8-HQð Þ2; k ¼ 1:0 � 107 ½26; 27�

According to Fig. 3I, the increase in CFe(III) ions causes the

appearance of new absorption peaks in the UV range of

(250 B k B 280) nm positioned at k = 258 and 272 nm,

suggesting the formation of a new species in accordance

with the TG–DTA data, which was attributed to the ternary

composite, SWy-1:8-HQ-Fe(III). To obtain these spectra, a

large concentration of 8-HQ was used to increase the

quantity of dimeric species, (8-HQ)2, adsorbed onto the

SWy-1 surface (Fig. 3I, curve a)).

Figure 4 shows SEM and optical images obtained for

the binary and ternary solid samples, where the changes in

morphology and roughness after the addition of 8-HQ

molecules into SWy-1 (Fig. 4I–III) to form the binary

composite can be seen and Fe(III) ions into the previous

binary composite, SWy-1:8-HQ. These morphological

changes are in agreement with XRD data (Table 1).

The analysis of spectra shown in Fig. 3 revealed three

absorption peaks: Ia, Ib, and Ic in the range of

(225 B k B 300) nm. The peak Ia (k = 239 nm) refers to

the dimeric species (8-HQ)2 as described above [26–28].

This peak showed a decrease on its absorption intensity

with the increase in CFe(III), while the other two peaks are

intense peaks at k = 258 nm (Ib) and k = 272 nm (Ic). In

order to confirm the presence of these two peaks, a

deconvolution process was applied to curve d, Fig. 3,

represented by the dotted lines. The deconvoluted spectrum

helped to confirm the effective presence of Ib and Ic peaks

due to the binary composite complex with Fe(III) ions. It

should be noted that these peaks (Ib and Ic) are absent in

the UV spectra of binary composite, SWy-1:8-HQ

(Fig. 3II).

The appearance and intensification of peak Ib at

k = 258 nm was effectively due to the formation of the

new ternary composite [SWy-1:8-HQ]-Fe(III). On the other

hand, the signal observed at k = 272 nm (peak Ic) could

not be attributed to the formation of a second new species,

but ascribed to an aromatic ring r ? p*-type transition

[28, 34], suggesting the formation of a bi-dentate complex,

with the participation of coordination sites: pyridine and

N–OH-phenolic group of 8-HQ molecules. This proposal

was based on the intensification of the signal observed at

k = 272 nm with a more effective participation of the

phenolic –OH group to the complex formation [35]. This is

because the pyridine groups probably interact with the acid

sites of the clay, considering that the pKa value of the

pyridine ring is 5.13 [36–38].

The ternary complex formation was indeed confirmed

by viewing the color change of the binary composite from

pale green to intense navy blue after the addition of Fe(III)

ions (Fig. 4IV–VI). This fact was registered by optical

images obtained from solid samples of clay, binary, and

ternary composites after complexing the Fe(III) ions. The

intense navy blue color was maintained for long time

(2012–2016) in the solid state after centrifugation and

draying the ternary composite (Fig. 4VI).

Parallel experiments run in test tubes using Fe(II) ions

instead of Fe(III) ions and in the presence of a binary clay

(SWy-1:8-HQ) suspension showed absence of navy blue

color and the original pale green color observed earlier for

the binary composite was maintained, suggesting that if the

ternary composite of ions Fe(II) was formed, it does not

show any color. This behavior is in agreement with the

literature information for the pair redox Fe(II)/Fe(III) ions

inside the [Fe(III)/(II) (1,10-phenanthroline)3] aqueous

complex [39, 40].

