Browsing by Author "Sivasubramanian, S.C."

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Conductivity and capacitance studies of silica glass composites containing [BMIM]Br and LiCl
(IOP, 2019) Dalvi, Anshuman; Sivasubramanian, S.C.
Ionic liquid (IL) 1-butyl-3methylimidaolium bromide ([BMIM]Br) confined Li+ ion containing silica glass composites have been prepared by hydrolytic sol-gel process. The IL dispersed amorphous systems exhibit improved ionic conductivity. It has been revealed that presence of IL in a low concentration (upto 1 mol %) facilitates Li+ ion motion. Conductivity does not show any appreciable change with increasing IL content in the matrix, particularly when salt content is fixed. However, when the IL content is fixed in the matrix and salt content is gradually increased, the conductivity exhibits a monotonic rise. A maximum ionic conductivity of 4.7 × 10−7 Ω−1 cm−1 with 30 mol % LiCl and only 1 mol% IL has been observed at 523 K. Incorporation of heavy metal ions (Pb2+) in the system further enhances the conductivity marginally. Optimized compositons exhibit high capacitance values of 14.1 Fg−1 at room temperature when sandwiched between high surface area (260 m2 g−1) activated carbon electrodes. These samples exhibit good potential as solid electrolytes in solid state supercapacitor applicatons.
Dioxygen binding and activation by a highly reactive Cr(II) compound containing S,N-donors derived from o-aminothiophenol
(Taylor & Francis, 2012-08-07) Sivasubramanian, S.C.
We report the synthesis, characterization, and reactivity of a Cr(II) complex, [Cr(H2O)(LISQ)2] (1) [(LISQ)1− is o-iminothionebenzosemiquinonate(1−) π-radical], that is highly stable in solid state in the presence of air but undergoes spontaneous change in solution, both in the presence and absence of air. Physicochemical studies in solution show that a superoxo-CrIII species, [Cr(O2)(OH)(LISQ)2]− is generated initially in DMF solution of 1 in the presence of air owing to its immediate deprotonation followed by O2 binding to the deprotonated species. The formation of this superoxo-CrIII species is prominent and gradual in the presence of CH3OH, a scavenger of CrO2+ species. This Cr(O2)2+ species in turn is converted to another highly reactive O=Cr(IV) intermediate [O=Cr(OH)(LISQ)2]− which undergoes disproportionation producing an unstable O=Cr(V) species, [O=Cr(OH)(LISQ)2] and a stable Cr(III) compound, [Cr(OH)(DMF)(LISQ)2] (2). The rate of this disproportionation is enhanced in the presence of MnCl2, [N(n-Bu)4]PF6 and KSCN. The generated O=Cr(IV) species interacts with DNA with complete cleavage. The O=Cr(V) species slowly disappears from solution as revealed from EPR studies.
Electrical conductivity and thermal studies on [EMIM]BF4, Li+ and Cu2+ confined silica gel composites
(AIP, 2020-11) Dalvi, Anshuman; Sivasubramanian, S.C.
Ionic liquid ([EMIM]BF4), Li+ and Cu2+ confined silica gel of composition 33.3LiNO3-xCuCl2-1IL-(65.7- x)SiO2 have been prepared via sol gel route. Structural, thermal and electrical conductivity investigations have been carried out on these composites which reveal interesting results. X-ray diffraction patterns of the samples confirm their amorphous nature. TGA shows continuous water elimination from the as prepared composite. EPR spectrum shows existence of Cu2+ ions in the solid matrix at room temperature. Electrical conductivity of the composites increases with increase in the amount of CuCl2 in the composite as well as due to the increase in temperature. As these composites exhibit good ion conducting properties, they seem to have good potential as solid electrolytes in Li+ ion battery applications.
