Sunlight assisted photocatalytic detoxification of sulfur mustard on vanadium ion doped titania nanocatalysts

Article abstract of DOI:10.1016/j.molcata.2014.02.022

Photocatalytic detoxification of sulfur mustard was studied on vanadium ion doped titania nanocatalysts under the irradiation of sunlight. Data obtained on vanadium ion doped titania nanocatalyst was compared with that of bare and commercial TiO₂

Full text of DOI:10.1016/j.molcata.2014.02.022

Journal of Molecular Catalysis A: Chemical 387 (2014) 38–44
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Sunlight assisted photocatalytic detoxification of sulfur mustard on
vanadium ion doped titania nanocatalysts
P.V.R.K. Ramacharyulua, J. Praveen Kumara, G.K. Prasada,∗, B. Singha,
B. Sreedharb, K. Dwivedic
a Defence Research and Development Establishment, Jhansi Road, Gwalior 474002, India
b Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad 500007, India
c School of Studies in Chemistry, Jiwaji University, Gwalior 474011, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 April 2013
Received in revised form 21 February 2014
Accepted 22 February 2014
Available online 2 March 2014
Photocatalytic detoxification of sulfur mustard was studied on vanadium ion doped titania nanocatalysts
under the irradiation of sunlight. Data obtained on vanadium ion doped titania nanocatalyst was com-
pared with that of bare and commercial TiO2 nanocatalysts. Vanadium ion doped titania nanocatalyst
was found to be more active than bare and commercial titania nanocatalysts towards the photocatalytic
detoxification of sulfur mustard in ecological sunlight irradiation. 100% of sulfur mustard was found to
be detoxified within 180 min on vanadium ion doped TiO2 nanocatalyst. Whereas, it took 240 min for
bare TiO2 and 420 min for commercial TiO2 nanocatalysts to completely degrade sulfur mustard. Sulfur
mustard was found to have degraded to products like acetaldehyde, carbon dioxide, disulfide, sulfoxide
and sulfone of sulfur mustard, chloro ethyl vinyl sulfide, chloro ethyl vinyl sulfoxide, etc.
Keywords:
Photocatalysis
Sunlight
Detoxification
Doped nano titania
Sulfur mustard
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
the doped TiO2 catalyst to efficiently degrade CWA into non toxic
products in ecological sunlight which contains more amount (46%)
Cleaning of surfaces tainted with chemical warfare agents
(CWAs) is of great concern for emergency responders and related
authorities who deal with terrorist attacks and stockpile destruc-
tion. Sulfur mustard (HD) (C4H8SCl2, 2,2ꢀ-dichloro diethyl sulfide)
is a vesicant, alkylates DNA and causes fatality to cells. Detoxifica-
tion of HD is a difficult process from the mechanism point of view
[1].
Photocatalysis has been established as a potential technique
for the detoxification of toxic chemicals and it has been playing
a promising role in the cleanup of environment [2]. Good chemical
stability, less toxicity, high photoactivity and economical viabil-
ity make TiO2 a potential candidate for photocatalysis. However,
disadvantage with TiO2 is its large band gap which requires UV-A
light (388 nm) to activate it [3,4]. Many methods have been used to
widen the spectral response of TiO2 to improve its photocatalytic
activity in visible light. TiO2 photocatalysts with enhanced visi-
ble light activity have been prepared by doping with metals [5–8],
non-metals [9–11], sensitizers [12,13], and reduced forms of tita-
nia [14]. Enhanced activity under visible light irradiation enables
of visible light in addition to UV-A light (4–5%) [15]. The visible
light activity of metal ion doped TiO2 can be explained by new
energy levels introduced in the band gap of TiO2 by dispersion
of metal ions in its matrix. Electrons can be excited from valence
band to defect states created below the conduction band of TiO2
by photon with enough energy. Additional benefit of transition
metal ion doping is the improved trapping and enhanced lifetime of
charge carriers which inhibit electron–hole recombination during
irradiation [8–17]. Decreased charge carrier recombination results
in enhanced photoactivity. Besides chemical modification of TiO2,
enhancement of photoreactivity can be achieved by reducing the
particle size to nano dimensions [16,17]. Recently, vanadium ion
doping on TiO2 has been a topic of interest [18–22] because of eco-
nomical viability, enhanced catalytic activity of V centres of oxide
˚
substrates. The ionic radius of vanadium ion (0.58 A) is similar to
˚
that of titanium ion (0.61 A) because of which vanadium ion can be
used as a substituent to titanium ion in its vacant sites.
