P. Tamilarasan

Ionic liquid-functionalized partially exfoliated multiwalled carbon nanotubes for high-performance supercapacitors

Partially exfoliated multiwalled carbon nanotubes (PEMWNTs) have great potential to play a major role in electrochemistry, because they have a combination of unique properties of multiwalled carbon nanotubes (MWNTs) and graphene such as high electrical conductivity, high surface area and porosity. In the present study, we have synthesized partially oxidized MWNTs by Hummers method with modest modification and exfoliated to unravel few of the outer layers. Furthermore, the surface of PEMWNTs was functionalized with an ionic liquid (PEMWNTs/IL). The specific capacitance of supercapacitor, fabricated with PEMWNTs/IL, was found to be 242 F g−1 at 2 A g−1 current density, which is 85% higher than that of PEMWNTs-based supercapacitors. The PEMWNTs/IL supercapacitor gains almost 2-fold improvement in energy density along with good cyclic stability. Nyquist plot clearly suggested that charge transfer resistance is significantly reduced by ionic liquid functionalization, but the electron transfer among PEMWNTs is not affected. The low frequency region of the Nyquist plot suggests the charge storage in the wrinkles and folds of unraveled graphene layers.

Integration of polymerized ionic liquid with graphene for enhanced CO2 adsorption

In this study, we have integrated an ionic liquid (IL) or polymerized ionic liquid (PIL) with graphene to demonstrate enhanced carbon dioxide adsorption properties. Graphene was non-covalently functionalized by IL or PIL, and the carbon dioxide adsorption and desorption properties were determined at low-pressures (<100 kPa). Upon functionalization, IL uniformly covers the graphene surface, while PIL forms highly distributed porous nanoparticles. The PIL functionalized graphene shows 22% higher adsorption capacity than graphene, while IL functionalization improves it only by 2%. This highlights the advantage of polymerizing the ionic liquid. Interestingly, the adsorption capacities of integrated system are higher than those of individual constituents (either graphene or IL or PIL). It is found that PIL functionalization offers more favorability of adsorption with a high adsorption energy. Isosteric heats of adsorption are calculated to be in the range of 18–28 kJ mol−1, suggesting an ease of adsorbent regeneration. These results encourage the integration of PIL with other high surface area nanostructures for further improvement in the adsorption capacity.

Effect of partial exfoliation in carbon dioxide adsorption-desorption properties of carbon nanotubes

In this study, we have experimentally studied the effect of partial exfoliation in low-pressure (<100 kPa) carbon dioxide adsorption and desorption behavior of multiwalled carbon nanotubes (MWNTs). MWNTs were partially exfoliated by controlled oxidation followed by hydrogen assisted low temperature exfoliation method. The adsorption capacity of partially exfoliated MWNTs (PEMWNTs) is 3.4 times that of MWNTs. Adsorption-desorption isotherms of MWNTs are unique, which shows trapping behavior. The desorption behavior in association with isothermal adsorbate retention of MWNTs and PEMWNTs suggests possible CO2 trapping inside the tubes and at interstitials. It is found that the CO2 adsorbed PEMWNTs system has higher molecular orbital energy than CO2 adsorbed MWNTs system. Areal adsorption capacity analysis suggests the significant influence of surface functional groups on adsorption capacity. Adsorption isosteres of both adsorbents follow the Arrhenius relation stating the temperature dependent adsorption rat...

Sub-ambient carbon dioxide adsorption properties of nitrogen doped graphene

Carbon dioxide adsorption on carbon surface can be enhanced by doping the surface with heterogeneous atoms, which can increase local surface affinity. This study presents the carbon dioxide adsorption properties of nitrogen doped graphene at low pressures (<100 kPa). Graphene was exposed to nitrogen plasma, which dopes nitrogen atoms into carbon hexagonal lattice, mainly in pyridinic and pyrrolic forms. It is found that nitrogen doping significantly improves the CO2 adsorption capacity at all temperatures, due to the enrichment of local Lewis basic sites. In general, isotherm and thermodynamic parameters suggest that doped nitrogen sites have nearly same adsorption energy of surface defects and residual functional groups. The isosteric heat of adsorption remains in physisorption range, which falls with surface coverage, suggesting the distribution of magnitude of adsorption energy. The absolute values of isosteric heat and entropy of adsorption are slightly increased upon nitrogen doping.

Amine-rich ionic liquid grafted graphene for sub-ambient carbon dioxide adsorption

The present study describes the synthesis of the adsorptivity based amine-rich ionic liquid (ARIL), namely, 3,5-diamino-1-methyl-1,2,4-triazolium tetrafluoroborate grafted graphene (HEG/ARIL), and its application in carbon dioxide adsorption. This ionic liquid occurs in the solid form at standard atmospheric temperature and pressure, and forms solid-like short range ordering on a graphitic substrate. Molecular vibrational spectroscopy suggests that the ARIL molecules are physically adsorbed on the graphene surface with no detectable chemical interactions. The CO2 adsorption on ARIL is not significantly accompanied by chemical interaction with the amine groups under sub-ambient conditions. The adsorption capacity of ARIL attained a significant improvement when it was grafted onto graphene. The favourability and energy of adsorption suggest that the cumulative interaction of CO2 with ARIL moieties is weaker than that with residual oxygen-containing functional groups in graphene. The adsorbate retention of graphene is largely increased upon grafting ARIL. The isosteric heat and entropy of CO2 adsorption on the HEG/ARIL is lower than that found on pristine HEG. Conclusively, ARIL functionalization improved the CO2 adsorption capacity and decreased the interaction energy between CO2 and graphene, because it enhances the density of the low affinity adsorption sites.