Cyclic voltammetry of [Pt-SWy-1:8-HQ]-Fe(III)

film-modified electrode

Figure 5I–III shows the set of cyclic voltammograms (CVs)

for different v values obtained for the Pt electrode modified

with a thin film of a binary composite (SWy-1:8-HQ) in the

225 250 275 300

0.5

1.0

1.5

2.0

/nmλ

/nmλ

A

Ι ΙΙ239 nm
a

b

c

d
e
f

g h i

Ιb

258 nm

272 nm

Ic

Ιa a

b

239 nm

220 240 260 280

[SWy-1:8-HQ]

Fig. 3 I Absorption spectra obtained for the [SWy-1:8-HQ]-Fe(III)

system by increasing the CFe(III) ions (1.0\CFe(III)\ 16.1) 9 10-6

mol L-1 and II for [SWy-1:8-HQ], C8-HQ = 6.0 9 10-5 mol L-1.

T = (25 ± 2) �C and (solid line) deconvolution of curve d

718 B. T. Franzin et al.

123



presence of (CFe(III) = 9.74 9 10-6 mol L-1) and in the

absence of aqueous Fe(III) ions.

The CVs obtained for Fig. 5I show two pairs of peaks,

A/D and B/C, which are mutually interrelated as demon-

strated in Fig. 5II. The peak potentials are: EA = -0.21 V,

ED = -0.27 V, EB = -0.47 V, and EC = -0.32 V. The

pair of peaks A/D is separated by a DE = (62 ± 3) mV and

shows a value of n = 0.95 ± 0.04, being then value

obtained from the relation of DE = 59.1/n [41]. This result

suggests an electrochemical reversible process; otherwise

the relation between log ip versus log v (not shown) sug-

gests an electrochemical process controlled by adsorption.

These results are in agreement with that showed by the

UV spectra (Fig. 3), TG–DTA data, SEM images (Fig. 4I–

III), optical images (Fig. 4IV–VI), and XRD data

(Table 1). As we can see from Table 1, clay interlayer

spaces (d) enlarge by (1.28 ± 0.04) A in comparison with

pure SWy-1, when 8-HQ molecules were inserted into the

Fig. 4 SEM and optical images

of clay and composites: SWy-1

(I, IV); SWy-1:8-HQ (II,

V) and SWy-1:8-HQ-Fe(III)

(III, VI). SEM images (93000):

I, II and III; optical images

(9200): IV, V and VI

–0.8 0.0 0.8
–8.0

0.0

8.0

E/V

i/µ
A

1.6

1.0

0.4

1.6

0.8

0.0

1.4 2.0 2.6

1.4 2.0 2.6

Log V/mV s–1

Log V/mV s–1

Lo
g 

ip
/μ

A
Lo

g 
i p/

μA

0.25

0.00

–0.25

–0.50
–0.4 –0.2 0.0

E/V

ΙΙ-

Ι-

Ei = Ef

a

b

C
D

A

B

i/u
A

Ei
A

D

a

b  25 mV s–1

50
75
100
125
150
175
200

log ipD

log ipA

log ipB

log ipC

y = 0.8539x - 0.8084

y = 0.7352x - 0.737

y = 0.3221x - 0.6183

y = 0.7512x - 1,0031

R  = 0.999

R  = 0.998

R  = 0.9984

R  = 0.9977

2

2

2

2

Fig. 5 I CVs of the modified electrode in absence (a;

v = 25 mV s-1) and presence (b) of Fe(III) ions, for

(25 B v B 200) mV s-1 obtained in 0.1 mol L-1 KCl and

v = 25 mV s-1; II Ek advance on peak A, 0.100 mol L-1 KCl,

CFe(III) = 9.74 9 10-6 mol L-1. Estart = Eand = -0.7 V and

Einv. = 0.5 V; T = (24 ± 3) �C; Ageom = 0.0314 cm2.

T = (25 ± 2) �C; III log ip versus v

Thermal and electrochemical studies of Fe(III) organophilic montmorillonite 719

123



interlayer spaces to form SWy-1:8-HQ binary composite

[26]. Likewise, insertion of Fe(III) ions into the interlayer

of the binary composite enlarges the space by

(2.49 ± 0.04) A. This interlayer space enlargement con-

sequently generated an expanded new surface on the Pt-

based electrode, facilitating ions diffusion from the aque-

ous solution into the clay ternary composite film.