Photocatalytic oxidation of HD and its simulants has been stud-
ied since 1990 over titania catalysts [23–29]. Regarding this, Neatu
et al. studied the photocatalytic degradation of HD on M/TiO2/SiO2
catalysts and observed the enhanced activity under visible light
irradiation on doped catalysts whereas the bare catalyst showed
activity only under UV irradiation [30]. Subsequently, they also
∗
Corresponding author. Tel.: +91 751 2390169; fax: +91 751 2341148.
E-mail address: gkprasad2001@gmail.com (G.K. Prasad).
http://dx.doi.org/10.1016/j.molcata.2014.02.022
1381-1169/© 2014 Elsevier B.V. All rights reserved.

P.V.R.K. Ramacharyulu et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 38–44
39
studied Au TiO2 catalyst for the detoxification of nerve gases and
HD at room temperature upon visible light irradiation [31]. There-
after, Prasad et al. reported the photocatalytic decomposition of
HD on ZnO and TiO2 nanoparticles. According to their observa-
tions, ZnO, TiO2 nanoparticles have degraded 100% of in 12 h and
4 h, respectively in natural sunlight [32,33]. Naseri et al. stud-
ied photolytic and photocatalytic degradation of HD using TiO2
nanoparticles and polyoxometalates and decontaminated HD com-
pletely in 3 h [34]. However, they used only UV irradiation for the
same. Application of sunlight and visible light active TiO2 nanocat-
alysts as sorbent decontaminant for the detoxification of CWA is
interesting as these materials can be sprayed on contaminated
surfaces for the cleansing applications. However, to the best of
our knowledge there are no reports available in the literature till
date on application of vanadium ion doped titania nanocatalyst for
the photocatalytic degradation of HD in the presence of sunlight.
Inspired by the above studies, we have synthesized vanadium ion
doped TiO2 nanocatalysts, characterized them by X-ray diffraction
(XRD), transmission electron microscopy (TEM), nitrogen adsorp-
tion (N2 BET), UV–vis spectroscopy, infrared spectroscopy (FT-IR)
and X-ray photoelectron spectroscopy (XPS) techniques. Subse-
quently, we have studied photocatalytic degradation reactions of
HD under the irradiation of sunlight by using gas chromatography
(GC) and gas chromatography mass spectrometry (GC–MS) tech-
niques.
adsorption measurements were done on ASAP 2020 surface area
analyser of Micrometrics, USA. Reflectance spectra were recorded
on Lambda 25 UV–vis spectrophotometer of PerkinElmer make by
taking spectralon as internal standard. FT-IR measurements were
done on PerkinElmer, USA instrument. XPS data was recorded on
KRATOS AXIS 165 instrument. GC of Nucon Engineers, India make
equipped with FID detector, BP5 column (30 m length, 0.5 mm i.d.)
was used to monitor degradation of HD. GC–MS system (5975 B)
of Agilent, USA make was used for quantification and identification
of reaction products. Calibrated equipment manufactured by Tech-
novation India Ltd., was used to monitor carbon dioxide (CO2) and
X-am 7000 detector of M/s. Drager, Germany make was used for
quantitative identification of acetaldehyde.
2.4. Photocatalytic degradation
Hundred milligrams of nanocatalyst (VT or HT or CT) was taken
in a quartz tube and 100 ␮L of dichloromethane solution contain-
ing 2 ␮L of HD was spiked on it. Dichloromethane was allowed
to evaporate. Subsequently, quartz tube containing the nanocat-
alyst was irradiated by sunlight. Intensity of light was measured
by digital light metre (SLM 110 model) of A.W. Sperry Instruments,
USA with help of adapters provided. Value of irradiance of sunlight
was determined to be 95 mW/cm2. Experimental setup already
reported [32] was used for this work also. All the experiments
were carried out at room temperature (30 2 C). The gaseous prod-
˚
2. Experimental
ucts formed on surface of catalyst when irradiated with light were
trapped by suction through liquid nitrogen trap of 40 mL/min. The
trapped solution was analyzed for CO2 and CH3CHO by the equip-
ment discussed in earlier section. Remaining HD was extracted after
periodic intervals of time using acetonitrile. The extracted samples
were analyzed with GC affixed with FID detector to monitor the
amount of degraded HD. Later, the solution was concentrated to
1 mL and analyzed for products by GC–MS. Degradation products
which formed in major quantity were quantified by GC–MS (Model
5975B and 6890N).
