Decontamination of 2-chloro ethyl ethyl sulphide and dimethyl methyl phosphonate from aqueous solutions using manganese oxide nanostructures

Article abstract of DOI:10.1016/j.molliq.2015.12.039

Current study investigates the efficiency of reactive adsorbent composed of MnO₂ nanoparticles and nanorods for the detoxification of 2-chloro ethyl ethyl sulphide (CEES) and dimethyl methyl phosphonate (DMMP), well-known simulants of sulphur mustard and sarin, respectively. The MnO₂ nanoparticles and nanorods were synthesised using novel reactive magnetron sputtering technique and then characterised by powder XRD, Raman spectroscopy, FE-SEM, TEM, BET, FT-IR and Thermogravimetry (TG) analysis. Powder XRD and Raman results confirm the formation of pure tetragonal phase of MnO₂ nanostructure material. The FE-SEM and TEM analysis exhibited the formation of aggregate MnO₂ nanoparticles and nanorods. The surface area of the synthesised aggregate MnO₂ nanoparticles and nanorods (164.28 m²/g) was found to be enhanced significantly in comparison with what was reported in the literature. Decontamination reactions of synthesised nanostructure material were examined by GC equipped with FID and the products obtained after reaction were analysed by GC-MS and FT-IR techniques. It was observed that the currently synthesised MnO₂ nanoparticles and nanorods exhibit much better decontamination results towards CEES as well as DMMP in comparison to or as per existing solid decontaminants. The reactions exhibited pseudo first order kinetic behaviour with rate constant and half life value 0.267 h^{- 1} and 2.58 h for CEES and 0.068 h^{- 1} and 10.10 h for DMMP, respectively. The data exhibits the formation of non-toxic hydrolysis products in the detoxification of CEES as well as DMMP.

Full text of DOI:10.1016/j.molliq.2015.12.039

Journal of Molecular Liquids 215 (2016) 285–292
Contents lists available at ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Decontamination of 2-chloro ethyl ethyl sulphide and dimethyl methyl
phosphonate from aqueous solutions using manganese
oxide nanostructures
Monu Verma a,b, Ramesh Chandra b, Vinod Kumar Gupta a,c,
⁎
a
Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India
Institute Instrumentation Centre, Indian Institute of Technology Roorkee, Roorkee 247667, India
b
c
Department of Applied Chemistry, University of Johannesburg, Johannesburg, South Africa
a r t i c l e i n f o
a b s t r a c t
Article history:
Current study investigates the efficiency of reactive adsorbent composed of MnO2 nanoparticles and nanorods for
the detoxification of 2-chloro ethyl ethyl sulphide (CEES) and dimethyl methyl phosphonate (DMMP), well-
known simulants of sulphur mustard and sarin, respectively. The MnO2 nanoparticles and nanorods were synthe-
sised using novel reactive magnetron sputtering technique and then characterised by powder XRD, Raman spec-
troscopy, FE-SEM, TEM, BET, FT-IR and Thermogravimetry (TG) analysis. Powder XRD and Raman results confirm
the formation of pure tetragonal phase of MnO2 nanostructure material. The FE-SEM and TEM analysis exhibited
the formation of aggregate MnO2 nanoparticles and nanorods. The surface area of the synthesised aggregate
MnO2 nanoparticles and nanorods (164.28 m2/g) was found to be enhanced significantly in comparison with
what was reported in the literature. Decontamination reactions of synthesised nanostructure material were
examined by GC equipped with FID and the products obtained after reaction were analysed by GC–MS and FT-
IR techniques. It was observed that the currently synthesised MnO2 nanoparticles and nanorods exhibit much
better decontamination results towards CEES as well as DMMP in comparison to or as per existing solid
decontaminants. The reactions exhibited pseudo first order kinetic behaviour with rate constant and half life
value 0.267 h−1 and 2.58 h for CEES and 0.068 h−1 and 10.10 h for DMMP, respectively. The data exhibits the for-
mation of non-toxic hydrolysis products in the detoxification of CEES as well as DMMP.
