Journal Articles
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Item Highly efficient catalytic reductive degradation of various organic dyes by Au/CeO2-TiO2 nano-hybrid(Springer India sanjiv.goswami@springer.co.in, 2017) Saikia, P.; Miah, A.T.; Das, P.P.Highly improved catalytic reductive degradation of different organic dyes, in the presence of excess NaBH4 over Au/CeO2-TiO2 nano-hybrid as the catalyst is reported in this study. CeO2-TiO2 nanocomposite was prepared by a facile co-precipitation method using ultra-high dilute aqueous solutions. Small amount of Au (only 1 wt%) was loaded onto the nanocomposite material by deposition-precipitation with urea (DPU) method to fabricate the ternary Au/CeO2-TiO2 nano-hybrid. The catalysts were characterized by the representative techniques like XRD, BET surface area, ICP-AES, UV-Vis diffuse reflectance spectroscopy, TEM and XPS. The Au/CeO2-TiO2 nano-hybrid along with NaBH4 exhibited remarkable catalytic activities towards all the probed dyes, namely Methylene Blue, Methyl Orange, Congo Red, Rhodamine B and Malachite Green, with a degradation efficiency of ?100% in a short reaction time. The degradation reaction followed pseudo-first-order kinetics with respect to the concentration of the dye. Different parameters that affect the rate of the reaction are discussed. A plausible mechanism for methylene blue degradation has also been proposed. [Figure not available: see fulltext.] © 2017, Indian Academy of Sciences.Item Dependence of the 0.5 × (2e2/h) conductance plateau on the aspect ratio of InAs quantum point contacts with in-plane side gates(American Institute of Physics Inc. subs@aip.org, 2017) Das, P.P.; Jones, A.; Cahay, M.; Kalita, S.; Mal, S.S.; Sterin, N.S.; Yadunath, T.R.; Advaitha, M.; Herbert, S.T.The observation of a 0.5 × (2e2/h) conductance plateau in asymmetrically biased quantum point contacts (QPCs) with in-plane side gates (SGs) has been attributed to the onset of spin-polarized current through these structures. For InAs QPCs with the same width but a longer channel length, there is roughly a fourfold increase in the range of common sweep voltage applied to the SGs over which the 0.5 × (2e2/h) plateau is observed when the QPC aspect ratio (ratio of length over the width of the narrow portion of the structure) is increased by a factor 3. Non-equilibrium Green's function simulations indicate that the increase in the size of the 0.5 × (2e2/h) plateau is due to an increased importance, over a larger range of common sweep voltage, of the effects of electron-electron interactions in QPC devices with a larger aspect ratio. The use of asymmetrically biased QPCs with in-plane SGs and large aspect ratio could therefore pave the way to build robust spin injectors and detectors for the successful implementation of spin field effect transistors. © 2017 Author(s).Item Graphene-mediated band gap engineering of WO3 nanoparticle and a relook at Tauc equation for band gap evaluation(Springer Verlag service@springer.de, 2018) Baishya, K.; Ray, J.S.; Dutta, P.; Das, P.P.; Das, S.K.Engineering the band gap of semiconductors is often crucial in the quest for developing new and advanced technologies. In this report, the implication of graphene on the band gap optimization of tungsten trioxide (WO3) is discussed. Simple one-step sol–gel process was followed to anchor WO3 nanoparticles in graphene. Graphene induces a redshift in the band gap of WO3. Band gap narrowing of 6.60% is observed for 7 wt% graphene-tethered WO3. Interestingly, a profound difference is observed in estimating the band gap energy values following the usual Tauc equation. Our observation suggests that the differential form of Tauc equation is better suited to determine the band gap energy of inorganic semiconductors than the typical extrapolation method. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.Item Capacitance and impedance spectroscopy studies of polymer light emitting diodes based on MEH-PPV:BT blends(Elsevier Ltd, 2019) K M, N.K.; Sterin, N.S.; Das, P.P.; Umesh, G.; Satyanarayan, M.N.Light emitting polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is blended with a wide bandgap electron transport material benzothiadiazole (BT) and its effect on the electronic properties has been studied by capacitance and impedance spectroscopy (IS) in PLEDs. The impedance data is fitted using equivalent circuit models and the minimum parallel resistance (Rp) at zero bias have been obtained for 1:3 ratio of MEH-PPV:BT blended devices. The negative capacitance (NC) shows the occurrence of the trap-assisted non-radiative recombination mechanism at low frequencies in the unblended MEH-PPV PLEDs. Further, this behavior is seen to be reduced in PLEDs with MEH-PPV:BT blends. This clearly suggests that the blending of MEH-PPV and BT at different weight ratios results in the suppression of trap-assisted recombination. This can be attributed to the elimination of trap states due to the dilution of semiconductor material on account of the addition of wide bandgap host material. Moreover, the blended devices have shown a significant improvement in the conductivity