Neetu Jha

Development of Au nanoparticles dispersed carbon nanotube-based biosensor for the detection of paraoxon

A disposable and sensitive biosensor has been fabricated for the detection of the organophosphorous (OP) compound paraoxon using an amperometric technique. For the measurements, gold nanoparticles dispersed on the outer surface of multiwalled carbon nanotubes (Au-MWNTs) has been used as the electrode material, as it possesses high electron transfer rates and provides large immobilization sites for the bioenzymes, which combines with the high electrocatalytic activity of MWNTs for thiocholine oxidation at low potential. Au-MWNTs have been synthesized by chemically reducing Au salt over functionalized MWNTs, and the same has been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution transmission electron microscopic (HRTEM) techniques. The ability of the Au-MWNTs nanocomposite-based biosensor has been demonstrated to reliably measure the concentration of paraoxon in the nanomolar range.

Thermal conductivity studies of metal dispersed multiwalled carbon nanotubes in water and ethylene glycol based nanofluids

High thermal conducting metal nanoparticles have been dispersed on the multiwalled carbon nanotubes (MWNTs) outer surface. Structural and morphological characterizations of metal dispersed MWNTs have been carried out using x-ray diffraction analysis, high resolution transmission electron microscopy, energy dispersive x-ray analysis, and Fourier transform infrared spectroscopy. Nanofluids have been synthesized using metal-MWNTs in de-ionized water (DI water) and ethylene glycol (EG) base fluids. It has been observed that nanofluids maintain the same sequence of thermal conductivity as that of metal nanoparticles Ag-MWNTs>Au-MWNTs>Pd-MWNTs. A maximum enhancement of 37.3% and 11.3% in thermal conductivity has been obtained in Ag-MWNTs nanofluid with DI water and EG as base fluids, respectively, at a volume fraction of 0.03%. Temperature dependence study also shows enhancement of thermal conductivity with temperature.

Functionalized Single-Walled Carbon Nanotube-Based Fuel Cell Benchmarked Against US DOE 2017 Technical Targets

Chemically modified single-walled carbon nanotubes (SWNTs) with varying degrees of functionalization were utilized for the fabrication of SWNT thin film catalyst support layers (CSLs) in polymer electrolyte membrane fuel cells (PEMFCs), which were suitable for benchmarking against the US DOE 2017 targets. Use of the optimum level of SWNT -COOH functionality allowed the construction of a prototype SWNT-based PEMFC with total Pt loading of 0.06 mgPt/cm2 - well below the value of 0.125 mgPt/cm2 set as the US DOE 2017 technical target for total Pt group metals (PGM) loading. This prototype PEMFC also approaches the technical target for the total Pt content per kW of power (<0.125 gPGM/kW) at cell potential 0.65 V: a value of 0.15 gPt/kW was achieved at 80°C/22 psig testing conditions, which was further reduced to 0.12 gPt/kW at 35 psig back pressure.

Carbon nanocoils for multi-functional energy applications

Bulk manufacturing of nanomaterials with multifunctional properties is fundamental to their applications. Here we describe large scale production of carbon nanotubular coils by a scalable catalytic chemical vapor deposition technique using a hydrogen decrepitated alloy hydride thin film catalyst supported on flexible carbon fabric. Several energy-related applications of this material, such as catalyst support for polymer electrolyte membrane fuel cells, direct methanol fuel cells, hydrogen storage, and electrodes for supercapacitors are evaluated. The nanocoil material showed improved performance over previously reported carbon nanomaterials suggesting high potential for this material for practical applications.

Synthesis, characterization and application of γ-MnO2/graphene oxide for the selective aerobic oxidation of benzyl alcohols to corresponding carbonyl compounds

A facile low temperature approach was used to synthesize γ-MnO2 on the surface of graphene oxide (GO) through a simple wet precipitation method using MnSO4 as a precursor. X-ray diffraction analysis and Raman spectroscopy confirmed the formation of γ-phase MnO2 in the MnO2/GO nanocomposites. Transmission electron microscopy studies showed that γ-MnO2 exists as flower and needle structures in GO with an average size of approximately 15 nm. Inductively coupled plasma atomic emission spectroscopy studies confirmed a 62.5 wt% loading of γ-MnO2 in the GO nanocomposites. The γ-MnO2/GO catalyst shows good activity for the selective aerobic oxidation of benzyl alcohols to corresponding carbonyl compounds even when present in sub-stoichiometric amounts giving 91% yield over 3 h under mild reaction conditions. The catalyst showed high activity even after three cycles indicating good recyclability.

