Faculty Publications
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Item Fabrication, characterization and catalytic activity of ?-MnO2 nanowires for dye degradation of reactive black 5(Elsevier B.V., 2016) Ramesh, M.; Nagaraja, H.S.; Rao, M.P.; Anandan, S.; Huang, N.M.?-MnO2 nanowires (NWs) prepared by hydrothermal method are characterized using XRD and FT-IR. The crystallite size, surface area of NWs increases, whereas dislocation density and band gap decreases with an increase in oxidizer molarity. The band gap decreases from 2.55 to 1.27 eV. The above observations correlate well with the enhanced catalytic activity of MnO2 NWs for degradation of azo dye reactive black 5 (RB5). About 70% of the dye were successfully removed in 60 min using 20 mg of MnO2 NWs in the presence of 6 mL of H2O2. MnO2 NWs show a good reusability, suggesting it as an effective and recyclable catalyst. © 2016 Elsevier B.V. All rights reserved.Item rGO/MnO2 nanowires for ultrasonic-combined Fenton assisted efficient degradation of Reactive Black 5(IWA Publishing 12 Caxton Street London SW1H 0QS, 2017) Ramesh, M.; Rao, M.P.; Rossignol, F.; Nagaraja, H.S.Reduced graphene oxide (rGO) coated manganese dioxide (MnO2) nanowires (NWs) were prepared by the hydrothermal method. Raman spectra confirmed the presence of rGO and the Brunauer-Emmett-Teller surface area of rGO/MnO2 NWs was found to be 59.1 m2g-1. The physico-chemical properties of prepared catalysts for the degradation of Reactive Black 5 (RB5) dye were investigated. 84% of RB5 dye in hydrogen peroxide solution was successfully degraded using rGO/MnO2 NWs, while only 63% was successfully degraded with pristine ?-MnO2 NWs in 60 min owing to the smaller crystallite size and large surface area. Further, the ultrasonic-combined Fenton process significantly enhanced the degradation rate to 95% of RB5 by the catalyst rGO/MnO2 NWs due to synergistic effects. The decomposition products identified using gas chromatography-mass spectrometry revealed a higher production rate of fragments in the ultrasonic-combined Fenton process. Therefore, rGO/MnO2 NWs with the ultrasonic-combined Fenton process is an efficient catalyst for the degradation of RB5, and may be used for environmental protection. © IWA Publishing 2017.Item Nickel selenide nanostructures as an electrocatalyst for hydrogen evolution reaction(Elsevier Ltd, 2018) Bhat, K.S.; Nagaraja, H.S.Electrochemical water splitting has gained momentum for the development of alternative energy sources. Herein, we report the synthesis of two different nickel selenide nanostructures of different morphology and composition employing hydrothermal method. NiSe2 nanosheets were obtained by the anion-exchange reaction of Ni(OH)2 with Se ions for 15 h. On the other hand, NiSe nanoflakes were synthesized by the direct selenization of nickel surface with the reaction time of 2 h. Tested as an electrocatalyst for hydrogen evolution reaction, NiSe2 nanosheets and NiSe nanoflakes can afford a geometric current density of 10 mA cm?2 at an overpotential of 198 mV and 217 mV respectively. The measured Tafel slope values of NiSe nanoflakes are 28.6 mV dec?1, which is three times lower as compared with NiSe2 nanosheets (72.1 mV dec?1). These results indicates the HER kinetics of NiSe nanoflakes are at par with the state-of-the-art Pt/C catalyst and also complimented with the short synthesis time of 2 h. Further, both nickel selenides exhibit ultra-long term stability for 30 h as evident from constant current chronopotentiometry and electrochemical impedance spectroscopy results. © 2018 Hydrogen Energy Publications LLCItem Influence of cations on the dielectric properties of spinel structured nanoferrites(Institute of Physics Publishing helen.craven@iop.org, 2019) Bindu, K.; Ajith, K.M.; Nagaraja, H.S.MFe2O4 (M: Fe, Zn, Ni and Sn) nanoparticles were prepared using single step hydrothermal method. Their structural, compositional and dielectric properties have been studied to investigate the effect of cations on spinel ferrites. XRD confirms the spinel structure of the samples with substitution of Zn, Ni and Sn in the lattice sites of Fe. FTIR