Received 20 November 2015
Received in revised form 8 December 2015
Accepted 12 December 2015
Available online xxxx
Keywords:
Sputtering
Adsorption
Degradation
Nanostructures
Decontaminating agent
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
steady state at the later phase of the reaction with pseudo first order ki-
netic behaviour. These metal oxide nanostructures degrade the CWA
Reactive sorbent systems composed of inorganic oxide nanoparticles
are currently under consideration as potential adsorbent materials for
the detoxification of worldwide chemical warfare agents (CWA) and
their well-known simulants. These materials possess interesting
physisorption and chemisorption properties which encourage their
use as reactive sorbents for the actual time decontamination of CWA
[1–5]. Some reactive adsorbents composed of nanocrystalline oxides
such as CaO, ZnO, Al2O3 and WO3 were established as favourable mate-
rials for the decontamination of CWA [6–9]. They have greater reactivity
towards CWA due to their higher surface area to volume ratio, large
amount of highly reactive edges and corner defect sites, and unexpected
lattice planes in comparison to bulk materials [10–12]. The reactions to
decontaminate the CWA with the above stated materials were analysed
using solid state MAS NMR and GC techniques at 25 °C temperature and
observed that the reaction kinetics were fast in the initial phase and
through hydrolysis and elimination reactions [13]. Also, the catalytic re-
action plays an important role in the CWA degradation [14–18]. Besides
that, nanoparticles have a proclivity to aggregate, due to some of the
existing reactive sites on the surface which are not available to the ad-
sorbate molecules. However, other variants of these materials such as
nanosheets, nanotubes or nanobelts combined to each other without
losing their surface area and due to which encouraging accessibility to
occur for sorbate molecules towards the surface active sites. This char-
acteristic interaction in the aggregated nanotubes or nanobelt materials
occurs to minimize the electrostatic and steric repulsion of remaining
charges which exist on their surface.
Recently, TiO2, V1.02O2.98, MnO2 nanotubes and nanosheets and ZnO
nanorods have been synthesised using different methods for the decon-
tamination of deadly CWA such as HD, GB and their simulants [19–22].
Prasad and Ramacharlu et al. reported that the TiO2 nanotubes were
synthesised using sol–gel and hydrothermal process for the decontam-
ination of HD and GB [23,24]. Of the above, titania nanotubes exhibit
huge importance because of their effective decontamination properties
towards photocatalytic, chemical biological warfare (CBW) agents and
⁎
Corresponding author at: Department of Chemistry, Indian Institute of Technology
Roorkee, Roorkee 247667, India.
E-mail addresses: vinodfcy@gmail.com, vinodfcy@iitr.ac.in (V.K. Gupta).
http://dx.doi.org/10.1016/j.molliq.2015.12.039
0167-7322/© 2015 Elsevier B.V. All rights reserved.

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M. Verma et al. / Journal of Molecular Liquids 215 (2016) 285–292
Table 1
Sputtering parameters for the synthesis of aggregates of MnO2 nanoparticles and nanorods.
Target
Mn
Base pressure
Working pressure
30 mTorr
Gas used
Deposition time
18 h
Distance (d)
5 Cm
Power (Watt)
60 W
Substrate temperature
6.4 ∗ 10−7 Torr
Ar:O2::40:10
−194 °C
d = Distance between target and substrate.
