Faculty Publications

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    A large-scale-oriented growth of ZnO nanorod array on glass substrate: Growth, structural and photoluminoscent properties
    (National Institute of Optoelectronics, 2014) Santhosh Kumar, A.S.; Nagaraja, H.S.
    We report a modified sol gel route for one step fabrication of large scale arrays of zinc oxide (ZnO) nanorods. The method is seed layer free, and nanorods are directly attached to a substrate. We studied the effect of PVA content on growth, crystallanity, orientation, microstructure and optical properties of ZnO. The XRD patterns confirm that samples grown with PVA have good crystallanity with (002) preferred orientation. The SEM micrographs show that the 1 Wt% PVA assisted grown films are covered with large scale oriented nanorod array. Raman spectrum represents that the 1 wt% PVA assisted grown ZnO nanostructures are highly crystalline with a hexagonal wurtzite phase. The room temperature PL spectrum exhibits a strong and sharp UV emission, which confirms that the grown arrays have good optical properties with few structural defects such as oxygen vacancies and zinc interstitials.
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    Synthesis and characterisation of nickel oxide nanofibre webs with alcohol sensing characteristics
    (Royal Society of Chemistry, 2014) George, G.; Anandhan, S.
    In this study, nickel oxide (NiO) nanofibres were obtained by a sol-gel electrospinning process followed by calcination from an aqueous sol of poly(2-ethyl-2-oxazoline)/nickel acetate tetrahydrate. Thermogravimetric analysis was used to determine the degradation temperature of the composite fibres, so as to get nickel oxide nanofibres. X-ray photoelectron spectroscopy and X-ray diffraction studies revealed the complete elimination of the organic phase from NiO fibres during calcination. The change in grain size with calcination temperature was determined by X-ray diffraction. The defects in fibres resulted in the modification of their Raman spectra as compared with that of a single crystal. The magnetic properties of the fibres were reduced as the calcination temperature was increased; this is due to the presence of non-stoichiometric defects. As the calcination temperature was increased, the amount of defects was reduced, which induced a difference in the band gap energy of the fibres. Sensitivity of the NiO fibres towards five different alcohols was studied, and the sensitivity towards ethanol was the highest. © The Royal Society of Chemistry 2014.
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    Preparation, characterization and photoelectrochemical properties of hydrophilic Sn doped TiO2 nanostructures
    (Elsevier, 2014) Santhosh Kumar, A.S.; Nagaraja, K.K.; Huang, N.M.; Nagaraja, H.S.
    Abstract Hydrophilic Sn doped TiO2 nanostructured thin films have been fabricated using a sol-gel method, and followed by calcination at 450 C. The samples are characterized by means of XRD, Raman, SEM and contact angle measurements. The XRD and Raman studies revealed that, the higher Sn doping content (3 at%) leads to the formation of mixed phases of TiO2. SEM micrographs revealed that all samples are porous in nature. The contact angle of TiO2 nanostructured films varied between 19 and 37 depending upon the Sn content. All the samples are photoelectrochemically active and 2% Sn doping significantly enhances the photoelectrochemical ability of TiO 2 film. The highest photocurrent density of 20 ?A cm-2 is measured for 2 at% Sn doped TiO2 in 0.2 M Na2SO 4 electrolyte, on light irradiation. Time dependent photoresponse tests have been carried out by measuring the photocurrent under chopped light irradiation. © 2014 Elsevier B.V.
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    Glass fiber-supported NiO nanofiber webs for reduction of CO and hydrocarbon emissions from diesel engine exhaust
    (Cambridge University Press, 2014) George, G.; Anandhan, S.
