An investigation of hydrogen generation and antibacterial activity of tio2 nanoparticles synthesized by the ionic liquid aided ionothermal method

Journal of Science: Advanced Materials and Devices (2018) 181e187 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Original Article An investigation of hydrogen generation and antibacterial activity of TiO2 nanoparticles synthesized by the ionic liquid aided ionothermal method L.S Reddy Yadav a, c, 1, K Manjunath b, 1, C Kavitha a, G Nagaraju c, * a b c Dept of Chemistry, BMS Institute of Technology, Bangalore, India Center for Nano and Material Sciences, Jain University, Bangalore, India Dept of Chemistry, Siddaganga Institute of Technology, Tumkur, Karnataka, India a r t i c l e i n f o a b s t r a c t Article history: Received 25 November 2017 Received in revised form 26 February 2018 Accepted 22 March 2018 Available online 28 March 2018 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 nanoparticles synthesis On the other hand, the significant role of TiO2 nanoparticles in the fields of photocatalysis, photovoltaics, batteries etc is noteworthy Here, by considering these two remarkable aspects, TiO2 has 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 TiO2 nanoparticles 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/) Keywords: Titanium oxide Ionic liquid Hydrogen generation Antibacterial activity Introduction The transition metal oxide TiO2 has 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 TiO2 play 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 hydrothermal, chemical vapour deposition, electro-deposition, a combustion, solvothermal, solegel, co-precipitation, etc [7,8] Ionic liquids (IL) have found great considerations for the room temperature preparation of TiO2 nanomaterials in the past two decades TiO2 NPs have distinctive properties such as wide liquid temperature range, high thermal stability, good ionic conductivity, * Corresponding author E-mail address: nagarajugn@rediffmail.com (G Nagaraju) Peer review under responsibility of Vietnam National University, Hanoi Indicates the equal contribution of both authors negligible vapour pressure, excellent solvent power for both organic and inorganic compounds which supports in the evolution and nucleation of nanoparticles [9] The important property of IL's for the preparation of nano metal oxides supports a surfactant like environment which hinders and stops the combination 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 H2 and O2 using semiconductor materials One of the reason for the wide spread utilization of TiO2 semiconductors as a photocatalyst is due to it's chemical stability and abundant availability 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, photocatalytic 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 watersplitting using TiO2 for hydrogen production in recent developments [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 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 (http://creativecommons.org/licenses/by/4.0/) 182 L.S.R Yadav et al / Journal of Science: Advanced Materials and Devices (2018) 181e187 effect 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 phasetuned synthesis of TiO2 nanoparticles for room temperature enhanced ammonia detection [18] Zhai et al confirmed the formation of a bidentate chelating complexation between the carboxylic 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 synthesis of hollow TiO2 microspheres in ionic liquids [20] In this current work, we have prepared anatase phase TiO2 nanoparticles via the ionothermal method The obtained TiO2 product is analysed by various techniques and used for the hydrogen generation and antibacterial activities the IL, and TiO2 nanoparticles were finally separated by centrifugation The obtained product was dried in an oven at 80  C overnight for further characterization 2.3 Photocatalytic H2 production measurements The photocatalytic H2 production reaction was carried out in a closed gas-circulating system within an inner irradiation type reactor In the reactor, mg of TiO2 nanoparticles were dispersed in 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 10e20  C, while tris (penta fluoroethyl) trifluoro phosphoric acid (99.0 g, 177.5 mmol) was added Stirring was continued for further 30 The upper aqueous layer was removed, and the remaining liquid was then washed with small portions (10 mL) of water Dichloromethane (250 mL) was subsequently added, and the solution was dried with sodium carbonate Solvent evaporation afforded the 1-1-(2-methoxyethyl)-3methylimidazolium tris (pentafluoroethyl) tri fluoro phosphate, as a pale amber liquid The schematic structure of the ionic liquid is shown in Figure Fig XRD pattern of TiO2 nanoparticles 2.2 Synthesis of TiO2 nanoparticles In the typical synthetic procedure, 0.5 