Article2016 experimentale

GMCL #1137271, VOL 628, ISS 1
Mesoporous materials from SiO and NiTiO
E. Achhal, H. Jabraoui, S. Ouaskit, and A. Gibaud
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Mesoporous materials from SiO2 and NiTiO3
E. Achhal, H. Jabraoui, S. Ouaskit, and A. Gibaud

MOL. CRYST. LIQ. CRYST.
, VOL. , –
http://dx.doi.org/./..
Mesoporous materials from SiO and NiTiO
E. Achhala,b
, H. Jabraouia
, S. Ouaskita
, and A. Gibaudb
a
Laboratoire de physique de la matière condensée, Faculté des Sciences Ben M’sik, Université Hassan II
Casablanca, Morocco; b
Institut des Molécules et des Matériaux du Maine, Université Maine, France
KEYWORDS
Mesoporous thin films; dip
coating; brij; X-ray
reflectivity
ABSTRACT
In this work, we synthesized and characterized mesoporous thin films
of SiO2 and NiTiO3 structured by a surfactant called Brij58. These films
werefabricatedbythemethodofdipcoatingandthebestconditionsfor
well-structured thin films were investigated as a function of surfactant
concentration and different types of substrates. These films have been
characterized by X-ray reflectivity which was calculated using the matrix
formalism. We demonstrated that the silicon substrate had a great effect
on the structure and porosity of the fabricated films for both SiO2 and
NiTiO3. Furthermore, we found that mesoporosity has been increased
as a function of the surfactant concentration in the solution. This exper-
imental procedure allows also to produce NiTiO3 powders which have
been characterized by X-ray diffraction. The XRD coupled to the crystal-
lographic software “Maud”shows that the samples are constituted by 98,
2% NiTiO3 powders.
1. Introduction
In the last decades, porous materials become the subject of several studies. According to
IUPAC (International Union of Pure and Applied Chemistry) [1] they are defined by the pore
size and are classified into three categories:
– The microporous materials with pore diameters less than 2 nm (dp<2 nm),5
– The macroporous materials having sizes of pores greater than 50 nm (dp> 50 nm) [2],
– Finally mesoporous materials with pore diameters between 2 and 50 nm (2 nm
<dp<50 nm) [3].
Mesoporous materials are obtained by mixing an organic surfactant with the precursor of
an oxide such as silica involving the sol-gel chemistry. The most cited applications are tech-10
nical applications such as catalysis [4], filtering [5], nanofluidic [6], chromatography [7], gas
storage and encapsulation materials [8], Sensors [9] and the controlled delivery medicines
[10]. Subsequently, several groups tried to elaborate these materials in the form of thin films.
In this work, we investigated the elaboration of mesoporous materials structured by a non-
ionic surfactant known by the acronym of Brij58 using sol-gel technique.15
CONTACT E. Achhal elmehdi.acchhal@gmail.com; S. Ouaskit s.ouaskit@ipnl.inp.fr
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
©  Taylor & Francis Group, LLC

2 E. ACHHAL ET AL.
2. Experimental procedure
Mesoporous films are fabricated by the method of self-assembly induced by solvent evaporate
ion. This procedure, known as the EISA (Evaporation-Induced Self-Assembly) [11] is very
well known for the synthesis of mesoporous thin films by sol-gel.
First, we prepared the initial SiO2 solution for different concentrations of Brij 58; a given 20
mass of Brij58 is dissolved in 36.79 g of pure Ethanol, in such manner to obtain a perfectly
homogeneous solution by agitation during ten minutes. To this solution, we add 0.8g of pure
water, 0.21g of hydrochloric acid and 2.5g of tetra ethyl ortho silicate (TEOS) and the resulting
mixture was aged for a time under magnetic stirring at room temperature.
To obtain surfactant structured NiTiO3 films; we prepared solutions with a given mass 25
of Brij 58 dissolved in 31.4 ml of pure ethanol and 1ml of nitric acid (HNO3). After that
the solution was introduced during ten minutes in an ultrasonic bath to obtain a perfectly
homogeneous mixture. We prepared second solution containing 1, 2g of the Nickel acetate
tetrahydrate (NA), 0, 66ml of nitric acid (HNO3) and 1, 46ml of titanium isopropoxide (TIP),
dissolved in 2, 28 ml of pure ethanol. Finally, we mixed the two solutions and we aged for a 30
given time under magnetic stirring at room temperature.
The mass of the Brij 58 is calculated from a percentage of the surfactant mass (ϕ[%]) fol-
lowing the equation:
ϕ(%) =
mBrij
mBrij + mSiO2
× 100 (1)
mBrij =
mSiO2
1
ϕ
− 1
(2)
Before the deposition of the films we cleaned substrates; this step is very important to avoid
any organic contamination. For this, the wafers are cleaned with acetone in an ultrasonic bath 35
for 5 minutes to remove the organic waste and then the substrates are washed with ethanol
for 5 minutes in an ultrasonic bath to remove the acetone and dried with compressed air.
Then the films were deposited on the substrates by the dip-coating technique; it consists
in immersing the substrate in the solution for a while and then removing the substrate from
the solution at a constant speed to obtain a film of uniform thickness [12], during removal, 40
the solution will flow along the substrate. At the end of flow, the substrate is covered with a
uniform porous film. The extraction speed affects the film thickness, which increases with
the drawing speed, but it also depends on the concentration of solute and solvent. The rela-
tive humidity (RH) in the dip-coater plays a crucial role in the structuring of thin films. The
humidity and temperature inside the dip coater were controlled automatically using a con- 45
troller managed by (ROTRONIC HW3 Hygro Win) software.
2.2. Characterization techniques
Analyses were made using a diffractometer ‘Empyrean Panalytical’. The reflectivity spectra
were recorded with a copper anticathode (I = 30 mA and V = 40 KV) using copper Kα
radiation of wavelength λ = 1.54056 ˚A with a detector ‘Pixel 3D’. Scanning was done in three 50
stages:
• Ref1: 0.1<2 <1.24;with a step of 0.01 and a time of 1 s.
• Ref2: 1.24<2 <3.04;with a step of 0.01 and a time of 5s.
• Ref3: 3.04<2 <10;with a step of 0.04 and a time of 10s.

