Ashish Kumar Mishra

Polyaniline–MnO2 nanotube hybrid nanocomposite as supercapacitor electrode material in acidic electrolyte

Herein, we report a preparation method of a novel binary hybrid nanocomposite based on polyaniline (PANI) and α-MnO2 nanotubes (MNTs) by in situpolymerization. The polymerization is carried out in acidic medium using α-MnO2 nanotubes as oxidant. A symmetrical supercapacitor is fabricated and the electrochemical performance of the supercapacitor is investigated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS) techniques using 1.0 M H2SO4 as electrolyte. The nanocomposite shows maximum specific capacitance of 626 F g−1 and corresponding energy density of 17.8 W h kg−1, as calculated from the charge–discharge curve at a specific current density of 2 A g−1 in the potential range 0–0.7 V.

Carbon dioxide adsorption in graphene sheets

Control over the CO2 emission via automobiles and industrial exhaust in atmosphere, is one of the major concerns to render environmental friendly milieu. Adsorption can be considered to be one of the more promising methods, offering potential energy savings compared to absorbent systems. Different carbon nanostructures (activated carbon and carbon nanotubes) have attracted attention as CO2 adsorbents due to their unique surface morphology. In the present work, we have demonstrated the CO2adsorption capacity of graphene, prepared via hydrogen induced exfoliation of graphitic oxide at moderate temperatures. The CO2adsorption study was performed using high pressure Sieverts apparatus and capacity was calculated by gas equation using van der Waals corrections. Physical adsorption of CO2 molecules in graphene was confirmed by FTIR study. Synthesis of graphene sheets via hydrogen exfoliation is possible at large scale and lower cost and higher adsorption capacity of as prepared graphene compared to other carbon nanostructures suggests its possible use as CO2 adsorbent for industrial application. Maximum adsorption capacity of 21.6 mmole/g was observed at 11 bar pressure and room temperature (25 oC).

Nanostructured polyaniline decorated graphene sheets for reversible CO2 capture

The current scientific community is extensively involved in developing novel materials for energy and environmental applications. Capture of CO2 to remove it from the atmosphere is one of the most important applications among them. In the present work, we have demonstrated for the first time, to the best of our knowledge, a polyaniline–graphene nanocomposite as a CO2 capture candidate. Graphene was prepared by hydrogen induced thermal exfoliation of graphite oxide and was further coated with polyaniline using a chemical method. The nanocomposite was characterized by different techniques and the capture capacity was measured using a high pressure Sievert’s apparatus. FTIR spectroscopy was used to confirm the possible CO2 capture mechanism in the nanocomposite. CO2 adsorption capacities at a pressure of 11 bar and different temperatures of 25, 50 and 100 °C were experimentally found to be 75, 47 and 31 mmol g−1, respectively. This nanocomposite shows much higher CO2 capture capacity compared to pure graphene and shows a high degree of recyclability.

Polyaniline/multiwalled carbon nanotubes nanocomposite-an excellent reversible CO2 capture candidate

Here we demonstrate the reversible CO2 capture capacity of polyaniline/multiwalled carbon nanotubes nanocomposite at high pressures for the first time to the best of our knowledge. High CO2 capture capacity was achieved for nanocomposite, which can be associated to the possible chemical interaction of CO2 molecules with nanocomposite. This study promotes the investigation of other polymer-carbon composites for CO2 capture.

Magnetite decorated graphite nanoplatelets as cost effective CO2 adsorbent

Investigation of cost effective CO2 adsorbent has been a long demanding task in the present scenario of global warming. The present work investigates the high pressure carbon dioxide capture capacity of low cost magnetite decorated functionalized graphite nanoplatelets novel nanocomposite. Graphite nanoplatelets were prepared by acid intercalation followed by thermal exfoliation. Functionalization of graphite nanoplatelets was done by treatment in acidic medium. Magnetite nanoparticles were decorated onto functionalized graphite nanoplatelets surface by a chemical method. Magnetite decorated functionalized graphite nanoplatelets nanocomposite was characterized by electron microscopy, X-ray powder diffraction pattern, surface area analysis, Raman spectroscopy and FTIR spectroscopy techniques. The carbon dioxide capture capacity was measured using high pressure Sieverts apparatus. Adsorption capacity was calculated using the gas equation and incorporating van der Waals corrections at three different temperatures (25, 50 and 100 °C). A large enhancement in carbon dioxide uptake capacity of 55%, 80%, and 90% at near 11.5 bar pressure for 100 °C, 50 °C and 25 °C, respectively, was achieved by decorating magnetite nanoparticles onto functionalized graphite nanoplatelet surface.