Impact of the degree of functionalization of graphene oxide on the electrochemical charge storage property and metal ion adsorption

Graphene oxide (GO) samples were prepared at room temperature using a modified Hummers method. The quantitative variation of oxidizing agent for the oxidation of graphene sheets resulted in increase of the oxygen functionalities on the GO samples. The qualitative analysis of functional groups and surface charge variation were studied using Fourier transform infra-red (FTIR) spectroscopy and zeta potential, respectively. Different oxidation degrees of GO were investigated by X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The electrochemical charge storage properties of the GO samples were studied using a two electrode supercapacitor cell. The fabricated supercapacitor demonstrates linear enhancement in the specific charge storage with an increase in the oxidation of the GO samples. A maximum charge storage of 71 F g−1 has been obtained with the highly oxidized GO sample at room temperature. The adsorption of metal ions from aqueous solution has also been studied with the variation in the degree of functionalization of the GO samples. It was observed that increasing oxygen functionalities from GO-1 to GO-5 amplifies the uptake of metal ions [Cd(II) and Cu(II)]. The experimental data fits well with the Langmuir adsorption model, indicating monolayer adsorption of metal ion on the GO samples.

A sodium modified reduced graphene oxide–Fe3O4 nanocomposite for efficient lead(II) adsorption

A simple, cost-effective and facile route was employed to synthesize a hydrophobic sodium modified reduced graphene oxide–magnetic iron oxide (SMGI) nanocomposite. The as-synthesized SMGI material was used as an adsorbent material for the removal of Pb(II) from aqueous solutions. The detailed characterization of the SMGI nanocomposite prepared was performed using material characterization techniques. X-Ray Diffraction (XRD) and Fourier transform infrared spectroscopic (FTIR) studies confirm the deposition of crystalline Fe3O4 nanoparticles on reduced graphene oxide (rGO). X-ray photoelectron spectroscopic (XPS) analysis shows the presence of 10% sodium cations in the nanocomposite. Transmission Electron Microscopy (TEM) images reveal that the magnetite nanoparticles are homogenously deposited on the 2-dimensional surface of the graphene sheets. The nanocomposite prepared possesses a superparamagnetic property, which was exploited for the easy recovery of the SMGI nanocomposite from water after Pb(II) adsorption. The effects of pH, contact time and concentration on Pb(II) sorption were investigated in detail. The sorption data were fitted using Freundlich and Langmuir models. The pseudo-second-order model was a better fit for Pb(II) adsorption. The maximum adsorption capacity of 1666.66 ± 59 mg g−1 was obtained. The adsorbent also showed more than 75% removal efficiency of Pb(II) after 3 cycles of regeneration.

Synthesis and fabrication of graphene oxide thin film

The primary aim of the investigation is to synthesize graphene oxide at room temperature and fabricate a flexible free standing graphene oxide thin film. Modified Hummers technique was employed for the synthesis of graphene oxide using graphite as the starting material. Graphene oxide is a layered material consisting of hydrophilic oxygenated functional groups on their basal planes and edges. Graphene-oxide thin film has been fabricated via solvent-evaporation technique. Functional, elemental and structural analysis of the samples was performed using several characterization techniques.

Ruthenium oxide - single walled carbon nanotube composite based high energy supercapacitor

Ruthenium oxide (RuO2) nanoparticles were supported on the outer surface of single walled carbon nanotubes (SWNTs) using chemical reduction technique. The nanocomposite was employed as an electrode material for charge storage capacitor using ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte solution. The electrochemical charge storage properties of the composite were investigated using two electrode cyclic voltammetry and galvanostatic charge-discharge techniques. The specific capacitance and energy density of the RuO2-SWNT nanocomposite electrode material based on the fabricated coin cell supercapacitor were measured to be as high as 174 F/g and 74 Wh/kg at current density of 1 A/g.

Non-platinum metal-organic framework based electro-catalyst for promoting oxygen reduction reaction

We developed two non-precious Metal Organic Framework (MOF) based electrocatalysts, MOF-5 and MOF-i using solvothermal and refluxing methods. The MOFs prepared has been characterized by powder X-ray diffractometer (XRD), Fourier Transform Infra-Red Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) for structural and morphological insights. SEM images reveal cubic shape for solvothermally synthesized MOF-5, whereas refluxing method leads to platelet morphology of MOF-i. The synthesized MOFs has been investigated for Oxygen Reduction Reaction (ORR) studies using Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV), with MOF modified Glassy Carbon (GC) as working electrode. The electrochemical data suggests higher activity of MOF-5 towards ORR compared to MOF-i.We developed two non-precious Metal Organic Framework (MOF) based electrocatalysts, MOF-5 and MOF-i using solvothermal and refluxing methods. The MOFs prepared has been characterized by powder X-ray diffractometer (XRD), Fourier Transform Infra-Red Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) for structural and morphological insights. SEM images reveal cubic shape for solvothermally synthesized MOF-5, whereas refluxing method leads to platelet morphology of MOF-i. The synthesized MOFs has been investigated for Oxygen Reduction Reaction (ORR) studies using Cyclic Voltammetry (CV) and Linear Sweep Voltammetry (LSV), with MOF modified Glassy Carbon (GC) as working electrode. The electrochemical data suggests higher activity of MOF-5 towards ORR compared to MOF-i.