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Papers by sony george

Research paper thumbnail of Solvent Effects: A Signature of J- and H-Aggregate of Carbon Nanodots in Polar Solvents

The Journal of Physical Chemistry A, 2019

The secret behind excitation dependent/independent photoluminescence of carbon nanodots (CDs) is ... more The secret behind excitation dependent/independent photoluminescence of carbon nanodots (CDs) is not yet revealed completely. To address this issue, a detailed investigation on solvent polarity dependent optical properties of citric acid-urea co-derived nitrogen doped carbon nanodots (NCDs) was carried out. The interpretation on UV-visible spectral data reveals presence of H-aggregates formed through hydrogen bonding. In addition, dipole-dipole interaction mediated J-aggregates is clearly evident. The broad and intense excitation band of NCDs is mostly contributed by highly emissive J-like self-assembly of H-aggregates in polar solvents. Time resolved fluorescence spectra of NCDs show tri-exponential decay kinetics. The three lifetime components corresponds to long lived H-aggregates, short lived J-aggregates and JH-aggregates of intermediate lifetime. Moreover, fluorescence of NCD is influenced by concentration and storage time. Accordingly, mismatch in spectral shapes of excitation and absorption spectra of NCD can be successfully correlated to aggregate species of NCDs exist even in very dilute solutions.

Research paper thumbnail of Polyethylene imine capped copper nanoclusters- fluorescent and colorimetric onsite sensor for the trace level detection of TNT

Sensors and Actuators B: Chemical, 2018

Detection of TNT by fluorescent and colorimetric method by using polyethylene imine capped fluore... more Detection of TNT by fluorescent and colorimetric method by using polyethylene imine capped fluorescent copper nanocluster Highlights  Polyethylene imine capped fluorescent copper nanoclusters were prepared via a one pot microwave assisted method.  The as prepared cost effective nanosensor was used for fluorescent as well as colorimetric detection of TNT and exhibited excellent sensitivity and selectivity.  In fluorescent and colorimetric detection LOD obtained is as low as 14 pM and 0.05 nM respectively.  A portable paper sensor was developed which can selectively detect TNT vapors.

Research paper thumbnail of Fluorescence Spectroscopic Investigation To Identify the Micelle to Gel Transition of Aqueous Triblock Copolymer Solutions

Journal of Physical Chemistry B, 2009

Steady-state and time-resolved fluorescence anisotropy measurements using probes coumarin 153 (C1... more Steady-state and time-resolved fluorescence anisotropy measurements using probes coumarin 153 (C153) and 4-heptadecylumbelliferon (HUF) have been carried out to understand the micelle to gel transition of an aqueous triblock copolymer P123 ((EO) 20 -(PO) 70 -(EO) 20 ) (EO ) ethylene oxide; PO ) propylene oxide) solution. Anisotropy results with a normal fluorescent probe, C153, do not show a characteristic change due to the micelle to gel transition. However, the probe HUF having a long hydrocarbon chain that helps its strong association with the micelle shows an increase in anisotropy above the sol-gel transition point. This difference has been explained as invoking a substantial contribution from the micellar structural fluctuations to the depolarization of HUF as its hydrocarbon chain is embedded in the micellar structure, which is not sensed significantly by the normal probe C153. That the extent of change in anisotropy for HUF upon gelation is not that large is possibly caused by the collective motion of the physically interconnected nodes, as observed from the dynamic light scattering studies, which acts in favor of a relatively faster depolarization in the gel phase. Similar studies in other copolymers, such as P85 ((EO) 26 -(PO) 40 -(EO) 26 ) and F127 ((EO) 100 -(PO) 65 -(EO) 100 ), further demonstrate the potential of probes latched with hydrocarbon chains in displaying a characteristic change for the micelle to gel transition which otherwise remains obscured for normal fluorescent probes.

Research paper thumbnail of Electrochemical impedance spectroscopic analysis of activation of Al–Zn alloy sacrificial anode by RuO 2 catalytic coating

Applied Surface Science, 2007

The uniform surface activation characteristics of RuO 2 -coated Al–Zn alloy sacrificial anodes we... more The uniform surface activation characteristics of RuO 2 -coated Al–Zn alloy sacrificial anodes were studied in the present work. Electrochemical impedance spectroscopic and SEM/EDAX analyses were carried out to evaluate the galvanic dissolution characteristics of the ...

Research paper thumbnail of Surface catalysis based on ruthenium dioxide for effective activation of aluminium sacrificial anodes

Corrosion Science, 2004

Several studies have been focusing on alloying and structural modification of aluminium alloy sac... more Several studies have been focusing on alloying and structural modification of aluminium alloy sacrificial anodes using different activators including intermetallic compounds. With a novel approach, the present work explore and evaluate the feasibility of effective aluminium activation by RuO 2 in 95 + 5 Al-Zn alloy substrates. The electrodes prepared in the present work, by making RuO 2 film on the substrate, were found to possess good surface interaction, low surface resistivity and facilitate interlayer diffusion of aluminium ions. The electrodes showed excellent galvanic performance under different experimental conditions in 3% NaCl electrolyte. The RuO 2 layer was found to persist on the electrode surface even after the electrode size was reduced to one-third of its original size due to long period of galvanic exposure, evidencing its mobile character. The electrodes are economically efficient, convenient to prepare as other conventional hanging electrodes, tolerable to very aggressive media and highly efficient even under high current load.

