Browsing by Author "Chiu, Yi-Hsuan"

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A facile green antisolvent approach to Cu2+-doped ZnO nanocrystals with visible-light-responsive photoactivities
(2014-08-07)
Lu, Yi-Hsuan
;
Lin, Wei-Hao
;
Yang, Chao-Yao
;
Chiu, Yi-Hsuan
;
Pu, Ying-Chih
An environmentally benign antisolvent method has been developed to prepare Cu2+-doped ZnO nanocrystals with controllable dopant concentrations. A room temperature ionic liquid, known as a deep eutectic solvent (DES), was used as the solvent to dissolve ZnO powders. Upon the introduction of the ZnO-containing DES into a bad solvent which shows no solvation to ZnO, ZnO was precipitated and grown due to the dramatic decrease of solubility. By adding Cu2+ ions to the bad solvent, the growth of ZnO from the antisolvent process was accompanied by Cu2+ introduction, resulting in the formation of Cu2+-doped ZnO nanocrystals. The as-prepared Cu2+-doped ZnO showed an additional absorption band in the visible range (400-800 nm), which conduced to an improvement in the overall photon harvesting efficiency. Time-resolved photoluminescence spectra, together with the photovoltage information, suggested that the doped Cu2+ may otherwise trap photoexcited electrons during the charge transfer process, inevitably depressing the photoconversion efficiency. The photoactivity of Cu2+-doped ZnO nanocrystals for photoelectrochemical water oxidation was effectively enhanced in the visible region, which achieved the highest at 2.0 at% of Cu2+. A further increase in the Cu2+ concentration however led to a decrease in the photocatalytic performance, which was ascribed to the significant carrier trapping caused by the increased states given by excessive Cu2+. The photocurrent action spectra illustrated that the enhanced photoactivity of the Cu2+-doped ZnO nanocrystals was mainly due to the improved visible photon harvesting achieved by Cu2+ doping. These results may facilitate the use of transition metal ion-doped ZnO in other photoconversion applications, such as ZnO based dye-sensitized solar cells and magnetism-assisted photocatalytic systems.
A facile green antisolvent approach to Cu2+-doped ZnO nanocrystals with visible-light-responsive photoactivities
(2014-08-07)
Lu, Yi-Hsuan
;
Lin, Wei-Hao
;
Yang, Chao-Yao
;
Chiu, Yi-Hsuan
;
Pu, Ying-Chih
An environmentally benign antisolvent method has been developed to prepare Cu2+-doped ZnO nanocrystals with controllable dopant concentrations. A room temperature ionic liquid, known as a deep eutectic solvent (DES), was used as the solvent to dissolve ZnO powders. Upon the introduction of the ZnO-containing DES into a bad solvent which shows no solvation to ZnO, ZnO was precipitated and grown due to the dramatic decrease of solubility. By adding Cu2+ ions to the bad solvent, the growth of ZnO from the antisolvent process was accompanied by Cu2+ introduction, resulting in the formation of Cu2+-doped ZnO nanocrystals. The as-prepared Cu2+-doped ZnO showed an additional absorption band in the visible range (400-800 nm), which conduced to an improvement in the overall photon harvesting efficiency. Time-resolved photoluminescence spectra, together with the photovoltage information, suggested that the doped Cu2+ may otherwise trap photoexcited electrons during the charge transfer process, inevitably depressing the photoconversion efficiency. The photoactivity of Cu2+-doped ZnO nanocrystals for photoelectrochemical water oxidation was effectively enhanced in the visible region, which achieved the highest at 2.0 at% of Cu2+. A further increase in the Cu2+ concentration however led to a decrease in the photocatalytic performance, which was ascribed to the significant carrier trapping caused by the increased states given by excessive Cu2+. The photocurrent action spectra illustrated that the enhanced photoactivity of the Cu2+-doped ZnO nanocrystals was mainly due to the improved visible photon harvesting achieved by Cu2+ doping. These results may facilitate the use of transition metal ion-doped ZnO in other photoconversion applications, such as ZnO based dye-sensitized solar cells and magnetism-assisted photocatalytic systems.