Imidazolium ionic liquid-tagged palladium complex: an efficient catalyst for the Heck and Suzuki reactions in aqueous media
(RSC, 2014) Kumar, Anil; Sivasubramanian, S.C.; Khungar, Bharti
An air stable, water soluble, and efficient ionic liquid-tagged Schiff base palladium complex was prepared. The synthesized complex was well characterized by NMR, mass spectrometry, FT-IR, UV-visible spectroscopy and powder X-ray diffraction. The complex was used as a catalyst for the Suzuki and Heck cross-coupling reactions in water. Good to excellent yields were achieved using a modest amount of the catalyst. In addition, the catalyst can be easily reused and recycled for six steps without much loss in activity, exhibiting an example of sustainable and green methodology
Investigations on enhanced ionic conduction in ionic liquid dispersed sol-gel derived LiTi2(PO4)3
(Elsevier, 2022-01) Dalvi, Anshuman; Sivasubramanian, S.C.
Ionic liquid dispersed Li+-Nasicon (LiTi2(PO4)3) composites have been prepared and systematically characterized. For this, the LiTi2(PO4)3 (LTP) has been synthesized by the sol-gel route to accommodate ionic liquid (IL) in a significant amount. The composite pellets exhibit nearly three orders of magnitude rise in conductivity as compared to LTP. High-temperature XRD along with TGA results suggest that these composites are stable at least up to 300 °C. The composites were also electrochemically characterized as an electrolyte in Li|LiCoO2 cells. These exhibit appreciable stability against lithium and are found to be suitable for low power devices. A mechanism for electrical transport has been proposed based on experimental evidences that suggest these composites as predominantly Li+ion conductors, and ionic liquid facilitates Li+ion transport by lowering the barriers at grain boundaries.
Ionic liquid composites with garnet-type Li6. 75Al0. 25La3Zr2O12: Stability, electrical transport, and potential for energy storage applications
(Elsevier, 2024-04) Dalvi, Anshuman; Sivasubramanian, S.C.
Garnet composites with ionic liquid dispersion have been prepared for electrolytic applications. Various ionic liquids (ILs) in small amounts were added to garnet type Li6.75Al0.25La3Zr2O12 (LALZO) to improve its ionic conductivity and electrode-electrolyte interfacial compatibility. The optimal composition having ∼6 wt% EMIM BF4 in LALZO showed a high ionic conductivity of 6 × 10-4 Ω-1cm-1 at room temperature, which is almost two orders of magnitude higher than the pristine garnet pellet. Such a high conductivity is attributed to the alteration of the ionic liquid-garnet interface by a weak non-uniform chemisorption. The thermal stability of the composites was confirmed by high-temperature X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry (DSC), and dynamic electrical transport measurements, which suggested their stability at least up to 200 °C. The electrochemical performance of the composite was evaluated by assembling 2032-type LFP//LALZO-IL//Li cell, which displayed promising candidature for energy storage applications.
Magnetic resonance lineshapes in powdered and amorphous systems
(IAS, 1986-04) Sivasubramanian, S.C.
A survey is made of the theory and applications ofEPR andNMR absorption lineshapes observed in powdered and amorphous materials. The ‘spin Hamiltonian’ and ‘resonance condition’ formalisms are reviewed, andepr andnmr lineshapes are discussed which typify the singularity characteristics in powdered materials. In the amorphous or ‘glassy’ state, the measurable spin resonance parameters often have to be viewed as being ‘randomly distributed’ according to a probability density function. Several recent probability-theory based approaches to lineshape computation for modelling the amorphous state are discussed.
A paramagnetic octahedral trans-dihydroxy chromium(IV) complex with dianionic tetradentate Schiff base salophen and crystal structure of its trans-diisothiocyanato analog
(Taylor & Francis, 2012-09-06) Sivasubramanian, S.C.
