Department Of Chemistry
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Item Novel Green Approach for Fabrication of Ag2CrO4/TiO2/Au/r-GO Hybrid Biofilm for Visible Light-Driven Photocatalytic Performance(American Chemical Society, 2020) Biswas, R; Mete, S; Mandal, M; Banerjee, B; Singh, H; Ahmed, I; Haldar, K.K.Development of cutting edge materials using a benevolent ecologically cordial methodology is an ideal approach for heterogeneous visible light photocatalysis. A new biogenic photocatalyst was developed by coupling titanium dioxide (TiO2) decorated elongated rhombic shape silver chromate (Ag2CrO4) with gold (Au) and reduced graphene oxide (r-GO) for dye degradation applications under visible light. An ecologically positive methodology was utilized to develop the quaternary Ag2CrO4/TiO2/Au/r-GO nanostructures biofilm with gold and reduced graphene oxide (r-GO) via impregnation and in situ reduction technique in the presence of acacia gum. The structural properties and morphology of the Ag2CrO4/TiO2/Au/r-GO nanostructures were described by several spectroscopic and microscopic methods such as XRD, XPS, ATR-FTIR, Raman spectroscopy, FE-SEM, etc. Alteration with Au and r-GO decreased the band vitality and essentially improved the visible light ingestion of the quaternary Ag2CrO4/TiO2/Au/r-GO composite biofilm photocatalyst and slowed down the recombination process of the photogenerated electrons and holes. To demonstrate how such a unique heterostructured biofilm might produce more outstanding photocatalytic activity, we examined a comparison of the photocatalytic performances of Ag2CrO4/TiO2/Au/r-GO hybrid biofilm with different inner structures. The photocatalytic debasement of MB reached almost 97% within 52 min, and it has been found that the Ag2CrO4/TiO2/Au/r-GO biofilm increased the degradation rate of MB by a factor of 10.8, 6.5, and 3.1 in comparison with exposed Ag2CrO4, Ag2CrO4/TiO2, and Ag2CrO4/TiO2/Au biofilms, individually. Further, the high electron movement capacity of Ag2CrO4/TiO2/Au/r-GO biofilm was explored by photoelectrochemical investigation and TCSPC to comprehend the mechanistic insight of the superior activity of this composite nanostructures under visible light illumination. Hence, the present investigation describes a facile, eco-friendly, and biomimetic approach for the fabrication of Ag2CrO4/TiO2/Au/r-GO biofilm based photocatalyst using acacia gum. Copyright � 2020 American Chemical Society.Item Fabrication of mesoporous titanium dioxide using azadirachta indica leaves extract towards visible-light-driven photocatalytic dye degradation(Elsevier, 2020) Dash, L; Biswas, R; Ghosh, R; Kaur, V; Banerjee, B; Sen, T; Patil, R.A; Ma, Y.-R; Haldar, K.K.An environmental benign, straightforward and financially savvy technique has been developed to fabricate mesoporous titanium dioxide (TiO2) nanostructure utilizing Azadirachta indica leaves extract. The aqueous extract of Azadirachta indica leaves act as a template which upon calcination at high temperature generated mesoporous TiO2. The structure of the mesoporous TiO2 was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and isothermal gas adsorption-desorption (BET). It has been found that the crystallinity and pore diameter of mesoporous titanium dioxide (TiO2) depends on the amount of Azadirachta indica leaves extract, resulting in enhanced crystallinity with an increasing amount of Azadirachta indica leaves extract. The pore diameter was found somewhere in the range from 16.67 to 46.19 nm, and the BET surface area varies from 8.55–157.35 m2/g.. Finally, we have explored as-synthesized mesoporous TiO2 for visible-light-driven photocatalytic degradation of rhodamine 6 G (R6 G) dye. It is noteworthy that the photocatalytic degradation rate of R6 G in presence of as-synthesized mesoporous TiO2 depends only on the amount of plant extract used and not on temperature and other factors. This is presumably due to the increased optical band gap of TiO2. - 2020 Elsevier B.V.Item One-Pot Synthesis of Au Embedded ZnO Nanorods Composite Heterostructures with Excellent Photocatalytic Properties(Wiley-Blackwell, 2018) Haldar, K.K.; Biswas, R.; Tanwar, S.; Sen, T.; Lahtinen, J.Here, we have designed a noble composite nanostructure by embedding gold (Au) nanoparticles into zinc oxide (ZnO) nanorods surface in one pot synthesis as a photocatalyst. The formation the composite nanostructure was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy and transmission electron microscopy investigations. Microscopic studies suggest that spherical Au nanoparticles are nucleated on the ZnO nanorods surface. XPS shows shifting of peak positions towards higher binding energy which indicates charge transfer from ZnO to Au in the composite nanostructures. This is unambiguously confirmed by the steady state spectroscopic studies. It was found that 95.7% (1.8 × 10?5 mM) of Methylene blue dye is degraded by the composite nanostructure after 140 min under UV light illumination and the apparent rate constant was found to be 0.015 min?1. This new class