Anchal Srivastava

Atomic layers of hybridized boron nitride and graphene domains

Two-dimensional materials, such as graphene and monolayer hexagonal BN (h-BN), are attractive for demonstrating fundamental physics in materials and potential applications in next-generation electronics. Atomic sheets containing hybridized bonds involving elements B, N and C over wide compositional ranges could result in new materials with properties complementary to those of graphene and h-BN, enabling a rich variety of electronic structures, properties and applications. Here we report the synthesis and characterization of large-area atomic layers of h-BNC material, consisting of hybridized, randomly distributed domains of h-BN and C phases with compositions ranging from pure BN to pure graphene. Our studies reveal that their structural features and bandgap are distinct from those of graphene, doped graphene and h-BN. This new form of hybrid h-BNC material enables the development of bandgap-engineered applications in electronics and optics and properties that are distinct from those of graphene and h-BN.

Synthesis Of Nitrogen-Doped Graphene Films For Lithium Battery Application

We demonstrate a controlled growth of nitrogen-doped graphene layers by liquid precursor based chemical vapor deposition (CVD) technique. Nitrogen-doped graphene was grown directly on Cu current collectors and studied for its reversible Li-ion intercalation properties. Reversible discharge capacity of N-doped graphene is almost double compared to pristine graphene due to the large number of surface defects induced due to N-doping. All the graphene films were characterized by Raman spectroscopy, transmission electron microscopy, and X-ray photoemission spectroscopy. Direct growth of active electrode material on current collector substrates makes this a feasible and efficient process for integration into current battery manufacture technology.

Quasi-Molecular Fluorescence from Graphene Oxide

Aqueous dispersions of graphene oxide (GO) have been found to emit a structured, strongly pH-dependent visible fluorescence. Based on experimental results and model computations, this is proposed to arise from quasi-molecular fluorophores, similar to polycyclic aromatic compounds, formed by the electronic coupling of carboxylic acid groups with nearby carbon atoms of graphene. Sharp and structured emission and excitation features resembling the spectra of molecular fluorophores are present near 500 nm in basic conditions. The GO emission reversibly broadens and red-shifts to ca. 680 nm in acidic conditions, while the excitation spectra remain very similar in shape and position, consistent with excited state protonation of the emitting species in acidic media. The sharp and structured emission and excitation features suggest that the effective fluorophore size in the GO samples is remarkably well defined.

Functionalized multilayered graphene platform for urea sensor.

Multilayered graphene (MLG) is an interesting material for electrochemical sensing and biosensing because of its very large 2D electrical conductivity and large surface area. We propose a less toxic, reproducible, and easy method for producing functionalized multilayer graphene from multiwalled carbon nanotubes (MWCNTs) in mass scale using only concentrated H(2)SO(4)/HNO(3). Electron microscopy results show the MLG formation, whereas FTIR and XPS data suggest its carboxylic and hydroxyl-functionalized nature. We utilize this functionalized MLG for the fabrication of a novel amperometric urea biosensor. This biosensor shows linearity of 10-100 mg dL(-1), sensitivity of 5.43 μA mg(-1) dL cm(-2), lower detection limit of 3.9 mg dL(-1), and response time of 10 s. Our results suggest that MLG is a promising material for electrochemical biosensing applications.

Ni filled flexible multi-walled carbon nanotube–polystyrene composite films as efficient microwave absorbers

In this letter, we report flexible, non corrosive, and light weight nickel nanoparticle@multi-walled carbon nanotube–polystyrene (Ni@MWCNT/PS) composite films as microwave absorbing material in the frequency range of S band (2-4 GHz). Dielectric permittivity and magnetic permeability of composites having 0.5 and 1.5 wt. % filler amount were measured using the cavity perturbation technique. Reflection loss maxima of −33 dB (at 2.7 GHz) and −24 dB (at 2.7 GHz) were achieved for 0.5 and 1.5 wt. % Ni@MWCNT/PS composite films of 6 and 4 mm thickness, respectively, suggesting that low concentrations of filler provide significant electromagnetic interference shielding.

Study of mechanism of enhanced antibacterial activity by green synthesis of silver nanoparticles

The extensive use of silver nanoparticles needs a synthesis process that is greener without compromising their properties. The present study describes a novel green synthesis of silver nanoparticles using Guava (Psidium guajava) leaf extract. In order to compare with the conventionally synthesized ones, we also prepared Ag-NPs by chemical reduction. Their optical and morphological characteristics were thoroughly investigated and tested for their antibacterial properties on Escherichia coli. The green synthesized silver nanoparticles showed better antibacterial properties than their chemical counterparts even though there was not much difference between their morphologies. Fourier transform infrared (FTIR) spectroscopic analysis of the used extract and as-synthesized silver nanoparticles suggests the possible reduction of Ag(+) by the water-soluble ingredients of the guava leaf like tannins, eugenol and flavonoids. The possible reaction mechanism for the reduction of Ag(+) has been proposed and discussed. The time-dependent electron micrographs and the simulation studies indicated that a physical interaction between the silver nanoparticles and the bacterial cell membrane may be responsible for this effect. Based on the findings, it seems very reasonable to believe that this greener way of synthesizing silver nanoparticles is not just an environmentally viable technique but it also opens up scope to improve their antibacterial properties.