Au-decorated GaOOH nanorods enhanced the performance of direct methanol fuel cells under light illumination
(2016-05-15)
Hsu, Yi-Han
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Nguyen, An T.
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Chiu, Yi-Hsuan
;
Li, Jing-Mei
;
Hsu, Yung-Jung
We reported for the first time that GaOOH nanorods, which were prepared using a facile chemical precipitation method, may display noticeable photocatalytic activities toward methanol oxidation under light illumination, a significant revelation for demonstrating their use as the anode photocatalyst in the half cell reaction of direct methanol fuel cells (DMFCs). The GaOOH nanorods were further decorated with Au nanoparticles to endow them with increasingly pronounced charge separation, which conduced to a remarkable enhancement in the photocatalytic performance. Time-resolved photoluminescence spectroscopy was employed to depict the charge transfer event across the interface of GaOOH/Au, from which a correlation between photocatalytic efficiency and interfacial charge dynamics was realized. By incorporating GaOOH nanorods into the traditional Pt-catalyzed half-cell reaction, a 12.7% increase in anodic current generation can be attained under light illumination, demonstrating the promising potential of GaOOH as a practical anode photocatalyst in DFMCs. A further enhancement in methanol oxidation current up to 70.8% can be achieved by employing Au-decorated GaOOH nanorods, which was attributed to the efficient charge carrier transfer rendered by the Au decoration. The current study delivers both fundamental and practical importance as it broadens the scope of electrocatalysts for fuel cells, specifically by introducing a new class of highly efficient photocatalysts for promoting electrochemical reactions. (C) 2015 Elsevier B.V. All rights reserved.
Au@Cu2O core@shell nanocrystals as dual-functional catalysts for sustainable environmental applications
(2019-03-01)
Kuo, Ming-Yu
;
Hsiao, Chih-Feng
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Chiu, Yi-Hsuan
;
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.
Au@Cu7S4 yolk@shell nanocrystal-decorated TiO2 nanowires as an all-day-active photocatalyst for environmental purification
(2017-01)
Chiu, Yi-Hsuan
;
Hsu, Yung-Jung
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A vital issue that degrades the entirety of photocatalysis on TiO2 is the requisite of light illumination for performing redox reactions. The ability to maintain the catalytic activity in dark environment has been the ultimate goal for the widespread deployment of TiO2 photocatalysts. Here, for the first time we reported the demonstration of an all-day-active photocatalyst model by employing Au@Cu7S4 yolk@shell nanocrystaldecorated TiO2 nanowires. The samples were obtained by depositing a Cu2O layer on the Au surface of Au particle-decorated TiO2 nanowires, followed by the sulfidation treatment on Cu2O layer to grow hollow Cu7S4 shell. By coupling the pronounced charge separation and distinctive peroxidase mimic properties from the constituents, the TiO2 -Au@Cu7S4 nanowires were capable of performing efficient methyl orange degradation under light illumination, 7yet still persisted noticeable activity of decomposing methyl orange after light irradiation was switched off. The present study has embodied a conceptually valuable design of permanently working photocatalysts, which may serve as a versatile platform for the widely distributed environmental and energy applications such as pollutant destruction and organic transformation.