mL TiCl4 was added in a teflon tube containing 10 mL of ionic liquid under continuous stirring After homogenization of the mixture, hydrolysis of TiCl4 occurred when 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 120  C for 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 Fig Schematic structure of 1-(2-Methoxyethyl)-3-methylimidazolium Tris (pentafluoroethyl) Tri Fluorophosphate Fig FTIR spectrum of TiO2 nanoparticles Fig Direct optical energy band gap of TiO2 nanoparticles and its corresponding UVVis spectrum (inset) L.S.R Yadav et al / Journal of Science: Advanced Materials and Devices (2018) 181e187 183 Chromatograph equipped with a thermal conductivity detector having 0.5 Å sieve packed column by purging argon as the carrier gas Using a gasetight syringe with a maximum volume of 50 mL the amount of H2 produced was measured at every 30 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 Fig Raman spectrum of TiO2 nanoparticles mL aqueous solution and sonicated for 20 mL ethanol was added as a sacrificial agent during the sonication Before the irradiation, the system was bubbled with argon gas for about 10e15 to remove all the dissolved oxygen Photocatalytic activities were evaluated by measuring H2 production using gas chromatography at room temperature During the experiment, the reaction temperature was kept at 25  C by eliminating the IR radiation with the circulation of water in the water jacket of the reactor The analysis was conducted on an Agilent 6820 GC The agar well diffusion method shall provide information on the antibacterial activity [21] of the TiO2 NPs against four bacterial strains, namely Gram-ve Klebsiella aerogenes, Escherichia coli, Pseudomonas desmolyticum and Gram ỵve bacteria Staphylococcus aureus Nutrient agar plates were prepared and swabbed using a sterile L-shaped glass rod with 100 mL 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 TiO2 NPs (500 and 1000 mg/well) were used to assess the antibacterial activity of the nanoparticles The TiO2 NPs were dispersed in sterile water This as the negative control and simultaneously the standard antibiotics Ciprofloxacin (5 mg/50 mL) (Hi-Media, Mumbai, India) as the positive control were tested against the bacterial pathogens Then the plates were incubated at 37  C for 48 h The zone inhibition of every well were measured in millimeters Triplicates were maintained at every concentration and also the average values were calculated for the ultimate antibacterial activity Fig XPS spectra of a) Oxygen b) Titanium and c) TiO2 nanoparticles 184 L.S.R Yadav et al / Journal of Science: Advanced Materials and Devices (2018) 181e187 Fig SEM images of TiO2 nanoparticles at different magnifications in term of respective scales: 3.0 mm (a) and mm (b) 2.5 Characterization D ¼ 0:9 l=b Cos q The Powder X-ray diffraction (PXRD) data were recorded on a Philips X'pert PRO X-ray diffractometer with graphite monochromatized 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 Arỵ laser 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 Results and discussion Fig shows the XRD pattern of the as-prepared TiO2 sample 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 (1) where D is the crystal size, l is the wavelength and b is the fullwidth half maximum of the diffraction peak at the scattering angle q In the FTIR spectrum (see Fig 3), the CeH stretching and the inplane vibrations of the imidazolium ring can be assigned to the weak bands at 1618 and 1425 cmÀ1 The bands at 1180 and 1058 cmÀ1 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 cmÀ1, respectively The TieOeTi band is observed at 426 cmÀ1 The UV absorption coefficient and the optical band gap (shown in Fig 4) have been estimated using the Tauc equation (see the inset of Fig 4.) aEịq ẳ 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 characterizes 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 linear fits of (aE)q versus E plots for q ¼ and 0.5 on the X-axis Here, the estimated value of the direct band gap is Fig TEM images of TiO2 nanoparticles at different magnifications in term of the respective scales of 0.2 mm (a) and 5.0 mm (b) L.S.R Yadav et al / Journal of Science: Advanced Materials and Devices (2018) 181e187 Fig Hydrogen generation of TiO2 nanoparticles, solid lines are guides to the eyes 185 about 3.23 eV for the preferred distribution of TiO2 nanoparticles 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 presents the Raman spectrum of the as-prepared TiO2 NPs The Raman lines of the anatase phase of TiO2 nanoparticles are observed at around 155 cmÀ1 (Eg), 360 cmÀ1 (B1g) and 560 cmÀ1 (B1g), which are in good agreement with the reported findings as well as with PXRD pattern Also, these vibrational peaks are slightly broadened due to the nanoscale small size of the TiO2 particles [24] In addition to