Sharma, Rakesh Kumar

Graphitic carbon is the ultimate source of carbon electrodes for practical application in energy storage devices as it is commercially available at a much lower cost in contrast to other forms of nanostructured carbon. Recently, fluorinated carbon with improved electrical conductivity and wettability has been found to possess better and efficient electrochemical storage properties. However, the development of a simple fluorination process is still a challenge. Herein, Selectfluor (F-TEDA) is explored as a fluorinating agent for Vulcan carbon. Fluorination of carbon material results in the formation of semi-ionic C—F (F = 8.02 at%) and ionic C—F (F = 2.71 at%) bonds as observed in X-ray photoelectron spectroscopy analysis along with an increase in defect density (ID/IG) by 33.4%. Symmetric two-electrode supercapacitor cells are assembled in Swagelok-type geometry, and the specific capacitance of fluorinated carbon is found to increase by ≈15 times in contrast to pristine carbon due to induced surface polarization despite the decrease in specific surface area by ≈34%, which is remarkable. The fabricated device is stable with ≈96% capacitance retention over 10 000 cycles, resulting in enhanced supercapacitive performance.

The current study reveals the synthesis of polymer appended Calix[4]amidocrown-5 with specific binding affinity for iodide at ppm-level. The low detection limits are observed via UV-vis and fluorescence spectroscopy. The time-dependent solution and solid-state 127I NMR studies with 18.8 and 19 ppm shifts, indicate a strong sensing nature of resin towards iodide ion. A significant reduction in surface area and pore volume with higher thermostability of resin after iodide uptake indicated iodide inclusion in the amidocrown cavity. The mechanism of iodide sensing may be governed by noncovalent interactions of NH and OH protons present in amidocrown and phenyl ring as observed in terms of emission enhancement in fluorescence spectroscopy. The binding affinity and stoichiometric determinations are determined by Benesi-Hildebrand and Jobs plots, respectively.

A series of dysprosium (Dy) doped LiMn2O4 based spinel cathode materials, LiMn2 − xDyxO4 (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05) for Li ion rechargeable battery application were synthesized by sol-gel process. The physical properties were explored through X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray diffraction (EDX), field emission scanning electron microscopy (FE-SEM), and micro-Raman spectroscopy. Swagelok cell configurations were used for electrochemical characterizations e.g. cyclic voltammetry, rate performance, cycleability and AC impedance. The doping amount of dysprosium has improved the surface morphology (particle size < 1 μm) by reducing particle size. The Dy(0.02) showed improved capacity of 122, 72 and 78 mAh g− 1 at C/10, C/5 and C/10 (recv.) respectively. The lower impedance of Dy(0.02) in comparison of pristine and other derivatives of synthesized cathode materials also supports these outcome.

Dendritic nanostructures of fluorinated α-Fe2O3 are synthesized using Potassium Ferrocyanide along with Selectfluor™ (F-TEDA), HF, TBABF4, NaF and NH4F as Fe and F precursors respectively in an in-situ hydrothermal process. The choice of sources is based on the nature of fluorine; F-TEDA uniquely acts as a source for electrophilic fluorine while others are nucleophilic in nature. The effect of fluorination on α-Fe2O3 nanostructures is examined from the interplay between (110) and (104) growth direction and crystallite size by X-Ray diffraction analysis and the amount of fluorination is observed by elemental analysis. A significant change in the magnetic property of α-Fe2O3 is observed for different concentrations of F-TEDA. Pristine α-Fe2O3 undergoes an antiferromagnetic to ferromagnetic transition with saturation magnetization value of ~ 13 emu/g and coercivity of 109.8 Oe. However, α-Fe2O3 nanostructures prepared with HF, NH4F, TBABF4 and NaF in absence of fluorination remain antiferromagnetic despite of changes in preferred orientation and crystallite size. The interesting magnetic properties arising from F-TEDA is attributed to surface fluorination that results in uncompensated surface spins.

Fluorinated α-Fe2O3 nanostructures are synthesized via a facile hydrothermal route using Selectfluor™ (F-TEDA) as a fluorinating as well as growth directing agent. The addition of incrementally increasing amount of F-TEDA to Fe precursor under hydrothermal conditions resulted in preferential growth of α-Fe2O3 along (110) orientation with respect to (104) direction by ~ 35%, the former being important for enhanced charge transport. On increasing fluorination, the heirarchical dendritic-type α-Fe2O3 changes to a snow-flake type structure (F-TEDA-20%) anisotropically growing along the six directions however, at higher F-TEDA concentrations (≥ 30%), loosely held particulate aggregates are seen to be formed. The X-Ray Photoelectron Spectroscopy (XPS) suggest the maximum fluorinarion of α-Fe2O3 at 1.21 at% in 30% F-TEDA. Further, optical absorption studies reveal reduction in optical band gap from 2.10 eV in case of pristine to 1.95 eV for fluorinated α-Fe2O3. A photoanode made by taking 20% fluorinated α-Fe2O3 in a ratio of 10:90 with respect to TiO2 (P-25) showed improved performance in dye sensitized solar cells with an increase in efficiency by ~16% in comparision to that of pristine Fe2O3 and TiO2. Furthermore, anode consisting of thin films of fluorinated α-Fe2O3 on FTO also exhibit enhanced current density on illumination of ~100 W/m2. The increase in photoelectrochemical activity seems to be due to the combination of two factors namely preferential growth of α-Fe2O3 along (110) direction resulting in an improved charge transfer efficiency and reduced recombination losses due to the presence of fluorine.