2.1. Materials
Vanadyl acetylacetonate, titanium tetraisopropoxide (TTIP)
were procured from Acros organics, UK. Dichloromethane, ethanol,
ethyl acetate and acetonitrile were obtained from E. Merck India
Ltd. Commercial TiO2 nanocatalyst (CT) of size (∼30 nm) was pur-
chased from Alfa Aesar, UK. HD of 99% purity was synthesized in our
establishment. (This is a very toxic agent; hence these experiments
should be done under the guidance of trained personnel equipped
with individual protective equipment only.)
3. Results and discussion
2.2. Preparation of photocatalysts
3.1. Characterization of photocatalysts
TiO2 nanocatalysts were prepared by sol–gel hydrolysis of tita-
nium (IV) isopropoxide (TTIP) followed by hydrothermal treatment.
TTIP was dissolved in anhydrous ethanol and the solution was
added dropwise to the mixture of distilled water and ethanol under
vigorous stirring at room temperature. Obtained precipitate was
3.1.1. XRD data
Fig. 1 shows the XRD data of synthesized VT and HT nanocata-
lysts. The data depict peaks at 2ꢀ values 25.2, 37.8, 48.0, 53.8, and
62.7. These peaks can be attributed to the presence of (1 0 1), (0 0 4),
˚
˚
˚
˚
˚
(2 0 0), (1 0 5), and (2 1 5) indices. This XRD pattern illustrates 2ꢀ val-
ues and relative intensities that match with (JCPDS 21-1272) data of
anatase phase of TiO2. It also illustrates peak broadening indicating
the formation of crystallites with size in nano dimensions. No peaks
corresponding to oxides of vanadium are observed even for samples
doped with 2 at.% of vanadium (2 VT). Apparently, VT nanocatalysts
were found to retain the anatase phase with no phase separation
leading to rutile titania or vanadia even after doing. This obser-
vation also indicates the incorporation of vanadium ion into TiO2
lattice. Crystallite sizes of VT catalysts were calculated by Scherrer
equation and they were found to be 6.12, 6.45, 5.85, and 6.76 nm,
respectively for 0.1 VT, 0.25 VT, 0.55 VT and 2 VT nanocatalysts. The
crystallite size of HT nanocatalyst was found to be 11 nm.
˚
transferred into a Teflon lined autoclave and heated at 80C for 24 h.
Resultant solid was dried at room temperature and finally labelled
as bare TiO2 nanocatalyst (HT) and washed with excess of ethanol
to remove remaining organic moieties [35]. Similarly, metal ion
dopant was introduced by adding appropriate amount of vanadyl
acetylacetonate into deionised water preceding to the hydrolysis
of TTIP. By varying concentration of vanadyl acetylacetonate, dif-
ferent samples were prepared. The samples were labelled as 0.1 VT
(0.1 at.% V in TiO2), 0.25 VT (0.25 at.% V in TiO2), 0.55 VT (0.55 at.%
V in TiO2), and 2.0 VT (2.0 at.% V in TiO2).
2.3. Characterization of photocatalysts
XRD data was recorded on X’Pert Pro Diffractometer of M/s
Panalytical, Netherlands make using Cu K␣ radiation. TEM mea-
surements were done on Tecnai transmission electron microscope
of FEI make. Samples were suspended in 30 mL of acetone, and
the suspension was sonicated for 30 min. Subsequently, suspen-
sion was placed on carbon coated copper grids of 3 mm diameter
and dried at room temperature prior to the analysis. Nitrogen
3.1.2. Electron microscopy data
TEM images of both doped (0.1 VT) and bare (HT) nanocatalysts
are shown in Fig. 2(a and b). No significant differences are observed
when the images of VT and HT nanocatalysts are compared. TEM
images clearly indicate that the particle size is homogeneous and
fairly small. It can also be seen from the images that spherically

40
P.V.R.K. Ramacharyulu et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 38–44
a
101
b
d
e
f
80
60
40
20
0
c
004
200
105
204
215
a
101
b
c
200
400
600
800
d
Wavelength (nm)
Fig. 3. UV–vis diffuse reflectance spectra of (a) Bare nano TiO2 (HT), (b) 0.1 VT, (c)
