Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory
The electronic properties of TiO₂ nanostructure are explored using density functional theory. The adsorption properties of acetone on TiO₂ nanostructure are studied in terms of adsorption energy, average energy gap variation and Mulliken charge transfer. The density of states spectrum and the band...
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irk-123456789-1570332019-06-20T01:28:19Z Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory Nagarajan, V. Sriram, S. Chandiramouli, R. The electronic properties of TiO₂ nanostructure are explored using density functional theory. The adsorption properties of acetone on TiO₂ nanostructure are studied in terms of adsorption energy, average energy gap variation and Mulliken charge transfer. The density of states spectrum and the band structure clearly reveals the adsorption of acetone on TiO₂ nanostructures. The variation in the energy gap and changes in the density of charge are observed upon adsorption of acetone on n-type TiO₂ base material. The results of DOS spectrum reveal that the transfer of electrons takes place between acetone vapor and TiO₂ base material. The findings show that the adsorption property of acetone is more favorable on TiO₂ nanostructure. Suitable adsorption sites of acetone on TiO₂ nanostructure are identified at atomistic level. From the results, it is confirmed that TiO₂ nanostructure can be efficiently utilized as a sensing element for the detection of acetone vapor in a mixed environment. Дослiджуються електроннi властивостi TiO₂ наноструктури з використанням теорiї функцiоналу густини. Властивостi адсорбцiї ацетону на TiO₂наноструктурi вивчаються в термiнах енергiї адсорбцiї, змiни середньої енергiї щiлини i переносу заряду Муллiкена. Спектр густини станiв та структура зони чiтко вказують на адсорбцiю ацетону на TiO₂ наноструктурах. Змiна енергiї щiлини та змiни густини заряду спостерiгаються пiсля адсорбцiї ацетону на базовому матерiалi TiO₂ n-типу. Результати спектру густини станiв показують, що перенос електронiв вiдбувається мiж парою ацетону i TiO₂ базовим матерiалом. Отриманi данi показують, що властивостi адсорбцiї ацетону є бiльш сприятливими на TiO₂ наноструктурi. Зручнi мiсця для адсорбцiї ацетону на TiO₂ наноструктурi iдентифiкуються на атомарному рiвнi. Згiдно з отриманими результатами, пiдтверджується, що TiO₂ наноструктуру можна ефективно використовувати в якостi чутливого елемента для виявлення випарiв ацетону у змiшаному довкiллi. 2017 Article Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory / V. Nagarajan, S. Sriram, R. Chandiramouli // Condensed Matter Physics. — 2017. — Т. 20, № 4. — С. 43708: 1–13. — Бібліогр.: 45 назв. — англ. 1607-324X PACS: 71.15.Mb DOI:10.5488/CMP.20.43708 arXiv:1712.05373 http://dspace.nbuv.gov.ua/handle/123456789/157033 en Condensed Matter Physics Інститут фізики конденсованих систем НАН України |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine |
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DSpace DC |
| language |
English |
| description |
The electronic properties of TiO₂ nanostructure are explored using density functional theory. The adsorption
properties of acetone on TiO₂ nanostructure are studied in terms of adsorption energy, average energy gap
variation and Mulliken charge transfer. The density of states spectrum and the band structure clearly reveals
the adsorption of acetone on TiO₂ nanostructures. The variation in the energy gap and changes in the density
of charge are observed upon adsorption of acetone on n-type TiO₂ base material. The results of DOS spectrum
reveal that the transfer of electrons takes place between acetone vapor and TiO₂ base material. The findings
show that the adsorption property of acetone is more favorable on TiO₂ nanostructure. Suitable adsorption
sites of acetone on TiO₂ nanostructure are identified at atomistic level. From the results, it is confirmed that
TiO₂ nanostructure can be efficiently utilized as a sensing element for the detection of acetone vapor in a mixed
environment. |
| format |
Article |
| author |
Nagarajan, V. Sriram, S. Chandiramouli, R. |
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Nagarajan, V. Sriram, S. Chandiramouli, R. Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory Condensed Matter Physics |
| author_facet |
Nagarajan, V. Sriram, S. Chandiramouli, R. |
| author_sort |
Nagarajan, V. |
| title |
Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory |
| title_short |
Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory |
| title_full |
Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory |
| title_fullStr |
Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory |
| title_full_unstemmed |
Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory |
| title_sort |
sensing behavior of acetone vapors on tio₂ nanostructures — application of density functional theory |
| publisher |
Інститут фізики конденсованих систем НАН України |
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2017 |
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http://dspace.nbuv.gov.ua/handle/123456789/157033 |
| citation_txt |
Sensing behavior of acetone vapors on TiO₂ nanostructures — application of density functional theory / V. Nagarajan, S. Sriram, R. Chandiramouli // Condensed Matter Physics. — 2017. — Т. 20, № 4. — С. 43708: 1–13. — Бібліогр.: 45 назв. — англ. |
| series |
Condensed Matter Physics |
| work_keys_str_mv |
AT nagarajanv sensingbehaviorofacetonevaporsontio2nanostructuresapplicationofdensityfunctionaltheory AT srirams sensingbehaviorofacetonevaporsontio2nanostructuresapplicationofdensityfunctionaltheory AT chandiramoulir sensingbehaviorofacetonevaporsontio2nanostructuresapplicationofdensityfunctionaltheory |
| first_indexed |
2025-07-14T09:22:31Z |
| last_indexed |
2025-07-14T09:22:31Z |
| _version_ |
1837613660889939968 |
| fulltext |
Condensed Matter Physics, 2017, Vol. 20, No 4, 43708: 1–13
DOI: 10.5488/CMP.20.43708
http://www.icmp.lviv.ua/journal
Sensing behavior of acetone vapors on TiO2
nanostructures— application of density functional
theory
V. Nagarajan, S. Sriram, R. Chandiramouli∗
School of Electrical and Electronics Engineering, Shanmugha Arts Science Technology and Research Academy
(SASTRA) University, Tirumalaisamudram, Thanjavur, Tamil nadu— 613 401, India
Received July 13, 2017, in final form September 5, 2017
The electronic properties of TiO2 nanostructure are explored using density functional theory. The adsorptionproperties of acetone on TiO2 nanostructure are studied in terms of adsorption energy, average energy gapvariation and Mulliken charge transfer. The density of states spectrum and the band structure clearly reveals
the adsorption of acetone on TiO2 nanostructures. The variation in the energy gap and changes in the densityof charge are observed upon adsorption of acetone on n-type TiO2 base material. The results of DOS spectrumreveal that the transfer of electrons takes place between acetone vapor and TiO2 base material. The findingsshow that the adsorption property of acetone is more favorable on TiO2 nanostructure. Suitable adsorptionsites of acetone on TiO2 nanostructure are identified at atomistic level. From the results, it is confirmed thatTiO2 nanostructure can be efficiently utilized as a sensing element for the detection of acetone vapor in a mixedenvironment.
Key words: TiO2, nanostructure, adsorption, acetone, energy gap
PACS: 71.15.Mb
1. Introduction
The expansion of industries in recent years leads to emission of hazardous gases and vapors into
the atmosphere. Moreover, volatile organic compounds (VOCs) are a major source of environmental
pollutants and cause a serious impact on humans. For instance, acetone (CH3COCH3) is a chemical
reagent utilized in laboratories and industries. Besides, this compound is widely used in purifying
paraffin, dissolving plastics and in pharmaceutics. Acetone may cause damages to human noses, eyes
and central nervous system when the permissible exposure limit exceeds 1000 parts per million (ppm)
according to Occupational Safety and Health Administration [1]. The high exposure to acetone to humans
may cause mood swings, respiratory irritation and nausea. In addition, breathing acetone in high ppm
value may cause dizziness, respiratory tract irritation and loss of strength [2]. Furthermore, acetone
is also highly inflammable. Meanwhile, acetone was found to be the final product for added ketone
bodies’ metabolism [3]. Among the transition metal oxide semiconductor, titanium dioxide (TiO2) is
extensively investigated as a key material for technological application and fundamental research in
the semiconductors, solar cell [4] and lithium-ion batteries [5] owing to its excellent chemical stability
and low cost [6]. TiO2 is also a promising candidate in the field of gas-sensor, photovoltaic, energy
storage and photocatalysis due to its photocatalytic properties, long-term stability and low toxicity [7, 8].
Besides, TiO2 polymorphs are mainly classified into three types, namely anatase, rutile and brookite with
corresponding space groups namely I41/amd-D19
4h (tetragonal), P42/mnm-D14
4h (tetragonal) and pbca-D
15
2h
(orthorhombic). Besides, only the first two crystal systems play a vital role in industrial applications.