Iron-manganese binary oxide coated functionalized multiwalled carbon nanotubes for arsenic removal

In the present study, we report, iron-manganese based amorphous binary oxide coated functionalized multiwalled carbon nanotubes (f-MWNTs) as an efficient adsorbent for arsenic removal. The Fe-Mn binary oxide/f-MWNTs (FeMn/f-MWNT) has been synthesized by co-precipitation of both oxides in the presence of f-MWNTs and characterized. The arsenic (both arsenate and arsenite) adsorption capacity of the nanocomposite has been studied by batch adsorption method at pH around 7. Langmuir and Elovich equations were used to extract the isotherm and kinetic constants, respectively. This nanocomposite shows fast adsorption kinetics and high adsorption capacity.

Ionic liquid functionalization – an effective way to tune carbon dioxide adsorption properties of carbon nanotubes

In this research, the influence of non-covalent functionalization by ionic liquids on carbon dioxide (CO2) adsorption–desorption properties of multi-walled carbon nanotubes (MWNTs) and partially exfoliated MWNTs (PEMWNTs) has been studied. In addition, the effect of polymerization of the ionic liquid on CO2 adsorption–desorption properties has also been studied at low pressures (<100 kPa) and at different temperatures. The thermodynamic parameters were also determined. It was found that ionic liquid functionalization significantly improved the adsorption capacity through weak CO2 complex formation with the substituted nitrogen of the imidazolium cation. Furthermore, the adsorption isotherm analysis suggested that the residual functional groups were more affine compared to the ionic liquid moieties. The heat of adsorption behaves differently upon polymerization of the ionic liquid on both substrates. The influence of polymerization on the entropy change was much more significant with the MWNTs substrate, whereas it was negligible with PEMWNTs.

Task-specific functionalization of graphene for use as a cathode catalyst support for carbon dioxide conversion

This study describes the potential advantages of task-specific functionalization of graphene for carbon dioxide capture and conversion. An ionic liquid was employed as a functional moiety on a graphene catalyst support since it shows reversible interactions with CO2 molecules. In this study, graphene was synthesized by a hydrogen-assisted low-temperature-exfoliation method and functionalized using a polymerized ionic liquid (PIL). Adsorption analysis shows that PIL functionalization improves the CO2 adsorption capacity of graphene significantly. Catalytic nanoparticles were dispersed over the catalyst supports by a microwave assisted polyol reduction method and the catalysts were employed as the cathode catalyst in a polymer electrolyte membrane (PEM) CO2 conversion cell. The cell hydrogenates CO2 into formic acid at the cathode, which was quantified by spectrophotometry. The PIL functionalized support shows a higher formic acid formation rate compared to a pure support under similar experimental conditions since PIL functionalization improves the interactions between the catalyst support and the CO2 molecules. The cells were tested with discontinuous and continuous CO2 supplies.

A polymerized ionic liquid functionalized cathode catalyst support for a proton exchange membrane CO2 conversion cell

This study aims at the efficient conversion of CO2 to formic acid using a proton exchange membrane cell by selective functionalization of a cathode catalyst support. We chose polymerized ionic liquid (PIL) as the surface functional moiety, since CO2 has good solubility in it. A multiwalled carbon nanotube (MWNTs) surface was functionalized with PIL and used as a cathode catalyst support. This novel catalyst support shows extremely good affinity towards CO2 and facilitates better dispersion of catalyst nanoparticles. Catalytic nanoparticles were decorated over the catalyst supports by a microwave assisted polyol reduction method, which gives better dispersion of finer particles on PIL functionalized MWNTs compared to pure MWNTs. The protonation of CO2 to formic acid has been studied in a polymer electrolyte membrane (PEM) CO2 conversion cell with synthesized catalysts. The cells were tested under continuous and discontinuous CO2 supply, where PIL functionalized MWNTs show a better formic acid formation rate than the pure support under identical experimental conditions, due to the improved interaction between the catalyst support and CO2 molecules.

Graphene/Ionic Liquid Binary Electrode Material for High Performance Supercapacitor

Herein, we report, the use of hydrogen exfoliated graphene (HEG)/ionic liquid (1-Butyl-3-methylimidazolium terafluoroborate ([BMIM]BF4)) binary electrode material for high performance supercapacitor. HEG/[BMIM] BF4 nanocomposite was prepared and the electrochemical characterization of the electrode has been carried out by cyclic voltammetry and chronopotentiometry. The nanocomposite electrode shows a high specific capacitance (268 F/g at 5mV/s scan rate. Since the ionic liquid has large electrochemical window of 2 V even at atmospheric conditions than the aqueous electrolytes, high energy density of 66.9 Wh/kg at 5 A/g current density could be achieved. KeywordsHydrogen exfoliated graphene; supercapacitor; ionic liquid; cyclic voltammetry