The TiO 2 NPs have shown the promising pho- tocatalytic activity for the water splitting reaction, which is revealed by producing 290 m mol g 1 of H 2 for 2.5 h exposure and also by the[r]
Trang 1Original Article
An investigation of hydrogen generation and antibacterial activity of
method
L.S Reddy Yadava,c,1, K Manjunathb,1, C Kavithaa, G Nagarajuc,*
a Dept of Chemistry, BMS Institute of Technology, Bangalore, India
b Center for Nano and Material Sciences, Jain University, Bangalore, India
c Dept of Chemistry, Siddaganga Institute of Technology, Tumkur, Karnataka, India
a r t i c l e i n f o
Article history:
Received 25 November 2017
Received in revised form
26 February 2018
Accepted 22 March 2018
Available online 28 March 2018
Keywords:
Titanium oxide
Ionic liquid
Hydrogen generation
Antibacterial activity
a b s t r a c t
Amongst soft chemical synthetic routes, the ionothermal synthesis method (using an ionic liquid) has attracted research tremendously due to their remarkable features especially in the case of TiO2 nano-particles synthesis On the other hand, the significant role of TiO2nanoparticles in thefields of photo-catalysis, photovoltaics, batteries etc is noteworthy Here, by considering these two remarkable aspects, TiO2has been prepared by using an ionic liquid The band gap of 3.2 eV has been determined through UV-Vis absorption spectra The crystallite size was found to be 62 nm by PXRD Additionally, TEM images have confirmed that the size of the particles is in the nanoscale Furthermore, the significant properties
of TiO2nanoparticles have been studied and utilized for photocatalytic water splitting, as well as for the development of antibacterial activities
© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)
1 Introduction
The transition metal oxide TiO2has been considered as one of
the best metal oxides because it is a low cost, wide band gap
(3.2 eV) and non-toxic semiconductor material TiO2 has been
widely used in photocatalysis, sensors, photovoltaics, cosmetics,
surface decoration materials (paints) etc.[1e3] The morphology
and particle size in the nanoscale crystalline phase of TiO2play an
important role in the various investigation with respects to their
relation to the chemical, physical, photosensitive, catalytic and
electrical properties of this oxide[4e6] Different techniques have
been used to prepare TiO2 nanoparticles (NPs) such as
hydro-thermal, chemical vapour deposition, electro-deposition, a
com-bustion, solvothermal, solegel, co-precipitation, etc [7,8] Ionic
liquids (IL) have found great considerations for the room
tem-perature preparation of TiO2 nanomaterials in the past two
de-cades TiO2 NPs have distinctive properties such as wide liquid
temperature range, high thermal stability, good ionic conductivity,
negligible vapour pressure, excellent solvent power for both organic and inorganic compounds which supports in the evolu-tion and nucleaevolu-tion of nanoparticles[9] The important property
of IL's for the preparation of nano metal oxides supports a sur-factant like environment which hinders and stops the combina-tion of nanomaterials [10] Fuzishima and his group's first invention was the realization of the photochemical water splitting reaction using TiO2[11] There have been increasing attention to and serious consideration of the photocatalytic decay of water into H2and O2using semiconductor materials One of the reason for the wide spread utilization of TiO2semiconductors as a pho-tocatalyst is due to it's chemical stability and abundant avail-ability There have been various reports on the synthesis of TiO2 nanoparticles using the ionothermal technique dealing with their applications towards solar cells, lithium-ion battery, photo-catalytic degradation of organic dyes, etc However, there are only few articles available on the ionothermal derived TiO2 NPs for water splitting reaction Ni et al studied the photocatalytic water-splitting using TiO2 for hydrogen production in recent de-velopments[12] Nagaraju and his group used imidazolium-based functionalized liquid for the synthesis of TiO2 nanoparticles for water splitting reaction[13,14]Gordon et al.[15]synthesized TiO2 nanocrystals using TiF4 and they also studied the morphological
* Corresponding author.
E-mail address: nagarajugn@rediffmail.com (G Nagaraju).
Peer review under responsibility of Vietnam National University, Hanoi.