spectra of all samples have characteristic ?1 and ?2 bands. SEM and EDS mapping show uniform distribution of cations throughout the samples. ZnFe2O4 and SnFe2O4 have higher ac conductivity and dielectric constant than that of Fe3O4 and NiFe2O4, which can be attributed to the different cationic distribution in the spinel structure. © 2019 IOP Publishing Ltd.Item Effect of isoelectronic tungsten doping on molybdenum selenide nanostructures and their graphene hybrids for supercapacitors(Elsevier Ltd, 2019) Bhat, K.S.; Nagaraja, H.S.Electrochemical supercapacitors are vital for the advancement of energy storage devices. Herein, we report the synthesis of molybdenum selenide (MoSe 2 ), tungsten-doped molybdenum selenide (W–MoSe 2 ) and their graphene (G) composites (W–MoSe 2 /G) via a facile hydrothermal method. Physiochemical properties of the as-synthesized samples are examined using X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy measurements. Used as working electrodes for supercapacitors, MoSe 2 nanostructures could deliver the specific capacitance of 106 F g ?1 at 2 mV s ?1 scan rate. Further, doping with tungsten (W) demonstrates the variation of specific capacitances with 2 M % of tungsten as the optimum doping amount, delivering the maximum specific capacitance of 147 F g ?1 . Furthermore, graphene composites of these nanostructures deliver the enhanced specific capacitances of 248 F g ?1 and complimented with excellent capacitance retention capability of 102% for 20000 cycles. © 2019 Elsevier LtdItem Modulations of physio-chemical and electronic properties of metalorganic KHO single crystals through Co(OH)2 nanoparticles doping(Springer New York LLC barbara.b.bertram@gsk.com, 2019) Mahendra, K.; Bhat, K.S.; Nagaraja, H.S.; Udayashankar, N.K.Semiorganic crystals play vital role in the design and development of optical devices. In this context, we report the synthesis of metalorganic potassium hydrogen oxalate oxalic acid dihydrate (KHO) single crystals using slow solvent evaporation technique. Further, Co(OH)2 nanoparticles pre-synthesized using hydrothermal method are doped to KHO single crystals. Doping of Co(OH)2 nanoparticles in the crystal system were confirmed through XRD, EDAX and PL measurements. The XRD measurements indicate a shift in the peak positions and variation in the overall intensities. On the other hand, PL measurements also indicate enhanced emission peaks confirming the successful doping of Co(OH)2 nanoparticles in the KHO system. As the effect of doping, the declination in the optical bandgap and improvement of electronic conductivity were also observed. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Item Enhanced Electrochemical Performance of Low-Content Graphene Oxide in Porous Co3O4 Microsheets for Dual Applications of Lithium-Ion Battery Anode and Lithium-Ion Capacitor(Springer, 2024) Lakshmi Sagar, G.; Brijesh, K.; Mukesh, P.; Amudha, A.; Bhat, K.S.; Nagaraja, H.S.The enhancement of electrochemical performance in lithium-ion battery (LIB) anode materials through nanostructures is of paramount importance, facilitated by the synergistic integration of these unique architectures with active materials, which increases the availability of active sites and decreases the diffusion path for lithium ions. In this investigation, we successfully synthesized cobalt oxide (Co3O4) microsheets composed of small nanoparticles (measuring 28–33 nm), employing a straightforward hydrothermal process followed by annealing. Furthermore, to enhance the composite’s ability to endure volume changes and increase its electrical conductivity, we created a Co3O4/reduced graphene oxide (rGO) composite embedding a judicious amount of graphene oxide (GO). This engineered composite exhibited remarkable specific discharge capacity of 1081 mAh g−1 at 100 mA g−1, a substantial improvement over the pristine material’s capacity of 718 mAh g−1. The composite demonstrated reduced irreversible capacity loss relative to the pristine counterpart and approached a reversible capacity of nearly 99%. Even after 400 cycles under the demanding conditions of high current density of 500 mA g−1, the composite managed to retain 81% of its initial capacity, underscoring its exceptional cycling stability. Moreover, the application of the Co3O4/rGO//carbon black (CB) assembly in lithium-ion capacitors (LIC) yielded notable energy density of 15.6 Wh kg−1 at elevated power density of 1007 W kg−1. These LIC devices demonstrated robust cyclic stability across extended cycles, sustaining 56% of their initial capacity after 2000 cycles while operating at a current density of 2 A g−1. Graphical Abstract: [Figure not available: see fulltext.]