V. Suryanarayanan

Porosity of core-shell nanoparticles

The porosity of titania and zirconia covered Ag and Au nanoparticles has been investigated using the metal core reactivity as a probe. The presence of pores was confirmed by a newly discovered reaction between halocarbons and core–shell nanoparticles, in which the core gets converted into ions, which are leached out through the shell. Halocarbons having different alkyl chain lengths react with metal cores at different rates due to the differences in the accessibility of the core. It is also observed that the electrochemical accessibility of the core can be reduced by blocking the pores by adsorbates such as cis-dithiocyanato-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid)ruthenium(II) dye (popularly called N3 dye). With the adsorbed dye molecules on the oxide shell, metal cores are stable for extended periods of time even after the addition of halocarbons. The porosity of the Au@SiO2 system, in which a silica shell is formed over the metal clusters through monolayers, has also been studied. Our studies show that the porosity of different kinds of shells is largely similar, allowing molecular and ion penetration.

Detection of nicotine based on molecularly imprinted TiO2-modified electrodes.

Amperometric detection of nicotine (NIC) was carried out on a titanium dioxide (TiO(2))/poly(3,4-ethylenedioxythiophene) (PEDOT)-modified electrode by a molecular imprinting technique. In order to improve the conductivity of the substrate, PEDOT was coated onto the sintered electrode by in situ electrochemical polymerization of the monomer. The sensing potential of the NIC-imprinted TiO(2) electrode (ITO/TiO(2)[NIC]/PEDOT) in a phosphate-buffered saline (PBS) solution (pH 7.4) containing 0.1M KCl was determined to be 0.88 V (vs. Ag/AgCl/saturated KCl). The linear detection range for NIC oxidation on the so-called ITO/TiO(2)[NIC]/PEDOT electrode was 0-5mM, with a sensitivity and limit of detection of 31.35 microA mM(-1)cm(-2) and 4.9 microM, respectively. When comparing with the performance of the non-imprinted one, the sensitivity ratio was about 1.24. The sensitivity enhancement was attributed to the increase in the electroactive area of the imprinted electrode. The at-rest stability of the ITO/TiO(2)[NIC]/PEDOT electrode was tested over a period of 3 days. The current response remained about 85% of its initial value at the end of 2 days. The ITO/TiO(2)[NIC]/PEDOT electrode showed reasonably good selectivity in distinguishing NIC from its major interferent, (-)-cotinine (COT). Moreover, scanning electrochemical microscopy (SECM) was employed to elucidate the surface morphology of the imprinted and non-imprinted electrodes using Fe(CN)(6)(3-)/Fe(CN)(6)(4-) as a redox probe on a platinum tip. The imprinted electrode was further characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR).

ZrO2 bubbles from core–shell nanoparticles

Selective removal of metal cores from core–shell Ag@ZrO2 (ZrO2 coated Ag) and Au@ZrO2 (ZrO2 coated Au) nanoparticles result in stable and freely suspendable oxide nanobubbles of varying dimensions, both in thickness and in diameter. The metal core is removed by a newly found reaction in which halocarbons, generally chlorides, oxidise the metal core and leach out the metal ions. Reduction in the surface plasmon excitation intensity and decrease in the voltammetric current during metal core removal were used to study the process.

Ethyl viologen dibromide as a novel dual redox shuttle for supercapacitors

Viologen (1,1ʹ-diethyl-4,4ʹ-bipyridinium bromide) based redox active electrolyte in 1.0 M H2SO4 has been proposed as a novel electrolyte for supercapacitor (SC) applications due to its dual cathodic and anodic redox behaviour. Unlike other reported redox additives, viologen as a single redox species can improve the performance of both positive and negative electrodes simultaneously through the redox behaviour of bromide and 1,1ʹ-diethyl-4,4ʹ-bipyridinium ions. The synergic redox behaviour of the ions and their effect towards the enhancement of the electrochemical performance of the activated charcoal based SC are compared with those of neat H2SO4 and triethylbutylammonium bromide (N2224Br). The maximum specific capacitance of 408.0 F g−1 and specific energy of 23.0 W h kg−1 at 0.25 A g−1 were obtained for the viologen mediated SC. Interestingly, the specific capacitance continuously increased for the viologen mediated SC on charge–discharge cycling and 30% increment was observed at the end of 1000 cycles. The relaxation time constant is compared for SCs with viologen, neat H2SO4 and N2224Br electrolytes.

Dye-sensitized solar cells containing mesoporous TiO2 spheres as photoanodes and methyl sulfate anion based biionic liquid electrolytes

Mesoporous TiO2 spheres (hereafter, MSs) were synthesized and incorporated into the photoanode of a quasi-solid state dye-sensitized solar cell (QSS-DSSC) containing an air stable ionic liquid electrolyte, namely 1-propyl-3-methylimidazolium iodide (PMII) along with triethylmethylammonium methyl sulfate (TEMAMS) (65 : 35 = v/v), in order to improve its performance. The presence of large pores in the MS, as confirmed using a high resolution scanning electron microscope (HR-SEM) and a mercury porosimeter, facilitates the penetration of QSS-electrolytes into the thin film, whereas their high surface area (108.1 m2 g−1) helps for high dye loading. Further, the large particle size increases the scattering ability of incident light leading to an excellent increment in the number of photons. The performance of DSSCs containing bi-ionic liquid (bi-IL) based electrolytes, namely, PMII/TEMAMS and PMII/1-ethyl-3-methylimidazolium tetrafluoborate (EMIBF4), with the addition of 0.2 M iodine, 0.4 M N-methylbenzimidazole (NMBI), and 0.15 M guanidiniumthiocyanate (GuSCN), was compared, where the DSSC based on PMII/TEMAMS bi-ILs demonstrates superior efficiency (6.18%) than that of PMII/EMIBF4 based one (4.53%). The DSSC with PMII/TEMAMS shows extraordinary durability and unfailing stability for 1200 h even though it was stored in the dark at 50 °C. Further, the PMII/TEMAMS bi-IL electrolyte shows a gel-state at room temperature naturally without adding any gelators or polymers.