were used in the detoxification of 2-chloro ethyl ethyl sulphide (CEES),
a simulant of well-known sulphur mustard (HD) agent. Also, Prasad and
Mahato et al. reported the detoxification of sarin (GB), HD and CEES
over the surface of MnO2 nanobelts and nanotubes, prepared using
flocculation and exfoliation methods, respectively [25,26]. The detoxifi-
cation of the above agents within the MnO2 nanotube and
nanobeltsurfaces occur through hydrolysis reactions. Moreover, these
MnO2 nanotubes and nanobelts displayed better decontamination
properties in comparison to the TiO2 nanotubes. Inspired by these re-
sults, we have synthesised MnO2 in the form of aggregates composed
of nanoparticles and nanorods (nanostructures) using reactive magne-
tron sputtering technique under highly controlled conditions and inves-
tigated their decontamination properties against CEES and dimethyl
methyl phosphonate (DMMP). This novel technique provides some im-
portant advantages such as high purity, uniformity and reproducibility
over chemical synthetic routes [27–30]. Recently, our group reported
superior decontamination results of CEES and DMMP on the surface of
magnetron sputtered CuO and WO3 nanoparticles through hydrolysis
reactions [5,9]. To the best of our knowledge, nobody has reported the
synthesis of aggregates composed of MnO2 nanostructures using mag-
netron sputtering technique and their use for the degradation of CWA
or their simulants. Thereafter, characterisation was done using XRD,
FE-SEM, TGA, TEM, and N2-BET, then the progress of reactions was ex-
amined by a gas chromatograph and the degradation products were
confirmed by GC equipped with MS and FT-IR analysis.
2.2. Characterisation
The crystallographic information of the synthesised aggregate MnO2
nanostructures were investigated using X-ray Diffractometer (XRD), D8
advance, Bruker AXS Germany with Cu Kα radiation (λ = 1.541 Å). The
measurements were conducted using a voltage of 40 kV, a current setting
of 30 mA, scanning rate 1 s/step and step size 0.02° at room temperature
in the range of 25–90°. Raman spectra were obtained on an inVia Raman
analyser (Renishaw, United Kingdom) with 514 nm laser as an excitation
wavelength. The surface morphology occurred using a field emission
scanning electron microscope (FE-SEM), Zeiss Ultra Plus 55. Elemental
composition of the synthesised MnO2 nanostructures was measured
with energy dispersive X-ray spectroscopy (EDS) attached to FE-SEM.
The morphologies and structures of the synthesised MnO2 were further
examined by transmission electron microscope (TEM), selected area elec-
tron diffraction pattern (SAED) and high resolution transmission electron
microscopy (HR-TEM), FEI TECNAI G2, Nederland Company, operating at
200 k voltage. N2 adsorption–desorption isotherm was collected at liquid
nitrogen temperature (−196 °C) using Autosorb 1C of Quantachrome an-
alyzer, USA. Brunauer–Emmet–Teller (BET) and Barret–Joyner–Halenda
(BJH) methods were used to determine the surface area and cumulative
desorption pore volume, respectively. Thermogravimetry (TG) analysis
was carried out on EXSTAR 6300, thermogravimetric analyzer in the
flow of air with a heating rate of 10 °C/min up to 500 °C. The Chemito
8610n gas chromatograph (GC) equipped with flame ionization detector
(FID) and BP5 column (30 m length and 0.5 mm inner diameter) was
used to examine the reaction kinetics of CEES and DMMP. Whereas, HP
Agilent gas chromatograph attached with mass spectrometer (5973
inert) was used to characterise the reaction products. The reaction prod-
ucts were also characterised using Fourier-transform infrared (FT-IR),
spectroscopy, Nicolet NEXUS Aligent 1100 spectrometer in the frequency
range of 4000–500 cm−1 using KBr pellets that contain the samples.
Sulphur mustard and sarin are highly toxic CWA, and are not pro-
posed in the research laboratory. Hence, CEES and DMMP which are
less toxic and well-known simulants of sulphur mustard and sarin, re-
spectively are widely used in the research. Therefore, in the current
study, we present the synthesis of aggregate MnO2 nanostructures
and their use as a reactive adsorbent for the adsorptive removal kinetics
of these simulants i.e. CEES and DMMP.
