Faculty Publications

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Author: search.filters.author.Udayashankar, N.K.Subject: search.filters.subject.Hydrogen

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    Gamma irradiation effect on structural, optical and electrical properties of organometallic potassium hydrogen oxalate oxalic acid dihydrate single crystal
    (Springer New York LLC barbara.b.bertram@gsk.com, 2018) Mahendra, K.; Nayak, K.K.; Fernandes, B.J.; Udayashankar, N.K.
    Potassium oxalate oxalic acid dihydrate (KHO) single crystals were grown from solvent evaporation technique at room temperature. Crystals were optically characterized using UV–Vis and photoluminescence analysis. The gamma irradiation effects on KHO crystals were also studied optically and the results were analyzed to compare the effect of irradiation on the crystal lattice for different dosage. Structural variations were studied using powder XRD, FTIR and the results were examined to study the defect states created inside the lattice due to irradiation and the effect on the functional vibrations of the host crystal. Surface morphology of the crystal was studied using scanning electron microscope (SEM). Photo conductivity of the synthesized crystals were studied and analyzed to compare the photo response as well as the conductivity of the materials when subjected to irradiation. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
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    Growth and comparative studies on oxalic acid dihydrate, potassium oxalate hydrate and potassium hydrogen oxalate oxalic acid dihydrate single crystals
    (Elsevier Ltd, 2020) Mahendra, K.; Udayashankar, N.K.
    Single crystals of Oxalic acid dihydrate (OAD), Potassium oxalate hydrate (KOH), Potassium hydrogen oxalate oxalic acid dihydrate (KHOOD) were grown using solvent evaporation technique. Unit cell parameters of the crystals were studied using single crystal XRD (SCXRD) and the crystal parameters were found to match with the reported values. Structural properties were studied using powder XRD analysis. Optical absorption studies were carried out to determine the light absorption by the crystal and the optical bandgap was also calculated using Tauc's relation. Emission and thermal properties of the OAD, KOH and KHOOD crystals were studied using photoluminescence spectroscopy (PL) and TGA-DTA measurements respectively and explained in detail. Electrical studies were also carried out to find the resistivity of the material. The hardness of the synthesized crystal was also explored and the parameters such as stiffness constant, yield strength, fracture toughness and brittleness were evaluated and compared. © 2019 Elsevier Ltd
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    Investigation on mechanical and temperature dependent electrical properties of potassium hydrogen oxalate oxalic acid dihydrate single crystal
    (Elsevier B.V., 2020) Mahendra, K.; Udayashankar, N.K.
    The potassium hydrogen oxalate oxalic acid dihydrate (KHOOD) single crystals were grown using solvent evaporation technique. The mechanical hardness of grown KHOOD single crystal was performed using Vickers microhardness tester and investigated for different loads starting from 10 g to 100 g and it was decided to include under hard material category. The mechanical parameters such as elastic stiffness and yield strength were calculated and discussed in detail. Temperature dependent I-V, dielectric studies were performed and explained in detail. © 2020 Elsevier B.V.
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    A novel approach to the synthesis of semiorganic ammonium hydrogen oxalate oxalic acid dihydrate single crystal and its characterization
    (Springer Science and Business Media B.V., 2021) Mahendra, K.; Fernandes, J.M.; Udayashankar, N.K.
    A different approach used in the synthesis of ammonium hydrogen oxalate oxalic acid dihydrate (NH4H3(C4O8)·2H2O) single crystals is presented. The crystals are synthesized using solvent evaporation technique. The analysis of the synthesized NH4H3(C4O8)·2H2O single crystals has been carried out through measurements such as single-crystal X-ray diffraction (SCXRD), powder XRD, UV–Vis and photoluminescence spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis (TG–DTA), Vickers microhardness measurements and current versus voltage (I–V) characteristics. The evaluation of the molecular structure of the crystals using SCXRD shows that they belong to the triclinic crystal system with space group P-1. The structural properties of the crystals are also evaluated using powder XRD measurements on their finely crushed powder. These measurements corroborate the results of SCXRD and confirm the triclinic system of the crystals. The optical properties like absorbance and emission of these crystals are determined using UV–Vis and photoluminescence spectroscopy, respectively. These measurements show that the crystals exhibit substantial emission in the blue region. The thermal stability and the decomposition mechanism of the crystals is studied using TG–DTA analysis. The mechanical strength of the crystals is determined using Vickers microhardness technique. The photoresponse of the NH4H3(C4O8)·2H2O crystals is analyzed from light-dependent I–V characteristics, and it is observed that the crystals exhibit photoresistive behavior. © 2020, Akadémiai Kiadó, Budapest, Hungary.