The second pair of peaks B/C, in the potential range of

(-0.37 B E B -0.79) V, Fig. 5, does not have a compar-

ison to the UV data of Fig. 3. The peak separation of

DE = 110 mV (CFe(III) = 2.40 9 10-6 mol L-1 and

25 mV s-1) and the log ip versus log v (not shown) crite-

rion [33] allowed us to suggest a controlled diffusion

process for both peaks, B and C.

In this way, we can tentatively ascribe the appearance

and enlargement of the peak separation of DE = 110 mV

to an increasing imposed resistance, possibly by the new

substrate formed, the ternary composite film: [SWy-1:8-

HQ]-Fen?, and by the fact that these electrochemical

reactions are controlled by a diffusion process.

Thus, peaks B/C are feasible to ascribe to a different

electrochemical process than that observed for peaks A/D,

now occurring on a new surface. This new surface has a

different morphology, which was confirmed by SEM

(Fig. 4I–III) and optical (Fig. 4IV–VI) images, enabling a

new process to occur on the new electrode surface. The

optical image makes the complex formation evident as the

ternary composite observed by the apparent color change

from a pale green to an intense navy blue and the structural

change of the ternary composite in comparison with the

binary one, as also confirmed by XRD data (Table 1).

Now it is important to note that DTG–DTA results show

the formation of only one complex specie present on the

surface of the investigated solid-state ternary composite,

represented by the Tpeak = 396 �C, in DTA curve (Fig. 1a–d).

So, there is internal evidence that the pair of peaks B/C is

derived from an electrochemical reaction not occurring by

surface control, but with species presents in the solution, as

suggested by the plotting log ip versus log v (Fig. 5II–IV).

Considering the behavior shown by peak B (Fig. 5I), pre-

liminary experiments were carried out to evaluate the

relationship of ip
c

B versus CFe(III), in the absence of O2

(figure not shown). A linear behavior was observed: y =

-2.698x - 1.673, r = 0.9990, for a range of (2.4 B

CFe(III) B 49.8) lmol L-1, showing a: 1—good sensitivity,

S = 25.1 lA/lmol L-1; 2—lower detection limit,

LOD = (2.40 ± 0.10) lmol L-1 [42]; and 3—good

repeatability, r = 4.0%, for n = 5 [43]. So, these param-

eter values are in agreement with those shown in the lit-

erature [42–45]. Thus, there are efforts in progress in our

laboratory to improve the analytical parameters, applying

the more sensitive square wave voltammetry (SWV)

technique, and subsequent method validation.

Considering the relevant information came from UV and

the others techniques used to characterize the film surface

before and after inserting Fe(III) ions into the binary

composite, the electrochemical behavior of the peaks A/D

and B/C, shown in Fig. 5, was investigated by the appli-

cation of diagnostic criteria for CE and EC mechanisms

[41]. The proposed mechanisms for these reaction steps are

shown further on in this text.

Homogeneous reactions study using Pt-SWy-1:

8-HQ-Fe(III) film-modified electrode

Figure 5I shows CVs obtained for different scan rates which

were used to (1) characterize the origin of the coupled redox

peaks, A/D and B/C; (2) confirm the electrochemical

dependence between the coupled peaks; and (3) elucidate

the mechanisms of electrochemical reactions. Figure 5II

shows CVs obtained using CFe(III) = 2.40 9 10-6 mol L-1

and 50 mV s-1 and inverting the scanning potential (Ek) at

different potential values: for peak A (0 B Ek B -0,34) V

and for peak B (-0.34 B Ek B -0.75) V.

Figure 5IV, V shows the log ip
a versus log v plots for the

A/D and B/C pair of peaks, respectively and suggests that

peaks A and D are controlled by adsorption, corroborating

the data obtained by UV, and peaks B and C are controlled

by diffusion. Another important aspect was the linearity of

anodic (Ep
a) and cathodic (Ep

c) peak potentials, Ep, with

v for both pairs of peaks (A/D and B/C), confirming the

reversibility of the processes [41].