    In this study, nickel acetate tetrahydrate (NACTH)/poly(styrene-co-acrylonitrile) (SAN) sol was used for the fabrication of nanocrystalline NiO nanofibers. An indigenous setup was developed to use these nanofibers for the oxidation of carbon monoxide (CO) and unburnt hydrocarbons (HC) from diesel engine exhaust. The morphological, compositional, and crystalline properties of the NiO nanofibers obtained after calcination were studied by scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction (XRD). Clear evidence of defects in the fibers was observed in ultraviolet-visible-near infrared (UV-Vis-NIR) spectra, Raman spectra, and magnetic property measurements. The NiO nanofiber mats supported by glass fiber mats were efficient in oxidizing CO and HC from diesel engine exhaust, and the maximum efficiency was achieved by using NiO nanofibers with the maximum amount of defects. © © Materials Research Society 2014.
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    Glass fiber-supported NiO nanofiber webs for reduction of CO and hydrocarbon emissions from diesel engine exhaust
    (Cambridge University Press, 2014) George, G.; Anandhan, S.
    In this study, nickel acetate tetrahydrate (NACTH)/poly(styrene-co-acrylonitrile) (SAN) sol was used for the fabrication of nanocrystalline NiO nanofibers. An indigenous setup was developed to use these nanofibers for the oxidation of carbon monoxide (CO) and unburnt hydrocarbons (HC) from diesel engine exhaust. The morphological, compositional, and crystalline properties of the NiO nanofibers obtained after calcination were studied by scanning electron microscopy, Fourier transform infrared (FTIR) spectroscopy, and x-ray diffraction (XRD). Clear evidence of defects in the fibers was observed in ultraviolet-visible-near infrared (UV-Vis-NIR) spectra, Raman spectra, and magnetic property measurements. The NiO nanofiber mats supported by glass fiber mats were efficient in oxidizing CO and HC from diesel engine exhaust, and the maximum efficiency was achieved by using NiO nanofibers with the maximum amount of defects. © © Materials Research Society 2014.
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    Comparison of structural, spectral and magnetic properties of NiO nanofibers obtained by sol-gel electrospinning from two different polymeric binders
    (Elsevier Ltd, 2015) George, G.; Anandhan, S.
    NiO is a p-type semiconductor with wide band gap energy. In this study, nickel oxide nanofibers were fabricated by sol-gel electrospinning followed by high temperature calcination, using two sacrificial polymeric binders. Poly(2-ethyl-2-oxazoline) (PEtOx) in water and styrene-acrylonitrile random copolymer (SAN) in N,N- dimethylformamide (DMF) along with nickel (II) acetate tetrahydrate (NATH), as metal oxide precursor, were the two distinct polymeric systems used in this study. The morphological and structural properties of NiO fibers obtained from the aforementioned systems were compared with each other. The degradation behavior of the sacrificial polymeric binder imparted a significant effect on the properties of the obtained NiO fibers. The grain sizes and the activation energies for grain growth of NiO fibers from two systems were different. The non-stoichiometric NiO fibers obtained from the SAN/NATH system had a better ferromagnetic behavior as compared with that produced from the PEtOx/NATH system. This non-stoichiometry made a difference also in the optical band gap energies of the NiO nanofibers. © 2015 Elsevier Ltd.
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    Morphological and structural characterisation of sol-gel electrospun Co3O4 nanofibres and their electro-catalytic behaviour
    (Royal Society of Chemistry, 2015) George, G.; Elias, L.; Hegde, A.C.; Anandhan, S.
    Evolution of hydrogen and oxygen are a crucial part of many renewable energy systems. The replacement of the essential and expensive components in such systems can reduce the capital cost and improve the effectiveness of those systems. In this study, Co3O4 nanofibres were fabricated from sol-gel assisted electrospun poly(styrene-co-acrylonitrile)/cobalt acetate tetrahydrate precursor composite fibres. The morphological and compositional features of the Co3O4 nanofibres obtained after calcination of the precursor nanofibers were studied using scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The results of X-ray diffraction study and Raman spectroscopy revealed that the average grain size of the fibres increased with the calcination temperature. Clear evidence of defects in the fibres was observed in ultraviolet-visible-near infrared and energy dispersive spectroscopic measurements. The electrocatalytic behaviour of Co3O4 nanofibres obtained at different calcination temperatures was studied using them for the water splitting reaction in an alkaline medium. The maximum efficiency in the hydrogen evolution reaction was achieved using the Co3O4 nanofibres obtained at the lowest calcination temperature, which had the highest surface area and the smallest grain size. © The Royal Society of Chemistry 2015.