∗Corresponding author
This work is licensed under a Creative Commons Attribution 4.0 International License . Further distribution
of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
43708-1
https://doi.org/10.5488/CMP.20.43708
http://www.icmp.lviv.ua/journal
http://creativecommons.org/licenses/by/4.0/
V. Nagarajan, S. Sriram, R. Chandiramouli
Experimental work on brookite crystal system is constrained owing to its difficulty in preparation [9].
The optical energy gap values of anatase, rutile and brookite TiO2 crystal structure are reported as
3.4 eV [10], 3.0 eV [11] and 3.3 eV [12], respectively. The density functional theory (DFT) method has
been widely used by the researchers to study rutile and anatase phases of TiO2 nanostructure [13]. The
previous reports on TiO2 electronic properties were presented in the literature using hybrid-functional
schemes [14]. Bhowmik et al. [15] have proposed TiO2 nanotubes as a good acetone sensor and the
authors observed that the response of the sensor reaches 3.35% against 1000 ppm acetone. Chen et al.
[16] have reported the sensing performance of acetone based on nanoporous morphology of TiO2 using
a facile hydrothermal method. Rella et al. [17] reported about the sensing properties of ethanol and
acetone vapors on TiO2 nanoparticles prepared from pulsed laser deposition. Chen et al. [18] studied
the adsorption properties of acetone on pristine and transition metal doped TiO2 clusters using DFT
study. Thus, from the previous literatures, to our knowledge, there are only limited reports based on DFT
method to study the adsorption properties of acetone on rutile TiO2 nanostructure. The motivation behind
the present work is to investigate acetone adsorption properties on TiO2 nanostructure and to identify the
most suitable adsorption site at the atomistic level.
2. Computational methods
The electronic and adsorption properties of acetone on TiO2 nanostructures are studied using DFT
method utilizing SIESTA package [19]. The atomic position in TiO2 nanostructures has been optimized
to their ground state by decreasing their Hellman-Feynman forces [20, 21] supported with conjugated
gradient algorithm. Moreover, all interatomic forces of rutile TiO2 nanostructures are observed to be
less than 0.05 eV/Å [22]. The generalized gradient approximation (GGA) combined with Perdew-Burke-
Ernzerhof (PBE) exchange correlation functional is utilized to investigate the electron-electron interaction
[23, 24]. The energy cut-off of plane-wave basis set was adjusted to 500 eV with energy convergence of
10−5 eV. The atomic positions in TiO2 nanostructure were relaxed until the force of 0.02 eV/Å is achieved.
The k-points in Brillouin zones under the Monkhorst-pack scheme [25], are kept as 10×10×10 k-points
with 3 × 3 × 3 super-cell size in the present study. The density of states, charge density, band structure
and electron localization function (ELF) of rutile TiO2 nanostructure were calculated with the help of
SIESTA code with Monkhorst-Pack k-point meshes of 10−3 Å−1. The acetone adsorption properties
on rutile TiO2 nanostructure is also studied using SIESTA package. Furthermore, the electronic wave
function of Ti and O atoms is expressed by basis set, which is directly related with the numerical orbitals.
The double zeta polarization (DZP) basis set is utilized for relaxation of rutile TiO2 nanostructure in the
present work [26].
3. Results and discussion
3.1. Electronic properties of rutile TiO2 nanostructure
The present work concentrates on the investigation of electronic properties and adsorption behavior
of acetone on TiO2 nanostructure. Figure 1 represents the schematic diagram of TiO2 nanostructure with
the periodic boundary condition (PBC). The optimized lattice constant and Wyckoff atomic positions,
including coordinates of TiO2 nanostructure are tabulated in table 1. In this work, we have chosen a
tetragonal— rutile TiO2 nanostructure (P42/mnm) for calculating the electronic properties and adsorption
behavior of acetone on TiO2 nanostructure.
The electronic properties of TiO2 base material are described in terms of band structure [27]. Figure 2
illustrates the band structure of an isolated TiO2 nanostructure. The band gap of TiO2 base material is
observed along the gamma point (G) and it is observed that the band gap value of an isolated TiO2
nanostructure is found to be 2.43 eV with indirect gap. Moreover, the channels along the conduction
band minimum and the valence band maximum are out of phase along the gamma point, which infers
the indirect band gap. Furthermore, the calculated band gap of TiO2 nanostructure is in good agreement
with the previously reported work [11]. In addition, based on the selection of exchange-correlation (XC)
43708-2
Investigation on TiO2 nanostructures
Figure 1. (Color online) Schematic diagram of an isolated TiO2 nanostructure with periodic boundary
condition.
