Faculty Publications
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Item Fabrication and high-temperature structural characterization study of porous anodic alumina membranes(2012) Choudhari, K.S.; Sudheendra, P.; Udayashankar, N.K.Porous anodic alumina (PAA) membranes with highly ordered array of nanopores were prepared by twostep anodization process. Studies on structural and thermal properties and the thermal stability of the prepared PAA membranes were carried out. Investigation using scanning electron microscopy, atomic force microscopy, X-ray diffraction, thermal analysis and infrared spectroscopy was performed on the prepared PAA membranes at room temperature and in the temperature range 600-1,400 °C. The as-prepared PAA membranes revealed the amorphous nature. Polycrystalline PAA membranes were obtained by annealing carried out at different temperatures. Annealing study confirmed that the heat treatment transformed the amorphous PAA membranes to their crystalline phases, namely, ?-alumina at about 870 °C and then to ?-alumina around 1,250 °C. © Springer Science+Business Media, LLC 2011.Item Morphological analysis and photoluminescence properties of hydrophilic porous anodic alumina formed in oxalic acid(Springer New York LLC barbara.b.bertram@gsk.com, 2016) Ramana Reddy, P.R.; Ajith, K.M.; Udayashankar, N.K.Porous anodic alumina (PAA) templates were prepared via two-step anodization process in 0.3 M oxalic acid for different anodization durations (2–10 h with a step of 2 h). In this article, we report our studies on the morphological analysis and photoluminescence (PL) properties of hydrophilic PAA templates prepared at 8 and 18 °C. Two-dimensional fast Fourier transform was used to study the regularity ratio of PAA. It was found that for a longer anodization time (6, 8 and 10 h) the better array of pores observed with anodization potential of 40 V. The effect of anodization duration on the structural aspects including pore diameter, interpore distance, porosity and pore density were investigated in detail. It was observed that increase in anodization duration led to an increase in pore diameter and porosity. Contact angle measurement of PAA templates was carried out to confirm the hydrophilic nature. The relationship between morphology of PAA and PL emission bands was studied. The PL spectra of PAA templates show two emission sub-bands, which can be ascribed to two luminescence centers, F+ (band-1) and F (band-2), respectively. © 2016, Springer Science+Business Media New York.Item Micro and nanoindentation analysis of porous anodic alumina prepared in oxalic and sulphuric acid(Elsevier Ltd, 2016) Ramana Reddy, P.R.; Ajith, K.M.; Udayashankar, N.K.In this article, the mechanical behavior of porous anodic alumina (PAA) structures obtained from two different electrolytes (oxalic and sulphuric acids) was investigated using micro and nanoindentation techniques. Regularity ratio (RR) of PAA structures was calculated using WSxM software and it was found that strength of the PAA structures varies with the RR of the pores. Micro hardness of the PAA structures was studied using 0.98, 9.8 N loads and it was observed that surface ring cracks were generated for 9.8 N load in oxalic acid. PAA structures formed in sulphuric acid exhibits an extremely high hardness of 7.5 GPa and Young's modulus as 146.5 GPa compared with oxalic acid due to low porosity. Results indicate that the indentation modulus and hardness of the PAA structures decrease with increasing pore size. Further the effect of porosity and regularity ratio of pores on mechanical properties of PAA structures was studied in detail. © 2016 Elsevier Ltd and Techna Group S.r.l.Item Synthesis and photocatalytic properties of graphitic carbon nitride nanofibers using porous anodic alumina templates(Institute of Physics Publishing helen.craven@iop.org, 2017) Suchitra, S.M.; Udayashankar, N.K.In the present study, we describe an effective method for the synthesis of Graphitic carbon nitride (GCN) nanostructures using porous anodic alumina (AAO) membrane as template by simple thermal condensation of cyanamide. Synthesized nanostructure was fully analysed by various techniques to detect its crystalline nature, morphology, luminescent properties followed by the evaluation of its photocatalytic activity in the degradation of Methylene blue dye. Structural analysis of synthesized GCNNF was systematically carried out using x-ray powder diffraction (XRD) and scanning electron microscope (SEM), and. The results confirmed the growth of GCN inside the nanochannels of anodic alumina templates. Luminescent properties of GCNNF were studied using photoluminescence (PL) spectroscopy. PL analysis showed the presence of a strong emission peak in the wavelength range of 350-600 nm in blue region. GCNNF displays higher photocatalytic performance in the photodegradation of methylene blue compare to the bulk GCN. Highlights 1. In the present paper, we report the synthesis of graphitic carbon nitride nanofibers (GCNNF) using porous anodic aluminium oxide membranes as templates through thermal condensation of cyanamide at 500 °C. 2. The synthesis of Graphitic carbon nitride nanofibers using porous andic alumina template is the efficient approach for increasing crystallinity and surface area. 3. The high surface area of graphitic carbon nitride nanofibers has a good impact on novel optical and photocatalytic properties of the bulkGCN. 4. AAO templating of GCN is one of the versatile method to produce tailorable GCN nanostructures with higher surface area and less number of structural defects. 