Now showing 1 - 10 of 12
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    Synthesis and photoelectrochemical catalytic properties of polyoxometalate supported on zeolitic imidazolate Framework, ZIF-9–PMo12
    (01-05-2023)
    Augustine, Chippy Alphons
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    Khatun, Nasima
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    Development of photocatalysts for hydrogen generation is highly imperative in the current scenario for resolving the worldwide energy crisis. Continuous efforts are being made to find low-cost and durable photocatalysts with better light absorption capacity to mitigate energy issues. Herein, a new p-n heterojunction photocatalyst has been synthesized successfully using a polyoxometalate (POM), phosphomolybdic acid (PMo12), and zeolitic imidazolate framework (ZIF-9). Photoelectrochemical studies under visible-light irradiation revealed that ZIF-9–PMo12 exhibits a higher photocurrent density than pure ZIF-9. The support of ZIF-9 prevented the instability of PMo12 in aqueous solutions and improved the photoresponse ability of ZIF-9. The p-n junction formation impedes the recombination of electrons and holes, resulting in the improved photocatalytic property. Photoelectrochemical experiments confirmed the photocatalytic features, and thus this work paves the way for the development of an efficient, stable, and low-cost photocatalyst for green H2 generation.
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    Enhanced H2evolution through water splitting using TiO2/ultrathin g-C3N4: A type II heterojunction photocatalyst fabricated by in situ thermal exfoliation
    (30-08-2021)
    Khatun, Nasima
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    Dey, Sutapa
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    Appadurai, Tamilselvan
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    Designing a photocatalyst material with reduced recombination of photogenerated charges is one of the most important aspects of hydrogen generation through solar water splitting. Here, we report hydrogen generation using the TiO2/ultrathin g-C3N4 (U-g-CN) heterostructure fabricated using a unique in situ thermal exfoliation process. Multilayer g-CN is converted into U-g-CN having a high surface (∼190 m2/g) area by calcination at ∼550 °C through oxygen-induced exfoliation, which also forms a robust heterostructure with TiO2. In addition, the presence of g-CN also inhibits further growth of TiO2 nanoparticles, thereby retaining a high specific surface area. The presence of U-g-CN causes a redshift (∼0.13 eV) in the absorption edge of heterostructure compared to that of bare TiO2, which extends the light absorption capability. Addition of 40 wt. % of multilayer g-CN to TiO2 shows an enhanced H2 evolution rate, which is ∼15 times and ∼4 times higher compared to that of bare TiO2 and U-g-CN, respectively. Photoluminescence (PL) and time-resolved PL (TRPL) studies indicate a reduced recombination rate of photogenerated charge carriers with an increase in the average lifetime from 10.53 (TiO2) to 13.32 ns (TiO2/U-g-CN40). The interfacial charge transport characteristics studied through impedance spectroscopy reveal a reduced charge transfer resistance at the semiconductor-electrolyte interface, which facilitates faster charge separation due to the heterostructure formation. The band edge positions are estimated through flatband potential from the Mott-Schottky measurements and optical absorption data, indicating a type-II heterojunction. More light absorption and enhanced separation of photogenerated charges at the heterojunction interface lead to better photocatalytic H2 generation.
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    Optimization of etching and sonication time to prepare monolayer Ti3C2Tx MXene flakes: A structural, vibrational, and optical spectroscopy study
    (01-07-2022)
    Khatun, Nasima
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    Two-dimensional (2D) Ti3C2Tx MXene and its heterostructure exhibit promising performances in several applications such as energy storage, optoelectronics, electrocatalysis, water purification, biomedical, etc. Our investigation shows that an etching duration of 24 h is sufficient to remove Al layers from Ti3AlC2 and to obtain a well-separated accordion-like structure. Different lateral size monolayer MXene flakes ranging from 2 μm to 35 nm are obtained by tuning the sonication time from 2 to 8 h. The monolayer nature of the flakes is confirmed by both Atomic Force Microscope (AFM) and Transmission Electron Microscope (TEM). Raman vibrational modes and X-ray photoelectron spectroscopy (XPS) show that the flakes are containing –O, –F, and –OH functional groups. A unique type of absorption spectra is observed that comes from both interband and intraband transition. An in-depth structural, vibrational, and optical property study gives a clear idea to use these flakes for heterostructure formation with other materials for various applications.