A paramagnetic octahedral trans-dihydroxychromium(IV) complex, [Cr(OH)2(salophen)] (1) (H2salophen = N,N′-bis(salicylidene)-1,2-phenylenediamine), has been synthesized and characterized by elemental analysis, magnetic moment measurement, IR, UV-Vis, and EPR spectroscopic studies. Measured room temperature (RT) magnetic moment value is 2.79 BM for 1, indicating a d2 (S = 1) system with a triplet ground state. Compound 1 exhibits powder EPR spectra at RT and LNT, which show the allowed transition ΔM s = ±1 (g = 2.0038) as well as the “forbidden” half-field transition (ΔM s = ±2) at g = 4.2080. Two successive reduction waves are observed in the cyclic voltammogram of 1 in CH3CN at −0.84 and −1.63 V (vs. Ag/AgCl), respectively. Compound 1 readily reacts with Mn2+ ion, a Cr(IV)–specific reductant and also undergoes –OH substitution reactions in solution with NCS− and imidazole. The trans-diisothiocyanato analog, [Cr(NCS)2(salophen)] (2), with μ eff = 2.80 BM has been structurally characterized by X-ray crystallography and found to contain two N-bonded axial thiocyanato ligands with slightly different axial Cr–N bond lengths (N(3)–Cr(1), 2.032(2); N(4)–Cr(1), 2.015(2) Å). Compound 2 and the corresponding Cr(III) compound K[Cr(NCS)2(salophen)] · H2O (3) show significant difference in their electronic structures as revealed from their electronic spectra.
Preparation and characterization of novel solid electrolytes based on [EMIM] BF4 and lithium nitrate confined silica gels
(Elsevier, 2019-11) Sivasubramanian, S.C.; Dalvi, Anshuman
Novel ionic liquid ([EMIM]BF4) and lithium nitrate confined silica gel composites have been prepared via hydrolytic sol-gel process and found to exhibit electrical conductivity up to 10−4 Ω−1cm−1 in the temperature range 150–300 °C. The composites are thermally stable at this temperature range and measurements are repeatable. Powder X-ray diffraction patterns suggest that the composites are amorphous in nature. FE-SEM (EDS elemental mapping) and DSC measurements further confirm IL confinement in the matrix. Electrical conductivity (150–300 °C) has been studied as a function of IL and Li+ ion content. The samples with no IL content are essentially electronic in nature. Addition of IL in small amounts (1 mol%) enhances the total conductivity at least by an order of magnitude. Further addition of salt (LiNO3) enhances ionic transport by orders of magnitude. The electronic conductivity and ionic mobility along with OCV measurements on cells of type Li/composite/LiCoO2 suggests facilitation of Li+ ion transport in presence of IL in small amount. However, further increasing the content of IL in the composition while keeping the salt ion concentration same, does not improve conductivity, rather reduces it. This complex behavior may be due to possibility of Li+ ions forming complex with IL anion and further investigations are required in this regard. Preliminary findings suggest that these materials have good potential for their applications in all-solid-state supercapacitors.
Solid-state supercapacitors using ionic liquid dispersed Li+-NASICONs as electrolytes
(Elsevier, 2022-12) Dalvi, Anshuman; Sivasubramanian, S.C.
Ceramic ionic conductors exhibit inadequate ionic conductivity for device applications. However, when added with a small amount of ionic liquid (IL), exhibit a substantial conductivity rise. This research demonstrates the use of such IL-ceramic composites, with IL content ≤ 13 wt%, for capacitor applications. These supercapacitors are designed using IL dispersed Li+ ion conducting fast ionic ceramics as an electrolyte, viz; LiTi2(PO4)3 (LTP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP). The cells are fabricated in 2032-coin cells using these composites and activated charcoal coated on the copper foil as the electrode. A typical supercapacitor containing LATP-13 wt% EMIM BF4 as electrolyte at ∼ 35 °C exhibits high specific capacitance of ∼181 F-g−1, specific energy ∼ 6.1 Wh-kg−1, and power of ∼140 W-kg−1 at 0.65 mA/cm2 (0.56 A-g−1) and 1 V. Importantly, the choice of IL (size of the ions), as well as the composition of fast ionic ceramic, influences the device performance. For a discharge at 0.56 A-g−1, a supercapacitor with this composite electrolyte exhibit stability at least up to ∼ 13,000 charge/discharge cycles with a fairly stable coulomb efficiency of ∼ 99%. At ∼ 100 °C these cells exhibit a maximum specific capacitance up to ∼ 600 F-g−1. These supercapacitors exhibit appreciable cycling performance at 30–100 °C. At higher discharge currents (≥ 0.34 A-g−1) electric double layer capacitor behavior is witnessed. A stack of two cells is able to glow a white light-emitting diode (3 V) successfully for ∼30 min.