The current function (ip/v1/2) versus v and the

anodic/cathodic current peak ratio (ip
a/ip

c) versus v were used

to elucidate the electrochemical mechanisms responsible

for the two pairs of peaks, A/D and B/C. Such relationships

were initially obtained for the pair of peaks A and D and

are presented in Fig. 6a, b, suggesting that a CE type

mechanism [37] is applied. This means that a fast prece-

dent chemical reaction is followed by a fast one-electron

charge transfer process [41].

Thus, considering only the aqueous species of

[Fe(OH2)6]3?[ 95%, present in aqueous solution at pH 6

[37, 38], a possible mechanism is being suggested as

follows:

1. Chemical step occurring with the formation of the

ternary complex by a fast and reversible chemical

reaction occurring on the surface of clay binary

composite (see Fig. 7I-CE):

Pt= [ Si-O½ �n Fe IIIð Þ OH2ð Þm� 8-HQð Þk

� �� �3�n�k
;

ð1Þ

where n = number of silanol groups; m = number of

water molecules (the number of water and 8-HQ

720 B. T. Franzin et al.

123



molecules was estimated by TG/DTG primary tech-

nique); k = number of molecules of 8-HQ [37].

2. Electrochemical step, a reversible one-electron charge

transfer (n = 1) reaction, involves the Fe(III) ion.

The metallic center of the complex is reduced to

Fe(II) ion, generating a new ternary species (see

Fig. 7I-CE):

Pt= [ Si-O½ �n Fe IIð Þ OH2ð Þm: 8-HQð Þk

� �� �2�n�k
; ð2Þ

where m = 3, number of H2O molecules and k = 1,

8-HQ molecule.

The same procedure was applied to the B/C couple of

peaks. The graphics of the current function (ip
c/v1/2) versus

–1.0

–2.0

–3.0

–4.0
40 120 200

40 120 200

40 120 200

40 120 200

6.0

4.0

2.0

–0.3

–0.6

–0.9

–2.8

–2.2

–0.8

/mV s–1ν

/mV s–1ν /mV s–1ν

/mV s–1ν

i p
A
/  

1/
2

ν

i p
D
/i p

A
 

i p
C
/i p

B
 

i p
C
/  

1/
2

ν

(a) (b)

(c) (d)

Fig. 6 Current function versus v plots for the SWy-1:8-HQ-Fe(III)

ternary composite to the peaks: A and D, a ip
A/v1/2 versus v; b ip

D/ip
A

versus v; (25 B v B 200) mV s-1; and peaks B and C c ip
C/v1/2 versus

v; d ip
C/ip

B versus v; (25 B v B 200) mV s-1; CFe(III) = 2.40 9 10-6

mol L-1; T = (24 ± 3) �C

Pt

Vidro

Fe+2

Fe+3

Fe+2

OH

N

Ι-CE
ΙΙ-EC

aq

O2

e–

Fig. 7 Scheme of the processes occurring on the electrode surface in

an aqueous solution. I-CE formation of the complex {Pt/[[Si–

O]n[Fe(III)(OH2)m:(8-HQ)k]}3-n-k and reduction of Fe(III) to Fe(II)

species to form {Pt/[[Si–O]n[Fe(II)(OH2)m:(8-HQ)k]}2-n-k; II-EC

reduction of the aqueous Fe(III) species on the modified electrode {Pt/

[[Si–O]n[Fe(II)(OH2)m:(8-HQ)k]}2-n-k and subsequent oxidation of

Fe(II) to Fe(III) aqueous species by O2 on the electrode surface

Thermal and electrochemical studies of Fe(III) organophilic montmorillonite 721

123



v and (ip
D/ip

A) versus v are shown in Fig. 6c, d and suggest

the presence of an EC-type mechanism [33] that consists of

two steps (see Fig. 7II-EC): a reversible one-electron

charge transfer reaction followed by a fast and reversible

chemical reaction.