Table 1. The Wyckoff atomic positions of TiO2 nanostructure.
Structure Space group Lattice Wyckoff atomic positions
Tetragonal — rutile TiO2 P42/mnm (136) a = 4.59 Å Ti: 2a (0, 0, 0)
b = 4.59 Å Ti: 16k (0.50, 0.50, 0.50)
c = 2.96 Å O: 8i (0.31, 0.31, 0)
O: 8i (0.70, 0.70, 0)
O: 16k (0.20, 0.81, 0.50)
O: 16k (0.81, 0.20, 0.50)
Figure 2. (Color online) Band structure of an isolated TiO2 nanostructure.
43708-3
V. Nagarajan, S. Sriram, R. Chandiramouli
Table 2. Energy gap calculation for isolated TiO2 nanostructure with various exchange-correlation
functional.
XC functional Eg (eV) Type
PBE 2.43 GGA
BLYP 2.50 GGA
PBEsol 2.38 GGA
RPBE 2.56 GGA
revPBE 2.48 GGA
Figure 3. (Color online) Density of states (DOS) spectrum of an isolated TiO2 nanostructure.
functional, the electronic properties of TiO2 nanostructure can be fine-tuned. Previously, Deak et al.
[14] reported the electronic band gap of TiO2 with hybrid HSE06 functional for both anatase and rutile
crystal structure, which are overestimated from the present work. Table 2 shows that the energy band gap
value of an isolated TiO2 nanostructure with different exchange correlation functional such as PBEsol,
BLYP, RPBE, PBE and revPBE [28]. Kaloni and co-workers [29–33] have suggested that the electronic
and structural properties of 2D nanosheets and organic compounds are in oligomer form, which can be
fine-tuned with the interaction of transition metal atoms.
The band structure of TiO2 nanostructure is underestimated in the present work since the density
functional theory method with GGA/PBE exchange correlation functional is utilized to calculate the
electron-electron interaction in their ground state. Moreover, the electronic and adsorption properties of
acetone in TiO2 nanostructure cannot be disturbed due to underestimation of the band gap, since the
isolated TiO2 base material is compared with acetone adsorbed TiO2 nanostructures. The density of states
(DOS) spectrum gives the insights on localization of charges in different energy intervals along TiO2
nanostructure. The visualization of band structure, PDOS and DOS spectrum are shown in figures 2 and
3, respectively.
The peak maxima are recorded near the Fermi energy level (EF), which is one of the favorable
conditions for the adsorption of target vapor/gas molecules. Thereby, the free electrons can easily transfer
between TiO2 base material and acetone molecules. The peak maximum in different energy intervals
arose owing to the orbital overlapping between Ti and O atoms in TiO2 nanostructure. Generally, for
chemiresistive type of vapor/gas sensors, metal oxide semiconducting materials are preferred owing to
the fact that the transfer of electrons is facilitated between target gas/vapor and TiO2 nanostructure and
the changes in the resistance can also be observed. From the observations of band structure and DOS
spectrum of TiO2 nanostructure it is inferred that TiO2 material can be used as a base material for the
possible application of chemical nanosensors.
43708-4
Investigation on TiO2 nanostructures
3.2. Adsorption properties of acetone on TiO2 nanostructure
In the initial stage of acetone adsorption study on TiO2 base material, acetone vapor should be studied
in vapor phase. The bond length between Ti and O atom in TiO2 nanostructure is 1.98 Å. Figure 4 (a)
refers the adsorption of carbon atom in acetone molecules adsorbed on Ti atom in TiO2 nanostructure
and it is referred to as position P. Figure 4 (b) illustrates the adsorption of H atom in acetone molecules
adsorbed on Ti atom in TiO2 nanostructure and it is referred to as position Q. Similarly, positions R and S
refer to the adsorption of C and H atom in acetone molecules adsorbed on O atom in TiO2 nanostructure
as shown in figure 4 (c) and (d), respectively. The adsorption energy of acetone on TiO2 nanostructure
can be calculated using equation (3.1)
Ead = [E(TiO2/CH3COCH3) − E(TiO2) − E(CH3COCH3) + E(BSSE)], (3.1)
where E(TiO2/CH3COCH3) refers to the energy of TiO2/CH3COCH3 complex. E(CH3COCH3) and
E(TiO2) refers to the isolated energy of CH3COCH3 and TiO2 molecules, respectively. BSSE represents
the basis set superposition error using counterpoise techniques in order to eliminate the overlapping effect
on basis functions during calculations.