1 Indicates the equal contribution of both authors.
Contents lists available atScienceDirect Journal of Science: Advanced Materials and Devices
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j s a m d
https://doi.org/10.1016/j.jsamd.2018.03.002
2468-2179/© 2018 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license
Journal of Science: Advanced Materials and Devices 3 (2018) 181e187
Trang 2effect on the H2 generation Dai and his group prepared TiO2
nanoparticles using the low-temperature hydrothermal synthesis
in ionic liquids/water and studied the photocatalytic degradation
of o-nitro phenol [16] Shuanfeng Hu and his group synthesized
mesostructure anatase TiO2 particles in ionic liquids at room
temperature [17] S M Sali and his group studied the
phase-tuned synthesis of TiO2 nanoparticles for room temperature
enhanced ammonia detection[18] Zhai et al confirmed the
for-mation of a bidentate chelating complexation between the
car-boxylic functional group of 1-methylimidazolium-3-acetate
chloride ([AcMIM][Cl]) and the titanate in the synthesis of rutile
TiO2 [19] Nakashima and his group synthesized interfacial
syn-thesis of hollow TiO2 microspheres in ionic liquids [20] In this
current work, we have prepared anatase phase TiO2nanoparticles
via the ionothermal method The obtained TiO2 product is
ana-lysed by various techniques and used for the hydrogen generation
and antibacterial activities
2 Experimental
2.1 Synthesis of 1-(2-methoxyethyl)-3-methylimidazolium tris
(pentafluoroethyl) tri fluorophosphate
In a typical synthesis, 1-(2-methoxy ethyl)-3-methylimida
zolium methane sulfonate (42.25 g, 169 mmol) was dissolved in
water (50 mL) under stirring at 10e20C, while tris (penta
fluo-roethyl) trifluoro phosphoric acid (99.0 g, 177.5 mmol) was added
Stirring was continued for further 30 min The upper aqueous layer
was removed, and the remaining liquid was then washed with small
portions (10 mL) of water Dichloromethane (250 mL) was
subse-quently added, and the solution was dried with sodium carbonate
Solvent evaporation afforded the
1-1-(2-methoxyethyl)-3-methylimidazolium tris (pentafluoroethyl) tri fluoro phosphate, as
a pale amber liquid The schematic structure of the ionic liquid is
shown inFigure 1
2.2 Synthesis of TiO2nanoparticles
In the typical synthetic procedure, 0.5 mL TiCl4was added in a
teflon tube containing 10 mL of ionic liquid under continuous
stirring After homogenization of the mixture, hydrolysis of TiCl4
occurred when 1 mL of distilled water was added slowly to the
above solution as indicated by the effervescence of HCl fumes The
above mixture was then exposed to an ionothermal treatment at
120C for 1 day After the reaction was completed, the Autoclave
was naturally cooled to room temperature and the product was
washed with water followed by ethanol several times to remove
the IL, and TiO2nanoparticles werefinally separated by centrifu-gation The obtained product was dried in an oven at 80C over-night for further characterization
2.3 Photocatalytic H2production measurements The photocatalytic H2production reaction was carried out in a closed gas-circulating system within an inner irradiation type reactor In the reactor, 8 mg of TiO2nanoparticles were dispersed in
Fig 1 Schematic structure of 1-(2-Methoxyethyl)-3-methylimidazolium Tris
(penta-fluoroethyl) Tri Fluorophosphate.
Fig 2 XRD pattern of TiO 2 nanoparticles.
Fig 3 FTIR spectrum of TiO 2 nanoparticles.
Fig 4 Direct optical energy band gap of TiO 2 nanoparticles and its corresponding
Trang 3UV-6 mL aqueous solution and sonicated for 20 min 2 mL ethanol was
added as a sacrificial agent during the sonication Before the
irra-diation, the system was bubbled with argon gas for about
10e15 min to remove all the dissolved oxygen Photocatalytic
ac-tivities were evaluated by measuring H2 production using gas
chromatography at room temperature During the experiment, the
reaction temperature was kept at 25C by eliminating the IR
ra-diation with the circulation of water in the water jacket of the
reactor The analysis was conducted on an Agilent 6820 GC
Chromatograph equipped with a thermal conductivity detector having 0.5Å sieve packed column by purging argon as the carrier gas Using a gasetight syringe with a maximum volume of 50mL the amount of H2produced was measured at every 30 min interval of time In a graph, the UV exposure time and the amount of gas liberated are plotted as a function
2.4 Procedure for antibacterial activity studies The agar well diffusion method shall provide information on the antibacterial activity[21]of the TiO2NPs against four bacterial strains, namely Gram-ve Klebsiella aerogenes, Escherichia coli, Pseudomonas desmolyticum and Gramþve bacteria Staphylococcus aureus Nutrient agar plates were prepared and swabbed using a sterile L-shaped glass rod with 100mL of 24 h mature broth culture
of individual bacterial strains In each petri-plate, the wells were created by using sterile cork borer (6 mm) Different concentrations
of TiO2NPs (500 and 1000mg/well) were used to assess the anti-bacterial activity of the nanoparticles The TiO2NPs were dispersed
in sterile water This as the negative control and simultaneously the standard antibiotics Ciprofloxacin (5mg/50mL) (Hi-Media, Mumbai, India) as the positive control were tested against the bacterial pathogens Then the plates were incubated at 37C for 48 h The zone inhibition of every well were measured in millimeters Trip-licates were maintained at every concentration and also the average values were calculated for the ultimate antibacterial activity
Fig 5 Raman spectrum of TiO 2 nanoparticles.
