Ponchami Sharma

High efficiency electron field emission from protruded graphene oxide nanosheets supported on sharp silicon nanowires

Graphene oxide (GO) potentially has applications in vacuum microelectronic devices for realization of field emission displays. Graphene and its derivatives are expected to be efficient field emitters due to their unique electrical properties. However, the flat sheet structure of graphene or GO allows electron field emission only from the edges of graphene and GO nanosheets. In order to extract maximum field emission current density at lower applied voltage from the GO nanosheets, we supported and stretched them on sharp tips of silicon nanowires (SiNWs). Highly efficient and stable field emission with low turn-on field was observed for these SiNW–GO heterostructures. The sharp protrusions created by stretching of the GO nanosheets on SiNWs locally enhance the electric field and thus enhance the field emission characteristics. The dominant use of silicon in electronic devices makes this approach robust for the development of field emission devices using graphene based field emitters.

Mitigating Greenhouse Gas Emission from Agriculture

Radiative forcing of Earth’s atmosphere is increasing at unprecedented rates, largely because of increases in the concentrations of atmospheric trace gases, mainly carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) – collectively known as greenhouse gases (GHG). Concentrations of CO2, CH4 and N2O have increased markedly as a result of human activities since 1750 and now far exceeded pre-industrial values as determined from ice cores spanning thousands of years (Table 15.1). The atmospheric concentrations of CO2 and CH4 in 2005 have exceeded the natural range over the last 650,000 years (IPCC 2007). The global atmospheric concentration of CO2 has increased at an annual growth rate of 0.5%, while that of CH4 at 0.6% and nitrous oxide at 0.25%. Agriculture plays a major role in the global fluxes of each of these gases and is considered as one of the major anthropogenic sources (Fig. 15.1). Agriculture comprises several activities, contributing to GHG emissions and globally, the most significant activities identified include (i) deforestation and other land-use changes as a source of CO2, (ii) rice-based production systems (including rice-wheat rotation) as sources of CH4 and N2O (and also source of CO2 due to burning of agricultural residues) and (iii) animal husbandry as a source of CH4.

Graphene Oxide Nanosheets at the Water–Organic Solvent Interface: Utilization in One‐Pot Adsorption and Reactive Extraction of Dye Molecules

Graphene oxide (GO) is amphiphilic in nature, due to its structure, which consists of hydrophilic oxygen-containing functional groups and a hydrophobic basal plane of polyaromatic benzene rings. Due to this amphiphilicity, GO can create stable bubbles at water-organic solvent interfaces. In this study, the formation of bubbles at aqueous-organic interfaces in the presence of GO is investigated with different organic solvents. Bubble formation and transfer of GO from water to the organic phase is more prominent in aromatic solvents compared to aliphatic solvents, due to π-π interactions. Maximum transfer of GO from the aqueous to the organic phase is achieved at pH 2, and decreases with rising pH of the aqueous phase. Based on this property, and the ability of GO to adsorb cationic and anionic dye molecules, its application as a carrier for reactive extraction of cationic and anionic dye molecules is explored in toluene, kerosene, and carbon tetrachloride at pH 2 and 25 °C. The kinetics of the adsorption of the dyes onto GO nanosheets that takes place in the aqueous phase is also evaluated with different models, and a pseudo-second-order (linear) model is found to be the best fit. The adsorption isotherm data are also analyzed with different isotherm models. The electrostatic interaction and π-π interaction between the dye molecules and GO nanosheets leads to dye extraction of up to 98.2% using this technique. The dye extraction is maximum in toluene and at low dye concentration.