When acetone molecules get adsorbed on TiO2 base material, negative values of adsorption energy
(Ead) indicate a strong adsorption of acetone on TiO2 nanostructure. Besides, in the present work, for all
positions namely P–S exhibits a negative value of Ead. This clearly confirms the adsorption of acetone
Figure 4. (Color online) (a)–(d) Adsorption of acetone on position P, Q, R and S.
43708-5
V. Nagarajan, S. Sriram, R. Chandiramouli
Table 3. Adsorption energy, Mulliken charge and average energy gap variation of TiO2 nanostructure.
Nanostructures Ead (eV) Q (e) Eg (eV) Ea
g (%)
Acetone adsorbed on TiO2 nanostructure
Isolated TiO2 − − 2.43 −
P −1.48 0.012 2.32 4.74
Q −1.46 0.105 1.32 84.09
R −1.46 0.171 0.82 196.34
S −1.29 0.013 0.68 257.35
H2O and O2 adsorbed on TiO2 nanostructure
A −1.62 0.224 2.39 1.67
B −1.60 0.17 2.41 0.83
C −1.78 0.029 2.18 11.47
D −1.71 −0.304 2.36 2.97
molecules on TiO2 nanostructure. The adsorption energy of TiO2 nanostructure for position P–S is
observed to be −1.48 eV, −1.46 eV, −1.46 eV and −1.29 eV, respectively. In addition, the band gap of
TiO2 nanostructure gets decreased due to the adsorption of acetone molecules on TiO2 base material
owing to the interaction of target VOCs with base material. Thus, the conductivity of TiO2 nanostructure
increases. The resistance of TiO2 base material decreases when it is exposed to the reducing vapors
such as acetone. The trend in the changes of resistance upon exposure towards acetone vapor is in good
agreement with the reported work of Sun et al. [34]. The changes in band gap of TiO2 nanostructure for
positions P–S are found to be 2.32 eV, 1.32 eV, 0.82 eV and 0.68 eV, respectively. Besides, the variation
in the energy gap and adsorption energy supports that TiO2 nanostructure can be used for the detection
of acetone vapor. Rella et al. [17] reported about the detection of ethanol and acetone vapors using TiO2
nanoparticles synthesized by pulsed laser deposition method. Chen et al. [16] studied the acetone sensing
performance of nanoporous titanium dioxide using a facile hydrothermal method. Epifani et al. [35]
reported about the design of an acetone sensor based on titanium dioxide nanocrystals functionalized
with tungsten oxide species. From the literature, it is evident that TiO2 nanomaterial can be utilized as a
two probe device for the detection of VOCs upon adsorption, which gives rise to change in the current.
The variation in the current is directly proportional to the concentration of acetone molecules present in
the atmosphere. From the previous reports, it is inferred that TiO2 nanostructure can be efficiently used as
acetone vapor sensor, which also strengthens the present work. Besides, the present investigation strongly
confirms the adsorption of acetone on TiO2 nanostructure at atomistic level. In addition, the most suitable
adsorption site of acetone on TiO2 base material can be concluded only after studying the percentage of
average energy gap variation (Ea
g , %) compared with its isolated counterpart. Table 3 refers the Mulliken
charge transfer, percentage of average energy gap variation and adsorption energy. From the results, it
is clearly observed that the prominent adsorption sites for acetone molecule on TiO2 nanostructure are
positions Q, R and S. The average energy gap variation is observed to be comparatively higher than P
site. The transfer of electron between acetone molecule and TiO2 nanostructure can be analyzed in terms
of Mulliken population analysis (Q) [36–38].