L.S.R Yadav et al / Journal of Science: Advanced Materials and Devices 3 (2018) 181e187 183
Trang 42.5 Characterization
The Powder X-ray diffraction (PXRD) data were recorded on a
Philips X'pert PRO X-ray diffractometer with graphite
mono-chromatized Cu-Ka(1.5418 Å) radiation, while a Bruker Alpha-P
spectrometer gave the Fourier transform infrared (FTIR) spectrum
of the sample A Perkin Elmer Lambda-750 UV-Vis spectrometer
measured the sample's absorption spectrum Raman spectrum is
recorded (Lab RAM HR, Horiba Jobin-Yvon, France) using the
514.5 nm, air-cooled Arþlaser with 50* objective laser intensity
Carl Zeiss ultra 55 scanning electron microscopy (SEM) examined
the surface morphology, and JEOL JEM 1200 Ex operating at 100 kV
was performed providing the transmission electron microscopy
(TEM) images
3 Results and discussion
Fig 2shows the XRD pattern of the as-prepared TiO2sample All
the observed peaks in the PXRD pattern are identiefied in the
tetragonal crystalline structure with the anatase phase of the TiO2
nanoparticles [JCPDS no 4-477] The derived unit cell parameters a:
3.783 Å, c: 9.51 Å confirm the sample in the tetragonal crystal
structure system with space group I41/amd (no 141) The average
crystallite size was calculated for the most intense diffraction peak
at the two-theta value of 25.4 using the DebyeeScherrer's equation
and was found to be 62 nm
where D is the crystal size,lis the wavelength andbis the full-width half maximum of the diffraction peak at the scattering angleq
In the FTIR spectrum (seeFig 3), the CeH stretching and the in-plane vibrations of the imidazolium ring can be assigned to the weak bands at 1618 and 1425 cm1 The bands at 1180 and
1058 cm1 can be assigned to the in-plane vibrations of the aliphatic compounds The organic cations are observed due to the respective out of plane vibrational bands at 935 and 784 cm1, respectively The TieOeTi band is observed at 426 cm1.
The UV absorption coefficient and the optical band gap (shown
inFig 4) have been estimated using the Tauc equation (see the inset
ofFig 4.)
ðaEÞq¼ A E Eg
(2)
where A is a constant that depends on the transition probability, E is the energy of an incident photon and q is an index that character-izes the optical absorption process
It is well known that the direct and indirect band gap energies for the semiconductor nanostructures can be obtained from the intersection of the linearfits of (aE)qversus E plots for q¼ 2 and 0.5
on the X-axis Here, the estimated value of the direct band gap is
Fig 7 SEM images of TiO 2 nanoparticles at different magnifications in term of respective scales: 3.0mm (a) and 5mm (b).
Fig 8 TEM images of TiO nanoparticles at different magnifications in term of the respective scales of 0.2mm (a) and 5.0mm (b).
Trang 5about 3.23 eV for the preferred distribution of TiO2nanoparticles by taking into account of the absorption peak around the 383 nm wavelength on the X-axis (shown in Fig 4) which is in good agreement with the literature values[22,23]
Fig 5presents the Raman spectrum of the as-prepared TiO2NPs The Raman lines of the anatase phase of TiO2 nanoparticles are observed at around 155 cm1(Eg), 360 cm1(B1g) and 560 cm1(B1g), which are in good agreement with the reportedfindings as well as with PXRD pattern Also, these vibrational peaks are slightly broad-ened due to the nanoscale small size of the TiO2particles[24] In addition to the PXRD and the FT-IR, the Raman spectrum further confirms the formation of the anatase TiO2nanoparticles[25] Fig 6(a) shows the XPS spectra of the as-prepared TiO2sample They are assignable[25]to the bond between the O and Ti atoms FromFig 6(b) it is clear that Ti 2p is a doublet with the Ti 2p3/2at
1021 eV and for the Ti 2p1/2at 1027 eV, typical of Ti in the oxidation state ofþ4.Fig 6(c) presents the XPS broad spectrum of the TiO2
Fig 9 Hydrogen generation of TiO 2 nanoparticles, solid lines are guides to the eyes.