. © 2024, The Minerals, Metals & Materials Society.Item Synergistic boost in Fe3O4 anode performance for li-ion batteries via Zn and Cu double doping and multi-walled carbon nanotube composite integration(Elsevier B.V., 2024) Kumar, A.; Mukesh, P.; Lakshmi Sagar, G.; Hegde, A.; Nagaraja, H.S.In this study, a novel nanocomposite material comprising pure Fe3O4 (FO), doped Zn0.5Cu0.5Fe2O4-3 (ZCFO-3), and Zn0.5Cu0.5Fe2O4-3@ Multi-walled carbon nanotube (ZCFO-3@MWCNT) nanocomposite material is carefully prepared using a simple one-step hydrothermal process. Comprehensive surface and morphological analysis are conducted using X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and High-resolution transmission electron microscopy (HRTEM), while compositional studies are investigated through Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The electrochemical performance is fully analyzed through Cyclic voltammetry (CV), Electrochemical impedance spectroscopy (EIS), rate capability tests, discharge/charge capacity, and cyclic stability evaluations. Among these three nanomaterials, ZCFO-3@MWCNT nanocomposite at 100 mA g−1 current density reveals the best performance, with a discharge capacity of 1974 mAh g–1, ZCFO-3 and FO reveal 1340 mAh g–1 and 1317 mAh g–1 respectively. After 800 cycles at 500 mA g−1 current density, ZCFO-3@MWCNT stays strong with a discharge capacity of 646 mAh g–1, while ZCFO-3 manages only 362 mAh g–1 and FO only 111 mAh g–1. After 1200 cycles at 500 mA g−1, the nanocomposite still delivers 518 mAh g–1. This study suggests that ZCFO-3@MWCNT could be a promising anode material for lithium-ion batteries. © 2024 Elsevier B.V.Item Reinforcing NiO microsphere structural stability via amorphous carbon sheets obtained from waste milk for lithium-ion capacitor application(Springer Science and Business Media B.V., 2025) Lakshmi Sagar, G.; Brijesh, K.; Mukesh, P.; Hegde, A.P.; Kumar, A.; Paliwal, A.; Bhat, K.S.; Nagaraja, H.S.In the pursuit of sustainable chemistry and environmentally friendly energy storage, the study addressed the limitations of nickel oxide utilized as the active material for the anode in lithium-ion capacitors. Despite its abundance and favorable environmental properties, NiO suffered from significant volumetric expansion and slow electrochemical kinetics compared to carbon materials. To overcome these issues, amorphous carbon was extracted from spoiled waste milk through a simple combustion process, effectively converting biomass waste into renewable resources. The engineered NiO/amorphous carbon composite, synthesized through hydrothermal and annealing processes, mitigated the limitations of NiO. Field Emission Scanning Electron Microscopy confirmed the deposition of amorphous carbon sheets encasing NiO microspheres, which preserved structural integrity during electrochemical cycling. The amorphous carbon acted as a stabilizing matrix, encapsulating NiO microspheres to mitigate volumetric expansion and enhance lithium-ion transport kinetics. Electrochemical tests demonstrated a specific discharge capacity of 1230 mAh g?1 at a current density of 100 mA g?1, retaining 401 mAh g?1 after 1000 cycles at 1 A g?1, nearly doubling the retention performance of pristine NiO. Furthermore, the NiO/AC//AC lithium-ion capacitor achieved an energy density of 25.4 Wh kg?1 at a power density of 1991 W kg?1, maintaining 96% capacity after 3500 cycles. This study highlighted the potential of waste-derived carbon in developing high-performance, sustainable energy storage systems. © The Author(s), under exclusive licence to Springer Nature B.V. 2025.