Research paper thumbnail of Solvent Effects: A Signature of J- and H-Aggregate of Carbon Nanodots in Polar Solvents

The Journal of Physical Chemistry A, 2019

The secret behind excitation dependent/independent photoluminescence of carbon nanodots (CDs) is ... more The secret behind excitation dependent/independent photoluminescence of carbon nanodots (CDs) is not yet revealed completely. To address this issue, a detailed investigation on solvent polarity dependent optical properties of citric acid-urea co-derived nitrogen doped carbon nanodots (NCDs) was carried out. The interpretation on UV-visible spectral data reveals presence of H-aggregates formed through hydrogen bonding. In addition, dipole-dipole interaction mediated J-aggregates is clearly evident. The broad and intense excitation band of NCDs is mostly contributed by highly emissive J-like self-assembly of H-aggregates in polar solvents. Time resolved fluorescence spectra of NCDs show tri-exponential decay kinetics. The three lifetime components corresponds to long lived H-aggregates, short lived J-aggregates and JH-aggregates of intermediate lifetime. Moreover, fluorescence of NCD is influenced by concentration and storage time. Accordingly, mismatch in spectral shapes of excitation and absorption spectra of NCD can be successfully correlated to aggregate species of NCDs exist even in very dilute solutions.

Research paper thumbnail of Polyethylene imine capped copper nanoclusters- fluorescent and colorimetric onsite sensor for the trace level detection of TNT

Sensors and Actuators B: Chemical, 2018

Detection of TNT by fluorescent and colorimetric method by using polyethylene imine capped fluore... more Detection of TNT by fluorescent and colorimetric method by using polyethylene imine capped fluorescent copper nanocluster Highlights  Polyethylene imine capped fluorescent copper nanoclusters were prepared via a one pot microwave assisted method.  The as prepared cost effective nanosensor was used for fluorescent as well as colorimetric detection of TNT and exhibited excellent sensitivity and selectivity.  In fluorescent and colorimetric detection LOD obtained is as low as 14 pM and 0.05 nM respectively.  A portable paper sensor was developed which can selectively detect TNT vapors.

Research paper thumbnail of Fluorescence Spectroscopic Investigation To Identify the Micelle to Gel Transition of Aqueous Triblock Copolymer Solutions

Journal of Physical Chemistry B, 2009

Steady-state and time-resolved fluorescence anisotropy measurements using probes coumarin 153 (C1... more Steady-state and time-resolved fluorescence anisotropy measurements using probes coumarin 153 (C153) and 4-heptadecylumbelliferon (HUF) have been carried out to understand the micelle to gel transition of an aqueous triblock copolymer P123 ((EO) 20 -(PO) 70 -(EO) 20 ) (EO ) ethylene oxide; PO ) propylene oxide) solution. Anisotropy results with a normal fluorescent probe, C153, do not show a characteristic change due to the micelle to gel transition. However, the probe HUF having a long hydrocarbon chain that helps its strong association with the micelle shows an increase in anisotropy above the sol-gel transition point. This difference has been explained as invoking a substantial contribution from the micellar structural fluctuations to the depolarization of HUF as its hydrocarbon chain is embedded in the micellar structure, which is not sensed significantly by the normal probe C153. That the extent of change in anisotropy for HUF upon gelation is not that large is possibly caused by the collective motion of the physically interconnected nodes, as observed from the dynamic light scattering studies, which acts in favor of a relatively faster depolarization in the gel phase. Similar studies in other copolymers, such as P85 ((EO) 26 -(PO) 40 -(EO) 26 ) and F127 ((EO) 100 -(PO) 65 -(EO) 100 ), further demonstrate the potential of probes latched with hydrocarbon chains in displaying a characteristic change for the micelle to gel transition which otherwise remains obscured for normal fluorescent probes.

Research paper thumbnail of Electrochemical impedance spectroscopic analysis of activation of Al–Zn alloy sacrificial anode by RuO 2 catalytic coating

Applied Surface Science, 2007

The uniform surface activation characteristics of RuO 2 -coated Al–Zn alloy sacrificial anodes we... more The uniform surface activation characteristics of RuO 2 -coated Al–Zn alloy sacrificial anodes were studied in the present work. Electrochemical impedance spectroscopic and SEM/EDAX analyses were carried out to evaluate the galvanic dissolution characteristics of the ...

Research paper thumbnail of Surface catalysis based on ruthenium dioxide for effective activation of aluminium sacrificial anodes

Corrosion Science, 2004

Several studies have been focusing on alloying and structural modification of aluminium alloy sac... more Several studies have been focusing on alloying and structural modification of aluminium alloy sacrificial anodes using different activators including intermetallic compounds. With a novel approach, the present work explore and evaluate the feasibility of effective aluminium activation by RuO 2 in 95 + 5 Al-Zn alloy substrates. The electrodes prepared in the present work, by making RuO 2 film on the substrate, were found to possess good surface interaction, low surface resistivity and facilitate interlayer diffusion of aluminium ions. The electrodes showed excellent galvanic performance under different experimental conditions in 3% NaCl electrolyte. The RuO 2 layer was found to persist on the electrode surface even after the electrode size was reduced to one-third of its original size due to long period of galvanic exposure, evidencing its mobile character. The electrodes are economically efficient, convenient to prepare as other conventional hanging electrodes, tolerable to very aggressive media and highly efficient even under high current load.