Advances in Nanoparticles, 2013, 2, 229-235 Published Online August 2013 (
Chemical Structure of TiO Organometallic Particles
Obtained by Plasma
Ma. Guadalupe Olayo1, Francisco González-Salgado1,2, Guillermo J. Cruz1*, Lidia Ma. Gómez1,3,
Genoveva García-Rosales2, Maribel Gonzalez-Torres1,3, Osvaldo G. Lopez-Gracia1,4
1Departamento de Física, Instituto Nacional de Investigaciones Nucleares, Ocoyoacac, México
2Departamento de Posgrado, Instituto Tecnológico de Toluca, Metepec, México
3Posgrado en Ciencia de Materiales, Facultad de Química, Universidad Autónoma del Estado de México, Toluca, México
4Posgrado en Ciencias Químicas, Facultad de Química, Universidad Autónoma del Estado de México, Toluca, México
Email: *
Received April 3, 2013; revised May 3, 2013; accepted May 10, 2013
Copyright © 2013 Ma. Guadalupe Olayo et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This work presents a study about the chemical structure of titanium oxide (TiO) particles synthesized by plasmas using
titanium tetrapropoxide, Ti(-O-CH2-CH2-CH3)4. In plasmas, practically all chemical bonds are susceptible to participate
in the reactions producing different results than those obtained by the traditional chemical routes. The particles obtained
this way are semispheres and fibers grouped in random and layered structures in the 120 - 500 nm interval and mean
diameter of 86.4 nm (fibers) and 308.6 nm (semispheres). The analysis of the resulting TiO structure was performed by
IR and XPS finding that the main chemical state of Ti in these conditions was O2-Ti-O2 (Ti surrounded by O) which is
part of the precursor structure, however, in O, the main chemical state was Ti-O-Ti formed with the rupture of the pre-
cursor Ti-O-C bonds. These last bonds reduce the conjugation between the structure of both elements, O2-Ti-O2 and
Ti-O-Ti, to produce organometallic compounds. Other chemical states appeared showing consecutive dehydrogenation
steps during the synthesis with the formation of multiple bonds as a consequence of the continuous collisions in the
plasma. These results allow us to follow the chemical reactions promoted by this kind of plasmas to produce TiO
nanoparticles which are essentially conformed of intensive dehydrogenation.
Keywords: TiO; Particles; Plasma; Degradation; XPS; TTP
1. Introduction
Under plasma conditions, degradation and/or synthesis of
materials can be carried out with different results than
those obtained by the traditional chemical routes. This is
because in plasmas the accelerated electrons can reach
kinetic energies beyond the bonding energy of the atoms
promoting, by collisions, chemical reactions among radi-
cals and/or ions without involving other reagents or sub-
stantially increasing the temperature of the synthesis which
could damage the reagents [1]. Plasma techniques have
already been used to prepare amorphous and/or crystal-
line phases of titanium oxides [2]. In these conditions,
the TiOx configuration of crystalline phases in which x =
2 can be displaced from 2 to other ratios, obtaining mate-
rials generically known as TiO.
Some photochemical applications of TiO are based on
its capacity to absorb an incident light transferring part of
this energy to other materials through its surface. This
energy can be applied to oxidize molecules or to create
free radicals in other substances to be used in the oxida-
tion or in degradation of contaminants [3,4]. In this su-
perficial activity, materials with TiO need to have a large
superficial area, as in nanoparticles.
Spherical TiO nanoparticles produced by chemical tech-
niques with titanium tetraisopropoxide (TTIP) have been
obtained with diameters below 100 nm with characteris-
tics depending on the precursor and on the type of syn-
thesis [5-9]. The main precursors of TiO nanoparticles in
chemical syntheses up to now have been TTIP [10,11]
and TiCl4 [12,13]. In plasma syntheses, commercially pure
titanium oxidized in Ar/O mixtures [14] and TTIP de-
graded in resistive coupling discharges [15] have been
used. Plasma degradation of titanium tetrapropoxide (TTP),
Ti(-O-CH2-CH2-CH3)4, to produce organometallic parti-
cles has also been focused on the electric properties and
on the amorphous structure of the particles [16,17]. Now,
*Corresponding author.
opyright © 2013 SciRes. ANP
in this work, the chemical structure of TiO particles syn-
thesized by plasma glow discharges of TTP and water in
gas-phase is studied with IR and XPS spectroscopies with
the objective of exploring the different steps of TTP deg-
radation under the plasma collisions which promote the
formation of TiO organometallic nanoparticles.