Structural and conductivity studies on ionic liquid confined lithium silicate glasses prepared by sol-gel route
(IAEA, 2018) Dalvi, Anshuman; Sivasubramanian, S.C.
Electrical conductivity and ionic mobility measurements suggests that salt ions (probably Li+ ions) dominate the ionic transport. The cations and anions of IL do not contribute to long range migration, due to their bigger size and narrow channels/ pathways available in the glass-matrix. Studies to understand the effect of IL's counterion on conducting properties of the prepared glass composites are in progress
Synthesis and characterization of two stable paramagnetic octahedral chromium(IV) complexes with dianionic tridentate SNO donor ligands and of a chromium(III) complex with a ONO donor ligand
(Elsiever, 2008-04-01) Sivasubramanian, S.C.
Two novel paramagnetic octahedral chromium(IV) complexes with dianionic tridentate SNO donor ligands containing extended π-system have been synthesized while only a paramagnetic octahedral chromium(III) complex is obtained when a related dianionic tridentate ONO donor ligand is used under similar conditions. These bischelate complexes [Cr(abtsal)2] (1) (abtsalH2 is the Schiff base of o-aminobenzenethiol and salicylaldehyde), [Cr(4-PhTSCsal)2] · H2O (2) (4-PhTSCsalH2 is the Schiff base of 4-phenylthiosemicarbazide and salicylaldehyde) and K[Cr(sap)2] · H2O (3) (sapH2 is the tridentate Schiff base of salicylaldehyde and o-aminophenol) are characterized by elemental analyses, magnetic moment measurements, IR, UV–Vis and EPR spectroscopic studies. Compound 3 has been structurally characterized by X-ray crystallography. Measured room temperature (RT) magnetic moment values are 2.98 BM for 1 and 2.83 BM for 2 indicating a d2 system with a triplet ground state in both the cases. On the other hand, the magnetic moment value for 3 is found to be 3.74 BM at RT and is consistent with the presence of three unpaired electrons for a d3 Cr(III) ion. The magnetic moment values rule out the large spin–orbit coupling which is substantiated by the presence of RT EPR signals. Compounds 1 and 2 exhibit very similar powder EPR spectra at RT and LNT, which show the allowed transition ΔMs = ±1 (g = 2.004 for both 1 and 2) as well as the “forbidden” half-field transition (ΔMs = ±2) at g = 4.105 for 1 and g = 4.318 for 2, respectively. The X-band LNT frozen glass EPR spectrum of 1 in DMF shows the presence of zero-field split rhombic symmetry character, and results in the parameters g ≅ 2.0, D = 740 G, and E = 260 G. It suggests that the intensity of ΔMs = ±2 forbidden transition is large due to the large D value. The X-band frozen glass EPR spectrum of compound 3 in DMF is found to be very similar to that reported for trans-[Cr(py)4F2]+ in DMF–H2O–MeOH glass. The large difference (∼700 mV) in the reduction potential for the two octahedral complexes 1 (−1.40 V) and 3 (−0.70 V) is attributed to the difference in their metal ion oxidation states.
Synthesis, characterization and applications of imidazolium ionic liquid-tagged zinc(II) complex
(Elsiever, 2018) Khungar, Bharti; Nehra, Pankaj; Sivasubramanian, S.C.; Jha, Prabhat N.
A multi-functional zinc(II) complex of an imidazolium ionic liquid-tagged ligand was synthesized and characterized. The DSC and TGA analysis showed the thermal stability of the complex. The complex showed emission λmax at 368–467 nm with quantum yields up to 0.06. The time-resolved fluorescence study revealed enhancement in lifetime on complexation with zinc(II) ion indicating conformational rigidity. The complex showed good DNA cleavage, antifungal and antibacterial activities against Gram +ve and Gram −ve bacteria. The complex was found to be a good catalyst for the reaction of aromatic aldehydes and indole substrates in water to synthesize bis(indolyl)methanes.
