P. Ghosal

Dual purpose poly(3,4-ethylenedioxypyrrole)/vanadium pentoxide nanobelt hybrids in photoelectrochromic cells and supercapacitors

Poly(3,4-ethylenedioxypyrrole) (PEDOP)/vanadium pentoxide (V2O5) nanobelt hybrid films were prepared for the first time. V2O5 nanobelts with a monoclinic structure were grown by a hydrothermal route and a PEDOT layer was coated onto V2O5 nanobelts by electropolymerization to yield the PEDOP/V2O5 hybrid. The hybrid showed a fourfold increment in electrical conductivity compared to the pristine oxide, and a work function of 4.71 eV (by Kelvin probe force microscopy), which was intermediate to that of PEDOP and V2O5. Both oxide and hybrid showed green-red luminescence. The PEDOP/V2O5 hybrid or V2O5 films were assembled into energy saving photoelectrochromic cells, by combining with a photovoltaic electrode of CdS/titania, and in response to 1 sun illumination for different durations, the hybrid showed a dynamic transmission modulation (ΔT), as it switched from a yellow to a dark green optical state, without the application of any external bias, by simply consuming the electrical current produced by the irradiated CdS/titania. The hybrid exhibited a maximum ΔT of 65.5% at 475 nm, which was greater by 82% compared to pristine V2O5 at the same wavelength. The ability of PEDOP to provide facile conduction pathways for fast and improved electron transfer and transport in the PEDOP/V2O5 hybrid, enhances the optical contrast produced. The versatility of the hybrid was established by assembling asymmetric supercapacitors with the hybrid or polymer or oxide and a liquid electrolyte. The synergistic effects of PEDOP (high electrical conductivity) and V2O5 nanobelts (large surface area) and their ability to store/release charge by undergoing reversible Faradaic reactions were reflected in a high specific capacitance of 224 F g−1 delivered by the hybrid, higher by 83% and 69% relative to pristine V2O5 and PEDOP. The hybrid shows an energy density of 223 W h kg−1 at a power density of 3.8 kW kg−1, and an acceptable cycling performance with 90% capacitance retention after 5000 cycles. The PEDOP/V2O5 hybrid is useful for advanced next-generation self-powered electrochromic smart windows and supercapacitors.

Low-Cost Copper Nanostructures Impart High Efficiencies to Quantum Dot Solar Cells

Quantum dot solar cells (QDSCs) were fabricated using low-cost Cu nanostructures and a carbon fabric as a counter electrode for the first time. Cu nanoparticles (NPs) and nanoneedles (NNs) with a face-centered cubic structure were synthesized by a hydrothermal method and electrophoretically deposited over a CdS QD sensitized titania (TiO2) electrode. Compared to Cu NPs, which increase the light absorption of a TiO2/CdS photoanode via scattering effects only in the visible region, Cu NNs are more effective for efficient far-field light scattering; they enhance the light absorption of the TiO2/CdS assembly beyond the visible to near-infrared (NIR) regions as well. The highest fluorescence quenching, lowest excited electron lifetime, and a large surface potential (deduced from Kelvin probe force microscopy (KPFM)) observed for the TiO2/CdS/Cu NN electrode compared to TiO2/CdS and TiO2/CdS/Cu NP electrodes confirm that Cu NNs also facilitate charge transport. KPFM studies also revealed a larger shift of the apparent Fermi level to more negative potentials in the TiO2/CdS/Cu NN electrode, compared to the other two electrodes (versus NHE), which results in a higher open-circuit voltage for the Cu NN based electrode. The best performing QDSC based on the TiO2/CdS/Cu NN electrode delivers a stellar power conversion efficiency (PCE) of 4.36%, greater by 56.8% and 32.1% than the PCEs produced by the cells based on TiO2/CdS and TiO2/CdS/Cu NPs, respectively. A maximum external quantum efficiency (EQE) of 58% obtained for the cell with the TiO2/CdS/Cu NN electrode and a finite EQE in the NIR region which the other two cells do not deliver are clear indicators of the enormous promise this cheap, earth-abundant Cu nanostructure holds for amplifying the solar cell response in both the visible and near-infrared regions through scattering enhancements.