MOL. CRYST. LIQ. CRYST. 3
The calculation of X-ray reflectivity curves is done via the matrix technique, written by55
William Vignaud and Alain Gibaud [13, 14], on Matlab. This program requires some input
parameters and characteristics of the deposited material. A simple qualitative analysis of the
experimental curves allows to access to the number of periodic layers present in each sample,
their thicknesses, and their average electron density.
XRD analysis of the crystalline phase existing in the powders was made using a diffrac-60
tometer X’pert. X-Ray diffraction spectra were recorded with copper anticathode (I = 30m A
and V = 40 KV) using the Kα copper radiation wavelength λ = 1.54056 ˚A. The diffractome-
ter is coupled to a computer which allows the installation control, acquisition, storage and
processing of data. Structural information is obtained from a powder pattern collected in the
angular range 2θ: 20–100° with an angular pitch of 0.04 and a counting time of 20 seconds65
per step.
3. Results and discussion
After synthesizing the mesoporous films of SiO2 deposited on glass and silicon sub-
Q1
strates, all sample were annealing at 80°C for 48 hours in an oven allowed the conden-
sation of the gel. The sample was washed with ethanol and dried in an oven at 80°C for70
1h30min, allowing to remove completely the surfactant and obtaining pure mesoporous silica
film.
We can see from reflectivity curves that the increase in concentration of Brij58 is accom-
panied by an increase in the number of Kiessig fringes. This phenomenon can be explained
by the fact that an increase of the concentration of Brij58 produces an increase of the75
solution viscosity and consequently increases the film thickness. This phenomenon is well
known in the dip-coating method the thickness of the elaborated film is directly related to
the solution viscosity. Moreover, as we can see in Figure (1) and Figure (2), the reflectiv-
ity curves show that the films are well structured for concentrations 35%, 43%, 53% and
62%. The absence of the second Bragg peak for the corresponding curves at the concen-80
trations 35% and 43% can be explained by the fact that the silica wall is as thick as the
stratum containing the surfactant. Another explanation is possible considering the rough-
ness. Indeed, if the roughness is very important the intensity of the second peak of Bragg be
overlooked.
B/w in print, colour online
Figure .

4 E. ACHHAL ET AL.
Figure .
The two figures (3) and (4) represent the reflectivity curves of the films deposited on 85
washed glass and silicon substrates for different concentrations of Brij58, for each concen-
tration, we can see a shift of the Bragg peaks to the large values after the extraction of the
surfactant.
The mesoporous films of silica concentration 53% Brij 58 were used to study the possible
influence of the substrate on which we make filing our films. The study focused on two types 90
of substrates: the glass and silicon.
In the case of glass substrate: the reflectivity curves corresponding to the unwashed film
and at the film washed with ethanol, obtained at a concentration of 53%, are analyzed using
the matrix technique.
The extraction of the surfactant produces a shift of the critical Angles qc 0.025–0.022˚A−1
95
as shown in Figure (5), this shift produces a decrease in the electron density reflects the exis-
tence of pores in the film. Note also that both the Bragg peaks of the mesoporous thin film
reflectivity curve located at positions 0.13 ˚A−1
and 0.27 ˚A−1
are moving to the great values of
qc after washing with pure ethanol positions 0.16 ˚A−1
and 0.31 ˚A−1
. This displacement of the
Figure .

