Showing papers by "Sundara Ramaprabhu published in 2015"
TL;DR: In this article, Boron atoms were doped into graphene framework with an atomic percentage of 5.93% via hydrogen induced thermal reduction technique using graphite oxide and boric acid as precursors.
143 citations
TL;DR: In this paper, the role of multiwalled carbon nanotubes as a spacer which avoids face to face agglomeration of graphene sheets has also been studied for both the samples.
58 citations
TL;DR: In this article, an ionic liquid (IL) or polymerized Ionic Liquid (PIL) was integrated with graphene to demonstrate enhanced carbon dioxide adsorption properties, and the results showed that PIL functionalization offers more favorability of adsoration with a high adsorization energy.
Abstract: 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.
46 citations
TL;DR: In this paper, a new cathode material Na 4 Ni 3 (PO 4 ) 2 P 2 O 7 has been successfully synthesized by facile solution combustion synthesis (SCS) technique using various fuels such as glycine, urea and hexamine.
39 citations
TL;DR: In this paper, an iron nanoparticle encapsulated nitrogen and sulfur co-doped few layer graphene (Fe-NSG) non-precious electrocatalyst was used for proton exchange membrane fuel cells.
Abstract: A novel strategy was followed to prepare an iron nanoparticle encapsulated nitrogen and sulfur co-doped few layer graphene (Fe-NSG) non precious electrocatalyst. For this purpose, initially graphite oxide was coated with the polyelectrolyte poly-(sodium 4-styrenesulfonate), followed by the nitrogen-containing polymer polyaniline. An iron precursor was added to this suspension and heated to 300 °C in a hydrogen atmosphere. The final heating of this nanocomposite at 900 °C in a N2 atmosphere and further acid leaching gave a non-precious Fe-NSG catalyst. X-ray photoelectron spectroscopy (XPS) data of the Fe-NSG catalyst illustrates the presence of a large amount of pyridinic and graphitic nitrogen species within the catalyst along with sulfur species. Half-cell and full cell electrochemical measurements prove the four electron transfer pathway of the oxygen reduction reaction with a high current density in an acidic environment. The special confined morphology of Fe nanoparticles within the graphene layers suppresses the agglomeration and dissolution of particles and gives long term durability. The present study illustrates a non-precious electrocatalyst for proton exchange membrane fuel cells with promising performance and stability.
30 citations
TL;DR: In this paper, the combined effect of oxygen and nitrogen functional groups on highly crystalline carbon supports like multiwalled carbon nanotubes (MWCNT) and MWCNT-few layer graphene hybrid structures was investigated towards oxygen reduction reaction (ORR) performance and carbon corrosion durability in PEMFC applications.
Abstract: The combined effect of oxygen and nitrogen functional groups on highly crystalline carbon supports like multiwalled carbon nanotubes (MWCNT) and MWCNT-few layer graphene hybrid structures (MWCNT+FLG) have been investigated towards oxygen reduction reaction (ORR) performance and carbon corrosion durability in polymer electrolyte membrane fuel cell (PEMFC) applications. The pristine carbon supports were modified with oxygen and nitrogen functionalities by treating with concentrated mineral acids and subsequent nitrogen plasma treatment assisted with R.F. magnetron sputtering. Pt nanoparticles were dispersed over these chemically modified carbon supports by polyol reduction method. The physicochemical properties of as synthesized electrocatalysts were studied by different techniques such as XRD, TEM, FTIR, Raman and XPS. Electrochemical properties were investigated by cyclic voltammetry and linear sweep voltammetry in 0.1M HClO4 medium. Compared to commercial Pt/C catalysts, durability show ∼30 % enhancement for the as prepared electrocatalysts due to the presence of large amount of pyrrolic nitrogen and highly oriented graphitic nature of the catalyst supports. The ORR performance were comparable with Pt/C (TEC10E30E) in terms of MSA, 259, 270, 252 A g−1 for Pt/C, Pt/N-f-MWCNT, Pt/N-f-(MWCNT+FLG) respectively.
29 citations
TL;DR: It is elucidated that PEG-CNT films supported a dedicated differentiation of hMSCs into a skeletal myogenic lineage and can work as a promising material towards skeletal muscle injury repair.