Structure–property correlation of a boron and carbon modified as castβtitanium alloy

Beta titanium alloys, Ti-15V-3Cr-3Al-3Sn, with minor additions of boron and carbon were prepared by consumable vacuum arc melting. Detailed microstructural characterizations were carried out using optical, scanning electron microscopes and transmission electron microscopes. Addition of boron resulted in refinement of the as cast beta grain while carbon addition resulted in the precipitation of extremely fine α phase during ageing. Formation of boride and carbide particles due to addition of boron and carbon, respectively, and refinement of the aged microstructure increased the hardness and strength as compared to the base alloy but reduced elongation to failure considerably, especially in the carbon-containing alloy where no measurable plasticity was observed. Fracture toughness values, however, were comparable for the boron- and carbon-containing alloys but these were lower than that of the base alloy.

Novel synthesis of C, N doped rice grain shaped ZnS nanomaterials – towards enhanced visible light photocatalytic activity for aqueous pollutant removal and H2 production

Novel single step syntheses of visible active C, N doped zinc sulfide (ZnS) photocatalysts with rice grain morphology have been achieved without using expensive surfactants, capping agents and inert atmospheric conditions by using solution combustion synthesis in an energy and time efficient manner. Several ZnS samples such as ZnS (1:2), ZnS (1:3), ZnS (1:4), ZnS (1:5) and ZnS (1:6) have been synthesized by varying the metal and sulfur precursor ratio in order to obtain ZnS with desirable characteristics for visible light activity. X-ray diffraction indicated the nanocrystalline size and hexagonal ZnS phase, whereas, transmission electron microscopy confirmed the nanocrystalline size and also revealed the rice grain morphology for ZnS (1:5). Diffuse reflectance UV-Vis spectra indicated a red shift in the absorption maxima, possibly due to the decreasing band gap by C, N-doping, which was further confirmed by the elemental analysis and X-ray photoelectron spectroscopy. The visible light photocatalytic activity of the ZnS nanomaterials was assessed by high H2 production (up to 10000 μmol h−1 g−1 for ZnS (1:5)) by water splitting in the presence of Na2S and Na2SO3 sacrificial reagents, whereas, the simultaneous oxidation of MB and reduction of Cr(VI) under natural sunlight complemented the activity of ZnS.

Phenol and Cr(vi) degradation with Mn ion doped ZnO under visible light photocatalysis

Mn ion doped ZnO with different percentages of Mn content (Zn0.9Mn0.1O (1), Zn0.8Mn0.2O (2), Zn0.7Mn0.3O (3), and Zn0.6Mn0.4O (4)) was synthesized via a solution combustion method, with urea used as the fuel. The optical, morphological, and structural properties were studied using Raman, UV-DRS, SEM, TEM, XPS, and powder XRD techniques. The average crystallite sizes of Zn1−xMnxO (1, 2, 3, 4), which are around 30–60 nm, were confirmed via powder X-ray diffraction studies, whereas transmission electron microscopy studies confirmed the formation of a ZnO wurtzite crystal phase. Scanning electron microscopy indicated the spherical morphology of the samples. Raman spectroscopy studies confirmed a decrease in oxygen vacancies with increasing Mn content, whereas confirmation of the doping of Mn ions into the ZnO lattice was obtained using X-ray photoelectron spectroscopy. The band gap energies of samples were calculated using UV-DRS spectroscopy, whereas BET surface area measurements confirmed the surface area. The visible light activity of Zn1−xMnxO (1, 2, 3, 4) was identified through studies of phenol degradation and Cr(VI) reduction under visible light photocatalysis, which highlight that Zn0.8Mn0.2O (2) shows the best activity. Typical degradation profiles indicated that the simultaneous degradation of pollutants is more effective than the removal of individual pollutants.

Launching particle to constant reinforcement ratio as a parameter for improving the nanoreinforcement distribution and tensile strength of aluminum nanometal matrix composites

Abstract Pelletization of ball milled powder, although a better technique for distributing nanoreinforcements into the metal melt, increases the production line. Here, we report our attempt to improve the distribution of nanoreinforcements without increasing the production line. We observed the effect of increase in a novel parameter, launching particle to constant reinforcement ratio (by weight; 1.5 wt.% Al2O3), on the nanoreinforcement distribution and ultimate strength of composites fabricated by stir casting. The medium used for launching the nanoreinforcements into the Al–Cu matrix is aluminum powder prepared by ball milling. An increase in the launching particle to constant reinforcement ratio leads to an improvement in the nanoreinforcement distribution and tensile strength of the composite. The X-ray maps indicate the absence of iron contamination and iron intermetallics.