Effect of solvents and solvent mixtures on intercalation/de-intercalation behaviour of Li+ and ClO4- ions in polypropylene-graphite composite electrodes

Abstract The intercalation of Li + and ClO 4 − ions in polypropylene–graphite composite electrodes in different single solvents and 1:1 binary solvent mixtures is studied by means of cyclic voltammetry and scanning electron microscopy. The intercalation/de-intercalation efficiency as a potential dual-intercalation battery electrode for cationic intercalation (positive electrode) is found to be generally lower than that for anionic intercalation in most of the solvents. 1:1 solvent mixtures do not enhance intercalation/de-intercalation efficiency significantly beyond the values found in a single solvent. The mixed-solvent system leads, however, to less co-solvent intercalation and graphite exfoliation, and hence better cycle-life as a potential battery electrode.

Hierarchically assembled microspheres consisting of nanosheets of highly exposed (001)-facets TiO2 for dye-sensitized solar cells

In this work, the mono-dispersed TiO2 microspheres with highly exposed (001)-facets (ca. 82%), high surface area (112.2 m2 g−1), and self-ordered 3D porous network have been rapidly synthesized by an in situ facet-controlling approach without any organic templates and employed as photoanodes of dye-sensitized solar cells (DSSCs). Owing to the stacking of 3D nanosheets of microspheres, the self-ordered internal porous network (ca. 30 nm) provides an efficient pathway for electrolyte and dye molecules penetrating into the interior part of a microsphere. Besides, the large voids among microspheres (ca. 300 nm) establish a highway for electrolyte diffusion. The formation processes of the prepared microspheres have been discussed, in which oriented self-assembly is involved. A reasonable mechanism is proposed to explain its high dye loading capacity (dye loading per gram/surface area of TiO2). Furthermore, according to the difference of normalized photocurrents of the cells with (001)-facet TiO2 and Ref-TiO2, the long wavelength region (600 to 800 nm) contributes 67.5% of the integrated photocurrent density; this result confirms its superior light scattering property. Finally, under 100 mW cm−2 light irradiation, a high photoelectric conversion efficiency of about 11.13% was achieved, as compared to that of the cell with a Ref-TiO2 film (8.11%). In light of their successful application in high-performing I3−/I−-based DSSCs, it is envisaged that these TiO2 microspheres with highly exposed (001)-facets can be used as excellent semiconductor materials in mass transfer limited cobalt-based DSSCs, and also in other fields, such as photocatalysis, water splitting, and lithium ion battery.

Aniline incorporated silica nanobubbles

We report the synthesis of stearate functionalized nanobubbles of SiO2 with a few aniline molecules inside, represented as C6H5NH2@SiO2@stearate, exhibiting fluorescence with red-shifted emission. Stearic acid functionalization allows the materials to be handled just as free molecules, for dissolution, precipitation, storage etc. The methodology adopted involves adsorption of aniline on the surface of gold nanoparticles with subsequent growth of a silica shell through monolayers, followed by the selective removal of the metal core either using sodium cyanide or by a new reaction involving halocarbons. The material is stable and can be stored for extended periods without loss of fluorescence. Spectroscopic and voltammetric properties of the system were studied in order to understand the interaction of aniline with the shell as well as the monolayer, whilst transmission electron microscopy has been used to study the silica shell.

Ciprofloxacin@SiO2: Fluorescent nanobubbles

We report a new nanomaterial in which ciprofloxacin molecules are incorporated inside silica nanobubbles, denoted as ciprofloxacin@SiO2. The material has been characterised using UV/Vis absorption spectroscopy, transmission electron microscopy, cyclic voltammetry, and emission spectroscopy. The material is stable and the freestanding particles can be precipitated and redispersed in several solvents. Confinement of the molecule is complete as leaching through the shell is minimal. The material behaves like free ciprofloxacin in solution; however, effects of confinement are manifested. Energy transfer reaction between ciprofloxacin@SiO2 and Tb3+ was monitored by emission spectroscopy. The emission intensity decreased with metal ion exposure indicating selective electronic interaction.

High lithium anodic performance of N-doped porous biocarbon-integrated indium sulfide thin nanosheets

A mesoporous 3D marigold flower-like indium sulfide (In2S3) microstructure grafted with nitrogen-doped porous carbon nanosheets was synthesised from fish scale biowaste using a simple, scalable, and cost-effective method. The as-obtained composite exhibited a larger surface area (307 m2 g−1) than pristine InS (57 m2 g−1). As the anode in a lithium ion battery, the synthesised composite and pristine materials retained capacities of about 751 and 397 mA h g−1, respectively, after 100 cycles at a current density of 500 mA g−1. Furthermore, the composite material delivered capacities in the range 1260–297 mA h g−1 when the current density was varied from 0.025 to 10.0 A g−1. The impressive electrochemical performance of the composite material is associated with the synergetic effect of porous carbon nanosheets in alleviating volume expansion and enhancing reversibility, allowing practical application in lithium ion batteries.