at small bias voltages. © 2019 Elsevier B.V.Item Width dependence of the 0.5 × (2e2/h) conductance plateau in InAs quantum point contacts in presence of lateral spin-orbit coupling(Nature Publishing Group Houndmills Basingstoke, Hampshire RG21 6XS, 2019) Das, P.P.; Cahay, M.; Kalita, S.; Mal, S.S.; Jha, A.K.The evolution of the 0.5Go (Go = 2e2/h) conductance plateau and the accompanying hysteresis loop in a series of asymmetrically biased InAs based quantum point contacts (QPCs) in the presence of lateral spin-orbit coupling (LSOC) is studied using a number of QPCs with varying lithographic channel width but fixed channel length. It is found that the size of the hysteresis loops is larger for QPCs of smaller aspect ratio (QPC channel width/length) and gradually disappears as their aspect ratio increases. The physical mechanisms responsible for a decrease in size of the hysteresis loops for QPCs with increasing aspect ratio are: (1) multimode transport in QPCs with larger channel width leading to spin-flip scattering events due to both remote impurities in the doping layer of the heterostructure and surface roughness and impurity (dangling bond) scattering on the sidewalls of the narrow portion of the QPC, and (2) an increase in carrier density resulting in a screening of the electron-electron interactions in the QPC channel. Both effects lead to a progressive disappearance of the net spin polarization in the QPC channel and an accompanying reduction in the size of the hysteresis loops as the lithographic width of the QPC channel increases. © 2019, The Author(s).Item Improved electrochemical performance of graphene oxide supported vanadomanganate (IV) nanohybrid electrode material for supercapacitors(Elsevier Ltd, 2020) Kumari, S.; Maity, S.; Anandan Vannathan, A.A.; Shee, D.; Das, P.P.; Mal, S.S.Graphene oxide (GO)-supported polyoxometalates (POMs) have been considered as promising electrode materials for energy storage applications due to their ability to undergo fast and reversible redox reactions. Herein, vanadomanganate-GO composites (K7MnIVV13O38.18H2O-GO with 2:1 and 4:1 ratio) were investigated for use as potential electrode materials in supercapacitors (SCs). The K7MnIVV13O38.18H2O (MnV13) was synthesized and anchored on GO through electron transfer interaction and electrostatic interaction to make the composite electrodes for the present study. All synthesized electrode materials were fully characterized by various techniques, e.g., Fourier Transform Infrared (FTIR) Spectroscopy, Powder X-ray Diffraction (XRD), Scanning Electron Microscopy/Energy Dispersive X-ray Spectroscopy (SEM/EDS) and High Resolution-Transmission Electron Microscopy (HR-TEM). The electrochemical properties of MnV13/GO composites with different MnV13/GO ratios were investigated by two-electrode cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) in different electrolytes. The MnV13/GO composite of ratio 2:1 in 1 M LiCl electrolyte and that of ratio 4:1 in 1 M Na2SO4 electrolyte showed significant specific capacitance values of 269.15 F/g and 387.02 F/g, respectively and energy density of 37.38 Wh/kg and 53.75 Wh/kg, respectively for a scan rate of 5 mV/s. Interestingly, the 1:1 (MnV13/GO) composite in 1 M Na2SO4 and 1 M LiCl electrolytes showed very low specific capacitance values as the deposition of MnV13 on GO was not sufficient, as indicated by FTIR and SEM. Thus, it is evident that the specific capacitance value of these composite materials depends on the amount of MnV13 deposited on GO and these composite materials exhibit the potential to improve the performance of GO-based SCs. © 2019Item Redox-Active Vanadium-Based Polyoxometalate as an Active Element in Resistive Switching Based Nonvolatile Molecular Memory(Wiley-VCH Verlag info@wiley-vch.de, 2020) Sterin, N.S.; Basu, N.; Cahay, M.; Satyanarayan, M.N.; Mal, S.S.; Das, P.P.Resistive switching (RS)-based random access memory has been envisaged as a viable alternative to existing memory technology due to its nonvolatility, high switching speed, high endurance/retention, and considerably low operating voltage. Herein, a new uniform, repetitive, and stable RS phenomenon is demonstrated based on very low-cost two-terminal metal–insulator–metal stack fabricated using a highly redox-active vanadium-based polyoxometalate (POM) molecular clusters, [V10O28]6?—belonging to polyoxovanadate (POV) family. The RS is observed to be unipolar and nonvolatile in nature, and occur at a fairly low operating bias voltage (less than 2 V), making it suitable for low-power operations. The switching event is attributed to the cycling between formation and rupture of tiny conductive nanofilaments formed due to trapping and detrapping of positively charged ionized oxygen vacancy sites present in the active switching layer of [V10O28]6?. POMs, in their rich abundance, are highly stable early transition-metal oxide nanosized clusters, capable of storing as well as releasing a large number of electrons. In addition, they can undergo fast and reversible redox reactions (both in solid and liquid electrolyte media) in “stepwise” manner—a property that