Abstract: This study explored the influence of polyethylene glycol-linked multi-walled carbon nanotube (PEG-CNT) films on skeletal myogenic differentiation of human mesenchymal stem cells (hMSCs). PEG-CNT films were prepared with nanoscale surface roughness, orderly arrangement of PEG-CNTs, high hydrophilicity and high mechanical strength. Notably, PEG-CNT films alone could direct the skeletal myogenic differentiation of hMSCs in the absence of myogenic induction factors. The quantitative real-time polymerase chain reaction (RT-PCR) showed that the non-induced hMSCs plated on the PEG-CNT films, compared to the negative control, presented significant up-regulation of general myogenic markers including early commitment markers of myoblast differentiation protein-1 (MyoD) and desmin, as well as a late phase marker of myosin heavy chain-2 (MHC). Corresponding protein analysis by immunoblot assays corroborated these results. Skeletal muscle-specific markers, fast skeletal troponin-C (TnC) and ryanodine receptor-1 (Ryr) were also significantly increased in the non-induced hMSCs on PEG-CNT films by RT-PCR. For these cells, the commitment to specific skeletal myoblasts was further proved by the absence of enhanced adipogenic, chondrogenic and osteogenic markers. This study elucidated that PEG-CNT films supported a dedicated differentiation of hMSCs into a skeletal myogenic lineage and can work as a promising material towards skeletal muscle injury repair.
28 citations
TL;DR: In this article, the authors demonstrate that the d-orbitals of Au nanoparticles exhibit little or no rehybridization with graphene and result in an enhanced optical limiting behavior at a low fluence of ∼0.4
28 citations
TL;DR: The fabrication of a novel amperometric biosensor based on selective determination of dopamine (DA) using nafion coated cerium oxide nanoparticles (NPs) decorated graphene nanosheets (CeO2-HEG-nafion) as a transducer candidate is reported.
Abstract: The fabrication of a novel amperometric biosensor based on selective determination of dopamine (DA) using nafion coated cerium oxide nanoparticles (NPs) decorated graphene nanosheets (CeO2-HEG-nafion) as a transducer candidate is reported. Graphene was synthesized by hydrogen exfoliation technique. Decoration of CeO2NPs over graphene nanosheets was done by chemical reduction method. The electrochemical impedance spectroscopy (EIS) study shows the enhanced electron transfer kinetics of the composite compared to HEG modified and bare glassy carbon electrode (GCE). The response of the composite towards dopamine displays a lower oxidation potential of 0.23 V and a high oxidation current. The sensor exhibits linearity from 10 µM to 780 µM with a detection limit of 1 µM. In the presence of nafion, it shows excellent selectivity for coexisting interference species like Ascorbic acid (AA) and Uric acid (UA). The excellent performance of the biosensor can be attributed to large active surface area, enhanced electron transfer kinetics and high catalytic activity of the composite.
25 citations
TL;DR: It is concluded that MWCNT-induced pulmonary toxicity is considerable even on single exposure, characterized by progressive elevation of TNF-α and IL-4.
Abstract: We have investigated the time-dependent effect of multi-walled carbon nanotubes (MWCNTs) in rats upon single inhalation exposure followed by intermittent sacrifice. The effects were monitored by analyzing the bronchoalveolar lavage fluid (BALF) and histopathological analysis. Cell count, neutrophils, lymphocytes, lactate dehydrogenase, alkaline phosphatase, protein and cytokines (tumor necrosis factor-alpha (TNF-α) and interleukin 4 (IL-4)) were significantly increased, while cell viability and alveolar macrophage count significantly decreased in the BALF of MWCNT-treated rats on day 1, day 7 and day 14 post-exposure, when compared to control rats. Histopathological analysis revealed inflammation, fibrosis and granuloma in the lungs of MWCNTs-treated rats on day 7 and day 14 post-exposure. We interpret that MWCNT induces inflammation, fibrosis and granuloma characterized by progressive elevation of TNF-α and IL-4. Histopathological studies further support our view and reveal the distribution of MWCNT in lungs and tracheobronchial lymph nodes (TBLN). We conclude that MWCNT-induced pulmonary toxicity is considerable even on single exposure.
21 citations
TL;DR: This study shows the phenomenal pH responsive drug release to the cancerous microenvironment and prolonged release and suggests that MWNTs have a great potential as a drug carrier.
Abstract: The main aim of the current study is to formulate the Doxorubicin loaded functionalized carbon nanotubes to deliver the drug only to the cancer cells by using pH difference. Multi walled Carbon Nanotubes (MWNTs) have been identified as an efficient drug carrier through π-π linkage, because this covalent bond is sensitive to tumor microenvironments. This bond is acid cleavable, thereby providing a strong pH-responsive drug release, which may facilitate effective release near the acidic tumor microenvironment and thus reduces its overall systemic toxicity. Doxorubicin was released at low pH and taken up by tumor cells via adenosine triphosphate (ATP)-dependent endocytosis. By varying the Concentration of MWNTs with the Doxorubicin, it forms a conjugate. It is due to supra molecular interactions between the drug and MWNTs, so it shows high loading, prolonged release and improved cytotoxicity against cancer cells. This study shows the phenomenal pH responsive drug release to the cancerous microenvironment and prolonged release. This study suggests that MWNTs have a great potential as a drug carrier; the efficient formulation strategy requires further study.