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    Defect-induced measurements of semi-organic ammonium hydrogen oxalate oxalic acid dihydrate single crystals using gamma irradiation
    (Taylor and Francis Ltd., 2022) Mahendra, K.; Maria Fernandes, J.; Udayashankar, N.K.
    The structural, optical, mechanical and electrical properties of pure and 5—20-kGy gamma-irradiated semi-organic single crystals of ammonium hydrogen oxalate oxalic acid dihydrate (NH4H3(C4O8).2H2O) are presented. The crystals were synthesized at room temperature using facile solvent evaporation technique. Powder XRD measurements indicate gradual enhancement in crystallinity and lattice defect annihilation for low radiation dosage. Radiation-induced increase in optical band gap (4.01–4.16 eV) indicates high damage threshold of the crystals. Quenching of photoluminescence is attributed to the lowering of surface defect density with radiation. The influence of gamma radiation on the functional vibrations of the crystals is studied using FTIR-Raman spectroscopy. Vickers microhardness measurements show gradual enhancement in crystal hardness with the increase in radiation. An increase in forward resistance with irradiation is observed from I–V measurements and is attributed to high transparency of the crystals. These results indicate the viability of NH4H3(C4O8) 2H2O crystals in potential space optoelectronic applications. © 2022 Informa UK Limited, trading as Taylor & Francis Group.
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    Systematic investigation and comparison of oxalic acid dihydrate, ammonium oxalate hydrate and ammonium hydrogen oxalate oxalic acid dihydrate single crystals
    (Elsevier Ltd, 2023) Mahendra, K.; Fernandes, B.J.; Pattar, J.; Pujar, S.; Nagaraja, B.S.; Ramesh, K.P.; Udayashankar, N.K.
    Semiorganic crystals are hybrid materials that have captured the interest of researchers due to their improved material characteristics and applications. In the current work, single crystals of oxalic acid dihydrate (OAD), Ammonium oxalate hydrate (AHO), and Ammonium hydrogen oxalate oxalic acid dihydrate (AHOOD) were grown using a slow evaporation method. Single crystal and powder XRD measurements were carried out to elucidate their unit cell parameters, crystal system, and structural information. To comprehend the interplay of light and matter, optical investigations like UV–Vis Spectroscopy and photoluminescence studies were performed. Interaction of ammonium with oxalic acid, and thus formed crystals, was investigated using impedance spectroscopy. Detailed dielectric parameters such as dielectric constant, dielectric loss, impedance, conductivity, and electric modulus were explored as a function of frequency. Vickers hardness test was used to calculate the hardness, Meyer's number, brittleness, and fracture toughness. The crystals were determined to be of the hard materials group. © 2022 Elsevier B.V.
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    Cu- and Bi-codoped LaFeO3-Decorated MXene Nanosheets for Photo-Fenton Catalysis and Hydrogen Evolution
    (American Chemical Society, 2025) James, A.; Ray, S.; Rodney, J.D.; Carva, K.; Udayashankar, N.K.; Kim, B.C.
    The increasing release of contaminants into the environment and the demand for sustainable energy solutions have prompted the exploration of advanced oxidation methods such as photo-Fenton and photoelectrochemical water splitting. Herein, hierarchical heterostructures of Cu- and Bi-codoped LaFeO3(Bi0.05La0.95Cu0.1Fe0.9O3) (LFOBC)-decorated Ti3C2(MXene) nanosheets were developed by a low-cost one-pot combustion approach. The optimized LFOBC/Mx-7 (Bi0.05La0.95Cu0.1Fe0.9O3/Ti3C2-7) composite demonstrated superior photo-Fenton degradation of tetracycline (TC), achieving 1.69 times higher efficiency than LFOBC and 10.65 times more efficiency than pristine LaFeO3(LFO). This enhanced performance is attributed to strong interfacial coupling, which suppressed photoexcited carrier recombination, as confirmed by PL, TRPL, EIS, and photocurrent studies. Experimental and theoretical work function analyses revealed band bending and the formation of an Ohmic junction at the interface. Furthermore, a degradation mechanism and a reaction pathway were proposed, and the reduction in toxicity levels was identified. The LFOBC/Mx-7 catalyst also exhibited promising results for H2evolution with an overpotential of 156 mV vs RHE under visible-light illumination, which was 2.37 times less than that of LFOBC. These results, therefore, showcase the LFOBC/Mx composite as a multifunctional photocatalyst for both pollutant degradation and sustainable energy generation. © 2025 American Chemical Society