Size effect on thermal stability of nanocrystalline anatase TiO2

Thermal stability of nanocrystalline anatase TiO2 against coarsening and anatase–rutile phase transformation was studied using both a pyroprobe heater and a conventional furnace. The pyroprobe heater, because of the programmable control and the ultra-fast heating rate (up to 20 000 °C s−1), for the first time, allows us to access the very early stage of the sintering and phase-transformation processes. Our short time (0–30 s) heat treatments reveal that rapid grain growth takes place first in anatase nanoparticles (NPs) upon the initial heating due to the lower activation energy compared with that for the anatase–rutile phase transformation. Meanwhile, rutile-like structural elements develop at the interface between anatase NPs during the fast grain growth period, which evolve into rutile nuclei with time, followed by nuclei growth, to convert nanocrystalline anatase into rutile rapidly in the temperature range where the phase transformation does not occur in coarse anatase TiO2. Overall, both grain growth and phase transformation in smaller anatase NPs happen at lower temperatures and faster than in bigger ones. The coupled sintering–phase-transformation mechanism can be exploited to design thermally stable nanocrystalline anatase TiO2 by reducing the sintering kinetics, for example, via minority additives.

Eco-friendly synthesis of metal dichalcogenides nanosheets and their environmental remediation potential driven by visible light.

Exfoliated transition metal dichalcogenides (TMDs) such as WS2 and MoS2 have shown exciting potential for energy storage, catalysis and optoelectronics. So far, solution based methods for scalable production of few-layer TMDs usually involve the use of organic solvents or dangerous chemicals. Here, we report an eco-friendly method for facile synthesis of few-layer WS2 and MoS2 nanosheets using dilute aqueous solution of household detergent. Short time sonication of varying amount of bulk samples in soapy water was used to scale up the production of nanosheets. Thermal stability, optical absorption and Raman spectra of as-synthesized WS2 and MoS2 nanosheets are in close agreement with those from other synthesis techniques. Efficient photocatalytic activity of TMDs nanosheets was demonstrated by decomposing Brilliant Green dye in aqueous solution under visible light irradiation. Our study shows the great potential of TMDs nanosheets for environmental remediation by degrading toxic industrial chemicals in wastewater using sunlight.

Enhanced CO2 capture in Fe3O4-graphene nanocomposite by physicochemical adsorption

Cost effective and efficient methods for CO2 capture are the need of the hour to render the clean environment in the era of rising energy demand. Here, we report the physicochemical adsorption of carbon dioxide (CO2) in iron oxide decorated graphene nanocomposite at elevated pressures and temperatures. Nanocomposite was prepared by scalable and cost effective technique and its suitability for CO2 capture was studied at elevated pressures (3–13 bar) and temperatures (25–100 °C) using Sieverts apparatus. The higher CO2 capture capacities of 60, 35, and 24 mmol g−1 were observed at 11 bar pressure and 25, 50, and 100 °C, respectively, compared to other studied porous materials. Nature of interaction (Physicochemical adsorption) of CO2 with nanocomposite was identified using Fourier transform infrared spectroscopy. Degassing was performed to examine the recovery of nanocomposite.

Ultrahigh arsenic sorption using iron oxide-graphene nanocomposite supercapacitor assembly

In response to the increasing water demand, electro-sorption method has shown promise in context of high removal efficiency of metals with less energy consumption. Here, we report for the first time ultrahigh sorption capacity of iron oxide-graphene (Fe3O4-HEG) nanocomposite supercapacitor assembly for both inorganic arsenic species (arsenate and arsenite). Graphene has been synthesized by hydrogen induced exfoliation of graphitic oxide and decorated with iron oxide (Fe3O4) nanocrystals by chemical route. Electrochemical sorption behavior of nanocomposite electrodes for arsenic has been examined by cyclic voltammetry and kinetic studies. Adsorption isotherm models have been tested to calculate the maximum adsorption capacities (using Langmuir isotherm) for arsenate and arsenite and found to be nearly 172.1 and 180.3 mg/g, respectively, using supercapacitor assembly. These values are higher than other adsorbents for arsenic.

Removal of metals from aqueous solution and sea water by functionalized graphite nanoplatelets based electrodes

In the present wok, we have demonstrated the simultaneous removal of sodium and arsenic (pentavalent and trivalent) from aqueous solution using functionalized graphite nanoplatelets (f-GNP) based electrodes. In addition, these electrodes based water filter was used for multiple metals removal from sea water. Graphite nanoplatelets (GNP) were prepared by acid intercalation and thermal exfoliation. Functionalization of GNP was done by further acid treatment. Material was characterized by different characterization techniques. Performance of supercapacitor based water filter was analyzed for the removal of high concentration of arsenic (trivalent and pentavalent) and sodium as well as for desalination of sea water, using cyclic voltametry (CV) and inductive coupled plasma-optical emission spectroscopy (ICP-OES) techniques. Adsorption isotherms and kinetic characteristics were studied for the simultaneous removal of sodium and arsenic (both trivalent and pentavalent). Maximum adsorption capacities of 27, 29 and 32 mg/g for arsenate, arsenite and sodium were achieved in addition to good removal efficiency for sodium, magnesium, calcium and potassium from sea water.