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Chowdhury D.,Institute of Advanced Study in Science and Technology | Gogoi N.,Institute of Advanced Study in Science and Technology | Majumdar G.,Assam Engineering College
RSC Advances | Year: 2012

In this communication we report the preparation of fluorescent carbon dots (CDs) from chitosan gel. We also studied the photoluminescent (PL) properties of CDs prepared in different pH conditions. While CDs prepared at pH 3 give an intense sharp blue fluorescence, those prepared at pH 1 or 5 give a broad emission. In addition, we also investigated CDs prepared from chitosan/Ag and chitosan/Au nanocomposites. It was observed that although the emission was broad and less well defined, there was an enhancement of PL emission for the CDs prepared from chitosan/Ag or chitosan/Au nanocomposites. © 2012 The Royal Society of Chemistry. Source


Hazarika D.,Assam Engineering College
IET Generation, Transmission and Distribution | Year: 2012

The study presents a new method for monitoring the voltage stability condition of a bus using measurements of the bus variables. For this purpose, bus real power, bus reactive power and bus voltage of a target/selected bus have to be measured (sampled) for two consecutive time frames. These measured values are used to monitor the voltage stability condition of a bus using the mathematical basis developed in this study. The validity and applicability of the proposed method has been established through simulation on IEEE 30 and IEEE 118 bus system. © 2012 The Institution of Engineering and Technology. Source


Konwar A.,Institute of Advanced Study in Science and Technology | Gogoi N.,Institute of Advanced Study in Science and Technology | Majumdar G.,Assam Engineering College | Chowdhury D.,Institute of Advanced Study in Science and Technology
Carbohydrate Polymers | Year: 2014

In this work we report novel chitosan-carbon dots nanocomposite hydrogel films. A new green source "tea" was used as precursor for carbon dots (CDs). The electrostatic interaction of positive charge on chitosan and negative charge on CDs prepared from tea was used for the successful preparation of a stable and robust chitosan-carbon dots nanocomposite hydrogel film. The hydrogel films were characterized by UV-visible spectroscopy, X-ray diffraction (XRD), Fourier transformed infra-red spectroscopy (FTIR), scanning electron microscope (SEM), fluorescent microscopy, thermogravimetric analysis (TGA) and contact angle analysis. It was observed that chitosan-carbon dots hydrogel films are soft but tough with superior UV-visible blocking, swelling, thermal and mechanical properties in comparison to chitosan hydrogel film. Moreover chitosan-carbon dots films are more water repellent (hydrophobic) as indicated by their high contact angle values. Thus, fabrication of such green soft but tough biocompatible chitosan-carbon dots nanocomposite hydrogel films offers tremendous bio-medical and industrial applications. © 2014 Elsevier Ltd. All rights reserved. Source


Baruah U.,Institute of Advanced Study in Science and Technology | Gogoi N.,Institute of Advanced Study in Science and Technology | Majumdar G.,Assam Engineering College | Chowdhury D.,Institute of Advanced Study in Science and Technology
Carbohydrate Polymers | Year: 2015

In this work we have designed a novel system based on carbon dots prepared from chitosan gel capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol for sensitive and selective detection of fluoride ions in aqueous media. Fluorescent carbon dots prepared from chitosan gel when capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol results in quenching of its fluorescence intensity. Introduction of F- ions to carbon dots capped with β-cyclodextrin and calix[4]arene-25,26,27,28-tetrol system results in enhancement and restoration of fluorescence intensity leading to detection of F- ion. Minimum detection limit was determined to be ∼6.6 μM. The detection is selective as with other halide ions i.e. Cl-, Br- and I- and hydroxyl ion (OH-), there is observed decrease of fluorescence intensity. A possible mechanism to justify the observation is also discussed in the paper. © 2014 Elsevier Ltd. All rights reserved. Source


Gogoi N.,Institute of Advanced Study in Science and Technology | Barooah M.,Institute of Advanced Study in Science and Technology | Majumdar G.,Assam Engineering College | Chowdhury D.,Institute of Advanced Study in Science and Technology
ACS Applied Materials and Interfaces | Year: 2015

A robust solid sensing platform for an on-site operational and accurate detection of heavy metal is still a challenge. We introduce chitosan based carbon dots rooted agarose hydrogel film as a hybrid solid sensing platform for detection of heavy metal ions. The fabrication of the solid sensing platform is centered on simple electrostatic interaction between the NH3 + group present in the carbon dots and the OH- groups present in agarose. Simply on dipping the hydrogel film strip into the heavy metal ion solution, in particular Cr6+, Cu2+, Fe3+, Pb2+, Mn2+, the strip displays a color change, viz., Cr6+ → yellow, Cu2+ → blue, Fe3+ → brown, Pb2+ → white, Mn2+ → tan brown. The optical detection limit of the respective metal ion is found to be 1 pM for Cr6+, 0.5 μM for Cu2+, and 0.5 nM for Fe3+, Pb2+, and Mn2+ by studying the changes in UV-visible reflectance spectrum of the hydrogel film. Moreover, the hydrogel film finds applicability as an efficient filtration membrane for separation of these quintet heavy metal ions. The strategic fundamental feature of this sensing platform is the successful capability of chitosan to form colored chelates with transition metals. This proficient hybrid hydrogel solid sensing platform is thus the most suitable to employ as an on-site operational, portable, cheap colorimetric-optical detector of heavy metal ion with potential skill in their separation. Details of the possible mechanistic insight into the colorimetric detection and ion separation are also discussed. © 2015 American Chemical Society. Source

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