2. Material and Methods
The degradation of TTP to produce TiO was obtained
with water vapor plasmas through the constant collisions
of accelerated ions and electrons in the plasma to reduce
the organic part of TTP molecules and to increase the
metal oxide fraction. Due to the polarity, the electrons
tend to collide with the most electropositive segments in
TTP, and depending on the energy applied; this effect
may produce the breaking and formation of new chemical
bonds promoting the formation of TiO compounds.
This process was made in a vacuum tubular glass reac-
tor, 9 cm diameter and 20 cm length, with stainless steel
flanges and electrodes, which are plates of 6.5 cm in di-
ameter separated by 8 cm. The electric discharges were
produced with resistive coupling in the 0.3 - 0.9 mbar
interval at 13.56 MHz, 240 min and 100 W. As TTP (Al-
drich, 98%) is a volatile and reactive liquid at room con-
ditions, it was spread over a sample holder, frozen with
liquid nitrogen at approximately 180˚C and placed in-
side the reactor between the electrodes. This procedure
was intended to reduce the reactivity and evaporation of
TTP to prepare the electric discharges with water, which
was introduced into the reactor from another recipient
and vaporized due to the difference of pressure between
the recipient and the reactor. The heat produced by the
discharges slowly increased the temperature in the reac-
tor and vaporized the frozen TTP, which reacted with the
particles in the gas-phase. The synthesis process of TiO
is described in the flow chart of Figure 1.
Figure 1. Flow chart that describes the synthesis of TiO.
During the synthesis, the inorganic fraction remained
on the sample holder, but the smallest organic molecules
evaporated from the holders. However, some organic frag-
ments reacted among them to form large molecules which
are difficult to evaporate. These fragments formed com-
plex organometallic compounds in the final TiO powder.
No further treatment was done to the titanium oxide ob-
tained after the syntheses. The characterization of the
TiO particles was focused on the chemical structure and
3. Results and Discussion
3.1. Micro Morphology
Figure 2 is composed of 2 images of scanning electron
microscopy (Jeol 5900 LV) of TiO particles taken at
10,000× and 50,000×. The images show semispherical,
Figure 2(a), and fibered particles, Figure 2(b), arranged
in layers or in agglomerates of fibers with diameters from
25 to 500 nm.
Figure 2. Different morphology in TiO par ticles. (a) M on ol ay -
ers of semispherical particles with an average diameter of
308.6 nm grown with different orientation; (b) Agglomer-
ates of fibers aligned in approximately the same direction
with an average diameter of 86.4 nm.
Copyright © 2013 SciRes. ANP
Ma. G. OLAYO ET AL. 231
Both morphologies were obtained in the same experi-
mental conditions. The spherical particles form surfaces
of layered structures with different orientation. The di-
ameter distribution is between 120 and 500 nm [15] with
a center at 308.6 nm, see Figure 2. These particles have
the largest average. The fibered structures were formed
as groups of consecutive particles stacked in one direc-
tion. The alignment may be promoted by the electric field
applied to the reactor. The diameter of fibers slightly
decreases on top, which is in the 25 - 230 nm interval
with center at 86.4 nm, see Figure 2(b). Fibers with
length up to 1 µm were observed in the micrographs.
Figure 3 shows the histogram of frequencies of each
group with the arithmetic mean of diameters (ϕ). The
histogram shows that the greater diameter and wider dis-
tribution belong to the particles, however, in the 150 -
200 nm diameter interval, both structures can be found.
3.2. Chemical Structure of Titanium Oxides
The TTP molecule has a central atom of Ti surrounded
by four oxygen atoms, this structure is related to the in-
organic part, each oxygen atom has a chain of three car-
bons that corresponds to the organic fraction, the mole-
cule of TTP can be written as Ti(-O-CH2-CH2-CH3)4.
The chemical structure of TiO particles obtained in the
synthesis was analyzed with a Thermo Scientific Nicolet
iS5 FTIR spectrophotometer in ATR mode with a dia-
mond cell in the 550 - 4000 cm1 interval using 150
scans, see Figure 4 where TTP is in black and TiO in
The absorption of C-H groups in TTP can be seen in
the following wavenumbers, 2956, 2870, 988, 887 and
783 cm1. The other absorptions belong to C-O in 1377
and 1071 cm1, and to the C-C structure, 1472 cm1. The
most important group for this work is located in the wide
050100 150 200 250 300 350 400 450 500
308.6 nm
86.4 nm
Particles in monolayers
Figure 3. Diameter distribution frequency histogram of
semispheres and fibers. The fiber diameter is centered in
86.4 nm and in particles is centered in 308.6 nm.