0.25 VT, (d) 0.55 VT, (e) 2.0 VT nanocatalysts and (f) V2O5.
e
20
30
40
50
60
70
80
also observed to have controlled the nucleation, growth, and aggre-
gation of titania nanocrystallites which facilitated the formation of
more number of mesopores relative to HT nanocatalyst. On fur-
ther increase of dopant concentration upto 2 at.%, vanadium ion
might have partially blocked the pores which led to decreased val-
ues of pore volume and surface area. This observation is consistent
with the data mentioned in Table 1. All the nanocatalysts exhibited
Type IV adsorption isotherm with H3 type hysteresis indicating the
presence of slit type of pores (Fig. 1 of ESM).
Fig. 1. XRD patterns of (a) Bare TiO2, (b) 0.1 VT, (c) 0.25 VT, (d) 0.55 VT and (e) 2.0
VT nanocatalysts.
shaped nanocrystallites are found to be embedded in the agglom-
erates with sizes around 6 to 11 nm. These values are found to be
comparable to the values of average crystallite sizes determined
from XRD data.
3.1.4. Diffuse reflectance spectra
3.1.3. Nitrogen adsorption data
Fig. 3 shows the diffuse reflectance spectra of HT, VT nanocata-
lysts, and vanadium (v) oxide measured at room temperature. Band
gap values were calculated by E = hc/ꢁ (eV) (h is Planck’s constant, c
is velocity of light, ꢁ is wave length) following the extrapolation of
reflectance spectrum of individual nanocatalysts. The HT nanocata-
lyst shows sharp absorption at 383 nm, indicating band gap energy
of ∼3.26 eV corresponding to anatase phase of TiO2. In the spectra
of VT nanocatalysts, additional broad absorption below ∼560 nm
(∼2.2 eV) is apparent. Doping of vanadium ion in TiO2 nanocatalyst
results into red shift of absorption edge compared to HT nanocata-
lyst. The increased doping level results into a progressive decrease
in diffuse reflectance in the visible light region. VT nanocatalysts
exhibit new optical properties which are found to be different from
both the titania and vanadium (V) oxide. The effect becomes more
prominent with increased vanadium ion concentration. The band
gap energy of VT nanocatalysts was calculated from UV–vis dif-
fuse reflectance spectra. It is evident in Fig. 3 that the band gap
energy decreases from 3.26 to 2.85 eV with increase in vanadium
Table 1 shows the nitrogen adsorption data of prepared nanocat-
alysts (VT and HT). All the nanocatalysts exhibited surface areas in
the range of 230–274 m2/g. Vanadium ion doping (0.1 to 2.0 at.%)
slightly changed the values of surface area. Up to 0.55 at.%, the
value of surface area was found to be increasing slightly and then
decreased to 237 m2/g. At lower levels of doping (0.1–0.55 at.%)
vanadium ion might have been incorporated in the titania lattice. It
Table 1
Nitrogen adsorption data of VT and HT nanocatalysts.
Type of the nano
catalyst
BET surface area
(m2/g)
Total pore volume Micro pore volume
(mL/g)
(mL/g)
Bare TiO2
0.1 VT
0.25 VT
0.55 VT
2.0 VT
230.4
234.6
239.1
274.6
237.9
0.4
0.4
0.4
0.5
0.4
0.05
0.05
0.05
0.05
0.05
Fig. 2. TEM images of (a) V doped TiO2 and (b) Bare TiO2 nanocatalysts.

P.V.R.K. Ramacharyulu et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 38–44
41
Fig. 4. XPS spectra of VT nanocatalyst showing the resolved spectra of (a) vanadium, (b) Titanium, and (c) Oxygen.
ion doping concentration in TiO2. Observed decrease in band gap
energy with the addition of vanadium ion could be attributed to
substitution of Ti+4 ions with vanadium ion in the TiO2 lattice [36].
could be accredited to the surface functional groups present on
the 0.1 VT nanocatalyst and the rest 70% can be ascribed to photo-
catalysis as 30% of HD was observed to be degraded in absence of
light in 180 min. On HT nanocatalyst, 100% of HD was degraded in
240 min and only 45% of HD was found to have degraded on CT in
180 min. This observation indicates the superior sunlight activity
of VT nanocatalyst over HT nanocatalyst and the same is shown in
Fig. 5.
