Gupta, Ritu

A stretchable and compliant electrode surface of Au metal on polydimethylsiloxane (PDMS) is introduced in this study. A thin layer of Au nanoparticles is thus formed by a simple chemical reduction from aqueous Au salt solution with the AuPDMS gel surface itself acting as a reducing site. Employing the swelling behaviour of PDMS and Au nanoparticles affinity to bind with sulphur, an in-plane molecular device has been realized for measuring the conductance of thiol molecules. The device is capable of forming stable and robust linkages with Au. The molecules anchored between the Au islands are able to undergo reversible compression and tension, which shows the flexibility of the device.

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 scalability and stability of electrocatalysts is one of the biggest challenges for their practical applicability. In this context, Co3O4 nanoparticles conformally coated on a light weight, 3D and highly conducting carbon cloth are fabricated using an easily synthesized cobalt hexadecylthiolate complex as ink. This method is especially useful for large-scale production as the complex is synthesized in large quantities and coated on 3D substrates by a simple dip-coating method. The optimum loading of the catalyst is achieved through a layer-by-layer (LbL) assembly of a cobalt hexadecylthiolate complex via repeated dip coating of the carbon cloth electrode in the solution. The Co3O4/CC undergoes electrochemical oxidation and converts to CoOOH as an active species and acts as a highly efficient electrocatalyst with optimized loading. The Co3O4-16/CC with 16 times dip coating exhibits remarkable stability over 24 h with an overpotential of 300 mV at 10 mA cm−2 and a Tafel slope of 77.06 mV dec−1. The electrocatalytic activity of Co3O4-16/CC prepared by LbL coating is better than conventional Co3O4 and comparable to IrO2 and RuO2 electrocatalysts with the future possibility of commercial-scale production at lower cost.

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.

Monitoring live movements of human body parts is becoming increasingly important in the context of biomedical and human machine technologies. The development of wearable strain sensors with high sensitivity and fast response is critical to address this need. In this article, we describe the fabrication of a wearable strain sensor made of a Au micromesh partially embedded in polydimethylsiloxane substrate. The sensor exhibits a high optical transmittance of 85%. The effective strain range for stretching is 0.02%-4.5% for a gauge factor of over 10 8 . In situ scanning electron imaging and infrared thermal microscopy analysis have revealed that nanometric break junctions form throughout the wire network under strain; strain increases the number of such junctions, leading to a large change in the sheet resistance of the mesh. This aspect has been examined computationally with the findings that wire segments break successively with increasing strain and resistance increases linearly for lower values of strain and nonlinearly at higher values of strain because of formation of current bottlenecks. The semi-embedded nature of these Au microwires allows the broken wires to retract to the original positions, thus closing the nanogaps and regaining the original low resistance state. High repeatability as well as cyclic stability have been demonstrated in live examples involving human body activity, importantly while mounting the sensor in strategic remote locations away from the most active site where strains are highest.

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.

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.

This paper is a study of ZnO doped TiO2 in various percentages ranging from 0% (undoped) up to 10%. The effect of doping was observed via the change in morphological, optical, electrical and physical properties of ZnO-TiO2 nanospheres. Hydrothermally grown nanospheres are used for removing contaminants photo-catalytically from waste water and also as photoanodes in dye-sensitized solar cells (DSSCs) with graphene as counter electrode. Of the many approaches that have been explored for purification of contaminated water, this work presents designing of an environmental friendly solution, based on easily available filter paper membrane and incorporating it with the synthesized catalyst for photodegradation of the harmful toxic substances. These reusable membranes assist in the photodegradation process by creating room for better light-catalyst-dye interaction via large surface sites. The spherically structured heterojunction of ZnO-TiO2 generates excitons that oxidize methyl orange (MO) and reduce harmful Cr(VI) to non-toxic Cr(III) with high efficacy. Additionally, the agile nanostructures were employed as efficient photoanode material by fabricating dye sensitized solar cells with graphene as counter electrode.

Black titania (H-TiO2) as a photoanode material has attracted huge attention due to its extremely high optical absorption in the visible region. Herein, black TiO2 doped with HfO2 shows ∼45.7% higher photo-conversion efficiency than H-TiO2 under identically similar conditions. The incorporation of HfO2 nanodots increased the optical scattering in H-TiO2 only when it underwent hydrogenation along with TiO2. Hafnia-doped TiO2 (HfO2/TiO2) is synthesized by a combination of simple sol-gel and hydrothermal method followed by thermal annealing under controlled hydrogen atmosphere. The hydrogenated H-(TiO2/HfO2) exhibited very high optical absorption but slightly lower than H-TiO2 due to light scattering by HfO2 nanodots. We observed a sharp decrease in optical band gap of TiO2/HfO2 from 3.2 to 2.4 eV up on hydrogen annealing, which is important in solar applications as demonstrated by the fabrication of high efficiency dye sensitized solar cells (DSSC).