Au@Cu7S4 yolk@shell nanocrystal-decorated TiO2 nanowires as an all-day-active photocatalyst for environmental purification
(2017-01)
Chiu, Yi-Hsuan
;
Hsu, Yung-Jung
;
材料科學與工程學系
;
Department of Materials Science and Engineering
A vital issue that degrades the entirety of photocatalysis on TiO2 is the requisite of light illumination for performing redox reactions. The ability to maintain the catalytic activity in dark environment has been the ultimate goal for the widespread deployment of TiO2 photocatalysts. Here, for the first time we reported the demonstration of an all-day-active photocatalyst model by employing Au@Cu7S4 yolk@shell nanocrystaldecorated TiO2 nanowires. The samples were obtained by depositing a Cu2O layer on the Au surface of Au particle-decorated TiO2 nanowires, followed by the sulfidation treatment on Cu2O layer to grow hollow Cu7S4 shell. By coupling the pronounced charge separation and distinctive peroxidase mimic properties from the constituents, the TiO2 -Au@Cu7S4 nanowires were capable of performing efficient methyl orange degradation under light illumination, 7yet still persisted noticeable activity of decomposing methyl orange after light irradiation was switched off. The present study has embodied a conceptually valuable design of permanently working photocatalysts, which may serve as a versatile platform for the widely distributed environmental and energy applications such as pollutant destruction and organic transformation.
Facet-Dependent Photocatalytic Behaviors of ZnS-Decorated Cu2O Polyhedra Arising from Tunable Interfacial Band Alignment
(2019-01-23)
Naresh, Gollapally
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Hsieh, Pei-Lun
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Meena, Vandana
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Lee, Shih-Kuang
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Chiu, Yi-Hsuan
ZnS particles were grown over Cu2O cubes, octahedra, and rhombic dodecahedra for examination of their facet-dependent photocatalytic behaviors. After ZnS growth, Cu2O cubes stay photocatalytically inactive. ZnS-decorated Cu2O octahedra show enhanced photocatalytic activity, resulting from better charge carrier separation upon photo excitation. Surprisingly, Cu2O rhombic dodecahedra give greatly suppressed photocatalytic activity after ZnS deposition. Electron paramagnetic resonance spectra agree with these experimental observations. Time-resolved photoluminescence profiles provide charge-transfer insights. The decrease in the photocatalytic activity is attributed to an unfavorable band alignment caused by significant band bending within the Cu2O(110)/ZnS(200) plane interface. A modified Cu2O-ZnS band diagram is presented. Density functional theory calculations generating plane -specific band energy diagrams of Cu2O and ZnS match well with the experimental results, showing that charge transfer across the Cu2O(110)/ZnS(200) plane interface would not happen. This example further illustrates that the actual photocatalysis outcome for semiconductor heterojunctions cannot be assumed because interfacial charge transfer is strongly facet-dependent.
Fully Depleted Ti-Nb-Ta-Zr-O Nanotubes: Interfacial Charge Dynamics and Solar Hydrogen Production
(2018-07-11)
Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
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Chen, Chun-Yi
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Hsieh, Ping-Yen
;
Ozasa, Kazunari
Poor kinetics of hole transportation at the electrode/electrolyte interface is regarded as a primary cause for the mediocre performance of n-type TiO2 photoelectrodes. By adopting nanotubes as the electrode backbone, light absorption and carrier collection can be spatially decoupled, allowing n-type TiO2, with its short hole diffusion length, to maximize the use of the available photoexcited charge carriers during operation in photoelectrochemical (PEC) water splitting. Here, we presented a delicate electrochemical anodization process for the preparation of quaternary Ti-Nb-Ta-Zr-O mixed-oxide (denoted as TNTZO) nanotube arrays and demonstrated their utility in PEC water splitting. The charge transfer dynamics for the electrodes was investigated using time-resolved photoluminescence, electrochemical impedance spectroscopy, and the decay of open-circuit voltage analysis. Data reveal that the superior photoactivity of TNTZO over pristine TiO2 originated from the introduction of Nd, Ta, and Zr elements, which enhanced the amount of accessible charge carriers, modified the electronic structure, and improved the hole injection kinetics for expediting water splitting. By modulating the water content of the electrolyte employed in the anodization process, the wall thickness of the grown TNTZO nanotubes can be reduced to a size smaller than that of the depletion layer thickness, realizing a fully depleted state for charge carriers to further advance the PEC performance. Hydrogen evolution tests demonstrate the practical efficacy of TNTZO for realizing solar hydrogen production. Furthermore, with the composition complexity and fully depleted band structure, the present TNTZO nanotube arrays may offer a feasible and universal platform for the loading of other semiconductors to construct a sophisticated heterostructure photoelectrode paradigm, in which the photoexcited charge carriers can be entirely utilized for efficient solar-to-fuel conversion.