of Au nanoparticles embedded ZnO nanorods composite nanostructure opens up new possibilities in photocatalytic, solar energy conversion, photovoltaic, and other new emerging applications.Item Structural and electronic investigation of metal-semiconductor hybrid tetrapod hetero-structures(Springer Verlag, 2017) Haldar, K.K.; Muley, V.Y.; Datar, S.; Patra, A.This article highlights the new electronic properties of tetrapod hetero-structures with metal Au core and semiconductor CdSe arms, which is one of the new classes of hybrid metal-semiconductor nanostructures. From the analysis of XRD, HRTEM, HAADF-STEM images, and EDAX line-scan studies, the growth mechanism of all these hetero-structures is proposed. These findings are important from the basic fundamental aspects of understanding the shape control of hetero-structures. Scanning tunneling spectroscopic study confirms the coulomb staircase-like features near Au which is characteristic of Au nanoparticles and the gap increases as we move the tip towards CdSe. Analysis suggests that the resonance tunneling occurs between valance band edge (conduction band edge) of CdSe and coulomb stairs of Au dot. These tetrapod hetero-structures could pave the way for designing new optical-based materials for developing new challenging photonic devices. ? 2017, Springer International Publishing Switzerland.Item Nonlinear optical switching and optical limiting in colloidal CdSe quantum dots investigated by nanosecond Z-scan measurement(Elsevier Ltd, 2016) Valligatla, S.; Haldar, K.K.; Patra, A.; Desai, N.R.The semiconductor nanocrystals are found to be promising class of third order nonlinear optical materials because of quantum confinement effects. Here, we highlight the nonlinear optical switching and optical limiting of cadmium selenide (CdSe) quantum dots (QDs) using nanosecond Z-scan measurement. The intensity dependent nonlinear absorption and nonlinear refraction of CdSe QDs were investigated by applying the Z-scan technique with 532 nm, nanosecond laser pulses. At lower intensities, the nonlinear process is dominated by saturable absorption (SA) and it is changed to reverse saturable absorption (RSA) at higher intensities. The SA behaviour is attributed to the ground state bleaching and the RSA is ascribed to free carrier absorption (FCA) of CdSe QDs. The nonlinear optical switching behaviour and reverse saturable absorption makes CdSe QDs are good candidate for all-optical device and optical limiting applications. ? 2016 Elsevier Ltd.Item Core size matters! High Raman enhancing core tunable Au/Ag bimetallic core-shell nanoparticles(Springer Verlag, 2017) Paital, D.; Sen, T.; Patra, A.; Haldar, K.K.Bimetallic core-shell nanostructures have been attracted tremendous attention due to their ability to form novel materials with unique chemical, optical, and physical properties. Here, we have studied the influence of core size of Au/Ag bimetallic core-shell nanostructures on the Raman enhancement efficiency with the Raman-active probe methylene blue. The surface-enhanced Raman scattering intensity is increased with increase in the core size of Au/Ag bimetallic core-shell nanoparticles. Interestingly, the enhancement factor is found to be 6.58?נ107 for the Au100/Ag core-shell nanoparticles and allows easy detection of analyte methylene blue. Thus, surface-enhanced Raman scattering properties of the metal nanoparticles are significantly enhanced due to the Au/Ag core-shell structures and the enhancement factor is dependent on the size of the core of the bimetallic nanoparticles. ? 2017, Springer International Publishing AG.Item DNA Origami Directed Au Nanostar Dimers for Single-Molecule Surface-Enhanced Raman Scattering(American Chemical Society, 2017) Tanwar, Swati; Haldar, Krishna Kanta; Sen, Tapasi; Tanwar, S.; Haldar, K.K.; Sen, T.We demonstrate the synthesis of Au nanostar dimers with tunable interparticle gap and controlled stoichiometry assembled on DNA origami. Au nanostars with uniform and sharp tips were immobilized on rectangular DNA origami dimerized structures to create nanoantennas containing monomeric and dimeric Au nanostars. Single Texas red (TR) dye was specifically attached in the junction of the dimerized origami to act as a Raman reporter molecule. The SERS enhancement factors of single TR dye molecules located in the conjunction region in dimer structures having interparticle gaps of 7 and 13 nm are 2 ? 1010 and 8 ? 109, respectively, which are strong enough for single analyte detection. The highly enhanced electromagnetic field generated by the plasmon coupling between sharp tips and cores of two Au nanostars in the wide conjunction region allows the accommodation and specific detection of large biomolecules. Such DNA-directed assembled nanoantennas with controlled interparticle separation distance and stoichiometry, and well-defined geometry, can be used as excellent substrates in single-molecule SERS spectroscopy and will have potential applications as a reproducible platform in single-molecule sensing. ? 2017 American Chemical Society.