Vol.2, No.5, 464-468 (2010) Natural Science
http://dx.doi.org/10.4236/ns.2010.25057
Mesolamellar composite of TiN and CTAB using fluoride
ion bridge: synthesis, mechanism & characterization
Tumbavanam Venkateswaran Anuradha
Department of Materials Engineering, Indian Institute of Science, Bangalore, India;
Received 29 December 2009; revised 10 February 2010; accepted 5 March 2010.
ABSTRACT
In an attempt to synthesize hexagonal mesopo-
rous titanium nitride, a mesolamellar composite
based on titanium nitride and cetyltrimethylam-
monium bromide (CTAB) is obtained by the
sol-gel route involving templating at 80oC. The
mechanism underlying the above synthesis is
discussed for the first time in the literature and
till date there are no reports on the synthesis of
mesoporous nitrides. The above mesolamellar
composite is found to form an oxide of titania
(anatase) upon heat treatment at 335oC for 1h.
Keywords: Mesolamellar; Templating; Sol-Gel
Method; XRD; FT-IR; SEM
1. INTRODUCTION
Mesoporous materials are generally produced by the
templating approach using various surfactant species as
template. The template acts like an imprint molecule
which could then be extracted by either calcination or
solvent extraction leaving behind pores in the regions
where they are present. At the first critical micelle con-
centration (cmc1), the surfactant species forms self-as-
sembled aggregates with a spherical shape which chan-
ges to a rod shape on further increase in the concentra-
tion of the surfactant species (cmc2). Different liquid
crystalline phases with cubic, hexagonal and lamellar
structures are formed by further increase in the concen-
tration of the surfactant species (above cmc2) which
indeed acts as the template for the production of meso-
porous materials.
There are a few reports based on the synthesis of me-
solamellar phases based on zirconia [1] and silica [2].
Certain species like F- ions and acetylacetone are found
to favour the formation of lamellar phases when present
in the reaction medium [3,4]. There are no reports on the
synthesis of mesoporous materials based on TiN due to
the non-availability of suitable metal-organic precursor
that could be used for the sol-gel synthesis. The precur-
sors of TiN are also found to be highly oxophilic and
hence there is always a possibility that they will result in
the formation of oxynitrides rather than pure nitrides.
The present experiments involved the formation of a me-
solamellar composite based on TiN and CTAB in the
medium enriched with F- ions by sol-gel route at 80oC.
The mechanism underlying the above synthesis is dis-
cussed in this communication in more detail for the first
time in the literature.
2. EXPERIMENTAL PROCEDURES
2 g of TiN, 2 g of CTAB, 25 cc of HF-HNO3 mixture
and 25 cc of distilled water were taken. TiN is dissolved
in 1:1 solution of HF-HNO3 mixture (9:1) in water
forming species like [Ti1-xFxNy]3n+ to which an aqueous
solution of CTAB is added to result in the yellow col-
ored solution which is kept in the oven for 3 h at 80oC
and then it is kept aside at RT for 24 h. The yellow solid
thus obtained has the composition [CTA] (H2O)n [Ti1-x
FxNy]. Thus a mesolamellar composite based on TiN and
CTAB is formed with the F- ion acting as the bridge be-
tween them. The lamellar composite obtained above is
characterized by x-ray diffraction (XRD) and FT-IR spe-
ctroscopy.
JEOL diffractometer (reflection type-model 8030) is
used for the characterization of the materials by x-ray
diffraction (XRD). Cu target is used. A voltage of 30 kV,
a current of 20 mA, and a step angle of 0.020o with de-
tection times of 0.5 sec at each step are used. A JEOL
2000FX-IItransmission electron microscope operating at
the accelerating voltage of 200 kV is used for TEM
studies. The powder samples are crushed thoroughly and
dispersed in a suitable organic solvent (acetone or high
purity ethanol/methanol) and subjected to ultrasonication
before supporting on the carbon-coated grids for loading
in the TEM equipment. FT-IR studies are carried out
using Perkin Elmer FT-IR equipment. Differential Scan-
ning Calorimetry (DSC) is performed with a Perkin
Elmer DSC-2C calorimeter to study the thermal stability
of the material. The measurements are carried out under
dynamic argon flow condition. Before starting the ex-

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465
465
periment the base line was corrected and the calibration
of the instrument is done using pure indium. A heating
rate of 20 K/min is used.