Mechanistic Insights into Photodegradation of Organic Dyes Using Heterostructure Photocatalysts
(2019-05-01)
Chiu, Yi-Hsuan
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Chang, Tso-Fu Mark
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Chen, Chun-Yi
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Sone, Masato
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Hsu, Yung-Jung
Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO2, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems.
Metal-Particle-Decorated ZnO Nanocrystals: Photocatalysis and Charge Dynamics
(2016-12-07)
Lin, Wei-Hao
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Chiu, Yi-Hsuan
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Shao, Pao-Wen
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Hsu, Yung-Jung
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材料科學與工程學系
Understanding of charge transfer processes is determinant to the performance optimization for semiconductor photocatalysts. As a representative model of composite photocatalysts, metal-particle-decorated ZnO has been widely employed for a great deal of photocatalytic applications; however, the dependence of charge carrier dynamics on the metal content and metal composition and their correlation with the photocatalytic properties have seldom been reported. Here, the interfacial charge dynamics for metal-decorated ZnO nanocrystals were investigated and their correspondence with the photocatalytic properties was evaluated. The samples were prepared with a delicate antisolvent approach, in which ZnO nanocrystals were grown along with metal particle decoration in a deep eutectic solvent. By modulating the experimental conditions, the metal content (from 0.6 to 2.3 at%) and metal composition (including Ag, Au, and Pd) in the resulting metal-decorated ZnO could be readily controlled. Time-resolved photoluminescence spectra showed that an optimal Au content of 1.3 at% could effectuate the largest electron transfer rate constant for Au-decorated ZnO nanocrystals, in conformity with the highest photocatalytic efficiency observed. The relevance of charge carrier dynamics to the metal composition was also inspected and realized in terms of the energy level difference between ZnO and metal. Among the three metal-decorated ZnO samples tested, ZnO-Pd displayed the highest photocatalytic activity, fundamentally according with the largest electron transfer rate constant deduced in carrier dynamics measurements. The current work was the first study to present the correlations among charge carrier dynamics, metal content, metal composition, and the resultant photocatalytic properties for semiconductor/metal heterostructures. The findings not only helped to resolve the standing issues regarding the mechanistic foundation of photocatalysis but also shed light on the intelligent design of semiconductor/metal composite systems to consolidate their utility in photocatalytic fields.
Nano-Au Catalysts Modified with TiO2: Enhancement of Electrocatalytic Activity for 1-Propanol Oxidation in Alkaline Media
(2019-07-16)
Chiu, Wan-Ting
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Chiu, Yi-Hsuan
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Hsieh, Ping-Yen
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Chang, Tso-Fu Mark
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Sone, Masato
Electrocatalytic activity of the anode for alcohols oxidation is a critical issue in fuel cell which is considered as a clean energy. Performance deterioration of the catalyst takes place due to the adsorption of carbonaceous residues on the electrode surface, which is also known as poisoning of the electrode. Desorption of carbonaceous residues is thought to be an essential solution but not has been studied systematically. In this work, we investigate both the desorption of carbonaceous residues and the promotion of electrocatalytic activity to alcohols oxidation reactions by using Au nanoparticles (NPs)-TiO2/polyaniline (PANI) composite to boost the overall activity of electrocatalytic alcohol oxidation reactions. Desorption of carbonaceous residues and electrocatalytic activity of alcohol oxidation reactions are evaluated by cyclic voltammetry (CV) measurements in various alcohols. The chronoamperometric i-t curves are measured to evaluate the stability. Mechanisms for desorption of carbonaceous residues and enhancement of the electrocatalytic activity are elaborated and summarized. Electrodes with TiO2 decoration show better performance than TiO2-free specimens. In addition, Au NPs-decorated composites not only show an extra characteristic peak of alcohol oxidation reactions but also perform a constructive effect on the already existing oxidation reaction, indicating the promotion of electrocatalytic oxidation of alcohols. (C) 2019 The Electrochemical Society.