2. Experimental
2.3. Reaction procedure
2.1. Synthesis of reactive sorbent composed of MnO2 nanoparticles and
nanorods
The reactions of CEES and DMMP with aggregate MnO2 nanostruc-
tures were studied by treating 100 μl of dichloromethane (DCM)
The aggregates of MnO2 nanostructures were synthesised using re-
active magnetron sputtering technique in custom designed vacuum
chamber (Excel Instrument, Mumbai). A turbo molecular pump and a
rotatory pump were attached with the chamber to create the required
high vacuum. Sputtering was carried out using high purity (99.98%)
manganese target of 2 in. diameter and 5 mm thickness. Initially, the
vacuum (lower than 10−7 Torr) was created in the chamber. The high
purity argon and oxygen gases were introduced into the chamber
during sputtering. The standard mass flow controller (MFC) and ma-
nometers were used to control and measure the flow of the gases re-
spectively. During sputtering, the copper cold finger becomes cooled
up to −194 °C using Liq-N2 and it was continuously filled up to make
constant temperature. Lower temperature stopped the grain growth
in the plane of the film on the substrate to produce nanostructure
materials. Also, low temperature minimized the impurity due to diffu-
sion of atoms from the substrate to the synthesised materials. During
sputtering, Mn atoms reacted with O2 atoms in the chamber during
transit or on the substrate surface to form aggregates of MnO2 nano-
structures. After deposition, the samples were collected carefully at
room temperature. The sputtering parameters for the preparation of
MnO2 nanostructures are listed in Table 1.
Fig. 1. Powder XRD pattern of reactive sorbent based on MnO2 nanoparticles and
nanorods.

M. Verma et al. / Journal of Molecular Liquids 215 (2016) 285–292
287
Fig. 4. EDS spectra of synthesised reactive sorbent MnO2 nanoparticles and nanorods.
characterised using powder XRD as is given in Fig. 1. XRD pattern
shows the high crystalline nature with peaks situated at 28.77°, 37.36°,
42.53°, 56.69°, 64.87° and 72.61° which can be indexed as (110), (101),
(111), (211), (002) and (112) reflection planes of tetragonal phase of
MnO2 materials. The XRD pattern shows the high purity MnO2 which
matches very well with the standard XRD pattern phase (JCPDS file No:
00–024-0735; a = 4.3999, b = 4.3999, c = 2.8740 with space group =
P42/mnm). FT-IR spectra were used to analyse the functionality of the
synthesised MnO2 materials. There are five main adsorption bands
observed at 3440 cm−1, 1640 cm−1, 1118 cm−1, 522 cm−1 and
492 cm−1. The band situated at 3440 cm−1 represents the O–H stretching
of the physisorbed or intercalated water molecules while the band at
1640 cm−1 represents the bending vibrations of H–O–H molecules. The
band observed at 1116 cm−1 is due to the presence of bending vibrations
of –OH group attached to the Mn atoms (Mn–OH bond). The peaks ob-
served at 522 cm−1 and 492 cm−1 ascribed to the formation of Mn–O
and Mn–O–Mn vibrations. To further investigate the structure feathers
of the synthesised nanostructural material, Raman spectra were carried
out as shown in Fig. 2. The Raman spectra of synthesised MnO2 display
two peaks, one peak at 352 cm−1 due to Mn–O bending vibrations, and
another peak of high intensity at 640 cm−1 at the high-frequency region
due to Mn–O stretching vibrations, which belongs to Ag spectroscopic
species that originate from breathing vibrations of octahedral MnO6 with-
in a tetragonal hollandite-type framework [32–34]. The relative intensity
of these two modes is correlated to the nature of the tunnel species.
Hence, the Raman spectrum exhibits good crystallinity of the synthesised
MnO2 nanostructures, which is in agreement with the tetragonal structur-
al studies reported above in XRD. The FE-SEM images of synthesised
MnO2 material are shown in Fig. 3 at low magnification and higher mag-
nification. At lower magnification (Fig. 3 (a)), aggregation of nanoparti-
cles and nanorod-like structure occurs. The nanorods are randomly
oriented and the nanoparticles are situated in the space of these randomly
oriented nanorods. At higher magnification the same behaviour occurs.