Futuristic healthcare technology including glucose sensors demands wearable components that ought to be transparent and flexible. Nickel nanostructures have proven to be highly efficient as electrocatalysts for glucose sensors. In this study, we explore single-source precursors of nickel alkylthiolate, Ni(SR)2, complexes as active electrode materials and coat them on a transparent gold (Au) mesh network to fabricate a transparent and highly efficient glucose sensor. The metal thiolate complex is electrooxidized in the alkaline medium by repeated cyclic voltammetry measurements to give rise to Ni redox-active centers with sharp anodic and cathodic peaks. Among different chain length metal alkylthiolates, nickel butanethiolate with the shortest carbon chain (C4) is found to be the most efficient in retaining sharp oxidation at low potential value and high current density. The electrochemical property of nickel butanethiolate toward glucose oxidation is examined on different electrode surfaces such as Au thin film, Au mesh, and fluorine-doped tin oxide (FTO). Interestingly, glucose oxidation takes place most efficiently on a Au mesh network compared to Au film and FTO substrates. The Ni(SC4H9)2/Au mesh exhibited two linear ranges of detection from 0.5-2 and 2-11 mM with a sensitivity value of 675.97 μA mM-1 cm-2 and a limit of detection of 2.2 μM along with excellent selectivity and reproducibility. The present study demonstrates that nickel butanethiolate on a Au mesh acts as a promising functional and transparent electrode material with the possibility of large-scale production for practical glucose detection.

Different aluminum and calcium based particles, montmorillonite (MMT), zeolites (NaY), bayerite (BAY) and hydroxyapatite (CaHAp), were compared and evaluated for water defluorination. The effect of parameters such as temperature of the medium, concentration (mass of adsorbent), reaction time and pH on the defluorination capacity were studied for the particles with best performance. MMT and CaHAp adsorbents showed increased fluoride rejections in batch experiments (≈45 and 100%). The defluorination capacity of MMT is influenced by the concentration and pH, while for CaHAp is independent of the evaluated parameters within the measured range. Further, polymer composite membranes based on poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) and the adsorbents with higher defluorination capacity were prepared by thermally induced phase separation in order to produce active filters for fluoride removal from water. The composite membranes presented a homogeneous porous structure with degrees of porosity ranging between ≈20 and 76% and average pore size in the micron range. The permeability of the composite membranes ranged between 12,500 and 10,000 L/h·m2·bar. A maximum fluoride rejection of 68% was obtained after 6 filtrations for the CaHAp/P(VDF-HFP) composite membranes. Thus, the composite membranes of P(VDF-HFP) with MMT and CaHAp show suitable performance for defluorination in water purification systems.

Photocatalytic activity of low band gap hydrogenated HfO2 doped TiO2 (H-HfO2/TiO2), HfO2 doped TiO2 (HfO2/TiO2) and TiO2 (pristine) were investigated by photocatalytic degradation of five different industrial dyes. The current study envisages the effect of doping hydrogen and HfO2 up on TiO2 for photocatalytic degradation of different chemically structured dyes. Methylene Blue attains fast degradation efficiency of 90%, within 10 min of the reaction due to high photocatalytic adsorption and degradation over the rough TiO2 surface. Effect of pH on dye degradation is observed, leading to disintegration and mineralization.

Fluorine chemistry has gained tremendous attention in the area of electrochemical energy devices such as lithium ion batteries, fuel cells and solar cells. With the advent of novel fluorinating systems, it is interesting to study the effect of fluorine on the electrochemical characteristics of such energy devices. In this study, an organo-fluorine compound, SelectfluorTM (F-TEDA) is used as a co-electrolyte with organic electrolyte, tetrabutyl ammonium tetrafluoroborate (TBABF4) to facilitate the formation of electrostatic double layer. F-TEDA is a commercially available N−F fluorinating agent existing as ion-pair resembling conventional electrolytes. The ionic conductivity of 0.5 M F-TEDA/TBABF4 is found to be 5.10 mS/cm that increases on introduction of ppm level of water indicating its sensitivity towards water. Symmetric Swagelok-type cells in two electrode geometry are fabricated using carbon cloth as electrodes and F-TEDA/TBABF4 as electrolyte. F-TEDA/TBABF4 in inert condition (Device C) exhibits superior supercapacitive behaviour in terms of high rate capability and capacitance retention. The devices are assembled in ambient and inert conditions to examine the influence of moisture on supercapacitor performance. Interestingly, device based on F-TEDA assembled in ambient condition despite of decrease in voltage window exhibits a remarkable increase in specific capacitance by 102 % with respect to control electrolyte.

In this study, a series of mineral and organic acids are introduced to natural clay modification. Several analytical techniques are employed to identify the physical and chemical changes in clay. The effect of surfactants on these properties is also investigated. The samples are prepared using simple acid treatment without filtration. The alteration in surface morphology is proportional to the acid strength as evident from SEM and XRD analyses. Therefore, the treatment with mineral acid and organic acid/HNO3 results in the formation of new layers by surface modification as depicted in SEM images, and a higher degree of suppression in characteristic XRD reflections of clay is noticed. However, the treatment with organic acids modifies the existing interlayer spacing of clay, and therefore, the XRD characteristic reflections of clay are less affected. These observations are also supported by FT-IR analysis. The surface area of modified clay is dependent on the acid strength, composition and size of counter-anion of acid. An increase in surface area and porosity is noticed after surfactant modification of HNO3-treated clay, where the change is more prominent at the concentration higher than their respective critical micelle concentration. Thermal stability is dependent on the chemical composition and surface area of clay materials. A relatively higher absorbance is observed for modified clay materials compared with untreated clay during DRS analysis. The catalytic efficiency of modified clay materials in Eriochrome Black T degradation has been demonstrated.