TL;DR: The present work provides an incredible route towards achieving the ideal Li ion battery anode material with high specific capacity and rate capability as a result of unraveling a few upper layers of multiwalled carbon nanotubes as graphene nanoribbons attached to the core MWNT.
Abstract: The present work provides an incredible route towards achieving the ideal Li ion battery anode material with high specific capacity and rate capability as a result of unraveling a few upper layers of multiwalled carbon nanotubes (MWNTs) as graphene nanoribbons attached to the core MWNT. These partially exfoliated nanotubes when used as an anode material show an 880 mA h g−1 capacity at a 100 mA g−1 current density and high rate capability by delivering a stable 157 mA h g−1 capacity at a current density of 10 A g−1. The enhanced performance of this anode material can be attributed to the synergistic effect of the homogeneous distribution of the hybrid carbon nanostructure of 1-D multiwalled carbon nanotubes and 2-D graphene nanoribbons. This configuration provides a large available surface area, high electrical conductivity and a high number of defect sites, leading to improved Li intercalation with a better transfer rate compared to only graphene, multiwalled carbon nanotubes or other reported combinations of the two.
TL;DR: In this paper, the performance of a hybrid carbon structure of one dimensional (1D) multi-walled carbon nanotubes and 2D graphene sheets as the catalyst support material for proton exchange membrane fuel cells was reported.
TL;DR: In this article, a large scale root to assemble hierarchical copper-based nanostructures on nitrogen-doped graphene sheets by a pH followed by a temperature-directed self-assembly process and their electron field emission studies was reported.
Abstract: We report a large scale root to assemble hierarchical copper-based nanostructures on nitrogen-doped graphene sheets by a pH followed by a temperature-directed self-assembly process and their electron field emission studies. Starting with a controlled pH directed self-assembly root, we assembled Cu(OH)2 NRs on NGS and further reassembled it to 1D Cu NPAs and CuO NRs by thermal annealing in H2 and Ar atmosphere, respectively. The field emission characteristics are precisely studied, which depicts a significantly lower threshold and turn-on field for 1D Cu NPAs-NGS-based emitter compared to CuO NRs-NGS and Cu(OH)2 NRs-NGS. Also it exhibited about 3 and 27 times higher emission current density than its oxide and hydroxide counterpart under a moderate field of 1 V/μm. The enhanced field emission behavior of 1D Cu NPAs-NGS is attributed to the low work function, the easy electron tunneling from the one-dimensional arrangement of Cu NPs, which increases the emission sites and hence the FE current density. On the...
TL;DR: In this paper, a multiwalled carbon nanotube (MWNTs) surface was functionalized with PIL and used as a cathode catalyst support, which showed extremely good affinity towards CO2 and facilitates better dispersion of catalyst nanoparticles.
Abstract: 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.
TL;DR: The improved performance of N-HEG based supercapacitor is attributed to the presence of nitrogen atoms in the graphene lattice which in turn increases the lattice-ion interaction and the electrical conductivity.
Abstract: Graphene is a promising electrode material for supercapacitor applications due to its unique properties. Interaction of electrolyte ions with graphene lattice sites is a crucial factor in ionic liquid electrolyte based supercapacitors. In an effort to increase the interaction of high viscous electrolyte with electrode material, here, we here report the results of a systematic study carried out on a supercapacitor with nitrogen doped graphene as electrode material and [BMIM][TFSI] as electrolyte. In this study, nitrogen doped hydrogen exfoliated graphene (N-HEG) is prepared by radio frequency (R.F) magnetron sputtering and employed as electrode material for [BMIM][TFSI] electrolyte based high performance supercapacitor. N-HEG shows a high specific capacitance of 170.1 F/g compared to that of electrolyte modified graphene (124.5 F/g), at a specific current of 2 A/g. The improved performance of N-HEG based supercapacitor is attributed to the presence of nitrogen atoms in the graphene lattice which in turn increases the lattice-ion interaction and the electrical conductivity. In addition, the presence of wrinkles on the graphene surface provides a shortest directional path to access pores and surface. The device shows high charge storage capacity (72.37 Wh/kg) along with wide operating voltage (3.5 V) and high cyclic stability.
TL;DR: Li et al. as mentioned in this paper presented a graphitization on LiFePO4/C composite cathode material, where layered sheets of graphene were wrapped on the LiFeP4 particles to provide void between graphene sheets and LiP4 surfaces, which facilitated the diffusion of Li+.
