Browsing by Author "Seema Awasthi"

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Formation of single and multi-walled carbon nanotubes and graphene from Indian bituminous coal
(Elsevier Ltd, 2015) Seema Awasthi; Kalpana Awasthi; A.K. Ghosh; S.K. Srivastava; O.N. Srivastava
Single-walled carbon nanotubes (SWCNTs) have been synthesized by electric arc discharge method using annealed coal electrode in the presence of Fe as well as Ni-Y as catalysts. Multi-walled carbon nanotubes (MWCNTs) have been synthesized without using any catalysts. The efforts have also been made to synthesized graphene like nanosheets from bituminous coal. The as-synthesized samples have been characterized through scanning and transmission electron microscopy, Raman and Fourier transform infrared spectroscopy. The formation of SWCNTs which holds nearly perfect one dimensional structure is confirmed by the presence of radial breathing mode. A feasible mechanism of CNTs formation from coal described here with the help of Fourier transform infrared spectroscopy. © 2015 Elsevier Ltd. All rights reserved.
Formation of single-walled carbon nanotube buckybooks, graphene nanosheets and metal decorated graphene
(Trans Tech Publications Ltd, 2018) Seema Awasthi; Kalpana Awasthi; O.N. Srivastava
The present study deals with the systematic study of the synthesis of various useful carbon nanostructures e.g. single-walled carbon nanotubes (SWCNTs) and graphene in large quantity by electrical arc discharge method by only varying the argon atmosphere pressure. The as-synthesized nanostructures were characterized by different characterization techniques such as XRD, SEM, TEM, Energy dispersive X-ray spectroscopy, Raman and FTIR spectroscopy. The SWCNT webs of length ~6 cm abundantly containing aligned SWCNTs have diameter of about 1.8 nm and form buckybook like structure. Few layer graphene (FLG) sheets were prepared by electric arc discharge of high purity graphite electrodes in a varying argon gas atmosphere (250 -500T). The largest areal extent of graphene (with lowest number of layer i.e. four) has been found at 350T argon pressure. A one step method is reported for the decoration of the graphene nanosheets with iron and nickel nanoparticles through arc discharge method. © 2018 Trans Tech Publications, Switzerland.
Functionalization effects on the electrical properties of Multi-walled carbon nanotube-polyacrylamide composites
(2009) Seema Awasthi; Kalpana Awasthi; Rajesh Kumar; O.N. Srivastava
Multi-walled carbon nanotubes (MWNTs)-polyacrylamide (RAM) composites have been prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A comparative study has been made on the electrical property of these MWNTs-PAM composites with different MWNTs loadings. It has been shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. As the MWNTs loading increases from 0 to 40 wt% electrical conductivity of composite film increases by ∼7 orders of magnitude whereas the electrical conductivity of functionalized composite film increases only ∼4 orders of magnitude with respect to the pure RAM film. A model based on power law percolation for the electronic behavior of above composite has been developed and shows good agreement with the experimental data. Copyright © 2009 American Scientific Publishers.
Graphene decorated with Fe nanoclusters for improving the hydrogen sorption kinetics of MgH 2 - Experimental and theoretical evidence
(Royal Society of Chemistry, 2016) M. Sterlin Leo Hudson; Keisuke Takahashi; A. Ramesh; Seema Awasthi; Ashish Kumar Ghosh; Ponniah Ravindran; Onkar Nath Srivastava
Graphene decorated with Fe clusters is proposed to be a possible alternative catalyst for the hydrogenation and dehydrogenation reactions of MgH 2 . In particular, graphene decorated with Fe clusters is effective for both hydrogenation and dehydrogenation processes of MgH 2 . The change in enthalpy and entropy values of hydrogen absorption determined for MgH 2 with 5 wt% graphene decorated with Fe clusters is -50.4 ± 2.9 kJ per mole of H 2 and 99.8 ± 5.2 J K -1 per mole of H 2 , respectively. This is significantly lower than those for well-established metal catalysts and nano-interfacial confined MgH 2 . Moreover, the graphene decorated with Fe clusters facilitates the fast rehydrogenation kinetics of MgH 2 , which reabsorbed 90% of the total reabsorption capacity in less than 4 minutes at 300 °C and 20 atm. In addition, TEM analysis reveals that MgH 2 particles are covered by graphene with Fe clusters, resulting in the reduction of grain growth. Density functional theory shows that the defects in graphene act as the active sites for the dehydrogenation of MgH 2 , while the Fe clusters reduce the adsorption of dissociated H atoms, resulting in low-temperature dehydrogenation. Thus, graphene decorated with metal clusters could open up a new way of designing a new type of catalyst which could replace transition metal catalysts. © The Royal Society of Chemistry 2016.