Temperature-tolerant solid-state supercapacitors using Li+-garnet-ionic liquid composite electrolyte
(Springer, 2025-10) Sivasubramanian, S.C.; Dalvi, Anshuman
This investigation uses garnet-structured Li+ conductors added with a nominal amount of ionic liquid (IL) as an electrolyte to develop solid-state supercapacitors (SSCs) that operate across a wide temperature range from 0 to 100 ℃. A composite of LALZO (Li6.75Al0.25La3Zr2O12) with ~ 6 wt% of IL-EMIM BF4, having high conductivity ≥ 10−4 Ω−1 cm−1, is used as an electrolyte by compressing it between high surface area activated carbon (~ 1500 m2-g−1) electrodes and assembled in 2032 type cell geometry. A typical SSC at 35 °C exhibits a specific capacitance value of ~ 562 F-g−1 at 2 V/1 mA (0.57 A-g−1). Such SSCs exhibit stable performance at least up to ~ 4000 galvanostatic charge-discharge (GCD) cycles with a maintained coulombic efficiency of ~ 99%. These SSCs are found to be essentially electric double-layer type for operating voltages of ≤ 1.5 V. However, for 1.5 < V ≤ 2.5 V, pseudo-capacitive effects become significant in charge storage. A stack of four SSCs can effectively power two white LEDs (6 V) in series for about 30 min during direct discharge. The SSCs demonstrate stable GCD and CV cycles at 0 °C and 100 °C, with high performance parameters. The findings indicate that the LALZO-ionic liquid composites can be effectively utilized in high-performance, thermally stable supercapacitors.
X-ray diffraction, electron paramagnetic resonance, and electron spin echo modulation studies of the lead oxide-lead chloride-cupric chloride ternary glass system
(ACS, 1991-08-01) Sivasubramanian, S.C.
X-ray diffraction, EPR, and ESEM studies are reported for a novel ternary glass 43PbO-56PbCl2-1 CuCl2. The X-ray PDF data lead to a structural model in which octahedral building units of Cu04Cl2 are predominant. EPR spectra of the glass at X and Q bands have been fitted, by line shape simulation, to the distributed spin Hamiltonian parameters g^rnean) = 2.34, = 0.03, gx(mean) = 2.06, ± = 0.008, p = 0.95, /4,(mean) = 131.1 X 10"4 cm"1, and /4x(mean) = 5.8 X 10"4 cm"1. These data suggest a distribution of bonding geometries for Cu2+ in the glass structure, with the above-mentioned elongated octahedral Cu04Cl2 dominating. ESEM results suggest that Cu2+ may be surrounded by four Pb2+ in the second coordination shell at a distance of 3.8 Á.
X-ray diffraction, electron paramagnetic resonance, and electron spin echo modulation studies of the lead oxide-lead chloride-cupric chloride ternary glass system
(ACS, 1991-08-01) Sivasubramanian, S.C.
X-ray diffraction, EPR, and ESEM studies are reported for a novel ternary glass 43PbO-56PbCl2-1 CuCl2. The X-ray PDF data lead to a structural model in which octahedral building units of Cu04Cl2 are predominant. EPR spectra of the glass at X and Q bands have been fitted, by line shape simulation, to the distributed spin Hamiltonian parameters g^rnean) = 2.34, = 0.03, gx(mean) = 2.06, ± = 0.008, p = 0.95, /4,(mean) = 131.1 X 10"4 cm"1, and /4x(mean) = 5.8 X 10"4 cm"1. These data suggest a distribution of bonding geometries for Cu2+ in the glass structure, with the above-mentioned elongated octahedral Cu04Cl2 dominating. ESEM results suggest that Cu2+ may be surrounded by four Pb2+ in the second coordination shell at a distance of 3.8 Á