5. Towards photocatalytic degradation of dyes, the tuning of physical properties is very essential thing hence we are succeeded in achieving better catalytic performance of GCN nanostructures by making use of AAO templates. © 2017 IOP Publishing Ltd.Item Influence of porewidening duration on the template assisted growth of graphitic carbon nitride nanostructures(Institute of Physics Publishing helen.craven@iop.org, 2018) Suchitra, S.M.; Udayashankar, N.K.Porous anodic aluminium oxide (AAO) membranes with a highly ordered pore arrangement are typically used as ideal templates for the synthesis of numerous nanostructured materials. Highly ordered templates gained significant attraction due to the fact that they are readily fabricated through self-organised simple anodization process. In this paper, the effect of different pore-widening treatments on the quality of the pores of the AAO templates prepared with different electrolytes were inspected. Results confirmed that, without altering the interpore distance different pore dimensions and diameters of the AAO templates can be easily achieved by chemical pore widening process at room temperature. Also, graphitic carbon nitride nanorods of different dimension have been fabricated from AAO template after porewidening process. These nanostructures are widely used in case of metal free visible light driven photo catalysis, photo degradation of organic pollutants, photo electric conversion and water splitting applications. © 2018 IOP Publishing Ltd.Item Optical and mechanical studies on free standing amorphous anodic porous alumina formed in oxalic and sulphuric acid(Springer Verlag service@springer.de, 2018) Ramana Reddy, P.R.; Ajith, K.M.; Udayashankar, N.K.Anodic porous alumina (APA) membranes with a uniform pore arrangement typically serve as an ideal template for formation of different types of nanostructured materials. In the present work, APA membranes were synthesized using two-step anodization in 0.3 M of oxalic and 0.3 M of sulphuric acid under the anodization potential of 40 V and 20 V respectively, at 8 °C. Alumina nanowires (ANW) were synthesized by the chemical etching of the APA membranes using phosphoric acid solution. The optical absorbance and reflectance measurements of APA membranes were performed on a spectrometer in the wavelength range of 200–600 nm. The band-gap energy (3.7 and 4.3 eV for oxalic and sulphuric acid) of APA membranes was determined from UV–visible absorption data. The photoluminescence (PL) investigations have revealed the presence of F and F+ defect centers, which could be attributes to oxygen vacancy-related defect centers in oxalic (483 and 466 nm) and sulphuric (423 and 421 nm) alumina. The mechanical properties of amorphous APA membranes were investigated by micro- and nanoindentation techniques. The results indicate that highest hardness (7.70 GPA) and Young’s modulus (138.80 GPA) for sulphuric alumina compared with oxalic alumina. In sulphuric alumina, more number of ANW were observed compared with oxalic alumina. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.Item Effect of electrolyte concentration on morphological and photoluminescence properties of free standing porous anodic alumina membranes formed in oxalic acid(Elsevier Ltd, 2020) Ramana Reddy, P.; Ajith, K.M.; Udayashankar, N.K.The free-standing porous anodic alumina membranes (AAM) were prepared in oxalic acid by varying electrolyte concentration from 0.1 to 0.9 M with a constant potential of 40 V at 8 °C. The influence of electrolyte concentration on the morphological and optical features of AAM has been studied. Regularity ratio (RR) of AAM was measured using WSxM software, highest RR obtained for AAM formed in 0.3 M. From X-ray diffraction (XRD) analysis, it was found that prepared AAM were amorphous in nature. UV–Vis absorbance spectra reveal that absorbance bands slightly moves towards the higher wavelength side with increasing electrolyte concentration. Photoluminescence (PL) of AAM has been studied and related with RR of AAM. PL measurements of AAM exhibit strong PL peak in blue region, having a slight change with increasing electrolyte concentration. PL bands were originating from two kinds of oxygen-deficient defects (F and F+), their distributions were discussed on the basis of PL spectrum. © 2019 Elsevier LtdItem Morphology and photoluminescence of nano-porous anodic alumina membranes obtained in oxalic acid at different anodization potentials(Institute of Physics, 2020) Ramana Reddy, P.; K M, A.; Udayashankar, N.K.Porous Anodic alumina (PAA) with highly ordered pore geometry serves as an ideal template for future development of nanodevices. In the present work, PAA was prepared by varying anodization potential from 10 to 50 V in oxalic acid at 8 °C with a constant electrolyte concentration of 0.3 M. The influence of anodization potential on the structural and photoluminescence (PL) properties of PAA has been studied. The effect of anodization potential on the main pore characteristics of PAA such as pore diameter, interpore distance, pore density, porosity and circularity was studied. It was observed that circularity of PAA was nearly equal to one in the case of anodization potential of 40 V. Highest regularity ratio (RR) obtained for PAA formed in 40 V and it was calculated by WSxM software. It was noticed that with increasing anodization potential there is a slight change in PL spectra of PAA and shows a strong PL peak in blue region. © 2020 The Author(s). Published by IOP Publishing Ltd