Browsing by Author "Gogoi, Abhijit"

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    Benzimidazole and Benzothiazole Based Chemosensors For Biologically Important Analytes
    (2015) Gogoi, Abhijit
    This thesis reports the efforts made in the improvisations of certain benzothiazole/benzimidazle functionalized receptors towards colorimetric and/or fluorescent cation and anion sensing in biologically relevant medium. Ninhydrin functionalized benzothiazole probe L1 is an excellent Zn2+ sensor and emits in the NIR (near infrared) region without no interference from the other metal ions. A visual distinction of H2PO4- from other phosphate related anion was also achieved with the probe-Zn2+ ensemble. Such long wavelength emissive chemosensors are very important for fluorescent imaging as they can penetrate much deeper into the sample. Next benzothiazole functionalized schiff base probe L2 senses Zn2+ and Cd2+ ion in physiological medium. The metal ensembles are further found to sensitive to both H2PO4- and PPi anion. Dipodal benzothiazole Schiff base L3 also selectively sense Zn2+ ion in nanomolar level. Furthermore, PPi anion could be separated from H2PO4- with this ‘L3-Zn2+’ ensemble even in the presence of other interfering anions.Direct anion sensing is always superior to that of metal assisted anion sensing but an intriguing task in pure aqueous medium. Aggregation induced emission (AIE) phenomenon could boost the emission intensity in aqueous medium. Benzimidazole functionalized probe L4 demonstrate AIE induced PPi sensing in physiological medium with any assistance from the metal ion. In addition, apart from metal based selectivity study, such benzimidazole functionalized AIE probes could also be applied to study sensing behavior of certain H-donor molecules, such as inorganic acids, organic acids like picric acid, amino acids etc.
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    Graphene Oxide and Graphene in Membrane Applications: A Molecular Dynamics Simulation Study
    (2020) Gogoi, Abhijit
    The applicability of graphene oxide (GO) and graphene for separation and purification applications is investigated using non-equilibrium molecular dynamics (MD) simulations. The effect of internal structure of the layered GO membrane on its performance as a forward osmosis (FO) membrane for sea water desalination and dehydration of acetic acid is studied. GO membranes composed of nanosheets of smaller lateral dimensions found to have higher water permeance and lower salt rejection than GO membranes composed of nanosheets of larger lateral dimensions. The performance of layered GO membrane is also dependent on its interlayer distance. The water permeance increases and the draw solute rejection decreases as the interlayer spacing between the GO layers increases to an optimum value, after that, with further increase in the interlayer spacing the water permeance decreases and the salt rejection of the membrane increases. The presence of the cations can also significantly influence the performance of layered GO membranes both in FO and reverse osmosis (RO) processes. For the same interlayer spacing, the cation intercalated layered GO membranes have higher water flux as compared to corresponding pristine layered GO membranes. On the other hand, the intercalation of the cations (K+, Mg2+) lead to higher rejection of Na+ ions whereas the rejection of Cl- ions slightly decreases. In this present study, the electro-osmotic flow behavior through a graphene nanochannel with surfaces having striped charge distribution are also discussed in detail using non-equilibrium molecular dynamics simulations. The velocity of the water molecules and the water permeance through the nanochannel gradually increases with the increase in surface charge density from 0.005 Cm-2 to 0.025 Cm-2. With further increase in the surface charge density beyond 0.025 Cm-2, the velocity of the water molecules and the water permeance through the nanochannel gradually decreases. Here the thickness of the diffuse layer and the interaction between water molecules and the wall play significant roles in determining the flow behavior through the nanochannel.