The particle size was found to be less than 10 nm and the diameter of
Fig. 2. Room temperature Raman spectra of synthesised sorbent composed of MnO2 nano-
particles and nanorods.
solution containing 5 μl of CEES or DMMP with 100 mg of MnO2 synthe-
sised powder. DCM provides uniform distribution of CEES/DMMP agent
molecules. The remaining agent was extracted using 5 mL acetonitrile
within different intervals of time until 24 h in order to study the kinetics
of degradation. Acetonitrile was used to extract the remaining agent from
the solutions analysed by GC-FID under isothermal conditions at 110 °C
for CEES and under a temperature programme from 60 to 210 °C at a
rate of 8 °C/min for DMMP. The calibration of the extracted CEES and
DMMP was carried out with the standard solution for perfect quantifica-
tion. The injection and detector ports were kept at 240 and 250 °C,
respectively.
3. Results and discussion
Generally, metal oxides that have basic surface interact with the
toxic agents and covert them into non-toxic products through hydroly-
sis reactions. Also with basic surface sites, metal oxides hold Lewis and
Bronsted acid sites, which degrade the toxic agents into non-toxic by
forming surface bound alkoxy species and surface complexation
products.
The basic nature was found for the MnO2 nanostructure surface as
reported in literature [26]. This material easily decontaminates to the
CWA and their simulants through hydrolysis reactions. The mechanism
of these reactions is similar to the solution chemistry of the contaminat-
ed molecules as reported earlier [29]. In order to study the decontami-
nation of CEES and DMMP, aggregate MnO2 nanostructures were
synthesised using reactive magnetron sputtering technique and then
studied against CEES and DMMP. After synthesis, the material was
Fig. 3. Field emission scanning electron micrograph of the reactive sorbent composed of aggregated MnO2 nanoparticles and nanorods at (a) low magnification (b) high magnification.

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M. Verma et al. / Journal of Molecular Liquids 215 (2016) 285–292
Fig. 5. Transmission electron microscope images of reactive sorbent based on MnO2 nanoparticles and nanorods at (a) low magnification (b) high magnification.
the nanorods is ~4–8 nm while length is less than 100 nm. The X-ray en-
ergy dispersive spectroscopy (EDS) result (Fig. 4) demonstrates that the
synthesised materials contain mainly Mn and O elements which are in
proper stoichiometric ratio (33.6:66.4). The others signals of Au and C el-
ements occurred due to gold coating and double side carbon tape used for
FE-SEM analysis. The morphology and size of the MnO2 nanostructures
were further confirmed by the TEM image in Fig. 5. At low magnification,
the aggregation of nanoparticles and nanorods was clearly observed. The
TEM image at higher magnification (Fig. 5 (b)) depicts clearly spherical
type nanoparticles and rod-like nanorods that are in irregular manner.
These rods are found to be stacking at their tips. Thus show typical struc-
ture where nanoparticles are situated in the randomly distributed nano-
rods. The particles are ~8 nm diameter while the rods are 5 nm in
diameter and the length lies in the range of 55–90 nm. The HR-TEM
image of the nanorods is shown in Fig. 6 (a), which clearly shows that
the synthesised MnO2 nanostructures were crystallized with the
interplanar spacing 0.234 nm, corresponding to the (101) plane of the te-
tragonal MnO2 nanostructure. The SAED pattern exhibits polycrystalline
nature of synthesised aggregate MnO2 nanostructure and is shown in
Fig. 6 (b). The lattice fringes attributing to the (110), (101) and (211)
planes were clearly visible which are in well agreement with the XRD re-
sult. To find out the values of surface area and pore size distribution of the
synthesised material, N2-BET adsorption and desorption isotherm was
carried out as shown in Fig. 7 (a). The adsorption–desorption isotherm
is type IV adsorption isotherm with a distinct type H3 hysteresis loop.
