Dinesh Pratap Singh

Graphene oxide: strategies for synthesis, reduction and frontier applications

Till now, several innovative methods have been developed for the synthesis of graphene materials including mechanical exfoliation, epitaxial growth by chemical vapor deposition, chemical reduction of graphite oxide, liquid-phase exfoliation, arc discharge of graphite, in situ electron beam irradiation, epitaxial growth on SiC, thermal fusion, laser reduction of polymers sheets and unzipping of carbon nanotubes etc. Generally large scale graphene nanosheets are reliably synthesized utilizing other forms of graphene-based novel materials, including graphene oxide (GO), exfoliated graphite oxide (by thermal and microwave), and reduced graphene oxide. The degree of GO reduction and number of graphene layers are minimized mainly by applying two approaches via chemical or thermal treatments. The promising and excellent properties together with the ease of processability and chemical functionalization makes graphene based materials especially GO, ideal candidates for incorporation into a variety of advanced functional materials. Chemical functionalization of graphene can be easily achieved, by the introduction of various functional groups. These functional groups help to control and manipulate the graphene surfaces and help to tune the properties of the resulting hybrid materials. Importantly, graphene and its derivatives GO, have been explored in a wide range of applications, such as energy generation/storage, optical devices, electronic and photonic devices, drug delivery, clean energy, and chemical/bio sensors. In this review article, we have incorporated a general introduction of GO, its synthesis, reduction and some selected frontier applications.

Hydrothermal synthesis of a uniformly dispersed hybrid graphene–TiO2 nanostructure for optical and enhanced electrochemical applications

Highly dispersed TiO2 nanoparticles on graphene nanosheets were achieved by hydrothermal treatment of graphene nanosheets obtained by modified Hummers method followed by thermal exfoliation. The hybrid graphene TiO2 nanostructure composite (H-GTN) showed enhanced optical and electrochemical properties for future application as a supercapacitor. The structural, optical and electrochemical properties of the composite are systematically investigated. The as-prepared H-GTN showed a quenching phenomenon of its photoluminescence properties, which was attributed to the specific properties of graphene. Remarkably, the CV test obtained for H-GTN showed a very high specific capacitance value up to 530 F g−1 at a scan rate of 3 mV s−1, and nearly stable capacitance of 400 F g−1 above 20 mV s−1. The cyclic stability test shows stable behavior after some initial cycles and the stability was then retained without obvious aging or performance degradation, showing long cyclic stability. This is attributed to the excellent electrochemical performance of the H-GTN electrode material for practical application in energy storage devices.

Synthesis of Micron-sized Hexagonal and Flower-like Nanostructures of Lead Oxide (PbO2) by Anodic Oxidation of Lead

Micron sized hexagon- and flower-like nanostructures of lead oxide (α-PbO2) have been synthesized by very simple and cost effective route of anodic oxidation of lead sheet. These structures were easily obtained by the simple variation of applied voltage from 2–6 V between the electrodes. Lead sheet was used as an anode and platinum sheet served as a cathode. Anodic oxidation at 2 V resulted in the variable edge sized (1–2 μm) hexagon-like structures in the electrolyte. When the applied potential was increased to 4 V a structure of distorted hexagons consisting of some flower-like structures were obtained. Further increment of potential up to 6 V resulted in flower like structures of α-PbO2 having six petals. The diameter of the flower-like structures was ∼200–500 nm and the size of a petal was ∼100–200 nm.