Photoelectrochemical cells for solar hydrogen production: Challenges and opportunities
(2019-08-01)
Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
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Kuo, Ming-Yu
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Hsieh, Ping-Yen
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Hsu, Yung-Jung
As the Holy Grail to a carbon-free hydrogen economy, photoelectrochemical (PEC) water splitting offers a promising path for sustainable production of hydrogen fuel from solar energy. Even though much progress has been made over the past decade, the effectiveness and robustness of PEC cells are still far from a mature phase that would allow for widespread deployment. This perspective discusses the key challenges facing the current level of PEC development and proposes experimental approaches and strategies that can be adopted to address the issues. Focuses are mainly placed on the employment of in situ and operando spectroscopic measurements, the introduction of alternative, high value-added oxidation reactions, and the creation of near infrared-responsive photoelectrodes. A brief outlook that may assist the future advancement of PEC technology is also presented. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Plasmon-mediated charge dynamics and photoactivity enhancement for Au-decorated ZnO nanocrystals
(2018-03-14)
Chiu, Yi-Hsuan
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Chang, Kao-Der
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Hsu, Yung-Jung
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材料科學與工程學系
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Department of Materials Science and Engineering
With the capability of localizing optical energy via surface plasmon resonance (SPR), plasmonic Au nanostructures hold great promise for enhancing the solar water splitting of semiconductor photocatalysts. While the content of Au plays a critical role in mediating interfacial charge transfer, its quantitative influence on the efficiency of plasmon-assisted water splitting is still not fully understood. This work aimed to explore the correlations among plasmonic metal content, SPR-mediated charge transfer and electromagnetic response, and the resultant photoactivity enhancement toward photoelectrochemical (PEC) water splitting. The PEC system was constructed by employing Au particle-decorated ZnO nanocrystals (ZnO-Au) as the plasmonic photoanode. Time-resolved photoluminescence spectroscopy and finite-difference time-domain simulations were utilized to evaluate the optimal Au content which attained effective charge separation and imposed a significant SPR effect for achieving the largest photoactivity enhancement. The charge transfer at the photoanode/electrolyte interface and its dependence on the Au content were examined with electrochemical impedance analysis, which manifested the effectiveness of the optimal Au content in facilitating the hole transfer kinetics. The present study reports a technical advance in the realization of the quantitative effect of Au for designing sophisticated plasmonic PEC systems that enabled efficient solar-to-fuel energy conversion.
Reduced graphene oxides-wrapped ZnO with notable photocatalytic property
(2020-07-01)
Hu, Wei-Chen
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Chen, Yi-An
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Hsieh, Ping-Yen
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Tsao, Chun-Wen
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Chiu, Yi-Hsuan
A facile, environmentally benign antisolvent method has been developed to prepare for reduced graphene oxides (RGO)-wrapped ZnO nanocrystals with controlled RGO contents. Because of the high electrical conductivity of RGO, the photogenerated electrons at ZnO mostly transported to RGO, leaving positively charged photoexcited holes in ZnO to result in charge separation. The steady-state photoluminescence, time-resolved photoluminescence spectroscopy and photovoltage decay analysis were employed to investigate charge carrier dynamics and charge transfer behaviors of RGO-ZnO. The influence of RGO content on the charge dynamics and photoconversion efficiency of RGO-ZnO toward dye degradation and water splitting has been realized. (C) 2020 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
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
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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.