Fig 10 Photographs of the zone of inhibition of a) Klebsiella aerogenes b) Staphylococcus aureus c) Escherichia coli d) Pseudomonas desmolyticum in the presence of the TiO 2
nanoparticles.
L.S.R Yadav et al / Journal of Science: Advanced Materials and Devices 3 (2018) 181e187 185
Trang 6nanoparticles revealing the good agreement with the XPS spectrum
of O1s and Ti 2p[20] This further confirmed that the TiO2
nano-particles are in the anatase phase
Fig 7presents the SEM images of the as-prepared TiO2
nano-particles The SEM images reveal the spherical shape of the TiO2
particles Fig 7 shows the morphology and average size of the
formation of TiO2 nanoparticles are further confirmed by TEM
images Spherical shaped particles with particle size 30e50 nm of
TiO2can be found in TEM images By considering the average
par-ticle size, we are proposing the parpar-ticles are under the nanoscale
region (seeFig 8)
4 Hydrogen evolutions
Photocatalytic water splitting reactions have been performed to
check the production of H2using as-prepared TiO2nanoparticles
and the results are demonstrated inFig 9 The rate of hydrogen
generation of the water-ethanol system in the presence of TiO2
nanoparticles was determined by gas chromatography using an
air-tight syringe The amount of gas liberated was taken out into the
syringe and measured at every 30 min interval of time and is
plotted as the function of UV exposure time in the diagram where
the amount of H2generated in Y-axis and the UV exposure time on
the X-axis We have observed that 290 m∙mol∙g1 of H2 was
generated for 2.5 h of UV exposure time
The generation of H2gas was also found stopped when the UV
light was turned off This indicates that the gas evolution was
induced by the UV irradiation From the graph, it is clear that TiO2
nanoparticles act as a good photocatalyst for the hydrogen
gener-ation through the water splitting reaction
5 Antibacterial activity studies
The antibacterial properties of the TiO2nanoparticles of the are
evaluated against Gram-ve K aerogenes, E coli and P desmolyticum,
Gramþve bacteria S aureus by the agar well diffusion method In
the agar well diffusion method the TiO2NPs shows the significant
antibacterial activity on all the four bacterial strains The bacterial
strains of Gram-ve K aerogenes, E coli, P desmolyticum Gramþve
bacteria S aureus with 500 and 1000mg concentration of TiO2NPs
show the zone of inhibition as presented inFig 10 The data are
collected inTable 1
6 Conclusion
The TiO2 nanoparticles have been synthesized by the
ion-othermal method The structural properties have been confirmed
by PXRD which showed that TiO2 formed completely into the
anatase phase The average size of the TiO2particles was found to
be 30e50 nm which are in the spherical form as confirmed by TEM
and SEM images The optical properties of the TiO2nanoparticles
have been studied through UV-Vis absorption spectra and the band
gap was estimated in the order of 3.2 eV Two significant activities,
namely the studies on the photocatalytic hydrogen production and
the antibacterial activity have been performed using the
as-prepared TiO2NPs The TiO2NPs have shown the promising pho-tocatalytic activity for the water splitting reaction, which is revealed by producing 290mmol g1of H2for 2.5 h exposure and also by the recorded antibacterial properties against four bacterial strains using the agar well diffusion method
Acknowledgements Authors Dr K Manjunath thanks CNPq-TWAS for sandwich fellowship at UFRGS, Porto Alegre, Brazil and Dr G Nagaraju ac-knowledges DST Nanomission, Govt of India, (No SR/NM/NS-1262/ 2013) forfinancial support
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Table 1
Antibacterial activity of TiO 2 nanoparticles on pathogenic bacterial strains.
(Mean ± SE)
Escherichia coli (Mean ± SE)
Staphyloccus aureus (Mean ± SE)
Pseudomonas desmolyticum (Mean ± SE)
Values are the mean ± SE of inhibition zone in mm * Symbols represent statistical significance, *P < 0.05, **P < 0.01 as compared with the control group.
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