Fast and clean functionalization of MWCNTs by DBD plasma and its influence on mechanical properties of C–epoxy composites

Multiwalled carbon nanotubes (MWCNTs) were functionalized under helium/air plasma and the surface characteristics were compared with that of chemical functionalization. Changes in surface functional groups of MWCNTs due to plasma/chemical treatment were estimated by using temperature programmed decomposition (TPD), elemental analysis, Raman spectroscopy and BET surface area analysis. Raman spectroscopic studies highlighted that chemical functionalization increases the degree of disorder for MWCNTs when compared to plasma treatment. TPD also confirmed that air plasma treatment leads to the highest number of acidic groups on the surface that decomposes to evolve carbon dioxide. The modified MWCNTs were used as additional reinforcements to fabricate carbon fiber reinforced plastics (CFRPs). It has been observed that air plasma treated MWCNTs improved the tensile and flexural strength of C–epoxy composites significantly as compared to conventional chemical functionalization, whereas the best performance of air plasma treated MWCNTs is due to higher acid functional groups on the surface, which improves interface compatibility between the MWCNTs to the epoxy matrix.

An experimental and micrographical investigation on aluminum nano metal matrix composites

In the present investigation, a comparative study using X-ray mapping analysis and Field emission gun scanning electron micrographs is performed to understand the distribution and the mechanical properties of aluminum nano metal matrix composites. Parameters considered for comparison have two different forms for adding nanoreinforcement into metal melt. One form is produced by the addition of mechanically alloyed powders with an increasing launching vehicle weight percentage (L-1, L-3 and L-5), and the other form is produced by pellets of mechanically alloyed powders (PL-1). Micrographs reveal uniform distribution of nanoreinforcements, while X-ray mapping observations show Iron (Fe) contamination due to the addition of pellets in some areas unlike the mechanically alloyed powders. L-5 is observed to attain the highest tensile strength of 202 MPa for the Al-Cu/1.5 wt. % Al2O3 composite. The results illustrate an increase in composites strength with increase in launching vehicle content but on the expense of nanoreinforcement particle rejection from the melt.

Fabrication of Pd/CuFe2O4 hybrid nanowires: a heterogeneous catalyst for Heck couplings

The development of environmentally benign transformations is indispensable in organic synthesis. Herein, a hybrid heterogeneous catalyst, palladium(0) on copper ferrite nanowires, has been synthesized, characterized, and for the first time, employed in the Jeffrey Heck reaction between iodoarenes and allylic alcohols, and good to excellent yields have been obtained. In addition, the catalyst was found to be suitable for the usual Heck coupling. The nanocatalyst was recovered and reused up-to multiple runs without any noticeable loss of its catalytic activity.

New Antimony Selenide/Nickel Oxide Photocathode Boosts the Efficiency of Graphene Quantum-Dot Co-Sensitized Solar Cells

A novel assembly of a photocathode and a photoanode is investigated to explore their complementary effects in enhancing the photovoltaic performance of a quantum-dot solar cell (QDSC). While p-type nickel oxide (NiO) has been used previously, antimony selenide (Sb2Se3) has not been used in a QDSC, especially as a component of a counter electrode (CE) architecture that doubles as the photocathode. Here, near-infrared (NIR) light-absorbing Sb2Se3 nanoparticles (NPs) coated over electrodeposited NiO nanofibers on a carbon (C) fabric substrate was employed as the highly efficient photocathode. Quasi-spherical Sb2Se3 NPs, with a band gap of 1.13 eV, upon illumination, release photoexcited electrons in addition to other charge carriers at the CE to further enhance the reduction of the oxidized polysulfide. The p-type conducting behavior of Sb2Se3, coupled with a work function at 4.63 eV, also facilitates electron injection to polysulfide. The effect of graphene quantum dots (GQDs) as co-sensitizers as well as electron conduits is also investigated in which a TiO2/CdS/GQDs photoanode structure in combination with a C-fabric CE delivered a power-conversion efficiency (PCE) of 5.28%, which is a vast improvement over the 4.23% that is obtained by using a TiO2/CdS photoanode (without GQDs) with the same CE. GQDs, due to a superior conductance, impact efficiency more than Sb2Se3 NPs do. The best PCE of a TiO2/CdS/GQDs-nS2-/Sn2--Sb2Se3/NiO/C-fabric cell is 5.96% (0.11 cm2 area), which, when replicated on a smaller area of 0.06 cm2, is seen to increase dramatically to 7.19%. The cell is also tested for 6 h of continuous irradiance. The rationalization for the channelized photogenerated electron movement, which augments the cell performance, is furnished in detail in these studies.