Faculty Publications
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Item Advanced two-dimensional heterojunction photocatalysts of stoichiometric and non-stoichiometric bismuth oxyhalides with graphitic carbon nitride for sustainable energy and environmental applications(MDPI, 2021) Sridharan, K.; Shenoy, S.; Girish Kumar, S.G.; Terashima, C.; Fujishima, A.; Pitchaimuthu, S.Semiconductor-based photocatalysis has been identified as an encouraging approach for solving the two main challenging problems, viz., remedying our polluted environment and the generation of sustainable chemical energy. Stoichiometric and non-stoichiometric bismuth oxyhalides (BiOX and BixOyXz where X = Cl, Br, and I) are a relatively new class of semiconductors that have attracted considerable interest for photocatalysis applications due to attributes, viz., high stability, suitable band structure, modifiable energy bandgap and two-dimensional layered structure capable of generating an internal electric field. Recently, the construction of heterojunction photocatalysts, especially 2D/2D systems, has convincingly drawn momentous attention practicably owing to the productive influence of having two dissimilar layered semiconductors in face-to-face contact with each other. This review has systematically summarized the recent progress on the 2D/2D heterojunction constructed between BiOX/BixOyXz with graphitic carbon nitride (g-C3N4). The band structure of individual components, various fabrication methods, different strategies developed for improving the photocatalytic performance and their applications in the degradation of various organic contaminants, hydrogen (H2) evolution, carbon dioxide (CO2) reduction, nitrogen (N2) fixation and the organic synthesis of clean chemicals are summarized. The perspectives and plausible opportunities for developing high performance BiOX/BixOyXz-g-C3N4 heterojunction photocatalysts are also discussed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Item Superior Photostability and Photocatalytic Activity of ZnO Nanoparticles Coated with Ultrathin TiO2 Layers through Atomic-Layer Deposition(Wiley-VCH Verlag info@wiley-vch.de, 2015) Sridharan, K.; Jang, E.; Park, Y.M.; Park, T.J.Atomic-layer deposition (ALD) is a thin-film growth technology that allows for conformal growth of thin films with atomic-level control over their thickness. Although ALD is successful in the semiconductor manufacturing industry, its feasibility for nanoparticle coating has been less explored. Herein, the ALD coating of TiO2 layers on ZnO nanoparticles by employing a specialized rotary reactor is demonstrated. The photocatalytic activity and photostability of ZnO nanoparticles coated with TiO2 layers by ALD and chemical methods were examined by the photodegradation of Rhodamine B dye under UV irradiation. Even though the photocatalytic activity of the presynthesized ZnO nanoparticles is higher than that of commercial P25 TiO2 nanoparticles, their activity tends to decline due to severe photocorrosion. The chemically synthesized TiO2 coating layer on ZnO resulted in severely declined photoactivity despite the improved photostability. However, ultrathin and conformal ALD TiO2 coatings (?0.75-1.5 nm) on ZnO improved its photostability without degradation of photocatalytic activity. Surprisingly, the photostability is comparable to that of pure TiO2, and the photocatalytic activity to that of pure ZnO. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.Item Eliminated Phototoxicity of TiO2Particles by an Atomic-Layer-Deposited Al2O3Coating Layer for UV-Protection Applications(Wiley-VCH Verlag, 2016) Jang, E.; Sridharan, K.; Park, Y.M.; Park, T.J.We demonstrate the conformal coating of an ultrathin Al2O3layer on TiO2nanoparticles through atomic layer deposition by using a specifically designed rotary reactor to eliminate the phototoxicity of the particles for cosmetic use. The ALD reactor is modified to improve the coating efficiency as well as the agitation of the particles for conformal coating. Elemental and microstructural analyses show that ultrathin Al2O3layers are conformally deposited on the TiO2nanoparticles with a controlled thickness. Rhodamine B dye molecules on Al2O3-coated TiO2exhibited a long life time under UV irradiation, that is, more than 2 h, compared to that on bare TiO2, that is, 8 min, indicating mitigation of photocatalytic activity by the coated layer. The effect of carbon impurities in the film resulting from various deposition temperatures and thicknesses of the Al2O3layer on the photocatalytic activity are also thoroughly investigated with controlled experimental condition by using dye molecules on the surface. Our results reveal that an increased carbon impurity resulting from a low processing temperature provides a charge conduction path and generates reactive oxygen species causing the degradation of dye molecule. A thin coated layer, that is, less than 3 nm, also induced the tunneling of electrons and holes to the surface, hence oxidizing dye molecules. Furthermore, the introduction of an Al2O3layer on TiO2improves the light trapping thus, enhances the UV absorption. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Cadmium sulfide nanostructures: Influence of morphology on the photocatalytic degradation of erioglaucine and hydrogen generation(Elsevier B.V., 2019) Shenoy, S.; Jang, E.; Park, T.J.; Gopinath, C.S.; Sridharan, K.Size and shape of inorganic materials are known to have great effects on their physical and chemical properties. Here, for the first time we report the visible light driven photocatalytic degradation of erioglaucine – a stable organic dye molecule in the presence of chemically synthesized nanoscale CdS with 1D (nanorods), 2D (nanosheets) and 3D (hierarchical) morphology. Visible light driven photocatalytic degradation efficiency of both 1D and 3D CdS in the removal of erioglaucine are identical. Surprisingly, with 5 min of sonication, the highly crystalline 3D CdS stacked with many thin nanowires containing numerous active surface sites exhibited four-fold enhanced photodegradation efficiency in comparison to 1D and 2D CdS. Scavenger studies revealed that electrons and superoxide radicals are primary reactive species involved in the photodegradation of erioglaucine, while cyclic photodegradation studies revealed the good stability of 3D CdS against photocorrosion. Further, the photocatalytic hydrogen evolution studies also revealed the excellent activity of 3D CdS in comparison to 1D and 2D CdS. Thus, we find that the morphology indeed influences the photocatalytic activity. These results reveal that 3D CdS nanostructures investigated in the present work are efficient photocatalysts that could be fine-tuned for both environmental remediation and hydrogen generation applications. © 2019 Elsevier B.V.Item A robust photocatalyst using silver quantum clusters grafted in titanium dioxide nanotubes(Elsevier B.V., 2022) Shenoy, S.; Sridharan, K.Enhanced photocatalytic activity resulting from the direct electron transfer from noble metal nanoparticles coupled with semiconductor nanostructures is well reported. However, studies on the photocatalytic activity of semiconductor nanostructures coupled with noble metal clusters that exhibit fascinating chemical, optical, and electronic properties are still limited. In this context, we herein report the fabrication of silver quantum clusters grafted on titanium dioxide nanotubes (AgQCs-TNT) towards the photodegradation of ibuprofen and photoreduction of hexavalent chromium ions under visible light irradiation. The structural, chemical, morphological, and optical properties of the as-synthesized samples were studied through X-ray diffraction, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and UV-visible diffuse reflectance spectroscopy. Interestingly, AgQCs-TNT exhibited excellent photocatalytic efficiency in the degradation of ibuprofen and the reduction of hexavalent chromium ions under visible light irradiation in comparison to their pristine counterparts. Role of scavengers and plausible mechanisms pertaining to the improved photocatalytic activity of AgQCs-TNT due to the synergy between the pristine counterparts are discussed. © 2022