4000 35003000 25002000 1500 1000500
100 W, 240 min
988 596
2956 2870
Figure 4. IR spectra of TTP (in black) and TiO (in blue)
synthesized by plasma. Note that the organic phase in TiO
was greatly reduced leaving the most intense absorption to
Ti-O bonds. In the TTP molecule, Ti is in blue, O in red, C
in grey and H in white.
signal centered at 596 cm1, which is part of the Ti-O
absorption in TTP and TiO. This wide signal has been
reported before centered around 550 cm1 for TiO2 ob-
tained from TiCl4 [18].
In TiO, many C-H groups of TTP disappeared or re-
duced to very low expressions, leaving the Ti-O absorp-
tion as the most important. Other groups not present in
TTP appeared in TiO as a consequence of the plasma
reactions. The wide absorption centered in 3135 cm1
includes three groups, O-H, =C-H and C-H.
The first one belongs to the interaction with water in
the plasma, =C-H groups appear as a consequence of
dehydrogenation reactions due to the collisions of the
particles in the plasma, and C-H groups are remnants of
TTP in TiO. Other groups in TiO that can be seen in the
absorption centered in 1620 cm1 are C=C and C=O,
which are also a consequence of the dehydrogenation
reactions. The release of H atoms produces free radicals,
and if two of them are sufficiently near, both neutralize
forming multiple bonds.
3.3. Superficial Elemental Analysis
The superficial elemental analysis and the energetic dis-
tribution of Ti2p, O1s and C1s orbitals in TiO was ob-
tained with a monochromatic Al X-ray (1486.6 eV) Thermo
K-Alpha photoelectron spectroscope. The samples re-
mained in a pre-analysis chamber for approximately 1 hr
at 103 mbar before entering the analysis chamber. The
diameter of the analysis area was 400 µm.
The electrostatic charges in the samples were reduced
with a beam of Ar ions which increased the base pressure
from 109 to 107 mbar in which the XPS analyses were
Copyright © 2013 SciRes. ANP
performed. The elements involved in the analyses were
Ti, O, C and N and are presented in Figure 5 in survey
mode. This last element has a small participation (0.46%)
and can be due to the atmospheric interaction. The ele-
mental content of Ti is 16.91% and O is 46.34% with an
x = 2.74 (O/Ti atomic ratio). This means that there are
less oxygen atoms than in TTP molecules (x = 4), but
more than in TiO2 compounds with crystalline phases (x
= 2). However, O atoms can bond to C and Ti, which
displace the O/Ti ratio from 2. The content of C atoms
was reduced from 70.58% in TTP to 36.29% in TiO in-
dicating that the degradation of TTP molecules worked
in at least 50%.
3.4. Chemical States in TiO
The analysis of the chemical states in TiO particles was
based on the electronic energetic distribution of Ti2p,
O1s and C1s orbitals and on different chemical states that
may appear with the degradation of TTP molecules in
plasmas. The specific energetic atomic states were stud-
ied adjusting the distribution of the orbitals with internal
Gaussian curves considering the full width at half maxi-
mum (FWHM) parameters based on the Crist work for
advanced fitting of monochromatic XPS spectra [19]. As
the internal curves become wider, more chemical states
can be included in them.
Each energetic state can be associated with atomic
chemical states involving all bonding orbitals shared in
the atoms, and although the bonding orbitals are in the
exterior electronic shell and the orbitals analyzed in XPS
are further inside the atomic structure, any modification
in the valence orbitals adjust the energetic equilibrium of
the entire atom, modifying the orbitals studied in the
XPS analysis. Neighboring atoms also exert influence in
the energetic distribution of the atoms, although they are
0100 200 300 400 500 600 700 80090010001100
At. %
I (Adim)
BE (eV)
XPS Survey
TiO powder
4 hrs, 100 W
Figure 5. XPS survey of TiO powder. The elemental content
and atomic ratios are included.
not directly bonded. Thus, in analyzing the energy dis-
tribution of orbitals, the whole chemical environment has
to be considered.
The scattered points in the following graphs represent
the electronic binding energy (BE) of orbitals obtained
with the spectroscope, the blue internal curves represent
the deconvoluted distribution of the orbital and the red
line represents the sum of all adjusted curves along BE.
The representation of the atomic chemical states in this
work was done including all the possible bonding com-
binations. The notation used in this work indicates that
the atom in bold face is bonded with all atoms in the
formula. For example, the most common chemical state
of Ti in TiO is O2-Ti-O2, in which the central Ti atom is
bonded in its own spatial configuration with 4 O atoms.