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    Localized thermal spike driven morphology and electronic structure transformation in swift heavy ion irradiated TiO2nanorods
    (07-01-2022)
    Dey, Sutapa
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    Chakravorty, Anusmita
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    Mishra, Shashi Bhusan
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    Khatun, Nasima
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    Hazra, Arnab
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    Sudakar, Chandran
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    Kabiraj, Debdulal
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    Irradiation of materials by high energy (∼MeV) ions causes intense electronic excitations through inelastic transfer of energy that significantly modifies physicochemical properties. We report the effect of 100 MeV Ag ion irradiation and resultant localized (∼few nm) thermal spike on vertically oriented TiO2nanorods (∼100 nm width) towards tailoring their structural and electronic properties. Rapid quenching of the thermal spike induced molten state within ∼0.5 picosecond results in a distortion in the crystalline structure that increases with increasing fluences (ions per cm2). Microstructural investigations reveal ion track formation along with a corrugated surface of the nanorods. The thermal spike simulation validates the experimental observation of the ion track dimension (∼10 nm diameter) and melting of the nanorods. The optical absorption study shows direct bandgap values of 3.11 eV (pristine) and 3.23 eV (5 × 1012ions per cm2) and an indirect bandgap value of 3.10 eV for the highest fluence (5 × 1013ions per cm2). First principles electronic structure calculations corroborate the direct-to-indirect transition that is attributed to the structural distortion at the highest fluence. This work presents a unique technique to selectively tune the properties of nanorods for versatile applications.
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    Improved omnidirectional polarisation-insensitive optical absorption and photoelectrochemical water splitting using aperiodic and tapered slanted, kinked and straight silicon nanowires
    (10-06-2022)
    Adhila, T. K.
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    Khatun, Nasima
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    Barshilia, Harish C.
    We have experimentally demonstrated that slanted, kinked and straight silicon nanowire arrays form a broadband omnidirectional light-harvesting structure. The unique design of kinked and slanted nanowires allows them to trap more light effectively across a wide wavelength range than straight silicon nanowires (SiNWs). We report that the light absorption in slanted, kinked and straight wires is enhanced by controlling their geometrical parameters. The p-type SiNWs have less reflection than n-type SiNWs due to their larger porosity gradient structure. Aperiodic and tapered slanted, kinked and straight SiNWs are remarkably photoactive and promising low-cost materials for photoelectrochemical water splitting applications.
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    Improved photoelectrochemical performance of ultra thin g-C3N4nanosheet: A comparative study from bulk to nanoscale
    (13-09-2021)
    Khatun, Nasima
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    Dey, Sutapa
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    Ultrathin g-C3N4 (g-CN) nanosheets are prepared by a two-step thermal exfoliation process in an air atmosphere. X-ray diffraction pattern (XRD) shows that ultrathin g-CN nanosheets have the same crystal structure as that of the bulk g-CN with a slight shift in the peak positions due to the reduction of sheet thickness. Field emission scanning electron microscope (FESEM) images show that the bulk g-CN is converted into ultrathin g-CN nanosheets due to thermal oxidation in an atmosphere, which increases the number of reactive active sites for water splitting. Due to a reduction in sheet thickness of g-CN, quantum confinement happened and thereby increase the bandgap from 2.88 (bulk g-CN) eV to 3.10 eV (ultrathin g-CN). Steady-state photoluminescence (PL) shows a blue shift, and time-resolve photoluminescence (TRPL) shows that the average lifetime of photogenerated charge carrier increases when bulk g-CN is converted into ultrathin g-CN nanosheets. Enhancement in photoelectrochemical performance is observed in ultrathin g-CN nanosheets compared to bulk g-CN due to the increased average lifetime of photogenerated charge carriers and a large number of reactive active sites.
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    WS2 nanosheets functionalized Fe2O3 nanorod arrays as a type II heterojunction for photoelectrochemical water splitting
    (01-10-2022)
    Behera, Govinda C.
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    Rani, Sanju
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    Khatun, Nasima
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    Fe2O3 is a stable and low bandgap photocatalyst capable of absorbing a wide range of solar spectra. However, a shorter hole diffusion length impedes its performance as an efficient photocatalyst. The formation of a type II heterojunction is an effective approach to facilitate the quick separation of photogenerated carriers. In this work, we report photo-electrochemical characteristics of WS2 functionalized Fe2O3 nanorod arrays fabricated on FTO coated glass substrate. The Fe2O3 nanorods fabricated by chemical bath deposition and WS2 nanosheets by the hydrothermal technique are characterized by X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray analysis (EDS), X-ray photoelectron spectroscopy, optical absorption, Raman spectra, and FT-IR. A heterojunction architecture formed between these resulted in a higher photocurrent density compared to that of bare Fe2O3 nanorods. Electrochemical impedance spectroscopy and Mott-Schottky measurements reveal lower charge transfer resistance and higher interfacial charge density for WS2 functionalized Fe2O3 nanorods. An energy band diagram for the heterojunction has been proposed to show the charge separation at the interface.