Now, considering the new substrate formed on the sur-

face of the modified electrode {Pt/[[Si–O]n[Fe(II)(OH2)3:

(8-HQ)k]}2-n-k, as previously discussed, and the species

present in aqueous solution, [Fe(OH2)6]3? ions, the fol-

lowing mechanism is suggested:

1. The new substrate, {Pt/[[Si–O]n[Fe(II)(OH2)3:

(8-HQ)k]}2-n-k, acts as a facilitator of electron

transfer from the electrode to the aqueous Fe(III) ions

in the diffuse layer, reducing Fe(III) ions to Fe(II) ion

species, giving rise to the peak B (see Fig. 5I);

2. Afterward, the Fe(II) species (formed in 1) are oxidized

to Fe(III) ions species on the substrate to giving rise to

the peak C (see Fig. 5I, II); then, 3) a chemical step has

appeared as an homogeneous reaction of Fe(II) ions

with O2 molecules, partially oxidizing Fe(II) ions

(initially produced in peak B) to Fe(III) ions. This O2

molecules were incorporated by a counterflow stream

in the N2 stream; this reaction precedes the electro-

chemical reaction, peak C, in the reverse scan, conse-

quently reducing the current intensity of peak C.

The low influence of residual content of O2 on the

current intensity of peak C was ascribed to a decrease in the

experimental time by increasing v; this electrochemical

influence was absent when the experiment was performed

in a N2 atmosphere.

Thus, based on previous discussion, it was possible to

propose a scheme to represent the electrochemical process

developed on the modified Pt electrode, {Pt/[[Si–O]n

[Fen?(OH2)3:(8-HQ)k]}2-n-k (Fig. 7):

Conclusions

The results of thermal, UV, SEM and optical images, and

XRD studies allowed to propose the structure of the ternary

composite: [[Si–O]n[Fe(III)(OH2)3(8-HQ)k]}3-n-k.

This proposed structure was formed by mechanical

deposition of a thin solid film of SWy-1:8-HQ on Pt and

dipping the modified electrode in a Fe(III) ions aqueous

solution.

In the absence of Fe(III) ions, the modified electrode

showed two peaks of the CV assays, one in the anodic

branch at 0 V, and other in the cathode branch at

-0.395 V, both with adsorptive characteristics, and low

current intensity the nature of the corresponding com-

pounds being confirmed by UV spectrophotometric data.

The electrochemical behavior of the modified Pt elec-

trode with binary composite in the presence of Fe(III) ions in

aqueous solution showed four current peaks, mutually

dependent A/D and B/C. The pair of peaks A/D is related to

the formation of a new absorptive species into the clay when

Fe(III) ions were added to the binary aqueous suspension

and can be related to the UV spectra. The second pair of

peaks B/C does not have correspondence in the UV spectra.

The following mechanism was proposed for the global

electrode process:

1. CE: A/D peaks refer to the formation of the ternary

complex and reduction of Fe(III) to Fe(II) species

present in the complex;

2. EC: B/C peaks related to the reduction of aqueous

Fe(III) species to aqueous Fe(II) ions are facilitated by

the reduced form of ternary composite and oxidation of

the aqueous Fe(II) species to aqueous Fe(III) by O2.

The modified electrode showed a good sensitivity to low

concentrations of Fe(III) ions (2.40 ± 0.01 lmol L-1) and

high sensitivity to traces of O2 molecules, showing that this

system has great analytical potentialities.

Acknowledgements CAPES by grant of scholarship, Laboratório de

AnáliseTérmica of Departament Analytical Chemistry for the thermal

study, Laboratório de Microscopia Eletrônica (LME-IQ) for the SEM

facilities of Department of Chemical Physics, both of São Paulo State

University (Unesp), Institute of Chemistry, Araraquara, (IQ) UNESP,

Aguapé Soluções Ambientais Ltda. and Espaço Magistral Laboratório

de Análises, Serviço de Apoio Empresarial Ltda., by the financial

supporting for this work. X CBRATEC/ IV CPANATEC, paper 160B.

