School Of Basic And Applied Sciences

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Author: search.filters.author.Haldar, Krishna KantaSubject: search.filters.subject.II-VI semiconductors

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    Does Water Play a Crucial Role in the Growth of ZnO Nanoclusters in ZnO/Cu Catalyst?
    (American Chemical Society, 2023-05-04T00:00:00) Dastider, Saptarshi Ghosh; Panigrahi, Abhishek Ramachandra; Banerjee, Arup; Haldar, Krishna Kanta; Fortunelli, Alessandro; Mondal, Krishnakanta
    The catalytically active configuration of ZnO/Cu in the commercial ZnO/Cu/Al2O3 catalyst for methanol synthesis from CO2 is still not clear. In this study, we employ density functional theory based methods to shed light on the structure and stoichiometry of ZnO clusters both free in the gas phase and also deposited on the Cu(111) surface under methanol synthesis conditions. Specifically, we investigate the structural evolution of ZnO clusters in the presence of hydrogen and water. We find that the stability of ZnO clusters increases with the concentration of water until the ratio of Zn and OH in the clusters reaches 1:2, with a morphological transition from planar to 3D configurations for clusters containing more than 4 Zn atoms. These clusters exhibit weak interaction with CO2, and water is predicted to block the active center. The Cu(111) surface plays an important role in enhancing the adsorption of CO2 on the ZnO/Cu(111) systems. We infer that ZnO nanostructures covered with OH species may be the morphology of the ZnO during the methanol synthesis from the hydrogenation of CO2 on the industrial catalyst. � 2023 American Chemical Society.
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    Green Approach for the Fabrication of Au/ZnO Nanoflowers: A Catalytic Aspect
    (American Chemical Society, 2021-03-19T00:00:00) Biswas, Rathindranath; Banerjee, Biplab; Saha, Monochura; Ahmed, Imtiaz; Mete, Shouvik; Patil, Ranjit A.; Ma, Yuan-Ron; Haldar, Krishna Kanta
    An easy, environmentally benign, and biomimetic approach employing Azadirachta indica (neem) leaf extract as a reducing as well as capping agent was used for the fabrication of gold (Au)/zinc oxide (ZnO) hybrid nanoflowers in one pot without utilizing any hazardous chemicals. The different phytoconstituents, for example, nimbolide, azadirachtin, ascorbate, etc., present in A. indica (neem) leaf extract synergistically reduce gold(III) ions to gold(0), which later on acts as an active surface for the growth of zinc oxide (ZnO) via thermal decomposition of sodium zincate [Na2Zn(OH)4]. The development of Au/ZnO hybrid nanoflowers was observed by estimating the absorption maxima at various time intervals in the wake of adding a Au precursor to the aqueous extract. X-ray diffraction (XRD) studies and X-ray photoelectron spectroscopy (XPS) investigation unambiguously confirm the formation of highly crystalline Au/ZnO composed of Au(0) and ZnO. The as-synthesized Au/ZnO hybrid nanoflowers were analyzed utilizing different spectroscopic and microscopic techniques. The transmission electron microscopy (TEM) images clearly show that the synthesized hybrid Au/ZnO nanoflowers are monodisperse and uniform. The fabricated Au/ZnO nanoflowers were used as a catalyst for the efficient reduction of various aromatic nitro compounds to corresponding amino compounds with excellent yield (76-94%) in the presence of reducing agent sodium borohydride. The superior catalytic properties were credited to the extraordinary nanoflower morphology and the synergistic impact of the typified Au nanoparticles. � 2021 American Chemical Society.
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    Nickel oxide decorated zinc oxide composite nanorods: Excellent catalyst for photoreduction of hexavalent chromium
    (Academic Press Inc., 2018) Singh, Simranjeet; Ahmed,Imtiaz; Haldar, Krishna Kanta
    In light of the growing interest and ability to search for new materials, we have synthesized Nickel oxide (NiO) nanoparticles decorated Zinc (ZnO) nanorods composite (NiO/ZnO) nanostructure. The NiO/ZnO heterostructure formation was confirmed by X-ray powder diffraction and high-resolution transmission electron microscopy (HRTEM). The fabricated environmental friendly NiO/ZnO composite nanostructure shows a well-defined photoreduction characteristic of hexavalent Chromium (Cr) (VI) to tri-valent Chromium (Cr) (III) under UV-light. Such an enhanced photoreduction property is attributed due to the decreased electron-hole recombination process which was proved by photoluminescence (PL) spectroscopy, photocurrent study, and electrochemical impedance spectroscopy. Furthermore, the photocatalytic activity rate of the NiO decorated ZnO nanorods was much higher than that of bare ZnO nanorods for the reduction of chromium (VI) and the rate is found to be 0.306 min?1. These results have demonstrates that suitable surface engineering may open up new opportunities in the development of high-performance photocatalyst. ? 2018 Elsevier Inc.