The BJH pore size distribution of the synthesised aggregate MnO2 nano-
structures materials indicates the pore maxima at 4.49 nm as shown in
Fig. 7 (b). The surface area and pore volume were 164.28 m2/g and
0.304 ml/g, respectively. This unexpected large value of surface area can
be describe due to randomly-orientated synthesised aggregates of MnO2
nanostructures as shown in FE-SEM and TEM images. Thus XRD, Raman,
FE-SEM, EDS and TEM analyses clearly exhibit the formation of tetragonal
phase with high purity and narrow size distribution in the magnetron
sputtered MnO2 nanostructure material.
After characterisation, the obtained aggregate MnO2 nanostructures
were used to study the kinetics of reactions with CEES and DMMP at
room temperature. The reactions were analysed using GC equipped
with flame ionization detector. As per GC data, the remaining CEES
were extracted from their reaction mixture with MnO2 nanostructure
at different intervals of time and then quantitatively analysed by cali-
bration. Subsequently, the kinetics data were plotted by taking the log
of the remaining CEES on the Y axis and time on the X axis. Linear
plots occur illustrating the pseudo first order kinetics of reaction to-
wards CEES and the graph is shown in Fig. 8 (a). The figure indicates
the fast initial stage of the reaction and steady state at the later stage
of the reaction which depicts pseudo first order kinetic behaviour of
CEES towards aggregate MnO2 nanostructures. The rate constant
(k) and half life (t1/2) were found to be 0.267 h−1 and 2.58 h, respective-
ly. In the case of DMMP degradation, the same behaviour occurs during
decontamination on aggregate MnO2 nanostructures which indicates
Fig. 6. High resolution TEM image (a) and selected area electron diffraction pattern (b) of synthesised reactive sorbent based on MnO2 nanoparticles and nanorods.

M. Verma et al. / Journal of Molecular Liquids 215 (2016) 285–292
289
Fig. 7. N2 adsorption-isotherm (a) and pore size distribution (b) of the reactive sorbent composed of MnO2 nanoparticles and nanorods.
the pseudo first order kinetic behaviour. The rate constant (k) and half
life (t1/2) values were found to be 0.068 h−1 and 10.10 h, respectively.
The experiments were repeated more than six times to confirm the re-
producibility and accuracy in kinetics data. The experimental results
show that CEES molecules degrade completely (100%) while DMMP
molecules degrade up to ~64% within 24 h over the surface of aggregate
MnO2 nanostructures. The data exhibits that the CEES/DMMP molecules
interact immediately with the nanoaggregate MnO2 due to higher sur-
face area value (164.28 m2/g) and large number of reactive sites i.e.
MnO2 nanostructures have high reachability of CEES as well as DMMP
molecules towards the unreactive surface from bulk liquid. Moreover,
manganese oxide was mixed with incipient amount of dichloromethane
(DCM) solution of CEES/DMMP which promotes these molecules to
spread over the maximum surface through pore structure. This spread-
ing of liquid molecules helps in the search of unreactive surface sites,
which leads to fast initial reaction. When the solution was spread and
the CEES/DMMP molecules reach the fresh aggregate MnO2 nanostruc-
ture surface and reacted quickly to consume the surface active sites
which creates poisoning of the surface and due to which spreading of
agent molecules stopped and the steady state reaction occurs on the
surface of aggregate MnO2 nanostructures. Also, the CEES/DMMP mole-
cules come into contact with the fresh surface through diffusion of evap-
orated molecules, thereby steady state occurs within 8 h. Overall,
spreading of liquid, evaporation and diffusion of agent molecules
could have influenced pseudo first order kinetic reaction and results
match well with the earlier reported results [22,25,35,36].