References

1. Grotto HZW. Metabolismo do ferro: uma revisão sobre os prin-

cipais mecanismos envolvidos em sua homeostase. Rev Bras

Hematol Hemoter. 2009;30:390–7.

2. Hoffbrand AV, Pettit FE, Moss PAH. Hypochromic anemia and

iron overload in essential haematology, 5th ed, Chapter 3.

Oxford: Blackwell; 2006. p. 28–43.

3. U.S. Environmental Protection Agency. Secondary drinking

water regulations: guidance for nuisance chemicals. http://water.

epa.gov/drink/contaminants/secondarystandards.cfm. Accessed

20 Jan 2015.

4. Ali TA, Farag AA, Mohamed GG. Potentiometric determination

of iron in polluted water samples using new modified Fe(III)-

screen printed ion selective electrode. J Ind Eng Chem.

2014;20:2394–400.

5. Mashhadizadeh MH, Shoaei IS, Monadi N. A novel ion selective

membrane potentiometric sensor for direct. Talanta. 2004;64:

1048–52.

6. Wang RY, Wu J, Wang LJ, Wang R, Dou HJ. Spectrofluoro-

metric determination of iron II based on the fluorescence

quenching of cadmium/tellurium quantum dots. Spectrosc Lett.

2014;47:439–45.

7. Junmei A, Tianrong L, Zhengyin Y, Mihui Y. An off-on fluo-

rescent sensor with high selectivity and sensitivity for Fe(III).

J Coord Chem. 2014;67:921–8.

722 B. T. Franzin et al.

123

http://water.epa.gov/drink/contaminants/secondarystandards.cfm
http://water.epa.gov/drink/contaminants/secondarystandards.cfm


8. Kassem AM, Amin AS. Spectrophotometric determination of

iron in environmental and food samples using solid phase

extraction. Food Chem. 2013;1411:1941–6.

9. Gao X, Sun Y, Zhu G, Fan J. A green method for the determi-

nation of chromium(VI) and iron(III) in water by sequential

injection analysis and spectrophotometric detection. Instrum Sci

Technol. 2013;41:500–11.

10. Hassanpoor S, Khayatian G. Combination of directly suspended

droplet microextraction and flame atomic absorption spectrome-

try for determination of trace amounts of iron and copper. J Braz

Chem Soc. 2014;25:734–42.

11. Rahmana MM, Khana SB, Alamryb KA, Marwanib HM, Asiria

AM. Detection of trivalent-iron based on low dimensional semi-

conductor metal oxide nanostructures for environmental remedi-

ation by ICP-OES technique. Ceram Int. 2014;40:8445–53.

12. Fazelirad H, Taher MA. Preconcentration of ultra-trace amounts

of iron and antimony using Ion pair solid phase extraction with

modified multi-walled carbon nanotubes. Microchim Acta.

2014;181:655–62.

13. Beltagi AM, Ghoneim MM. Simultaneous determination of trace

aluminum(III), copper(II) and cadmium(II) in water samples by

square-wave adsorptive cathodic stripping voltammetry in the

presence of oxine. J Appl Electrochem. 2009;39:627–36.

14. Çiftçi H, Tamer U, Metin AÜ, Alver E, Kizir N. Electrochemical

copper(II) sensor based on chitosan covered gold nanoparticles.

J Appl Electrochem. 2014;44:563–71.

15. Stozhko NY, Malakhova NA, Fyodorov MV, Brainina KZ.

Modified carbon-containing electrodes in stripping voltammetry

of metals. Part II. Composite and microelectrodes. J Solid State

Electrochem. 2008;12:1219–30.

16. Wu Z, Jiang L, Zhu Y, Xu C, Ye Y, Wang X. Synthesis of

mesoporous NiO nanosheet and its application on mercury(II)

sensor. J Solid State Electrochem. 2012;16:3171–7.

