Faculty Publications

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Author: search.filters.author.Tarafder, K.Subject: search.filters.subject.Light

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    Enhanced photocatalytic efficiency of layered CdS/CdSe heterostructures: Insights from first principles electronic structure calculations
    (Institute of Physics Publishing helen.craven@iop.org, 2020) Shenoy, S.; Tarafder, K.
    Metal sulfides are emerging as an important class of materials for photocatalytic applications, because of their high photo responsive nature in the wide visible light range. In this class of materials, CdS with a direct band gap of 2.4 eV, has gained special attention due to the relative position of its conduction band minimum, which is very close to the energies of the reduced protons. However, the photogenerated holes in the valence band of CdS are prone to oxidation and destroy its structure during photocatalysis. Thus constructing a CdS based heterostructure would be an effective strategy for improving the photocatalytic performance. In this work we have done a detail theoretical investigation based on hybrid density functional theory calculation to get insight into the energy band structure, mobility and charge transfer across the CdS/CdSe heterojunction. The results indicate that CdS/CdSe forms type-II heterostructure that has several advantages in improving the photocatalytic efficiency under visible light irradiation. © 2020 IOP Publishing Ltd.
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    Graphitic C3N4/CdS composite photocatalyst: Synthesis, characterization and photodegradation of methylene blue under visible light
    (Elsevier B.V., 2020) Shenoy, S.; Tarafder, K.; Sridharan, K.
    Design and development of heterojunction photocatalysts is one among the main strategies for improving the photocatalytic activity of semiconductor materials. Here, we report the synthesis of a heterojunction photocatalyst by the embedment of cadmium sulphide (CdS) nanoparticles on the surface of graphitic carbon nitride (g-C3N4) layers through hydrothermal approach. The g-C3N4/CdS heterojunction photocatalyst exhibited two-fold and three-fold enhancement in the photodegradation efficiency in comparison to pristine CdS and g-C3N4, respectively in the removal of 20 ppm methylene blue dye molecules under visible light irradiation. The enhanced photocatalytic activity can be attributed to the formation of heterojunction and the synergistic effect of g-C3N4 and CdS in the promotion of charge separation and charge mobility that was tracked through photoluminescence spectroscopy. © 2020 Elsevier B.V.
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    Phenanthroimidazole-based chromophores for organic light-emitting diodes: synthesis, photophysical, and theoretical study
    (John Wiley and Sons Ltd, 2020) Tagare, J.; Verma, N.; Tarafder, K.; Sivakumar, S.
    Organic light-emitting diodes (OLED) are gaining attention and making a significant contribution to the area of lighting and displays technology. The synthesis of new materials that can act as a host as well as emissive materials is crucial and efforts have been made in this direction in this research. Here, four star-shaped fluorophores, with a donor–acceptor (D–A) structure and with triphenylamine and phenanthroimidazole groups with different substitutions at the N1 position of the imidazole moiety, were designed and synthesized. Synthesized fluorophores showed sufficient thermal stability (10% Td in the range 230–280°C). Ultraviolet–visible (UV–vis) spectra of the fluorophores showed multiple absorption bands (bands in the UV region, due to ?–?* transitions of the conjugated aromatic portion) and all fluorophores showed blue emission in dichloromethane solution. Electrochemical analysis indicated that all fluorophores had excellent oxidation and reduction characteristics. Theoretical calculations were also performed to better understand the structural and electronic properties of the synthesized fluorophores. All fluorophores had higher triplet (T1) energy (ranging from 2.49–2.52 eV) than the widely used green (Ir(ppy)3 –2.4 eV) and red (Ir (piq)2 acac – 2.2 eV) dopant materials. These results indicated that these fluorophores would be useful as host materials for efficient green and red phosphorescent OLEDs. © 2020 John Wiley & Sons, Ltd.
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    Bimetallic nanoparticles grafted ZnO hierarchical structures as efficient visible light driven photocatalyst: An experimental and theoretical study
    (Elsevier B.V., 2021) Shenoy, S.; Tarafder, K.; Sridharan, K.
    Bimetallic nanoparticles (NPs) exhibiting novel properties due to synergy between the individual elements have sparkled significant interest as a co-catalyst in enhancing the photocatalytic efficiency of semiconductor materials. Here, we report the photocatalytic activity of NiAg NPs embedded on hierarchical ZnO structures (NiAg-ZnO). Structural and morphological investigations through X-ray diffraction and scanning electron microscopy confirmed the formation of NiAg-ZnO. UV-Vis diffuse reflectance spectroscopy revealed the decrease in the bandgap energy of NiAg-ZnO (2.65 eV) in comparison to pristine ZnO (3.1 eV). Interestingly, the rate of photodegradation of methylene blue and rhodamine B dye molecules under visible light irradiation are two to three times enhanced with NiAg-ZnO in comparison to Ag-ZnO. Enhanced visible light absorption and effective charge separation due to the synergistic metal-semiconductor interface formed by the embedment of NiAg bimetallic NPs on ZnO led to the improved photocatalytic activity. Experimental results are further confirmed through the first principle electronic band structure calculations. © 2021