Graphene oxide: An efficient material and recent approach for biotechnological and biomedical applications

The two-dimensional (2D) derivative of graphite termed graphene has widespread applications in various frontiers areas of nanoscience and nanotechnologies. Graphene in its oxidized form named as graphene oxide (GO) has a mixed structure equipped with various oxygen containing functional groups (epoxy, hydroxyl, carboxylic and carbonyl etc.) provides attachment sites to various biological molecules including protein, deoxyribonucleic acid (DNA), ribonucleic acid (RNA) etc. The attached biological molecules with the help of functional groups make it a promising candidate in research field of biotechnological and biomedical applications. The ease of processability and functionalization in aqueous solution due to available functional groups, amphiphilicity, better surface enhanced Raman scattering (SERS), fluorescence and its quenching ability better than graphene make GO a promising candidate for various biological applications. The amphipathetic nature and high surface area of the GO not only prepare it as a biocompatible, soft and flexible intra/inter cellular carrier but also provides long-term biocompatibility with very low cytotoxicity. Inspite of this, still we lack a very recent review for advanced biological applications of graphene oxide. This review deals the bio application of GO and the recent advancement as a biosensors, antibacterial agent, early detection of cancer, cancer cell imaging/mapping, targeted drug delivery and gene therapy etc.

Highly zone-dependent synthesis of different carbon nanostructures using plasma-enhanced arc discharge technique

Three kinds of carbon nanostructures, i.e., graphene nanoflakes (GNFs), multi walled carbon nanotubes (MWCNTs), and spherical carbon nanoparticles (SCNPs) were comparatively investigated in one run experiment. These carbon nanostructures are located at specific location inside the direct current plasma-assisted arc discharge chamber. These carbon nanomaterials have been successfully synthesized using graphite as arcing electrodes at 400xa0torr in helium (He) atmosphere. The SCNPs were found in the deposits formed on the cathode holder, in which highly curled graphitic structure are found in majority. The diameter varies from 20 to 60xa0nm and it also appears that these particles are self-assembled to each other. The MWCNTs with the diameter of 10–30xa0nm were obtained which were present inside the swelling portion of cathode deposited. These MWCNTs have 14–18 graphitic layers with 3.59xa0Å interlayer spacing. The GNFs have average lateral sizes of 1–5xa0μm and few of them are stacked layers and shows crumpled like structure. The GNFs are more stable at low temperature (low mass loss) but SCNPs have low mass loss at high temperature.

Acetonitrile mediated facile synthesis and self-assembly of silver vanadate nanowires into 3D spongy-like structure as a cathode material for lithium ion battery

We report the facile, one-step acetonitrile-mediated synthesis and self-assembly of β-AgVO3 nanowires into three-dimensional (3D) porous spongy-like hydrogel (~xa04xa0cm diameter) as cathode material for lithium ion battery of high performance and long-term stability. 3D structures made with superlong, very thin, and monoclinic β-AgVO3 nanowires exhibit high specific discharge capacities of 165xa0mAhxa0g−1 in the first cycle and 100xa0mAhxa0g−1 at the 50th cycle, with a cyclic capacity retention of 53% at a current density of 50xa0mAxa0g−1. 3D structures are synthesized by reaction between ammonium vanadate and silver nitrate solution containing 5xa0mL of acetonitrile followed by a hydrothermal treatment at 200xa0°C for 12xa0h. Acetonitrile (used here for the first time in the silver vanadate synthesis) plays an important role in the self-assembly of the silver vanadate nanowires. A tentative growth mechanism for the 3D structure and lithium ions intercalation into β-AgVO3 nanowires has been discussed and described.

pH-Controlled Assembly of 3D and 2D Zinc-Based Metal-Organic Frameworks with Tetrazole Ligands

We report the synthesis and structural diversity of Zn(II) metal-organic framework (MOF) with in situ formation of tetrazole ligand 3-ptz [3-ptz = 5-(3-pyridyl)tetrazolate] as a function pH. By varying the initial reaction pH, we obtain high-quality crystals of the noncentrosymmetric three-dimensional MOF Zn(3-ptz)2, mixed phases involving the zinc-aqua complex [Zn(H2O)4(3-ptz)2]·4H2O, and two-dimensional MOF crystals Zn(OH)(3-ptz) with a tunable microrod morphology, keeping reaction time, temperature, and metal–ligand molar ratio constant. Structures are characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and UV–vis spectroscopy. We discuss the observed structural diversity in terms of the relative abundance of hydroxo-zinc species in solution for different values of pH.