Browsing by Author "Wu, Jhen-Yang"

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Au@Cu2O core@shell nanocrystals as dual-functional catalysts for sustainable environmental applications
(2019-03-01)
Kuo, Ming-Yu
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Hsiao, Chih-Feng
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Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
;
Fang, Mei-Jing
This work reports the synthesis of Au@Cu2O core@shell nanocrystals with controllable shell thicknesses and demonstrates their use as the dual-functional catalyst that can continuously operate under illumination and darkness conditions for efficient E. con inactivation. On account of the peroxidase mimics of the Au core and Fenton reactivity of the Cu2O shell, the Au@Cu2O nanocrystals exhibit intrinsic peroxidase-like property with the reaction kinetics in accordance with the typical Michaelis-Menten mechanism. On the other hand, time resolved photoluminescence spectra suggest the prevalence of pronounced charge separation for Au@Cu2O nanocrystals, an important advantage that is favourable for photocatalysis. By combining the photocatalytic capability with the peroxidase mimics features, Au@Cu2O nanocrystals can perform practical photocatalytic decomposition of E. coil under visible light illumination but still show vital activity towards E. coil inactivation after light illumination was turned off. The current study delivers a new catalyst configuration by exploiting the multiple functionalities of nanosized Au and Cu2O for advanced environmental and energy conversion applications.
Size and temperature dependence of photoluminescence of hybrid perovskite nanocrystals
(2019-10-21)
Naghadeh, Sara Bonabi
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Sarang, Som
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Brewer, Amanda
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Allen, A'Lester
;
Chiu, Yi-Hsuan
In this work, we studied the effects of particles' size and temperature on the photoluminescence (PL) of CH3NH3PbBr3 perovskite nanocrystals (PNCs), with the PNC size controlled by varying the surface passivating ligands. The structural and optical properties of the PNCs were investigated using UV-Vis and PL spectroscopy, revealing strong quantum confinement effects. Temperature dependent PL measurements showed the spectral blue shift of the PL peak for the small PNCs (3.1 +/- 0.2 nm) with decreasing temperature from 300 K to 20 K, which is opposite to the red shift with decreasing temperature observed for large- (9.2 +/- 0.5 nm) and middle-sized (5.1 +/- 0.3 nm) PNCs. The PL lifetime also increased with increasing temperature for the larger PNCs, while it remained about the same for the small and middle-sized PNCs. This increase in lifetime with temperature is attributed to exciton dissociation to free carriers at higher temperatures and to the formation of polar domains in the PNCs. However, the small and middle-sized PNCs did not show such a trend, which may be due to efficient defect passivation as higher concentration of 3-aminopropyl trimethoxysilane (APTMS) was used and to the role of particle size in surface state delocalization. Cryo-X-ray diffraction showed no new peak formation or peak splitting as temperature was varied, which suggests efficient crystal phase stabilization in PNCs of all three sizes controlled by the concentration of APTMS. These results emphasize the importance of size and surface properties of PNCs in their optical properties such as PL quantum yield, PL lifetime, and crystal phase stability. Published under license by AIP Publishing.