3. RESULTS & DISCUSSION
Porous materials i.e. materials with non-lamellar mesos-
tructures that are stable enough to be preserved after the
removal of the structure-directing amphiphile could only
be synthesized under aqueous conditions with the utili-
zation of cationic surfactants [5,6] and the other attempts
yielded lamellar phases only [7,8]. It is believed that a
larger variety of surfactants in the alcoholic medium
with a small quantity of water would result in the forma-
tion of non-lamellar materials [9]. But the utilisation of
alcoholic medium is avoided in this investigation since a
highly acidic medium is required for the dissolution of
titanium nitride. The only constraint in not making use
of the alcoholic medium for the synthesis is the
non-availability of a suitable organo-metallic precursor
for titanium nitride. There are continuous efforts to syn-
thesize mesoporous materials based on nitrides like sili-
con nitride for the catalytic applications [10,11] which
involves the ammonolysis of SiCl4 in organic solvent.
But the handling of halides of titanium like TiCl4 or the
organo-metallic precursor like (TiCl4L2) (where L =
ether, amine and pyridine) is very difficult at room tem-
perature since they are both air-sensitive and moisture -
sensitive.
Figure 1 shows the XRD of the mesolamellar com-
posite after templating TiN onto CTAB using F- ion as
the bridge at 80oC. The lamellar nature of the composite
is confirmed by XRD studies which is again reconfirmed
using SEM studies [12,13]. The lamellar nature is found
to be accompanied by atomic scale ordering and registry
of the layers [14] where the first peak has appeared at d
 19.4 Ao with the following peaks at d  {19.4/2 Ao,
19.4/3 Ao, 19.4/4 Ao). The clearly resolved six orders of
the diffraction peak as well as the plain baseline in the
20-30o 2 range suggest that the TiN layers sandwiched
between the surfactants are well crystallized as in the
case of lamellar TiO2 mesophase which was produced by
Lin et al. [15] using CTAB as the templating surfactant
for tetrabutylorthotitanate (precursor of TiO2) under ba-
sic conditions. This high degree of condensation of the
inorganic building units may be different from those of
the silicate [16,17] and aluminophosphate phase meso-
phases [18,19] whose frameworks are amorphous in
nature. The reflections present in the higher 2 region
are found to represent the internal structure involving the
organization of the lamellae and thus could not be in-
dexed to any impurities, but they could be indexed to an
orthorhombic cell with a reasonable justification and this
result compares very well with the mesocomposite of
zinc phosphate produced by Huo et al. [20].
Figure 2 gives the FT-IR spectra of CTAB and meso-
composite respectively. FT-IR studies of the composite
material showed many of the vibration modes like C-H&
C-N stretching and C-H bending similar to that of the
template i.e. CTAB which is used as standard for com-
parison, but the peaks had significantly different intensi-
ties and line widths in this case and there are some addi-
tional peaks which could be assumed to be due to the
transition metal co-ordination with the template. FT-IR
studies clearly indicated the formation of composite
where CTAB is intact. The peaks appeared at 3651 cm-1
and 3587 cm-1 corresponding to the O-H stretching fre-
quencies in the physisorbed water molecules and also the
peak at 1627 cm-1 corresponds to the bending mode as-
sociated with the physisorbed water molecules.
Differential Scanning Calorimetric (DSC) analysis in-
dicated the decomposition behaviour of the lamellar
Figure 1. XRD of the mesolamellar composite of TiN and
CTAB after templating at 80oC.
Figure 2. FT-IR spectrum of (a) CTAB; (b) mesolamellar
composite of TiN and CTAB.