fragmentation patterns based on NIH (National Institute of Health)
data bases. In the case of CEES decontamination reaction, data exhibits
the m/z values at 29, 47, 61, 75, 91 and 106 which displays the forma-
tion of HEES (hydroxyl ethyl ethyl sulphide) product. This formation
of hydrolysis product confirms emphasising the role of hydrolysis reac-
tion to convert it into non-toxic form. In addition to this, FT-IR data of
aggregate MnO2 nanostructures that were exposed to CEES displays
the disappearance of band at 700 cm−1 (C–Cl) and change of peak pat-
tern at 1440 cm−1 and 1295 cm−1 (CH2–Cl) occurs. Another one peak
occurs of small intensity at 3425 cm−1 (–O–H) indicating the formation
of hydrolysis product i.e. HEES. The results obtained from GC–MS and
FT-IR data confirm the formation of hydrolysis product of CEES on the
surface of aggregate MnO2 nanostructure material. According to the
above GC–MS and FT-IR data, the proposed reaction mechanism of
CEES decontamination on aggregate MnO2 nanostructures is shown in
Fig. 9 (a). As per this, CEES molecules reacted with aggregated MnO2
in two ways. In the first way, CEES molecules reacted with physisorbed
or encapsulated water molecules which were present on the MnO2 sur-
face to form non-toxic hydrolysis product i.e. HEES. The occurrence of
this hydrolysis reaction on the surface of aggregates composed of
MnO2 nanostructures can be attributed to their basic nature. During re-
action, cyclic sulfonium ion is formed in the initial stage as shown in the
figure. This sulfonium ion is highly unstable in nature, that's why, it
could not be detected by GC [37]. Subsequently, sulfonium ion reacts
with water molecules which are presence on the surface of aggregates
MnO2 nanoparticles and nanorods (no extra water was added during
reaction) and gives hydrolysis product i.e. HEES. In another way, CEES
molecules give surface bound alkoxy species after the reaction with iso-
lated hydroxyl group (Mn–OH) and Lewis acid (Mn4+) sites. The results
Thereafter, GC-MS and FT-IR techniques were applied on the reac-
tion mixtures obtained from aggregate MnO2 nanostructures to charac-
terise the reaction products. The data were confirmed for the product
Fig. 8. Kinetics of degradation reactions of (a) CEES and (b) DMMP on the surface of adsorbent composed of MnO2 nanoparticles and nanorods.

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M. Verma et al. / Journal of Molecular Liquids 215 (2016) 285–292
Fig. 9. (a). Reactions scheme of CEES occurring on the surface of sorbent composed of MnO2 nanoparticles and nanorods. (b) DMMP reaction scheme occurring on the surface of sorbent
composed of MnO2 nanoparticles and nanorods.
match very well with the earlier reported data [38–62]. Also, being a
potential oxidising agent, aggregate MnO2 nanostructures could not ox-
idise the CEES into its oxidation product. The observation can be attrib-
uted to the predominant formation of highly unstable cyclic sulfonium
ion intermediate which further reacted with the water molecules to
form HEES. Another reason is the poisoning of the essential existing
sites or functional groups on the aggregate MnO2 nanostructure surface
which are responsible for the oxidation reaction.
difficult due to its polar and non-volatile nature. Hence, they were
silylated by Bis (trimethylsilyl) trifluoro acetamide then analysed.
Data obtained after silylation illustrates the m/z values at 73, 133, 147,
225 and 240 illustrates the formation of hydrolysis product of DMMP
i.e. MPA further emphasises the role of hydrolysis reaction thereby
converting it into non-toxic form. Moreover, FT-IR investigations of
aggregate MnO2 nanostructures that were exposed to DMMP reveal
that the band intensity situated at 1275 cm−1 due to PO and
1025 cm−1 due to P–O–C of DMMP changed and another band occurs
at 1336 cm−1 which indicates the interaction of PO group with sur-
face function group of aggregate MnO2 nanostructures. Also, one
peak occurs at 3440 cm−1 which indicates the formation of a non-
toxic hydrolysis product. These observations obtained from GC–MS
and FT-IR results confirm the formation of MPA on the surface aggre-
gate MnO2 nanostructures and match well with the previous report-
ed data [7].