17. Promphet N, Rattanarat P, Rangkupanc R, Chailapakulb O,

Rodthongkum N. An electrochemical sensor based on graphene/

polyaniline/polystyrene nanoporous fibers modified electrode for

simultaneous determination of lead and cadmium. Sens Actuators

B. 2015;207:526–34.

18. Sun Y, Du H, Deng Y, Lan Y, Feng C. Preparation of polyacry-

lamide via surface-initiated electrochemicalmediated atom trans-

fer radical polymerization (SI-eATRP) for Pb2? sensing. J Solid

State Electrochem. 2015. doi:10.1007/s10008-015-3008-3.

19. Maghear A, Tertis M, Fritea L, Marian IO, Indreac E, Walcarius

A, Sãndulescu R. Tetrabutylammoniummodified clay film elec-

trodes: characterization and application to the detection of metal

ions. Talanta. 2014;125:36–44.

20. Filho NLD, do Carmo DR. Study of an organically modified clay:

selective adsorption of heavy metal ions and voltammetric

determination of mercury(II). Talanta. 2006;68:919–27.

21. Navratilova Z, Mucha M. Organo-montmorillonites as carbon

paste electrode modifiers. J Solid State Electrochem. 2015;19:

2013–22.

22. Khaorapapong N, Ogawa M. Solid-state intercalation of 8-Hy-

droxyquinoline into Li(I)-, Zn(II)- and Mn(II)montmorillonites.

Appl Clay Sci. 2007;35:31–8.

23. Keidar O, Lapides I, Shoval S, Yariv S. Thermogravimetry and

differential thermal analysis of montmorillonite treated with 1,4-

diaminoanthraquinone. J Therm Anal Calorim. 2015;120(1):

33–43.

24. Souza MA, Larocca NM, Pessan LA. Highly thermal

stable organoclays of ionic liquids and silane organic modifiers

and effect of montmorillonite source. J Therm Anal Calorim.

2016. doi:10.1007/s10973-0165501-z.

25. Souza GR, Fertonani FL, Pastre IA. Estudo espectro ele-

troquı́mico de sistemas estruturados argila-corante. Eclet Quim.

2003;28:77–83.

26. Pastre IA, Nascimento OI, Moitinho ABS, Souza GR, Ionashiro

EY, Fertonani FL. Thermal behaviour of intercalated 8-hydrox-

yquinoline (oxine) in montmorillonite clay. J Therm Anal

Calorim. 2004;75:663–9.

27. Khaorapapong N, Pimchan P, Ogawa M. Formation of mixed-

ligand zinc(II) complex-montmorillonite hybrids by solid–solid

reactions. Dalton Trans. 2011;40:5964–70.

28. Pimchana P, Khaorapapong N, Sohmiyab M, Ogawa M. In itu

complexation of 8-hydroxyquinoline and 4,40bipyridine with

zinc(II) in the interlayer space of montmorillonite. Appl Clay Sci.

2014;95:310–6.

29. Abollino O, Aceto M, Malandrino M, Sarzaninia C, Mentastia E.

Adsorption of heavy metals on Na-montimorilonita. Effect of pH

and organic substances. Water Res. 2003;37(7):1619–27.

30. Gök Ö, Özcan A, Erdem B, Özcan AS. Prediction of the kinetics,

equilibrium and thermodynamic parameters of adsorption of

copper(II) ions onto 8-hydroxy quinoline immobilized bentonite.

Colloids Surf. 2008;317:174–85.

31. Juiz SA, Leles MIG, Caires ACF, Boralle N, Ionashiro M.

Thermal decomposition of the magnesium zinc, lead and niobium

chelates derived from 8-quinolinol. J Therm Anal Calorim.

1997;50:625–32.

32. Olewnik E, Gaman K, Czerwinki W. Thermal properties of new

composites based on nanoclays, polyethylene and polypropylene.

J Therm Anal Calorim. 2010;101:323–9.

33. Kissinger PI, Heineman WR. Laboratory techniques in electro-

analytical chemistry. New York: Marcel Dekker; 1984.