The positive value of Q show that the electrons are transferred from acetone vapor molecule to TiO2
base material; whereas the negative value of Mulliken charge shows that the electrons are transferred
from TiO2 base material to acetone molecule [39–41]. The Mulliken charge transfer values of TiO2
nanostructure for positions P–S are found to be 0.012 e, 0.105 e, 0.171 e and 0.013 e, respectively. From
the observation, the positive value of Mulliken charge is recorded for all the positions upon adsorption
of acetone on TiO2 base material. Therefore, the concentration of electrons gets increased due to the
transfer of electrons from acetone to TiO2 base material [42–45]. Moreover, the decrease in the energy
gap and transfer of electrons from acetone molecule to TiO2 nanostructures leads to an increase in the
current flowing across the two probe TiO2 device. The TiO2 base material can be used for the design
and development of acetone sensor. Figures 5–7 represents the electron density of an isolated TiO2
nanostructure and for positions P, Q, R and S.
43708-6
Investigation on TiO2 nanostructures
Figure 5. (Color online) Electron density of an isolated TiO2 nanostructure.
Figure 6. (Color online) Electron density of position P and Q.
Figure 7. (Color online) Electron density of position R and S.
The variation in the electron density of an isolated TiO2 nanostructure and acetone adsorbed TiO2
nanostructure clearly infers that transition of electrons takes place between acetone and TiO2 nanos-
tructure, which is also in agreement with Mulliken charge transfer. The average energy gap value is
found to be high for positions R and S. Also the adsorption energy, Mulliken charge transfer and energy
gap variation are found to be favorable for position R. However, for position S, the average energy gap
variation is comparatively high with low values of Q and Ead. The Mulliken charge transfer for position P
43708-7
V. Nagarajan, S. Sriram, R. Chandiramouli
Figure 8. (Color online) (a)–(d) Band structure of TiO2 nanostructure for position P, Q, R and S.
is almost the same as that of position S, whereas the average energy gap variation is comparatively very
low. Figure 8 (a)–(d) illustrates the band structure of TiO2 nanostructure for positions P–S, respectively.
Figures 9–12 represent the corresponding PDOS including DOS spectrum for position P, Q, R and S.
From the observation of energy band diagram for positions P and Q, the energy gap is observed to be
around 2.32 eV and 1.32 eV, respectively, along the gamma point (G). In the case of position R and S,
the energy gap is observed to be around 0.82 eV and 0.68 eV, respectively. Comparing the changes in the
energy gap upon adsorption of acetone on TiO2 nanostructure, the variation is observed to be significant
for positions Q, R and S. Meanwhile, on looking at the density of states (DOS) spectrum for positions Q,
R and S, the density of charge is observed to be larger than an isolated TiO2 counterpart. (DOS spectrum
is drawn in multi-curve fashion, the magnitude is taken into consideration along y-axis).
An increase in the density of charge is due to the fact that since TiO2 is n-type semiconductor, the
adsorption of acetone molecules consequently gives rise to a transfer of electrons between the acetone
vapor and TiO2 base material. The transfer of electrons will increase the electron concentration in
TiO2 base material, subsequently increasing the density of charge, which is observed in DOS spectrum.
The density of states spectrum gives the insight that the electrons can freely transfer between acetone
molecule and TiO2 nanostructure, which can be used as chemical sensor. Thus, the DOS spectrum of
TiO2 nanostructure strongly supports the adsorption of acetone molecule on TiO2 material. In order to
strengthen the above result, the partial (or projected) density of states spectrum (PDOS) of an isolated
TiO2 nanostructure with adsorption sites for the positions P–S is illustrated in figures 9–12. Moreover,
the density of charges is noticed to be larger in positions Q, R and S compared to an isolated TiO2
nanostructure.
Furthermore, a prominent adsorption site of acetone vapor on TiO2 nanostructure can be concluded
only after analyzing the adsorption energy, Mulliken charge transfer, average energy gap variation and
energy band gap. From the observations, among all the positions it is found that when hydrogen atom
43708-8
Investigation on TiO2 nanostructures
Figure 9. (Color online) Projected density of states (PDOS) and (DOS) spectrum of position P.
Figure 10. (Color online) Projected density of states (PDOS) and (DOS) spectrum of position Q.
Figure 11. (Color online) Projected density of states (PDOS) and (DOS) spectrum of position R.
43708-9
V. Nagarajan, S. Sriram, R. Chandiramouli
Figure 12. (Color online) Projected density of states (PDOS) and (DOS) spectrum of position S.
in acetone gets adsorbed on O atom in TiO2 nanostructure, position S is found to be more prominent.
