Browsing by Author "Kharade, Aparna K."

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Contributions of Abundant Hydroxyl Groups to Extraordinarily High Photocatalytic Activity of Amorphous Titania for CO2 Reduction
(2020-05-21)
Kharade, Aparna K.
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Chang, Sue-min
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環境工程研究所
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Institute of Environmental Engineering
Despite severe charge recombination occurring within the bulk lattice, sol-gel-derived amorphous TiO2 particles with abundant OH groups (81.6 mg/g) and high surface area (274 m(2)/g) were for the first time demonstrated to exhibit respectively 8-14 and 9 times higher photocatalytic activity for CO2 reduction than their thermally derived anatase crystals and the commercial P25 powder. Moreover, the high density of the OH groups (12.45/nm(2)) enabled the amorphous oxide to exhibit higher specific surface reactivity than the crystals. The OH groups not only converted CO2 molecules into bonded bicarbonate/carbonate species to improve CO2 chemisorption but also trapped holes to form Ti-O-O-Ti species when the OH density was higher than a threshold value of 8.74/nm(2), which synergistically promoted interfacial charge transfer. Bidentate carbonate and center dot CO2- were two active species that were able to underwent CO32- -> Ti-OOCH2 -> Ti-O-CH3 -> CH4 and center dot CO2- -> CO22- -> Ti-COOH -> CO sequences on the hydroxylated surface to produce CH4 and CO products, respectively. High coverage of the chemisorbed carbonate species selected for CO2 reduction rather than H-2 evolution to proceed. Moreover, it led with CH4 as the major product. Oxygen vacancies were the major active sites on the anatase crystals. Their influences on the surface transformations were also characterized to comprehensively understand the surface-controlled activity and selectivity.
Mechanism of Photocatalytic CO2 Reduction by Bismuth-Based Perovskite Nanocrystals at the Gas-Solid Interface
(2019-12-25)
Bhosale, Sumit S.
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Kharade, Aparna K.
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Jokar, Efat
;
Fathi, Amir
;
Chang, Sue-min
We report here a series of nontoxic and stable bismuth-based perovskite nanocrystals (PeNCs) with applications for photocatalytic reduction of carbon dioxide to methane and carbon monoxide. Three bismuth-based PeNCs of general chemical formulas A(3)Bi(2)I(9), in which cation A(+) = Rb+ or Cs+ or CH3NH3+ (MK), were synthesized with a novel ultrasonication top-down method. PeNC of Cs3Bi2I9 had the best photocatalytic activity for the reduction of CO2 at the gas solid interface with formation yields 14.9 mu mol g(-1) of methane and 77.6 mu mol g(-1) of CO, representing a much more effective catalyst than TiO2 (P25) under the same experimental conditions. The products of the photocatalytic reactions were analyzed using a gas chromatograph coupled with a mass spectrometer. According to electron paramagnetic resonance and diffuse-reflectance infrared spectra, we propose a reaction mechanism for photoreduction of CO2 via Bi-based PeNC photocatalysts to form CO, CH4, and other possible side products.