In the same trend, C-CH2-C represents a C atom sur-
rounded by 2 C and 2 H atoms, and C3-C-H indicates a C
atom surrounded by 3 C and 1 H atom. If it is possible,
both sides of the central atom are used to clarify the
3.5. Ti Chemical States
Ti chemical states were studied with the energetic distri-
bution of Ti2p 3/2 orbitals, see Figure 6. Ti2p has a bi-
modal electronic distribution belonging to the 1/2 and 3/2
orbitals [20], in which the most intense signal belongs to
the 2p 3/2 orbital, which is studied in this work. The 3/2
orbital was observed from 456.5 to 460.6 eV and was
adjusted with 3 internal gaussian curves, FWHM 1.05
eV, which represent 3 Ti energetic states.
The greatest participation, 84.31%, was obtained with
Curve 2 centered at 458.74 eV, which can be assigned to
Ti surrounded by oxygen atoms, O2-Ti-O2. This state is
also the core of TTP molecules and it is found in the ma-
456.5 457.0 457.5 458.0 458.5 459.0 459.5 460.0 460.5 461.0
I (Adim)
BE (eV)
BE max
1- 457.97
2- 458.74
3- 459.40
Orbital Ti 2p 3/2
100 W, 240 min
Figure 6. Energetic distribution of Ti2p 3/2 orbital in TiO
particles. Note that the main Ti chemical state in TTP,
O2-Ti-O2, was preserved in 84.31% in the final compounds.
Copyright © 2013 SciRes. ANP
Ma. G. OLAYO ET AL. 233
jority of titanium oxides as well. The percentage suggests
that the main structure of Ti in TTP prevailed after the
synthesis. However, the experimental curve indicates that
at least 2 more energetic states participate in the particles,
which can be identified as the superposition of O3-Ti-Ti
and O3-Ti-H states centered at 457.97 eV with 8.71%,
see Curve 1. The other chemical configuration is O3-Ti-C
centered at 459.40 eV with 6.98%, see Curve 3.
All states indicate that there are ruptures of some Ti-O
bonds of the TTP structure to form Ti-Ti, Ti-H and Ti-C
new bonds in small percentages during the synthesis of
TiO particles by plasma.
3.6. O Chemical States
The analysis of O chemical states was supported in the
unimodal energetic distribution of O1s orbitals shown in
Figure 7. The O1s energetic distribution consists of the
528.5 - 534.3 eV interval and was adjusted with 4 curves
considering FWHM 1.2 eV. The greatest area belongs
to curve 1 centered at 530.19 eV, which can be assigned
to Ti-O-Ti and C-O-Ti chemical states with 71.71% area.
Curve 2 can be related to C-O-Ti and C-O-H centered at
531.32 eV, 13.83%. The energy required in the formation
of C-O-Ti chemical states derived from the degradation
of TTP is located between the formation energy of Ti-
O-Ti and C-O-H states. This is the reason why C-O-Ti is
related with both, Curves 1 and 2.
C-O-C can be identified in Curve 3, centered at 532
eV, with 9.89%, and finally C=O can be associated with
Curve 4 centered in 533 eV with 4.57% area. Ti-O-Ti
states are not part of the TTP structure and were formed
during the synthesis of TiO particles with the constant
breaking and formation of chemical bonds due to the
collisions among particles in the plasma, especially, the
528 529 530 531 532 533 534 535
I (Adim)
BE (eV)
FWHM= 1.2
BE max
1- 530.19
2- 531.32
3- 532.00
4- 533.00
100 W, 240 min
O 1s Orbital
Figure 7. Energetic distribution of O1s orbitals in TiO par-
ticles. The Ti-O-Ti chemical state was not part of the original
precursor and appeared after the plasma treatment.
breaking and rearrangement of some Ti-O bonds, which
occurs as the main transformation of the initial C-O-Ti
arrangement in TTP.
Ti-O-Ti and O2-Ti-O2 states in different conjugated
arrangements can be found in crystalline TiO oxides. The
percentage of Ti-O-Ti, 71.71%, can be related with the
efficiency of the synthesis. On its part, C-O-Ti is part of
the TTP structure that survived the energy of the dis-
charge. This is an indicative of the organometallic char-
acter of particles. The other chemical states, C-O-H and
C=O, were formed during the synthesis and are part of
the organic fraction in the final compounds.