Graphene: A revolutionary exotic material and its applications
(Nova Science Publishers, Inc., 2021) Seema Awasthi; O.N. Srivastava; A. Rajanikanth; C. Bansal
Materials science involves understanding of materials behavior based on their macro/microstructures. Nanoscience has emerged as one of the exciting area of materials science and has created an impact on almost every field of science and technology. Particles at the nanoscale length exhibit exotic physico-chemical properties as compared to their bulk counterparts. Carbon is the most studied material in nanoscience due to its versatility in being found in 0D, 1D, 2D and 3D structures. Graphene, a 2D honeycomb lattice of carbon atoms attracted the attention of scientists from all over the world after its discovery in 2004. This exotic form of carbon has versatile properties and manifold applications. It has also provided a whole new branch of materials known as two dimensional layered materials, which exhibits similar and superior properties and applications when combined with/without graphene. The present chapter deals with various synthesis methods, properties and applications of graphene. This chapter focuses mainly on electrochemical exfoliation method for the production of graphene through aqueous and non-aqueous route, since it is a promising bulk method for producing graphene from graphite and can produce single and multilayer graphene in less time.A summary of important characterization methods for graphene will also be discussed. Applications of graphene in many areas of materials science will also be discussed, due to which it has created huge impact on research and current societal development. Exfoliation of layers of graphene from bulk graphite has given a lead to exfoliate various other stable layered materials besides graphite. These types of new exotic materials other than graphene and their hybrid structure with graphene will also be discussed briefly. © 2021 by Nova Science Publishers, Inc. All rights reserved.
Hydrogen uptake of reduced graphene oxide and graphene sheets decorated with Fe nanoclusters
(Elsevier Ltd, 2014) M. Sterlin Leo Hudson; Himanshu Raghubanshi; Seema Awasthi; T. Sadhasivam; Ashish Bhatnager; Satoru Simizu; S.G. Sankar; O.N. Srivastava
Graphene oxide (GO) has been prepared by employing modified Staudenmaier's method through thermal exfoliation of graphite oxide. High pressure hydrogen sorption isotherms up to 50 bar of GO, reduced by thermal reduction (TR-GO), chemical reduction (CR-GO) and graphene sheets decorated with Fe nanoclusters (Fe-GS) have been investigated. Thermal reduction of GO at 623 K under high vacuum yields TR-GO. Chemical reduction of GO using hydrazine forms CR-GO. Fe-GS was synthesized through arc-discharge between the ends of two graphite rods with one rod carrying Fe nanoparticles. The surface areas of these graphene samples were determined from the nitrogen adsorption isotherm employing Brunauer, Emmett and Teller (BET) method. Kelvin's equation was used to determine the pore size distribution of all graphene based samples. Hydrogen pressure-composition isotherms (PCI) were determined at 300 K and at 77 K, between 0.1 and 50 bar. Further, in this paper, we present a comparative adsorption isotherm analysis of hydrogen and helium on TR-GO. This reveals that the volume of hydrogen and helium adsorbed by TR-GO is nearly equal. The similar uptake volume determined for both hydrogen and helium indicates the possibility of monolayer adsorption of hydrogen and also nearly similar binding energy between TR-GO and H2/He. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Notable electrical and mechanical properties of polyacrylamide (PAM) with graphene oxide (GO) and single-walled carbon nanotubes (SWCNTs)
(Walter de Gruyter GmbH, 2023) Seema Awasthi; Thakur Prasad Yadav; Kalpana Awasthi