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466
composite with three distinct stages of reaction. Figure
3 gives the ‘DSC’ trace of the mesolamellar composite
in argon atmosphere [12] The first split peak (endother-
mic) around 100oC is due to the desorption of water in-
dicating the presence of two different kinds of water
molecules associated with the mesocomposite structure
namely, water of hydration and associated (hydrogen
bonded) water. The second peak at 335oC, which is exo-
thermic in nature, indicates the decomposition of the
organic surfactant. But the appearance of the last two
peaks at 391oC and 500oC is not completely understood.
The XRD patterns of the mesocomposite after heating it
at 335oC, 391oC and 500oC for 1h, are shown in Figure
4. They indicated the formation of anatase form of nano-
crystalline titania (TiO2) at all the above temperatures
and average crystallite sizes less than 10 nm. Figure 5
gives the bright field TEM image of anatase after heat
treatment at 335oC for 1h, with its selected area electron
diffraction pattern and Figure 6 shows its corresponding
dark field TEM image. The dark field TEM image indi-
cated the presence of particles less than 10 nm though
agglomeration is also present.
Intercalated structure is indicated by TEM studies
with the average particle size less than 10 nm [11] which
in turn is composed of [Ti1-xFxNy]3n+and [CTA]+ with
the bridging F- ions. Hence it could be assumed that
the F- ion acts as bridge between positively charged
[Ti1-xFxNy]3n+ and [CTA]+ species. The bilayers of CTAB
between the layers of TiN are assumed to be interdigited
since it is believed that hydrated [Ti1-xFxNy]3n+ species is
large and thus interdigitation of the surfactant tails al-
lows the surfactant headgroups to be spaced well apart
which compares well with the earlier report on iron ox-
ide/surfactant composites [14] where the change in la-
mellar ‘d’ spacing with surfactant carbon chain length
for hydrated and dehydrated Fe(II) ions are studied.
Figure 7 demonstrates the mechanism underlying the
synthesis of lamellar mesophase based on TiN which is
found to follow the counter ion (here F- ion) mediated
pathway in Liquid Crystal Templating (LCT) approach.
Titania is found to be stable in rutile form when the par-
ticle size exceeds 14 nm and below this critical size,
anatase phase is stable [21]. Titania obtained by the heat
treatment of the mesolamellar composite of titanium
nitride fluoride and CTAB at 335oC for 1h is found to be
anatase with the average particle size less than ~10 nm.
4. CONCLUSIONS
There are no reports on the synthesis of mesostructured
nitrides till date in the literature and thus it is most re-
markable to produce the nanostructured mesolamellar
composite of titanium nitride fluoride and CTAB with an
average particle size less than ~ 10 nm by templating
TiN onto CTAB in the highly acidic medium enriched
with F- ions (pH ~ 2) at 80oC. The interlamellar spacing
is found to be ~ 19 Ao. The mechanism underlying the
above synthesis is also discussed for the first time where
F- ions act as the bridge between positively charged
[Ti1-x Fx Ny]3n+ and [CTA]+ species. The bilayers of
CTAB between the layers of TiN are interdigited since
that hydrated [Ti1-x Fx Ny]3n+ species are large and thus
Figure 3. DSC trace of the mesolamellar composite of TiN and
CTAB.
Figure 4. XRD pattern of the mesocomposite of TiN and
CTAB, after heat treatment at (a) 335oC; (b) 391oC; (c) 500oC,
for 1 h.
Figure 5. (a) The bright field TEM image of TiO2 (anatase)
obtained from the mesolamellar composite after heat treatment
at 335 oC for 1 h, and (b) its corresponding selected area elec-
tron diffraction pattern.

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Figure 6. The dark field TEM image of TiO2
(anatase) obtained from the mesolamellar com-
posite after heat treatment at 335 oC for 1 h.
Figure 7. The mechanism underlying the syn-
thesis of mesolamellar composite of titanium
nitride and CTAB in the medium enriched
with F- ions.
interdigitation of the surfactant tails allows the surfactant
headgroups to be spaced well apart. The above lamellar
composite has resulted in the formation of anatase form
of titania upon heat treatment at 335oC for 1h with the
average particle size less than 10 nm.
5. ACKNOWLEDGEMENTS
The support of the Council for Scientific & Industrial Research (India)
to T. V. Anuradha through a Senior Research Fellowship is gratefully
acknowledged.
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