A possible mechanism for the emergence of an additional band gap due to a Ti–O–C bond in the TiO2–graphene hybrid system for enhanced photodegradation of methylene blue under visible light

Here we report the experimental and theoretical study of two TiO2–graphene oxide (TG) and TiO2–reduced graphene oxide (TR) composites synthesized by a facile and ecological route, for enhanced visible light (∼470 nm) photocatalytic degradation of Methylene Blue (MB) (99% efficiency), with high rate constant values (1800% over bare TiO2). TG couples TiO2 nanopowder with Graphene Oxide (GO) while TR couples it with reduced graphene oxide (RGO). The present study, unlike previous reports, discusses never-before-reported double absorption edges obtained for both TG (3.51 eV and 2.51 eV) and TR (3.42 eV and 2.39 eV) composites, which represents the reason behind feasible visible light (2.56 eV) induced photocatalysis. TiO2 domains in the composites dominate the higher band edge, while GO/RGO domains explain the lower band edge. Formation of Ti–O–C bonds in both TG and TR drives the shifting upwards of the valence band edge and reduction in band gap. Further, these bonds provide a conductive pathway for charge carriers from TiO2 nanopowder to the degraded species via the GO/RGO matrix, resulting in decreased charge carrier recombination in TiO2 and enhanced efficiency. To attest that the developed theory is correct, density function theory (DFT) calculations were performed. DFT obtained energetics and electronic structures support experimental findings by demonstrating the role of the Ti–O–C bond, which results in double band edge phenomenon in composites. Finally, the mechanism behind MB degradation is discussed comprehensively and the effect of the weight percent of GO/RGO in the composite on the rate constant and photodegradation efficiency has been studied experimentally and explained by developing analytical equations.

Effect of Nitrogen Doping on the Mechanical Properties of Carbon Nanotubes

We report on the usage of a simple microfabricated device that works in conjunction with a quantitative Nanoindenter within a scanning electron microscope (SEM) chamber, for the in situ quantitative tensile testing of individual catalytically grown pristine and nitrogen-doped multiwall carbon nanotubes (MWNTs). The two types of MWNTs were found to possess similar strengths but different load-bearing abilities owing to the differences in their wall structures. Also, stress versus strain curves and fracture surfaces showed that while the pristine MWNTs deform and fail in a brittle fashion, the nitrogen-doped MWNTs deform plastically to varying degrees prior to failure. High resolution transmission electron microscope (TEM) images of the nitrogen-doped MWNT fracture specimens showed the presence of regions of reduced cross-section areas and kinks in close proximity to the fracture surfaces. The presence of nitrogen atoms in the graphitic sheets was assumed to have led to the formation of kinks whose motion induced by straining could have resulted in the plastic deformation of the carbon nanotubes.

Mediator-free microfluidics biosensor based on titania–zirconia nanocomposite for urea detection

Urease (Urs) and glutamate dehydrogenase (GLDH) co-immobilized onto titania–zirconia (TiO2–ZrO2) nanocomposite and integrated with microfluidics mediator-free sensor have been utilized for urea detection. The PDMS microchannels have been sealed with a glass substrate comprising of reference (Ag/AgCl), counter (ITO) and working (Urs-GLDH/TiO2-ZrO2/ITO) electrodes. This mediator-free microfluidics urea sensor shows linearity as 5–100 mg/dL with improved sensitivity as 2.74 μA [Log mM]−1 cm−2 and detection limit of 0.07 mg/dl (0.44 mM) using 3σb/m criteria. The Reynolds number has been found to be as 0.166, indicating that fluid flow is completely laminar, controllable and the pressure drop across the microchannels is found to be as 3.5 × 103 Pa.

SEM-EDX analysis of various sizes aerosols in Delhi India

Scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDX) was used to understand the differences in morphology, elemental composition and particle density of aerosols in different five size ranges to further investigate the potential sources as well as transport of pollutants from/at a much polluted and a very clean area of Delhi. Aerosol samples were obtained in five different size ranges viz. ≥10.9, 10.9−5.4, 5.4−1.6, 1.6−0.7 and ≤0.7µm from a considerably very clean and a much polluted area of Delhi. It was observed that at polluted area most of the particles irrespective of size are of anthropogenic origin. At clean area, in coarse size fractions particles are of natural origin while in fine size range the presence of anthropogenic particles suggests the transport of particles from one area to the other.