34. Ghedini M, La Deda M, Aiello I, Grisolia A. Synthesis and

photophysical characterisation of luminescent zinc complexes

with 5-substituted-8-hydroxyquinolines. J Chem Soc Dalton.

2002. doi:10.1039/B202945F.

35. Silvestein RM, Bassler GC, Morrill TC. Identificação Espectro-

fotométrica de Compostos Orgânicos, Editora Guanabara, 3. Rio

de Janeiro: Edição; 1979.

36. Bardez E, Devol I, Larrey B, Valeur B. Excited-state processes in

8-hydroxyquinoline: Photoinduced tautomerization and solvation

effects. J Phys Chem B. 1997;101:7786–93.

37. Sigel H. Coordination chemistry. Oxford: Pergamon Press; 1980.

p. 27–45.

38. Baes CF, Mesmer RE. The hydrolysis of cations. Library of

congress cataloging in publication data, 1976.

39. Kolthoff IM, Leussing DL, Lee TS. Reaction of ferrous and ferric

iron with 1, 10-phenanthroline. III. The ferrous monophenan-

throline complex and the colorimetric determination of phenan-

throline. J Am Chem Soc. 1950;72(5):2173–7.

40. Schilt AA. Analytical applications of 1, 10-phenanthroline and

related compounds: international series of monographs in ana-

lytical chemistry. Amsterdam: Elsevier; 2013.

41. Greff R, Peat R, Peter LM, Pletcher D, Robinson J. Instrumental

methods in electrochemistry. New York: Wiley/Ellis Horwood

Limited; 1985.

42. Ekmekci G, Uzun D, Somer G, Kalaycı S. A novel iron(III)

selective membrane electrode based on benzo-18-crown-6 crown

ether and its applications. J Membr Sci. 2007;288:36–40.

43. Ali TA, Farag AA, Mohamed GG. Potentiometric determination of

iron in polluted water samples using new modified Fe(III)-screen

printed ion selective electrode. J Ind Eng Chem. 2014;20:394–2400.

44. Anguiano DI, Garcıa MG, Ruız C, Torres J, Alonso-Lemus I,

Alvarez-Contreras L, Verde-Gómez Y, Bustos E. Electrochemi-

cal detection of iron in a Lixiviant solution of polluted soil using

a modified glassy carbon electrode. Int J Electrochem. 2012.

doi:10.1155/2012/739408.

45. Teixeira LSG, Brasileiro JF, Borges MM Jr, Cordeiro PWL.

Determinação espectrofotométrica simultânea de cobre e ferro

em álcool etı́lico combustı́vel com reagentes derivados da fer-

roı́na. Quim Nova. 2006;29:741–5.

Thermal and electrochemical studies of Fe(III) organophilic montmorillonite 723

123

http://dx.doi.org/10.1007/s10008-015-3008-3
http://dx.doi.org/10.1007/s10973-0165501-z
http://dx.doi.org/10.1039/B202945F
http://dx.doi.org/10.1155/2012/739408

	Thermal and electrochemical studies of Fe(III) organophilic montmorillonite
	Abstract
	Introduction
	Experimental
	Preparation of SWy-1 suspension
	Preparation of the SWy-1:8-HQ and SWy-1:8-HQ-Fe(III) composites
	Electrode surface modification
	Study of the electrochemical behavior of SWy-1:8-HQ composite film
	Study of the spectrophotometric behavior (UV) of the composites
	Thermal characterization and X-ray diffraction of composites
	SEM and optical images

	Results and discussion
	Thermal and X-ray diffraction (XRD) studies of the {[ greaterthan Si--O]n[Fe(III)(OH2)3:(8-HQ)k]}3minusnminusk composite or [SWy-1:Fe(III)(OH2)3-8HQ]
	Clay binary film investigation
	Cyclic voltammetry of [Pt-SWy-1:8-HQ]-Fe(III) film-modified electrode
	Homogeneous reactions study using Pt-SWy-1: 8-HQ-Fe(III) film-modified electrode

	Conclusions
	Acknowledgements
	References