Tessy Theres Baby

Graphene synthesis via hydrogen induced low temperature exfoliation of graphite oxide

A novel and facile technique for the rapid synthesis of few layered graphene sheets via hydrogen induced reduction–exfoliation of graphite oxide at a low temperature of ∼200 °C is reported.

Investigation of thermal and electrical conductivity of graphene based nanofluids

We report for the first time, the synthesis of highly stable exfoliated graphene based nanofluids with water and ethylene glycol as base fluids with out any surfactant and the subsequent studies on their thermal and electrical conductivities. Graphene was synthesized by thermal exfoliation of graphene oxide at 1050 °C in Ar atmosphere. The as-synthesized graphene has been suitably functionalized and further dispersed it in the base fluids without any surfactant. Thermal and electrical conductivities of these nanofluids were measured for varying volume fractions and at different temperatures. An enhancement in thermal conductivity by about 14% has been achieved at 25 °C with deionized water (DI) as base fluid at a very low volume fraction of 0.056% which increases to about 64% at 50 °C. Electrical conductivity measurements for these nanofluids indicate an enormous enhancement at 25 °C for a volume fraction of 0.03%in DI water.

SiO2 coated Fe3O4 magnetic nanoparticle dispersed multiwalled carbon nanotubes based amperometric glucose biosensor.

A new type of amperometric glucose biosensor based on silicon dioxide coated magnetic nanoparticle decorated multiwalled carbon nanotubes (Fe(3)O(4)@SiO(2)/MWNTs) on a glassy carbon electrode (GCE) has been developed. MWNTs have been synthesized by catalytic chemical vapour decomposition (CCVD) of acetylene over rare earth (RE) based AB(3) alloy hydride catalyst. The as-grown MWNTs have been purified and further functionlized. Functionalized MWNTs have been decorated with magnetic Fe(3)O(4) nanoparticles which have been uniformly coated with biocompatible SiO(2) using a simple chemical reduction method. The characterization of magnetic nanoparticle modified MWNTs have been done by X-ray diffraction (XRD), Fourier transform infra red spectroscopy (FT-IR), scanning electron microscope (SEM), transmission electron microscope (TEM), vibrating sample magnetometer (VSM), energy dispersive X-ray analysis (EDX) and UV-vis spectroscopy. Amperometric biosensor has been fabricated by the deposition of glucose oxidase (GOD) over Nafion-solubilized Fe(3)O(4)@SiO(2)/MWNTs electrode. The resultant bioelectrode retains its biocatalytic activity and offers fast and sensitive glucose quantification. The performance of the biosensor has been studied using cyclic voltammetry and amperometry and the results have been discussed. The fabricated glucose biosensor exhibits a linear response from 1 microM to 30 mM with an excellent detection limit of 800 nM indicating the potential applications in food industries.

Synthesis and nanofluid application of silver nanoparticles decorated graphene

In the present work we describe a novel synthesis procedure for silver decorated functionalized hydrogen induced exfoliated graphene (Ag/HEG) and preparation of nanofluids using this material. Further, thermal conductivity and convective heat transfer studies are carried out for these nanofluids. A simple chemical reduction method is implemented to synthesize uniformly coated Ag/HEG and characterized by different experimental techniques. Ag/HEG is used for making nanofluids considering the high thermal conductivity of graphene and silver nanoparticles. Ag/HEG has been dispersed in deionized water and ethylene glycol using ultrasonic agitation and proper dispersion is achieved without any surfactant. Thermal conductivity and heat transfer studies on Ag/HEG dispersed nanofluids show an enhancement in the corresponding values compared to the base fluid. The level of enhancement depends on the volume fraction and temperature at which the measurement is performed. Ag/HEG dispersed deionized water based nanofluid shows an enhancement of ∼25% for 0.05% volume fraction at 25 °C. Similarly, the heat transfer coefficient of Ag/HEG based nanofluids also shows a large enhancement compared to the base fluid. The synthesized nanofluid is stable for more than three months.

Enhanced convective heat transfer using graphene dispersed nanofluids

Nanofluids are having wide area of application in electronic and cooling industry. In the present work, hydrogen exfoliated graphene (HEG) dispersed deionized (DI) water, and ethylene glycol (EG) based nanofluids were developed. Further, thermal conductivity and heat transfer properties of these nanofluids were systematically investigated. HEG was synthesized by exfoliating graphite oxide in H2 atmosphere at 200°C. The nanofluids were prepared by dispersing functionalized HEG (f-HEG) in DI water and EG without the use of any surfactant. HEG and f-HEG were characterized by powder X-ray diffractometry, electron microscopy, Raman and FTIR spectroscopy. Thermal and electrical conductivities of f-HEG dispersed DI water and EG based nanofluids were measured for different volume fractions and at different temperatures. A 0.05% volume fraction of f-HEG dispersed DI water based nanofluid shows an enhancement in thermal conductivity of about 16% at 25°C and 75% at 50°C. The enhancement in Nusselts number for these nanofluids is more than that of thermal conductivity.