Compared to CT, HT nanocatalyst exhibited greater efficiency
to degrade HD. This observation can be attributed to smaller
crystal size (11 nm) of HT nanocatalyst which is not only ben-
eficial for adsorptive removal of HD but also for photocatalysis.
However, in the case of VT nanocatalyst due to its similar crys-
tal size and surface area as HT nanocatalyst, it was found to
have similar adsorption capacity towards HD molecules. Neverthe-
less, it exhibited enhanced photocatalytic activity under sunlight.
3.1.5. XPS data
XPS spectra of VT nanocatalysts are shown in Fig. 4(a–c). VT
nanocatalyst (Fig. 4(a)) shows peaks with binding energies at
517.5 eV and 519.7 eV characteristic of V 2p3/2 and satellite peak
of O 1s indicating the presence of vanadium ion in titania lattice.
It also shows peaks at 458.2 and 463.9 eV depicting Ti 2p3/2 and Ti
2p1/2 peaks (Fig. 4(b)) corresponding to Ti4+ oxidation state [37].
Due to similar radii vanadium ion seemed to have been incorpo-
rated in TiO2 lattice by substitutionally replacing some of Ti4+ ions
and formed Ti
O V bonds. The O 1s peak (Fig. 4(c)) is observed at
530 to 532 eV for both HT and VT nanocatalysts.
3.2. Photocatalytic behaviour
100
Only sunlight irradiation in the absence of catalyst showed neg-
ligible degradation or evaporation of HD even after 6–8 h. This
clearly demonstrates that photodegradation is not a significant pro-
cess to degrade HD as it does not absorb UV light above 290 nm
[30]. In the absence of light and in the presence of catalyst, only
70% of HD was observed to be degraded within 8 h. Degradation of
HD in absence of light could be ascribed to available surface area,
surface hydroxyl groups, Lewis acid sites and moisture present on
the surface (1–3% w/w) of the material. GC–MS data indicated the
formation of hydrolysis products like thiodiglycol and hemisul-
fur mustard. Reactions in the absence of light were found to be
very slow, incomplete, and contributed only to hydrolysis reac-
tions. To completely degrade HD in a relatively faster rate, sunlight
assisted photocatalysis was opted. In the presence of sunlight, 100%
of HD was found to be degraded on 0.1 VT nanocatalyst within
180 min (0.1 VT). Out of the above 100% degradation of HD, 30%
80
60
40
20
0
a
b
c
d
e
f
0
50 100 150 200
Time (Min)
Fig. 5. Decontamination of HD irradiated with sunlight on (a) 0.1 VT, (b) 0.25 VT,
(c) 0.55 VT, (d) 2.0 VT, (e) HT and (f) CT nanocatalysts.

42
P.V.R.K. Ramacharyulu et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 38–44
a
b
c
d
e
f
600
400
200
0
0
50
100
150
Fig. 7. Effect of vanadium dopant concentration on nano TiO2 towards photodegra-
dation of HD in sunlight.
Time (min)
Fig. 6. Product concentration profile of HD decontamination reaction on vana-
dium doped titania irradiated with sunlight. (a) CO2 (b) CH3CHO, (c) C4H8S2Cl2,
(d) C4H7S(O)Cl, (e) C4H8SOCl2) and (f) C4H7SCl.
3.3. Effect of dopant on TiO2 nanocatalyst towards the
photodegradation of HD
Photocatalytic degradation of HD in the presence of sunlight on VT
nanocatalyst could be attributed to cumulative effect of absorp-
tion of UV as well as visible light components of sunlight. However,
the enhanced sunlight activity can be attributed to enhanced visi-
ble light absorbance and the increased trapping of charge carriers
when compared to HT nanocatalyst. VT nanocatalysts were found
to have absorbed more amount of sunlight when compared to HT
nanocatalyst due to reduced band gap energies (discussed in earlier
section) as sunlight has large portion of visible light (46%) and HT
nanocatalysts are inactive in visible light. The degradation of HD
on HT nanocatalyst in the presence of sunlight can be ascribed to
UV-A light (4–5%) fraction present in the solar spectrum, whereas
VT nanocatalysts of different dopant concentration (0.25 VT–2.0
VT at.%) degraded 99% of HD in 240 min. In addition to these, VT
nanocatalysts were also studied for photocatalytic degradation of
HD in the presence of artificial UV-A or visible light irradiation
and the data was already reported [38]. VT nanocatalyst (0.1 VT)
exhibited better photocatalytic degradation efficiency against HD
in the presence of sunlight relative to UV-A or visible light due to
cumulative effect.
