BITS Faculty Publications

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Author: search.filters.author.Basu, MrinmoyeeSubject: search.filters.subject.Oxides

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    An Aminolytic Approach toward Hierarchical β-Ni(OH)2 Nanoporous Architectures: A Bimodal Forum for Photocatalytic and Surface-Enhanced Raman Scattering Activity
    (ACS, 2010) Basu, Mrinmoyee
    A surfactantless, trouble-free, and gentle wet chemistry approach has been used to interpret the precisely controlled growth of β-Ni(OH)2 with the assistance of ammonia and nickel acetate from seedless mild hydrothermal conditions. A thorough investigation of the reaction kinetics and product morphology with varied concentration of NH3 and different reaction times suggests that a putative mechanism of dissolution, recrystallization, and oriented attachment supports the intelligent self-assembly of nanobuilding blocks. Associated characterizations (FTIR, PXRD, FESEM, EDAX, HRTEM, and Raman) have identified it to be pure β-Ni(OH)2 without any signature of contamination. The assembled units result in porous frameworks (nanoflowers and nanocolumns) and are indeed full of communally intersecting nanopetals/nanoplates with both lengths and widths on the order of micrometer to nanometer length scale. The as-synthesized material could also be used as a precursor for nanometric black NiO under calcination. The hydroxide has been found to be a potent and environmentally benign material because it warrants its photocatalytic activity through dye mineralization. Finally, Ni(OH)2 has been photochemically derivatized with dosages of silver nanoparticles bringing a competent composite authority Ag@Ni(OH)2, to give a full-proof enhanced field effect of prolific SERS activity. In a nutshell, these results are encouraging and fetch new promise for the fabrication of a low-cost and high-yielding greener synthetic protocol for a functional material with promising practicability.
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    Near-Field and Far-Field Plasmonic Effects of Gold Nanoparticles Decorated on ZnO Nanosheets for Enhanced Solar Water Splitting
    (ACS, 2020) Basu, Mrinmoyee
    Photoelectrochemical (PEC) water splitting has become an essential tool for the straightforward production of hydrogen (H2) from solar energy. In this respect, earth-abundant materials can be exploited to have high solar-to-H2 conversion efficiencies, which may further smoothen the practical applicability of this technique. Here, an efficient photoanode and vertically grown ZnO are developed for the PEC water-splitting reaction. To understand the plasmonic effect, variable sizes of gold nanoparticles (Au NPs) are fabricated and adorned on the surface of two-dimensional (2D) ZnO nanosheets. The sizes of the Au NPs are varied from 12 to 135 nm, and the impact of the variable sizes on ZnO is determined under different light illumination conditions. The influences of light-absorbing and -scattering effects by Au NPs are studied separately. The ability of light trapping for enhancement of the PEC water-splitting performance of ZnO/Au through light-scattering and -absorbing effects is determined. Upon back illumination, the light-scattering effect predominates and 2D ZnO sheets decorated with 55 nm Au NPs show a maximum photocurrent density. Au NPs of 55 nm on ZnO can generate a maximum photoconversion efficiency of 0.514% under back illumination by successfully increasing the light absorbance of the material through the scattering effect. On the other hand, under the front illumination, the light-concentrating effect predominates and ZnO nanosheets decorated with 35 nm Au NPs result in a maximum enhancement in the photoconversion efficiency (0.605%). The stabilities of bare ZnO, ZnO/Au-55, and ZnO/Au-35 are determined for 1000 s under back illumination, and different physical techniques are employed after PEC water splitting to confirm the morphological and structural robustness. Hence, upon application of two different sizes of Au NPs on ZnO nanosheets, the plasmonic enhancement (radiative light-scattering and -concentrating) effect of Au is studied, and the mechanisms are explained.
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    ZnO Nanosheets Decorated with Graphite-Like Carbon Nitride Quantum Dots as Photoanodes in Photoelectrochemical Water Splitting
    (ACS, 2020) Basu, Mrinmoyee
    The efficient utilization of solar power is becoming an important strategy for its conversion into a storable, clean, and renewable energy source like H2. To generate H2 as a chemical fuel from solar power, attempts are being made to establish photoelectrochemical (PEC) water splitting as an efficient, greener pathway. Here, the surfaces of ZnO 2D nanosheets are adorned by graphite-like carbon nitride (g-C3N4) quantum dots (QDs) with the intention of developing efficient photoanodes. Sensitization of ZnO nanosheets with C3N4 QDs leads to a more enhanced PEC performance than that of bare ZnO. The observed enhancement in PEC is due to the high light absorbance and photon-generated charge-carrier separation. The best-obtained ZnO/C3N4 photoanode exhibits a nearly 2.29 times as high photocurrent density compared to bare ZnO. ZnO 2D sheets can generate a photocurrent density of 0.414 mA cm–2 at 0.5994 V versus reversible hydrogen electrode (RHE), whereas ZnO/C3N4 can produce 0.952 mA cm–2 at 0.5994 V versus RHE under uninterrupted conditions of light illumination. Further, there is improvement in the observed PEC activity of the heterostructure because of enhancement in the carrier density. The carrier density enhances nearly 2.2 times in the heterostructure compared to the bare ZnO sheet. ZnO/C3N4 shows a maximum photoconversion efficiency (η) of 0.70%. Both ZnO 2D sheets and the ZnO/C3N4 heterostructure show efficient stability under chopped irradiation of light for 1000 s. The stability of ZnO/C3N4 is also determined for 1 h under continuous illumination.
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    Type-II Heterostructure of ZnO and Carbon Dots Demonstrates Enhanced Photoanodic Performance in Photoelectrochemical Water Splitting
    (ACS, 2020) Basu, Mrinmoyee
    Hydrogen evolution through ecofriendly photoelectrochemical (PEC) water splitting is considered to be one of the most cost-effective and desirable methods for meeting ever-growing energy demands. However, the low photoconversion efficiency limits the practical applicability of PEC water splitting. To develop an efficient photoelectrode, here the morphology of ZnO is tuned from 0D to 3D. It is observed that vertically grown 2D nanosheets outperform other morphologies in PEC water splitting by generating nearly 0.414 mA cm–2 at 0 V vs Ag/AgCl. Furthermore, these perpendicularly developed 2D nanosheets of ZnO are sensitized by metal-free carbon (C) dots to improve the photoconversion efficiency of ZnO. The prepared ZnO/C dots work as an effective photoanode, which can produce a 0.831 mA cm–2 photocurrent density upon application of 0 V vs Ag/AgCl under constant illumination, which is 2 times higher than that of bare ZnO. The enhanced PEC performance of ZnO/C dots is confirmed by the photoconversion efficiency (η). The ZnO/C dots exhibit a 2-fold-higher photoconversion efficiency (η) compared to that of ZnO. Additionally, the enhancement in PEC activity of ZnO/C dots is attributed to the higher carrier concentrations in the heterostructure. Bare ZnO has a 1.77 × 1020 cm–3 carrier density, which becomes 3.70 × 1020 cm–3 after sensitization with C dots. Enhanced carrier density successively leads to higher PEC water splitting efficiency. Band alignments of ZnO and C dots indicate the creation of the type-II heterostructure, which facilitates successful charge transportation among C dots and ZnO, producing a charge-carrier separation. Two-dimensional sheets of ZnO and ZnO/C dots exhibit appreciable stability under continuous illumination for 1 and 2 h, respectively.