Synthesis of silver nanoparticle decorated multiwalled carbon nanotubes-graphene mixture and its heat transfer studies in nanofluid

The present study describes a novel synthesis procedure for a hybrid nanostructure consisting of multiwalled carbon nanotubes (MWNT), hydrogen exfoliated graphene (HEG) and silver nanoparticles. Moreover, synthesis of nanofluids using the above hybrid material and their heat transfer properties are discussed. The hybrid structure of MWNT and HEG (MWNT-HEG) has been synthesized by a simple mixing of MWNT and graphite oxide (GO) followed by exfoliation of this mixture in hydrogen atmosphere. The sample has been characterized with different experimental techniques. After surface functionalization, this hybrid material is decorated with silver nanoparticles (Ag/(MWNT-HEG)) and dispersed in ethylene glycol (EG) without any surfactant. The thermal conductivity and convective heat transfer properties are measured for different volume fractions. An enhancement of ∼8% in thermal conductivity is obtained for a volume fraction of 0.04% at 25°C. The convective heat transfer coefficient of these nanofluids is determin...

Cold field emission from hydrogen exfoliated graphene composites

In the present letter, field emission property of highly wrinkled hydrogen exfoliated graphene (HEG) was studied using an indigenously fabricated setup under ∼10−6 mbar pressure. Graphene was coated on a flexible carbon cloth by spin coating for the field emission study. The turn on voltage obtained for a HEG field emitter is around 1.18 V/μm. Further, the field emission property of HEG was improved by decorating metal oxide over HEG. The stability of the field emitter was tested and field enhancement factor was calculated using Fowler–Nordheim plot.

Green approach for the large-scale synthesis of metal/metal oxide nanoparticle decorated multiwalled carbon nanotubes

Herein we report a green approach for the synthesis of metal/metal oxide nanoparticle decorated multiwalled carbon nanotubes using focused solar radiation. The synthesis method demonstrates a large scale, cost effective and spontaneous production of carbon nanotube supported metal/metal oxide nanoparticles for energy and biological applications.

Experimental study on the field emission properties of metal oxide nanoparticle–decorated graphene

In the present study, electron field emission efficiency of metal oxide nanoparticle–decorated graphene has been investigated. Tin oxide and zinc oxide nanoparticle–decorated hydrogen exfoliated graphene (SnO2/HEG and ZnO/HEG) have been synthesized by chemical reduction and sol-gel techniques, respectively. The samples have been characterized by x ray diffraction, thermo-gravimetric analysis, Raman spectroscopy, and electron microscopy techniques. SnO2/HEG and ZnO/HEG-based field emitters have been fabricated by dispersing them in a suitable solvent, followed by spin coating onto a carbon cloth. The field emission measurement of these vacuum-dried thin films has been carried out under a vacuum of 10–6 mbar, as has their long-term stability. The obtained turn-on voltage for ZnO/HEG and SnO2/HEG is around 0.88 and 0.93 V/μm with field enhancement factors of 6535 and 6367, respectively.

Enhanced optical limiting and carrier dynamics in metal oxide-hydrogen exfoliated graphene hybrids

Hydrogen exfoliated graphene (HEG) is an interesting class of few-layer graphene, which is synthesized via hydrogen induced simultaneous exfoliation-reduction of graphite oxide. HEG exhibits strong optical limiting (OL) due to defect states arising from a large number of structural defects as well as oxygen functionalities present on its surface. Recently, we have shown that OL in HEG can be improved by simple acid functionalization, as it results in an increased number of defects. In the present study, we demonstrate that the OL performance of functionalized HEG (f-HEG) can be further improved, in both the short-pulse (nanosecond) and ultrafast (femtosecond) laser excitation regimes, using hybrids of f-HEG with transition metal oxide nanoparticles (NPs) such as CuO. The enhancement in the OL efficiency of the hybrid arises from strong nonlinear absorption in CuO NPs, which is determined mostly by interband and intraband transitions. The presence of defect states in the samples is confirmed using ultrafast pump–probe measurements, which reveal a delayed carrier relaxation due to carrier trapping by these states. Furthermore, we show that the occurrence of induced thermal scattering is minimal in these water dispersed systems, such that OL occurs predominantly due to nonlinear absorption.