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Kumar R.,JCDAV College | Al-Dossary O.,King Saud University | Kumar G.,JCDAV College | Umar A.,Najran University
Nano-Micro Letters | Year: 2014

Because of the interesting and multifunctional properties, recently, ZnO nanostructures are considered as excellent material for fabrication of highly sensitive and selective gas sensors. Thus, ZnO nanomaterials are widely used to fabricate efficient gas sensors for the detection of various hazardous and toxic gases. The presented review article is focusing on the recent developments of NO2 gas sensors based on ZnO nanomaterials. The review presents the general introduction of some metal oxide nanomaterials for gas sensing application and finally focusing on the structure of ZnO and its gas sensing mechanisms. Basic gas sensing characteristics such as gas response, response time, recovery time, selectivity, detection limit, stability and recyclability, etc are also discussed in this article. Further, the utilization of various ZnO nanomaterials such as nanorods, nanowires, nano-micro flowers, quantum dots, thin films and nanosheets, etc for the fabrication of NO2 gas sensors are also presented. Moreover, various factors such as NO2 concentrations, annealing temperature, ZnO morphologies and particle sizes, relative humidity, operating temperatures which are affecting the NO2 gas sensing properties are discussed in this review. Finally, the review article is concluded and future directions are presented. © 2014, SpringerOpen. All Rights Reserved. Source


Chauhan S.,iversity | Sharma K.,iversity | Rana D.S.,iversity | Kumar G.,JCDAV College | Umar A.,Najran University
Journal of Solution Chemistry | Year: 2013

Apparent molar volumes (φ v ), apparent molar adiabatic compressions (φ κ) and thermodynamic parameters of cetyltrimethyl ammonium bromide (CTAB) in 0.001, 0.01, 0.05 and 0.1 mol·dm-3 aqueous solution of glycine in the temperature range 25-40 C (at an interval of 5 C) have been determined from density, speed of sound and conductometric measurements, respectively. The above calculated parameters were found to be sensitive to the interactions prevailing in the glycine-CTAB-water system. The analysis of the data was found to suggest that the φ v and φ κ values decrease sharply in the pre-micellar region and thereafter the decrease is almost linear at all concentrations of glycine, showing the dominance of hydrophobic interactions and facilitating the process of micellization. The φ v and φ κ values of these surfactants are found to be completely consistent with temperature over the entire concentration range. From conductance studies, the value of critical micelle concentration has been calculated, which shows dependence on the concentration of glycine as well as on temperature. A reasonably good qualitative correlation is found to exist with regard to CTAB-glycine interactions obtained from the conductance measurements and those from density and sound velocity measurements. All these observations demonstrate that this amino acid-surfactant system behaves in a different manner as compared to amino acid-electrolyte systems. © 2013 Springer Science+Business Media New York. Source


Chauhan S.,iversity | Sharma K.,iversity | Rana D.S.,iversity | Kumar G.,JCDAV College | Umar A.,Najran University
Journal of Molecular Liquids | Year: 2012

In the present studies, micellization behavior of cetyltrimethylammonium bromide, CTAB (cationic surfactant) has been studied in the aqueous solution, containing 0.001, 0.005, 0.01, 0.025, 0.05, 0.075 and 0.1 M leucine as a solvent, using specific conductances (κ), densities (d) and velocities of sound (v), in the temperature range 25-40 °C at an interval of 5 °C. The cmc of CTAB was determined from the plots of specific conductance (κ) of CTAB in aqueous leucine solution. The cmc values of surfactant increase with increase in temperature but they decrease linearly with increase in the concentration of the leucine. By using cmc data various thermodynamic parameters have also been evaluated. The apparent molar volume (φ v) and apparent molar adiabatic compressibility (φ κ) have been computed using densities and velocities of sound data. The above calculated parameters were found to be sensitive towards the interactions prevailing in the leucine-CTAB-water systems. The analysis of the data is found to suggest that φ v and φ κ values in general are positive at all temperatures and increase with rise in temperature while decrease sharply to about 0.8 mM [CTAB] at all concentrations of leucine. Thereafter, the decrease is almost linear. The cmc as determined from the fluorescence measurements indicating a transition point of I 1/I 3 plot which shows that the cmc lies at ≈ 0.8 mM, the results of which are consistent with the other physico-chemical studies. A reasonably good qualitative correlation is found to exist with regard to CTAB-leucine interactions obtained from the different measurements. © 2012 Elsevier B.V. All rights reserved. Source


Gupta B.,JCDAV College | Srivastava S.K.,B.C.E.T
International Journal of Computational and Mathematical Sciences | Year: 2010

In this paper, we shall present sufficient conditions for the ψ-exponential stability of a class of nonlinear impulsive differential equations. We use the Lyapunov method with functions that are not necessarily differentiable. In the last section, we give some examples to support our theoretical results. Source


Chauhan S.,iversity | Sharma K.,iversity | Kumar K.,iversity | Kumar G.,JCDAV College
Journal of Surfactants and Detergents | Year: 2014

Densities (d) and sound velocities (v) of an ethoxylated alkyl phenol surfactant in aqueous solutions of two amino acids, namely glycine and leucine, have been measured over a temperature range of 25-40 °C at intervals of 5 °C by using density and sound analyzers. Experimental data have been used to calculate the isentropic compressibilities (ks), apparent molar volumes (φν) and apparent molar adiabatic compressions (φκ) in order to explain amino acid-surfactant interactions. The results have been discussed in terms of the effect of amino acids on the micellization behavior of the surfactant. A comparative study of both the amino acids has been carried out and is found that both amino acids produce a decrease in the CMC value of nonionic surfactant but to different extents. © AOCS 2013. Source

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