3.7. C Chemical States
The C chemical states resulted after the TiO synthesis
were studied with the C1s unimodal energy distribution
from 283 to 290.2 eV adjusted with 5 gaussian curves
using the restriction of FWHM 1.1 eV, see Figure 8.
The curve with the lowest energy is centered at 284.06
eV, 8.01% area, which represents the chemical arrange-
ments: H-C-C3, Ti-C-C3, and if there are some remnants
of the precursor, such as C-CH2-O and C-CH2-C [21],
they will be in this curve in small proportion, which has
the most hydrogenated configurations of C.
The presence of Ti-C bonds suggests that most chemi-
cal bonds in TTP can be broken by the plasma to form
new structures, because it needs the rupture of Ti-O
bonds, which have the highest bonding energy in TTP,
6.86 eV. The greatest participation belongs to Curve 2
centered in 284.85 eV, 54.96%, which can be assigned to
C2-C-C2 and C3-C-O, both with formation energy be-
tween 14.4 and 14.3 eV. The difference with the states of
the first curve is the replacement of one H for one C
atom as a consequence of the dehydrogenation promoted
282 283 284 285 286 287 288 289 290 291
C1s Orbital
100 W, 240 min
I (Adim)
BE (eV)
BE max
Figure 8. Energetic distribution of C1s orbitals in TiO par-
ticles. Most of C chemical states were formed during the
synthesis of TiO.
Copyright © 2013 SciRes. ANP
in the plasma. Note that these states do not have hydro-
gen atoms and have a great participation in the final
The next Curve 3 at higher BE is centered at 285.53
eV, 22.63%, and can be associated with double bonds
involving C=CO-C and C=C-C2 structures. The forma-
tion of multiple bonds can also be due to dehydrogena-
tion in consecutive C atoms in the TTP organic arms as a
consequence of the collisions in the plasma, and to the
neutralizations of the radicals left behind. More combi-
nations of double bonds appear in Curve 4 which is cen-
tered at 286.53 eV, C=C=C and O=C=C, due to other
steps in the dehydrogenation process. These bonds are
signals of complex structures, in which the final states
can be related with triple bonds as C-CC which can be
found in Curve 5 centered at 288.98 eV. These chemical
states represent the final oxidation stage of the organic
segment in the plasma conditions applied to the synthe-
In general terms, the energetic distribution of C1s or-
bitals suggests that many carbon chemical states may
appear in the particles product of the plasma reactions.
These states show a gradual oxidation of the TTP organic
arms in consecutive dehydrogenation steps with the for-
mation of multiple bonds and complex structures as a
consequence of the continuous collisions in the plasma.
4. Conclusions
Usually, the synthesis of TiO by plasmas is done by oxi-
dizing Ti with oxygenated combinations of gases to pro-
duce thin films of TiO on the surface. However, in this
work, TiO particles were synthesized modifying the struc-
ture of titanium tetrapropoxide by plasma to separate its
organic and inorganic components. In these conditions,
spherical and fibered organometallic particles were ob-
tained with diameters between 120 and 500 nm grouped
in random and layered arrangements. The arithmetic mean
diameter of fibers and spheres was 86.4 and 308.6 nm,
respectively, and the maximum length of fibers was ap-
proximately 1 µm.
The chemical structure of the particles and the mecha-
nism of formation were studied through the distribution
energy of Ti2p, O1s and C1s orbitals. The main chemical
states found in these conditions were O2-Ti-O2, in which
Ti is surrounded by O, and Ti-O-Ti, which is O sur-
rounded by Ti. This state was not part of the original TTP
precursor and is the main modification of the plasma reac-
tions to produce TiO particles. Both states usually pro-
duce conjugated structures of titanium oxides. However,
other chemical states appeared with combinations of C,
O and H, as O3-Ti-C and C-O-Ti, which are remnants of
the TTP precursor, that randomly inserted in the structure
reduce the conjugation between O2-Ti-O2 and Ti-O-Ti
producing organometallic compounds.
Chemical states in C with multiple bonds in different
combinations were formed, which are signals of con-
secutive dehydrogenation steps in the molecules with the
accelerated particles in the plasma. These carbon chemi-
cal states allow us to follow the mechanisms of reaction
in plasma conditions, which are essentially conformed of
intensive dehydrogenation.
5. Acknowledgements
The authors acknowledge DGEST and CONACYT in
Mexico for the partial financial support to this work with
the projects 004-09-02-PIA, 3402.10-P, 154757 and
130190, and to Jorge Perez for the assistance in the elec-
tron microscopy. F. Gonzalez acknowledges CONACYT
for the doctoral fellowship received to carry out this
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