makes them a promising candidate for ultrafast and multi-level nonvolatile molecular memory for high-density data storage. Preliminary investigations on the POV-based memory cells result in device resistance ratio ?25, endurance for more than 200 cycles, and stable retention time around 2200 s, in fully open air condition. © 2020 Wiley-VCH GmbHItem Ultra-broadband fabrication-tolerant mode division (de)multiplexer on thin film Lithium niobate(Elsevier B.V., 2020) Kaushalram, A.; T.r, Y.; Das, P.P.; Hegde, G.; Srinivas, S.Mode division (de) multiplexers based on asymmetric directional coupler are designed and analysed on the emerging thin film lithium niobate platform in rib, buried and strip waveguide configurations. Rib configuration offers a large bandwidth of ?215 nm with a crosstalk level lower than ?10 dB, and provides a large fabrication tolerance of ±50 nm. Strip configuration exhibits a better crosstalk of ?19.7 dB at the design wavelength of 1550 nm, and has a reasonable fabrication tolerance of ±30 nm. Performance of (de) multiplexers on all three waveguide configurations are analysed in terms of modal crosstalk, mode conversion efficiency, bandwidth, along with fabrication tolerance to width and sidewall angle. The influence of electro-optic effect on the coupling length of lithium niobate mode multiplexers is also investigated. © 2020 Elsevier B.V.Item In situ vanadophosphomolybdate impregnated into conducting polypyrrole for supercapacitor(Elsevier Ltd, 2020) Anandan Vannathan, A.A.; Maity, S.; Kella, T.; Shee, D.; Das, P.P.; Mal, S.S.The fast modernization and advancement in lifestyle increase the consumption of power daily due to all innovative technologies, e.g., hybrid vehicles, solar cells, smart power grid, communication devices, artificial hearts, etc. Conducting organic polymer-based energy storage devices had attracted much attention due to the conductive nature for a long time. However, its application has been restricted because of swelling and shrinking capability during the charge and discharge cycle. The combination of redox-active inorganic metal oxides, such as polyoxometalates (multi-metal oxide cluster) with conduction polymers, could enhance the material's stability due to its fast multi-electron redox property. Here, we report the two polypyrroles combined vanadophosphomolybdates, namely PPy-H4[PVMo11O40] and PPy-H5[PV2Mo10O40] nanohybrid electrode materials. The PPy-H5[PV2Mo10O40] electrode material behaves as pseudocapacitance and can deliver an excellent capacitance of 561.1 F/g in 0.1 M H2SO4 electrolyte solution at a 0.2 A/g current density, indicating capacitive composite material. The electrochemical impedance spectroscopy (EIS) reveals that PPy-H5[PV2Mo10O40] is more capacitive than PPy-H4[PVMo11O40] and PPy with equivalent series resistance (ESR) of 5.74 ?. The cell capacitance of PPy-H5[PV2Mo10O40] and PPy-H4[PVMo11O40] are found to be 5.38 and 9.15 mF, stipulating in small SC cell application. Likewise, the PPy-H5[PV2Mo10O40] nanohybrid electrode shows better responsive behavior with a relaxation time of 0.16 ms. Furthermore, the PPy-H5[PV2Mo10O40] electrode exhibits outstanding cycle stability, retaining ~95% of its capacitance after 4500 cycles as compare to PPy-H4[PVMo11O40] (~91%) electrode. © 2020Item Enhanced Power Density of Graphene Oxide–Phosphotetradecavanadate Nanohybrid for Supercapacitor Electrode(Springer, 2021) Maity, S.; Anandan Vannathan, A.A.; Kumar, K.; Das, P.P.; Mal, S.S.Successful exploration of supercapacitor (SC) material to integrate with high energy and high power density storage device still remains a daunting challenge. Conducting carbon nanostructures have been primarily used for this purpose; however, most of their surface area remains unutilized throughout the storage process. Herein, a new type of hybrid material has been reported by effectively using active sides of carbon nanostructures. Insertion of faradaic-type polyoxometalates (POMs), namely phosphotetradecavanadate (Na7[H2PV14O42], hereafter described as PV14), into the graphene oxide (GO) matrix creates a novel hybrid material for SC applications. Owing to the formation of nanohybrid, it can store charges both electrostatically and electrochemically. PV14/GO composite’s electrochemical behavior in different electrolyte (acidic/neutral) solutions shows different types of characteristics. The PV14/GO composite as a working electrode exhibits a high galvanostatic capacitance of 139 F/g while maintaining at a power density of 97.94 W/kg in 0.25 M H2SO4 electrolyte. The specific energy density was also found out to be around 56.58 Wh/kg at a 5 mV/s scan rate for the same electrolyte. Furthermore, in 1 M Na2SO4 solution, PV14/GO composite demonstrates a specific capacitance of 85.4 F/g at a scan rate of 5 mV/s. The equivalent series resistance for the device was found to be approximately 0.51 ? with a circuit resistance of 3.881 ?, using electrochemical impedance spectroscopy. The cell capacitance, employing the Nyquist plot, was calculated to be around 2.78 mF. © 2021, ASM International.
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