Moreover, the selectivity of TiO2 nanostructure towards acetone in the presence of other interfering
gases in the ambient condition is to be ascertained. It is well known to the sensor community that
sensitivity, selectivity and stability are important parameters to decide the performance of metal oxide
based gas sensors. Figure 13 depicts the selectivity of acetone in ambient condition with other interfering
gases, namely H2O (humidity) and O2 gas molecules. The adsorption studies of O2 and H2O on TiO2
nanostructure are carried out and the response towards O2 and H2O molecules is observed.
The results show that the response of TiO2 nanostructure towards acetone is found to be relatively
high compared with H2O and O2 molecules. Besides, band gap variation upon adsorption of H2O and
Figure 13. (Color online) The coss-selectivity of acetone in ambient condition with H2O (humidity) and
O2 gas molecules.
43708-10
Investigation on TiO2 nanostructures
Figure 14. (Color online) The insight on the adsorption behavior of acetone on TiO2 nanostructure.
O2 molecules on TiO2 nanostructure is found to be low. Figure 14 shows the insight on the adsorption
behavior of acetone on TiO2 nanostructure, which can be used to design a simple two probe device for a
possible detection of acetone vapors present in the atmosphere.
4. Conclusions
To sum up, the electronic properties and acetone adsorption properties on TiO2 nanostructure are
studied using density functional theorymethod, which is carried out withGGA/PBE exchange-correlation
functional. The band gap of an isolated TiO2 nanostructure is found to be around 2.43 eV. Furthermore,
the adsorption of acetone molecules on TiO2 nanostructures is confirmed by the change in the adsorp-
tion energy, Mulliken charge transfer and average energy gap variation. The results of DOS spectrum
clearly reveal that the transfer of electrons takes place between acetone vapor and TiO2 base material.
Furthermore, a prominent adsorption site is explored at atomistic level, which confirms that when a
hydrogen atom in acetone molecule gets adsorbed on the O atom in TiO2 nanostructure, the adsorption is
found to be favorable. Furthermore, the selectivity of TiO2 nanostructure towards acetone molecules with
other interfering gases, namely H2O and O2, is also studied and reported. The findings from the present
investigation strongly support that TiO2 nanostructure can be efficiently used to detect the presence of
acetone vapor in the mixed environment. Thus, we conclude that a properly tailored TiO2 nanostructure
can be used as a two-probe device to detect the presence of acetone vapors.
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Investigation on TiO2 nanostructures
Детектор для визначення поведiнки випарiв ацетону на TiO2
наноструктурах— застосування теорiї функцiоналу густини
В. Нагараджан, С. Срiрам, Р. Чандiрамулi
Школа електротехнiки та електронiки, Академiя мистецтв, наукових i технологiчних дослiджень Шанмуга
(унiверситет SASTRA), Танджавур, Тамiл-Наду— 613 401, Iндiя
Дослiджуються електроннi властивостi TiO2 наноструктури з використанням теорiї функцiоналу густини.
Властивостi адсорбцiї ацетону на TiO2 наноструктурi вивчаються в термiнах енергiї адсорбцiї, змiни сере-дньої енергiї щiлини i переносу заряду Муллiкена. Спектр густини станiв та структура зони чiтко вказують
на адсорбцiю ацетону на TiO2 наноструктурах. Змiна енергiї щiлини та змiни густини заряду спостерi-
гаються пiсля адсорбцiї ацетону на базовому матерiалi TiO2 n-типу. Результати спектру густини станiв
показують,що перенос електронiв вiдбувається мiж парою ацетону i TiO2 базовим матерiалом. Отриманi
данi показують, що властивостi адсорбцiї ацетону є бiльш сприятливими на TiO2 наноструктурi. Зручнi
мiсця для адсорбцiї ацетону на TiO2 наноструктурi iдентифiкуються на атомарному рiвнi. Згiдно з отрима-ними результатами, пiдтверджується,що TiO2 наноструктуру можна ефективно використовувати в якостiчутливого елемента для виявлення випарiв ацетону у змiшаному довкiллi.
Ключовi слова: TiO2, наноструктура, адсорбцiя, ацетон, енергетична щiлина
43708-13
Introduction
Computational methods
Results and discussion
Electronic properties of rutile TiO2 nanostructure
Adsorption properties of acetone on TiO2 nanostructure
Conclusions
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