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    Effect of acid dopants in biodegradable gel polymer electrolyte and the performance in an electrochemical double layer capacitor
    (Institute of Physics Publishing custserv@iop.org, 2015) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.
    Proton-conducting biodegradable gellan gum gel polymer electrolytes (GPEs) have been prepared using three different dopants, namely ortho-phosphoric (o-H3PO4), sulfuric (H2SO4) and hydrochloric acids (HCl). The GPEs were cross-linked using borax. The polymeric gels were characterized by spectroscopic, thermal, ionic conductivities and dielectric measurements. Proton conductivity was in the range of 5.1 × 10-3 to 3.7 × 10-4 s cm-1 and activation energies were between 0.14 meV and 0.19 meV, at different temperatures. Among the doped acids, the H3PO4 doped GPE exhibited thermal stability at varying temperature. Electrochemical double layer capacitors (EDLCs) were fabricated using activated carbon as electrode material and GPEs. The EDLCs were tested using cyclic voltammetry, ac impedance spectroscopic and galvanostatic charge-discharge techniques. The maximum specific capacitance value was 146 F g-1 at a scan rate of 2 mV s-1. Quite stable values were obtained at a constant current density up to 1000 cycles. © 2015 The Royal Swedish Academy of Sciences.
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    A comparative study on the physico-chemical properties of sol-gel electrospun cobalt oxide nanofibres from two different polymeric binders
    (Royal Society of Chemistry, 2015) George, G.; Anandhan, S.
    In this study, two different sacrificial polymeric binders, namely poly(2-ethyl-2-oxazoline) (PEtOx) and poly(styrene-co-acrylonitrile) (SAN) along with cobalt acetate tetrahydrate (CATH), as the metal oxide precursor, were used for the fabrication of Co3O4 nanofibres through sol-gel electrospinning. It was observed that the degradation behaviour and physical properties of SAN and PEtOx influenced the structure, morphology and spectral properties of Co3O4 nanofibres, as the properties of the nanofibres obtained from the aforementioned systems were compared with each other. The grain size, shape and the activation energies for grain growth of Co3O4 nanofibres obtained from these two polymeric systems were different. This difference in grain size and shape caused a difference in the optical band gap energies and the magnetic properties of the Co3O4 nanofibres. This study reveals that one can tailor the characteristics of cobalt oxide nanofibres by an appropriate selection of polymeric binders for sol-gel electrospinning. © The Royal Society of Chemistry.
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    Nonlinear transmittance and optical power limiting in magnesium ferrite nanoparticles: effects of laser pulsewidth and particle size
    (Royal Society of Chemistry, 2016) Perumbilavil, S.; Sridharan, K.; Abraham, A.R.; Janardhanan, H.P.; Kalarikkal, N.; Philip, R.
    We report comparative measurements of size dependent nonlinear transmission and optical power limiting in nanocrystalline magnesium ferrite (MgFe2O4) particles excited by short (nanosecond) and ultrashort (femtosecond) laser pulses. A standard sol-gel technique is employed to synthesize particles in the size range of 10-50 nm, using polyvinyl alcohol as the chelating agent. The structure and morphology of the samples are studied using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Growth of the particles in time is tracked through Fourier transform infrared spectroscopy. Nonlinear transmission measurements have been carried out using the open aperture Z-scan technique employing 532 nm, 5 nanosecond pulses and 800 nm, 100 femtosecond pulses, respectively. The measured optical nonlinearity is primarily of a reverse saturable absorption (RSA) nature, arising mostly from excited state absorption for nanosecond excitation, and two-photon absorption for femtosecond excitation. The optical limiting efficiency is found to increase with particle size for both cases. The calculated nonlinear parameters indicate that these materials are potential candidates for optical limiting applications. © The Royal Society of Chemistry.