Abstract: The graphene enfolded LiFePO4/C composite cathode material has been prepared via low temperature polyol process, followed by a simple chemical reaction method. The low viscous polyol solvent (DEG) (35.7 mPa s at 25°C) and usage of low temperature process (below 245°C) aid the graphene tightly encapsulated on the LiFePO4 surface that plays an important role, especially in the high rate performances over long cycles, efficiently preventing the separation of the graphene and LiFePO4 during the reaction processes, hence realizing the full potential of the active materials. The graphitization on LiFePO4/C remarkably increased the electronic conductivity of LiFePO4. The layered sheets of graphene wrapped on LiFePO4 particles provide void between graphene sheets and LiFePO4 surfaces, which facilitate the diffusion of Li+. This approach opens up a method to attain the theoretical capacity of LiFePO4. The material exhibits a superior electrochemical performance such as initial discharge capacities of 169.6 and 92 mAhg−1 at 0.1 and 30 C rates, respectively. It has an excellent capacity retention and diminutive capacity fading. The nanosize of LiFePO4 particle causes a shorter diffusion path, which reduces the time for Li+ migration between cathode and electrolyte.
TL;DR: In this paper, a 1-D monohybrid of multiwalled carbon nanotubes and graphene sheets, synthesized in a template-free simple chemical vapor deposition technique without any chemical functionalization, was employed as efficient anode material for Li ion battery.
TL;DR: In this paper, an ionic liquid was employed as a functional moiety on a graphene catalyst support since it shows reversible interactions with CO2 molecules and showed a higher formic acid formation rate compared to a pure support under similar experimental conditions.
Abstract: 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.
TL;DR: In this paper, the effect of saturable absorption in a dye decreases significantly in the presence of functionalized hydrogen-induced exfoliated wrinkled graphene (f-HEG), and the absorption spectra give strong evidence of complex formation in the ground state.
Abstract: The effect of saturable absorption in a dye decreases significantly in the presence of functionalized hydrogen-induced exfoliated wrinkled graphene (f-HEG). The absorption spectra give strong evidence of complex formation in the ground state. The fluorescence spectra and nonlinear optical properties of the dye are affected by f-HEG and silver decorated graphene (Ag-f-HEG) by various degrees. The open aperture Z-scan and degenerate four wave mixing (DFWM) techniques have been used to record the drastic changes in the nonlinear optical parameters of dye in presence of f-HEG and Ag-f-HEG. The results indicate a reduction in the average value of the nonlinearity due to formation of the non-fluorescent ground-state charge-transfer complex. At high input irradiance the optical limiting capability of the dye-f-HEG system has been found to be enhanced. The pre-existing charge transfer between silver nanoparticles and f-HEG reduces the strength of dye-f-HEG complex formation.
TL;DR: In this paper, the carbon dioxide adsorption properties of nitrogen doped graphene at low pressures (<100 kPa) were investigated. And it was found that nitrogen doping significantly improves the CO2 adsorbing capacity at all temperatures, due to the enrichment of local Lewis basic sites.
Abstract: 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.
TL;DR: In this paper, 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).
Abstract: 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.
TL;DR: It was observed that incorporation of MWNTs in the PPy NP CE greatly enhanced the catalytic activity for I3 reduction and significantly reduced the charge transfer resistance in thePPy NP/MWNTs composite CE finally improving short-circuit photocurrent density, fill factor, open circuit voltage and power conversion efficiency of DSSC.
Abstract: In this present work, Multi-walled carbon nanotubes (MWNTs) with different content by weight (10%, 20%, 30%, 50% and 70%) are introduced into Polypyrrole nanoparticles (PPy NP) matrix and fabricated as Pt free counter electrodes (CEs) for dye-sensitized solar cell (DSSC). For comparison DSSCs using pristine PPy NP, MWNTs and Platinum (Pt) were also fabricated. The incorporation of MWNTs acts as conductive channel and co-catalyst to the PPy NP CEs in the reduction of li to I-. The electrochemical catalytic activities of different CEs were analysed by Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) and photovoltaic performance was studied under standard AM 1.5 sunlight illumination. It was observed that incorporation of MWNTs in the PPy NP CE greatly enhanced the catalytic activity for I3 reduction and significantly reduced the charge transfer resistance in the PPy NP/MWNTs composite CE finally improving short-circuit photocurrent density, fill factor, open circuit voltage and power conversion efficiency of DSSC. DSSC fabricated from PPy NP/MWNTs composite CE with 50% MWNTs content reached the highest photoconversion efficiency of 5.80% which is 91% that of Pt CE based DSSC (6.37%).