Ramaprabhu Sundara

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...

Surfactant free magnetic nanofluids based on core-shell type nanoparticle decorated multiwalled carbon nanotubes

Magnetic nanofluids consisting of fluids suspended with magnetic materials are of current interest and have potential applications in both energy related and biomedical fields. In this paper, we present a novel magnetic nanofluid obtained by dispersing silicon dioxide (SiO2) coated on magnetite (Fe3O4) particle decorated multiwalled carbon nanotubes (MWNTs) (Fe3O4@SiO2/MWNTs) in de-ionized water. As compared to a magnetite decorated MWNT based nanofluid, the present system shows better stability and thermal properties without the use of any surfactants. Fe3O4/MWNTs and Fe3O4@SiO2/MWNTs have been synthesized via a simple chemical reduction technique and dispersed in de-ionized water via ultrasonication. Dispersed de-ionized water based nanofluids containing Fe3O4/MWNTs with surfactant and Fe3O4@SiO2/MWNTs without surfactant show a thermal conductivity enhancement of 20% and 24.5%, respectively, for a volume fraction of 0.03% in the presence of magnetic field. The enhancement in the thermal conductivity has...

Investigation of catalytic activity towards oxygen reduction reaction of Pt dispersed on boron doped graphene in acid medium

Boron doped graphene was prepared by a facile method and platinum (Pt) decoration over boron doped graphene was done in various chemical reduction methods such as sodium borohydride (NaBH4), polyol and modified polyol. X-ray diffraction analysis indicates that the synthesized catalyst particles are present in a nanocrystalline structure and transmission and scanning electron microscopy were employed to investigate the morphology and particle distribution. The electrochemical properties were investigated with the help of the rotating disk electrode (RDE) technique and cyclic voltammetry. The results show that the oxygen reduction reaction (ORR) takes place by a four-electron process. The kinetics of the ORR was evaluated using K-L and Tafel plots. The electrocatalyst obtained in modified polyol reduction method has shown the better catalytic activity compared to other two electrocatalysts.