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    Ti3C2Tx MXene functionalization induced enhancement of photoelectrochemical performance of TiO2 nanotube arrays
    (15-02-2022)
    Khatun, Nasima
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    Dey, Sutapa
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    Behera, Govinda C.
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    Due to a unique planar structure, hydrophilic functional groups, and excellent metallic conductivity, recently developed two-dimensional (2D) MXene offers great potential in applications such as energy storage, photothermal conversion, gas sensing, etc. Herein, we have fabricated 2D Ti3C2Tx MXene functionalized TiO2 nanotube arrays (TNTs) to achieve enhanced photoelectrochemical (PEC) water splitting. We have observed ∼30% increase in photocurrent density for MXene functionalized TNTs over that of bare TNTs. Impedance spectroscopy analysis suggests a decrease in charge transfer resistance from ∼11.38 kΩ to ∼2.94 kΩ at an optimal amount of MXene functionalization. Analysis of Mott-Schottky measurement shows that donor density increases in MXene functionalized TNT sample. Under light irradiation, Ti3C2Tx MXene shows a localized surface plasmon resonance (LSPR) effect and injects electrons to the conduction band of TNT thereby increasing the photogenerated charge carriers, which in turn, enhances the PEC performance of bare TNTs. The work provides a pathway to design new plasmonic heterostructure materials based on monolayers MXene flakes for overall water splitting application.
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    Enhanced photoelectrochemical performance of CeO2functionalized TiO2nanotube arrays with Ag coating
    (13-09-2021)
    Dey, Sutapa
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    Khatun, Nasima
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    The photoelectrochemical performance of Ag coated CeO2 functionalized TiO2 nanotube arrays (AgCeTNT) is investigated here. The sample is prepared via three steps, such as synthesis of TiO2 nanotube by electrochemical anodization, CeO2 functionalization by hydrothermal and Ag coating by Successive Ionic Layer Adsorption and Reaction (SILAR) method. X-ray diffraction (XRD) analysis showed the anatase phase formation after annealing of TiO2 nanotubes. Field Emission Scanning Electron Microscopic (FESEM) images showed the conformal coverage of CeO2 and Ag nanoparticles on the surface of TiO2 nanotubes. Energy Dispersive X-Ray (EDX) analysis confirmed the presence of Ce, Ag, Ti and O in the AgCeTNT sample. Diffuse Reflectance Spectroscopy (DRS) study revealed the enhancement in visible light sensitivity with CeO2 functionalization and further with Ag coating. The photoelectrochemical measurement showed that the AgCeTNT sample exhibits improved photoelectrochemical performance compared to bare TiO2 nanotubes (TNT), CeO2 functionalized TiO2 nanotubes (CeTNT) and Ag coated TiO2 nanotubes (AgTNT) under the illumination of sunlight. This improvement in photoelectrochemical performance happeneddue to the combined effect of favorable band alignment of CeO2 and TiO2 and Surface Plasmon Resonance (SPR) effect of Ag nanoparticles, which lead to superior charge separation, efficient charge transport and enhanced visible light response.
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    TiO2-g-C3N4 composite to boost photoelectrochemical performance under visible light irradiation and a charge carrier dynamic study
    (01-01-2022)
    Khatun, Nasima
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    TiO2-g-C3N4 composite material is fabricated by simple in situ thermal processes. From field emission scanning electrons spectroscopy (FESEM), it is observed that TiO2 nanoparticles are embedded on the surface of g-C3N4 (g-CN) sheets. The addition of g-CN with TiO2 reduces the bandgap from UV (3.10 eV) to visible (2.82 eV) light region, which helps to absorb more solar irradiation and shows higher photocurrent density for TiO2-g-CN compared to TiO2 and g-CN. Photoluminescence analysis reveals that the recombination rate of photogenerated charge carriers reduces, and impedance spectroscopy study shows charge transfer resistance decreases in TiO2-g-CN composite material. A type-II heterojunction between TiO2 and g-CN leads to the enhancement of the photoelectrochemical performance of the composite material.