In the present investigation, a polyacrylamide (PAM) - graphene oxide (GO)-single-walled carbon nanotubes (SWNTs) composite has been prepared through a cost effective solution cast method and physical properties (electrical and mechanical) measurements have been carried out. The GO sheets contain oxygen functional groups which enhance the interfacial adhesion with the polymer matrix, while the SWNTs act as wires joining the GO together in the composite matrix. This interconnected network creates a conducting path, lowering film resistance and improving PAM films' electrical, mechanical, and thermal properties. Raman study demonstrated that carbon nanofiller (SWNTs, GO) and polymer PAM have good interfacial bonding. The electrical conductivity and mechanical characteristics (hardness and elastic modulus) of these composite films were enhanced at a loading of 15 wt% GO and 15 wt% SWNTs in PAM matrix. Electrical conductivity of GO (15 wt%) - SWNTs (15 wt%)-PAM composite film was found to be 2.8 × 10-2 S/cm, which is five orders of magnitude higher than that of the PAM polymer. In comparison to pure PAM polymer, the elastic modulus and hardness are found to be 1.14 and 65 times higher, respectively. © 2023 Walter de Gruyter GmbH, Berlin/Boston.
Synthesis and characterization of carbon nanotube-polyethylene oxide composites
(2006) Kalpana Awasthi; Seema Awasthi; Anchal Srivastava; R. Kamalakaran; S. Talapatra; P.M. Ajayan; O.N. Srivastava
We have investigated the structural, electrical and mechanical properties of multi-walled carbon nanotube (MWNT)-polyethylene oxide (PEO) composites. Composites with different wt% (between 0 and 50wt% of MWNTs) were prepared and characterized by the scanning electron microscopic technique. Enhanced electrical conductivity and mechanical strength were observed for the MWNT-PEO composites. The conductivity measurements on the MWNT-PEO composite films with highest concentration of MWNTs (∼50wt%) showed an increase of eight orders (∼7.5 × 10-8 to 6.52Scm-1) of magnitude in conductivity from bare PEO film. The temperature dependence of the conductivity for MWNT (∼50wt%)-PEO composite showed predominantly semiconducting behaviour. The elastic modulus and tensile strength of an MWNT (∼50wt%)-PEO film were increased by about five-and tenfold respectively, as compared to the corresponding values for a PEO film. © IOP Publishing Ltd.
Synthesis of nano-carbon (nanotubes, nanofibres, graphene) materials
(Indian Academy of Sciences, 2011) Kalpana Awasthi; Rajesh Kumar; Himanshu Raghubanshi; Seema Awasthi; Ratnesh Pandey; Devinder Singh; T.P. Yadav; O.N. Srivastava
In the present study, we report the synthesis of carbon nanotubes (CNTs) using a new natural precursor: castor oil. The CNTs were synthesized by spray pyrolysis of castor oil-ferrocene solution at 850°C under an Ar atmosphere. We also report the synthesis of carbon nitrogen (C-N) nanotubes using castor oil- ferrocene-ammonia precursor. The as-grown CNTs and C-N nanotubes were characterized through scanning and transmission electron microscopic techniques. Graphitic nanofibres (GNFs) were synthesized by thermal decomposition of acetylene (C2H2) gas using Ni catalyst at 600°C. As-grown GNFs reveal both planar and helical morphology. We have investigated the structural and electrical properties of multi-walled CNTs (MWNTs)-polymer (polyacrylamide (PAM)) composites. The MWNTs-PAM composites were prepared using as purified, with ball milling and functionalized MWNTs by solution cast technique and characterized through SEM. A comparative study has been made on the electrical property of these MWNTs-PAM composites with different MWNTs loadings. It is shown that the ball milling and functionalization of MWNTs improves the dispersion of MWNTs into the polymer matrix. Enhanced electrical conductivity was observed for the MWNTs-PAM composites. Graphene samples were prepared by thermal exfoliation of graphite oxide. XRD analysis confirms the formation of graphene. © Indian Academy of Sciences.