Experiments were conducted to examine the effect of dopant
concentration on the photocatalytic degradation of HD for 60 min
of sunlight irradiation. The data was compared to that of HT and
CT nanocatalysts. Of all the nanocatalysts with different concen-
trations of vanadium ion in TiO2, 0.1 VT nanocatalyst exhibited
the highest photoactivity under sunlight irradiation (Fig. 7). Pre-
venting the recombination of photogenerated electrons and holes
leads to enhanced photocatalytic activity of TiO2. It occurs in a rel-
atively large extent on VT nanocatalyst due to the incorporation
of vanadium ion in TiO2 (0.1 VT) when compared to HT nanocata-
lyst. It seemed to have increased the lifetime of charge carriers and
assisted the enhanced photocatalysis. However, increase in concen-
tration (more than 0.1%) of vanadium ion further leads to decrease
in photocatalytic activity. This could be attributed to the fact that,
if the concentration of vanadium ion is high, they become recombi-
nation centres of photogenerated electrons and holes thereby ruin
the photo activity. This also indicates that optimum dopant loading
is necessary for inducing enhanced photo activity in sunlight.
3.4. Photocatalytic degradation mechanism
HD was found to have degraded to HD disulfide, HD sulfoxide,
chloro ethyl vinyl sulfide, chloro ethyl vinyl sulfoxide, hydroly-
sis products of HD disulfide, acetaladehyde, carbon dioxide, etc.
Acetaldehyde and CO2 were the gaseous products observed in
major quantity. Concentration of CO2 was found to be 50 ppm at
30 min, it increased to 210 ppm in 90 min and finally decreased
to 60 ppm in 180 min. Concentration of acetaldehyde increased
from 6 ppm to 34 ppm in 90 min and reached to 6 ppm in 180 min.
HD disulfide (–SC2H4Cl)2, a major product which was obtained
from the surface extract reached a value of 764 ppm in 90 min and
decreased to 18.7 ppm in 180 min. In addition to this, photo oxi-
dation product like HD sulfoxide (C4H8SOCl2) was also found to
be formed. It reached a maximum value of 438 ppm in 60 min and
finally decreased to 80 ppm in 180 min. Another oxidation prod-
uct, chloro ethyl vinyl sulfoxide (C4H7S(O)Cl) also was observed
in 60 min. Its concentration was found to be 60.7 ppm and then
it decreased to 25 ppm in 180 min. Minute amount of elimina-
tion product chloro ethyl vinyl sulfide (C4H7SCl) was also detected
(17.8 ppm in 90 min) which was shown in Fig. 6. In addition to
these, several products were formed in minute amounts, which
were not in the quantification limits. The intermediate product
bis(2-chloroethyl) disulfide (ClCH2CH2S2CH2CH2Cl) was found to
have suffered further oxidation to less toxic products on the TiO2
surface. This intermediate is of low volatility and it did not desorb
into the gas phase. All the products formed on the surface fur-
ther have degraded into CO2, HCl, H2SO4 and other degradation
products (Fig. 2 ESM).