In the case of DMMP degradation, GC–MS analysis of the expected
degradation product of DMMP i.e. Methyl phosphonic acid (MPA) is
Based on the GC–MS and FT-IR data, the proposed reaction scheme
of DMMP decontamination to form MPA and surface bound phospho-
nate is given in Fig. 9 (b). DMMP molecules also reacted with
nanoaggregate MnO2 in two ways. In one way, DMMP molecules
interacted with physisorbed/intercalated water molecules to form
MPA, a non-toxic product and in another way, they form surface
bound phosphonates after the reaction with isolated hydroxyl groups
(Mn–OH) and Lewis acid (Mn+4) sites. These observations match very
well with the previously reported results [9,20].
Overall, occurrence of reactions within the sorbent composed of ag-
gregate MnO2 nanostructures and formation of hydrolysis and surface
bound species confirmed the degradation of CEES and DMMP and con-
verted them into non-toxic form. In order to check the water content in
the aggregate MnO2 nanostructures, TG analysis was carried out as
depicted in Fig. 10. The figure shows 16.5% weight loss up to 220 °C
Fig. 10. TGA pattern of synthesised sorbent composed MnO2 nanoparticles and nanorods.

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291
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and it can be due to loss of water content present within the intercalated
spaces of aggregate MnO2 nanostructures.
Precisely, aggregates of MnO2 nanostructures synthesised using
reactive magnetron sputtering technique offer sufficient surface
area and facilitate the sorption and encapsulation of the CEES as
well as DMMP molecules. And then, water content in the intercalated
sites, surface hydroxyl groups, Lewis sites etc. will react with the
CEES/DMMP molecules thereby converting them into non-toxic
products. The decontamination results of CEES and DMMP molecules
on the reactive sorbent composed of aggregates MnO2 nanostruc-
tures, synthesised in the current study were compared with earlier
prepared and reported metal oxides nanostructures. In the case of
CEES decontamination, magnetron sputtered aggregate MnO2 nano-
structures display much better decontamination reactivity com-
pared to or with existing solid decontaminants such as nanosized
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tubes [8,13,19,21,23,24,31,38]. They exhibited relatively lower de-
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contamination (N80%) with less rate constant values (N0.02 h−1
)
than the currently synthesised aggregate MnO2 nanostructures
which decontaminate the CEES completely (100%) with better rate
constant value (0.267 h−1). Also, in the case of DMMP decontamina-
tion, currently synthesised aggregate MnO2 nanostructures exhibit-
ed better rate constant value (0.068 h−1) than earlier reported rate
constant values (N0.02 h−1) of WO3 nanoparticles and activated car-
bon [9,39]. These results show that sputtered deposited aggregate
MnO2 nanostructures provide encouraging decontamination results
with the existing solid decontamination sorbents.
4. Conclusion
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Sekhar, Reactive sorbent based on manganese oxide nanotubes and nanosheets
for the decontamination of 2-chloro-ethyl ethyl sulphide, Microporous Mesoporous
Mater. 106 (2007) 256–261.
Novel reactive adsorbent composed of aggregate MnO2
nanostructures was synthesised using novel reactive magnetron
sputtering technique and then characterised using XRD, FE-SEM,
TEM, Raman, FT-IR, TGA etc. Thereafter, decontamination reactions
of these MnO2 nanostructures with CEES and DMMP were studied.
The results indicate that aggregate MnO2 nanostructure is a promis-
ing sorbent for the decontamination of CEES as well as DMMP. It de-
stroy the agents (predominantly through hydrolysis reactions) by
pseudo first order kinetic reaction with constant rate and half life
value 0.267 h−1 and 2.58 h for CEES, also 0.068 h−1 and 10.10 h for
DMMP, respectively. Moreover, these synthesised aggregate MnO2
nanostructures offer large surface area and enhanced chemical reac-
tivity for immediate adsorption and detoxification of CWA in
converting them into non-toxic form.
Acknowledgement
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Monu Verma would like to thankMr. Shiv Kumar and Mr. Mukesh
Tripathi for the timely help and encouragement.
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