Figure .
Figure .
Bragg peaks, after extraction of the surfactant results in the decrease of the period T of the100
pattern which passed from 4.9 nm to 4.2 nm.
With silicon substrate : the results of the reflectivity curves before and after rinsing the
samples are presented in Figure (5) and the structural parameters extracted from these curves
are dressed in Table (1). These parameters are in perfect agreement with the values estimated
by the model based on matrix formalism.105
Table . Experimental parameters of unwashed and washed SiO mesoporous Films deposited on the glass
substrate for % concentration of Brij surfactant after reﬁnement.
qc (˚A−) σ (˚A) e (˚A)
Substrate ./. ./. —
Film-substrate interface ./. ./. ./.
Layer  ./. ./. ./.
Layer  ./. ./. ./.
Film-air interface ./. ./. ./.

6 E. ACHHAL ET AL.
Figure .
The analysis of the reflectivity curves allowed to calculate the average electron density of
SiO2 film and was estimated to be equal to 0.44 e-/˚A3
and mesoporosity of a film is estimated
of about 21%.
The reflectivity curves of films fabricated with 53% of the surfactant are presented in
Figure (6), in both cases where film washed or not. The same shift of the critical wave vector of 110
0.025 to 0.02 ˚A−1
after rinsing the film ethanol. This shift reflects the decrease in the electron
density of the film after extraction of the surfactant.
The electron density average of the washed and unwashed film based on data given in
Table (2) is the same result to that found for the film obtained with the glass, as a substrate
and mesoporosity of a such film is estimated at 39%. 115
We note that the mesoporosity of the film obtained with the silicon substrate is greater
than that obtained with the glass substrate. This suggests that the structural properties of the
obtained films are affected by the surfactant concentration and also by the type of substrate.
Table. ExperimentalparametersofunwashedandwashedSiO mesoporousfilmsdepositedonthesilicon
substrate for % concentration of Brij surfactant after refinement.
qc (˚A−) σ (˚A) e (˚A)
Substrate ./. ./. —
Film-substrate interface ./. ./. ./.
Layer  ./. ./. ./.
Layer  ./. ./. ./.
Film-air interface ./. ./. ./.
Table . Experimental parameters of NiTiO mesoporous Films deposited on the silicon substrate after
refinement for % concentration.
qc (˚A−) σ (˚A) e (˚A)
Substrate . . —
Film-substrate interface . . .
Layer  . . .
Layer  . . .
Film-air interface . . .

Figure .
After synthesis of the NiTiO3 mesoporous films, a heat treatment of the sample is carried
out at 80°C for 2 Hours in an oven allowed the condensation of the gel.120
The reflectivity curves show that well-structured film for the 50% concentration, beyond
this value of concentration, the films are not well structured as we can see in the Figure (7).
3.1. X-ray diffraction (XRD)
NiTiO3 powder is prepared from solution containing 65% Brij58. The solution was dried on a
heat plate at 70°C for several hours. The resulting gel was then placed in a furnace to be dried125
at 400°C for 2 hours. Finally, the obtained powder was annealed at 600°C for 2 hours.
XRD results are shown in Figure (8). The phases identification were studied by crystal-
lographic software “Maud” created by L. Lutterotti [15], this program allows to refine the
Figure .

8 E. ACHHAL ET AL.
diffraction patterns by adjusting the lattice parameters and other parameters such as the size
of the crystallites, deformation of the lattice and the preferential orientation. 130
Note that the profiles shown above are characterized by three phases in the R-3 space group,
the X-ray diffraction shows the existence of a phase: NiTiO3 of percentage of 98.2% and two
phases in the form of Anatase (TiO2) and bunsenite (NiO) impurities of percentage of 1.23 and
0.6%. The NiTiO3 lattice parameters after the refinement are: a = b = 5.0350˚A, c = 13.8159˚A,
α = β= 90°, γ = 120 and the volume V = |a. (b ^ c)| is considered to 303.32 ˚A3
. 135
4. Conclusion
We succeeded to synthesize and to characterize thin films of mesoporous structured by a
surfactant called Brij58. These films were formed by dip-coating, the conditions for well-
structured thin films were studied as a function of surfactant concentration and the choice
of substrates on which we make the deposit of our films. Then, we characterized these films 140
by X-ray reflectivity and using data obtained by calculating matrix formalism, we note that
the films are well structured with the following mass concentrations: 53% and 62% on silicon
substrate. Accordingly, we notice while mesoporosity has been increased as a function of the
amount of surfactant in solution.
Furthermore, we have also synthesized NiTiO3 powders which were characterized by X-ray 145
diffraction. The results of XRD were investigated using crystallographic software “Maud.” The
diffractogram shows the existence of 98.2% as a percentage of NiTiO3 which was described
in the hexagonal trigonal system of R-3 space group.
Acknowledgments
We acknowledge the financial support from CNRST-Maroc to Hassan II University of Casablanca (Pro-
jet URAC10). 150
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