The VT (0.1) nanocatalyst possesses higher visible light
absorbance than HT nanocatalyst due to reduced band gap, hence
it absorb more amount of sunlight as it has large fraction of vis-
ible light. Visible light active VT nanocatalysts photocatalytically
degrade HD by elimination, oxidation, and hydrolysis reactions and
the same is apparent from GC–MS data. Charge carriers are found
to be generated upon irradiation of sunlight. Holes are found to
react with hydroxyl groups and moisture to form hydroxyl radi-
cals (HO•). Electrons seem to react with oxygen molecules to form
superoxide anion radicals (O2−•). These superoxide anion radicals
further react with moisture and hydroxyl groups to form hydroxyl
radicals. All these species are highly reactive and are found to have
played a predominant role in the photocatalytic degradation reac-
tions of HD. Formation of hydroxyl radicals on the surface of VT
nanocatalyst in the presence of sunlight was monitored by the reac-
tion with dimethyl sulfoxide as a probe molecule. It was converted
to methane sulfonic acid ethyl ester and methane sulfonic acid due
to the reaction with hydroxyl radicals generated on the surface of
VT nanocatalyst and the same was confirmed by GC–MS data (as
depicted by m/z values at 124, 109, 97, 79, 65, 45 and 96, 79, 65, 48,
31) [39]. Further, superior sunlight absorbance of VT nanocatalysts
might be related to V 3d orbital. Due to the fact that the t2g level
of V 3d orbital lies a little below the conduction band edge of TiO2
[40,41], electrons are found to have excited from the valence band
of TiO2 to the t2g level of V 3d orbital under sunlight irradiation
which contains 46% of visible and 4–5% of UVA light.

P.V.R.K. Ramacharyulu et al. / Journal of Molecular Catalysis A: Chemical 387 (2014) 38–44
43
titania and exhibited superior photocatalytic activity towards
HD degradation under sunlight irradiation conditions. This was
attributed to reduced band gap and enhanced charge separation
on the surface of VT nanocatalyst. The C S bond cleavage, oxi-
dation of S atom, hydrolysis and elimination reactions seemed
to have assisted degradation of HD into non toxic products.
These interesting detoxification properties promise potential appli-
cation of VT nanocatalysts as sorbent decontaminant against
CWA.
a
0.8
0.6
0.4
0.2
b
c
1000
2000
3000
4000
Acknowledgements
Wavenumber (cm-1)
Authors thank Director, DRDE, Gwalior for his permission to
publish this work. They also thank Prof. Ramesh Chandra, IITR for
providing TEM facility. Authors also thank M. Sheik for technical
support during XPS analysis. One of the authors PVRK thank DRDO,
New Delhi for the financial support.
Fig. 8. FT-IR data of (a) VT, unexposed (b) VT (0.1) exposed with HD (immediately),
and (c) VT (0.1) exposed with HD (after complete degradation).
GC–MS data was found to be similar to that discussed in our ear-
lier study [30]. IR data indicate disappearance of band at 700 cm−1
(C–Cl), change of peak pattern at around 1440 and 1295 cm−1
(CH2–Cl), slight change in peak intensity at 3352 cm−1 (–O–H),
and a weak band at 1100 cm−1 (C–O–Ti) further confirming the
hydrolysis and surface complexation reactions. With irradiation
(sunlight) the band pattern observed to have changed. Weak bands
at 1126 cm−1, 1200 cm−1 illustrate the formation of sulfonate
species and band at around 1410 cm−1 indicate the formation
of–COOH group typical of acetic acid formed during photocatalytic
decontamination of HD on nano TiO2 (Fig. 8).
Appendix A. Supplementary data
Supplementary material related to this article can be
found, in the online version, at http://dx.doi.org/10.1016/
j.molcata.2014.02.022.
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after third use due to poisoning of catalysts due to the formation
of alkoxy species, H2SO4, HCl and other degradation products on
the surface. Initially it exhibited 100% of HD decontamination effi-
ciency and then it decreased to 87.2% for second use when it is
re-used after washing with acetonitrile. Subsequently, it decreased
to 78.5% after third use and then to 57.9% after fourth use and
attained to 50% for fifth use. Whereas, 100% of HD decontamina-
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VT nanocatalyst was thoroughly washed with 30% hydrogen per-
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ethanol and dichloromethane. Decreased activity of VT nanocata-
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seemed to happen mainly due to poisoning of catalyst surface
by reaction by-products formed due to cleavage of HD molecule.
The VT nanocatalyst was regenerated by washing with hydro-
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dichloromethane. On the other hand, scanty numbers of reports are
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properties. It had decontaminated 100% of HD within 6 h, whereas
nano ZnO decontaminated 100% of HD in 12 h. However, vanadium
doped titania nanocatalysts used in this paper had decontaminated
100% of HD in 3 h indicating their superior photocatalytic decon-
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4. Conclusion
The vanadium doped titania nanocatalysts were observed to
be photocatalytically more active than bare and commercial nano

44
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