the PXRD and the FT-IR, the Raman spectrum further confirms the formation of the anatase TiO2 nanoparticles [25] Fig 6(a) shows the XPS spectra of the as-prepared TiO2 sample They are assignable [25] to the bond between the O and Ti atoms From Fig 6(b) it is clear that Ti 2p is a doublet with the Ti 2p3/2 at 1021 eV and for the Ti 2p1/2 at 1027 eV, typical of Ti in the oxidation state of ỵ4 Fig (c) presents the XPS broad spectrum of the TiO2 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 TiO2 nanoparticles 186 L.S.R Yadav et al / Journal of Science: Advanced Materials and Devices (2018) 181e187 Table Antibacterial activity of TiO2 nanoparticles on pathogenic bacterial strains Treatment Klebsiella aerogenes (Mean ± SE) Escherichia coli (Mean ± SE) Staphyloccus aureus (Mean ± SE) Pseudomonas desmolyticum (Mean ± SE) Standard (5 mg/50 mL) TiO2 (500 mg/50 mL) TiO2 (1000 mg/10 mL) 13.67 ± 0.33** 0.33 ± 0.33** 2.67 ± 0.00 17.33 ± 0.33** 0.67 ± 0.33** 1.33 ± 0.00 14.37 ± 0.33** 1.00 ± 0.00 2.33 ± 0.33** 12.67 ± 0.33** 0.33 ± 0.33** 1.67 ± 0.33** 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 nanoparticles revealing the good agreement with the XPS spectrum of O1s and Ti 2p [20] This further confirmed that the TiO2 nanoparticles are in the anatase phase Fig presents the SEM images of the as-prepared TiO2 nanoparticles The SEM images reveal the spherical shape of the TiO2 particles Fig 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 TiO2 can be found in TEM images By considering the average particle size, we are proposing the particles are under the nanoscale region (see Fig 8) prepared TiO2 NPs The TiO2 NPs have shown the promising photocatalytic activity for the water splitting reaction, which is revealed by producing 290 m mol gÀ1 of H2 for 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 acknowledges DST Nanomission, Govt of India, (No SR/NM/NS-1262/ 2013) for financial support Hydrogen evolutions References Photocatalytic water splitting reactions have been performed to check the production of H2 using as-prepared TiO2 nanoparticles and the results are demonstrated in Fig The rate of hydrogen generation of the water-ethanol system in the presence of TiO2 nanoparticles was determined by gas chromatography using an airtight syringe The amount of gas liberated was taken out into the syringe and measured at every 30 interval of time and is plotted as the function of UV exposure time in the diagram where the amount of H2 generated in Y-axis and the UV exposure time on the X-axis We have observed that 290 m∙mol∙gÀ1 of H2 was generated for 2.5 h of UV exposure time The generation of H2 gas 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 generation through the water splitting reaction Antibacterial activity studies The antibacterial properties of the TiO2 nanoparticles of the are evaluated against Gram-ve K aerogenes, E coli and P desmolyticum, Gram ỵve bacteria S aureus by the agar well diffusion method In the agar well diffusion method the TiO2 NPs shows the significant antibacterial activity on all the four bacterial strains The bacterial strains of Gram-ve K aerogenes, E coli, P desmolyticum Gram ỵve bacteria S aureus with 500 and 1000 mg concentration of TiO2NPs show the zone of inhibition as presented in Fig 10 The data are collected in Table Conclusion The TiO2 nanoparticles have been synthesized by the ionothermal method The structural properties have been confirmed by PXRD which showed that TiO2 formed completely into the anatase phase The average size of the TiO2 particles was found to be 30e50 nm which are in the spherical form as confirmed by TEM and SEM images The optical properties of the TiO2 nanoparticles 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- [1] X Chen, S.S Mao, Titanium dioxide nanomaterials: synthesis, properties, modifications, and application, Chem Rev 107 (7) (2007) 2891e2959 [2] C Wessel, L Zhao, Nanostructured TiO2 and its application in lithium-ion storage, J Chem Eur 17 (2011) 3231e3241 [3] Y 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1-ethyl-3-methylimidazoliumbis(tri fluoro methyl sulfonyl) imide and 1-ethyl-3-methylimidazolium ethyl sulfate, Appl Spectrosc 61 (2007) 1306e1311  ... as-prepared TiO2 nanoparticles and the results are demonstrated in Fig The rate of hydrogen generation of the water-ethanol system in the presence of TiO2 nanoparticles was determined by gas chromatography... concentrations of TiO2 NPs (500 and 1000 mg/well) were used to assess the antibacterial activity of the nanoparticles The TiO2 NPs were dispersed in sterile water This as the negative control and simultaneously... imidazolium ring can be assigned to the weak bands at 1618 and 1425 cmÀ1 The bands at 1180 and 1058 cmÀ1 can be assigned to the in-plane vibrations of the aliphatic compounds The organic cations are