Tailor magnetic order and spin-polarized gap states of opto-spintronic compounds by carrier mediation
(2018-08-15)
Yang, Chao-Yao
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Chiu, Yi-Hsuan
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Tsai, Kai-An
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Hsu, Hua-Shu
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Lin, Jun-Xiao
We investigate the role of carriers in the presence of oxygen vacancies (Vo) in mediating the ferromagnetic order and spin-polarized gap states of Cu-doped ZnO nanoparticles. We demonstrate the tuning of magnetic order via post-annealing under Ar/O-2. Carrier (Vo)-rich condition (Ar-treatment) is found to favor higher magnetic order of the nanoparticles with enhanced thermal stability and wide spin-polarized gap states from ultra-violet (UV) to visible energy range. Conversely, carrier (Vo)-poor condition (O-2-treatment) reduces resistance to thermal fluctuations and quenched spin-polarization due to lack of carrier mediation. The proposed method is effective to tailor the magnetic order as well as the wide polarized band-gap states, of oxide opto-spintronic compounds by finding the physical equivalency between charge carriers and spin electrons. (C) 2018 Elsevier B.V. All rights reserved.
TiO2 Nanowire-Supported Sulfide Hybrid Photocatalysts for Durable Solar Hydrogen Production
(2019-01-23)
Hsieh, Ping-Yen
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Chiu, Yi-Hsuan
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Lai, Ting-Hsuan
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Fang, Mei-Jing
;
Wang, Yu-Ting
As the feet of clay, photocorrosion induced by hole accumulation has placed serious limitations on the widespread deployment of sulfide nanostructures for photoelectrochemical (PEC) water splitting. Developing sufficiently stable electrodes to construct durable PEC systems is therefore the key to the realization of solar hydrogen production. Here, an innovative charge-transfer manipulation concept based on the aligned hole transport across the interface has been realized to enhance the photostability of In2S3 electrodes toward PEC solar hydrogen production. The concept was realized by conducting compact deposition of In2S3 nanocrystals on the TiO2 nanowire array. Under PEC operation, the supporting TiO2 nanowires functioned as an anisotropic charge-transfer backbone to arouse aligned charge transport across the TiO2-In2S3 interface. Because of the aligned hole transport, the TiO2 nanowire-supported In2S3 hybrid nanostructures (TiO2 In2S3) exhibited improved hole-transfer dynamics at the TiO2-In2S3 interface and enhanced hole injection kinetics at the electrode surface, substantially increasing the long-term photostability toward solar hydrogen production. The PEC durability tests showed that TiO2-In2S3 electrodes can achieve nearly 90.9% retention of initial photocurrent upon continuous irradiation for 6 h, whereas the pure In2S3 merely retained 20.8% of initial photocurrent. This double-gain charge-transfer manipulation concept is expected to convey a viable approach to the intelligent design of highly efficient and sufficiently stable sulfide photocatalysts for sustainable solar fuel generation.
Yolk-shell nanostructures as an emerging photocatalyst paradigm for solar hydrogen generation
(2019-08-01)
Chiu, Yi-Hsuan
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Naghadeh, Sara Bonabi
;
Lindley, Sarah A.
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Lai, Ting-Hsuan
;
Kuo, Ming-Yu
With porous shells and mobile cores, yolk-shell nanostructures provide great structural advantage for mass transport-related applications such as photocatalysis. In this work, Au-Cu7S4 yolk-shell nanostructures are synthesized from Au-Cu2O core-shell templates. The Cu7S4 shell is then converted to CdS through a cation exchange process to produce Au-CdS yolk-shell photocatalysts for hydrogen generation. Ultrafast transient absorption and finite-difference time-domain simulation are used to investigate electronic interaction between Au nanoparticle core and the surrounding CdS shell. Additionally, a new method is presented to simulate chemical transport and quantitatively compare diffusion kinetics by monitoring mass transport through the porous CdS shell with dye molecules as optical probes. The highest hydrogen generation rate of 3390 mu mol g(-1) h(-1), corresponding to an adequate apparent quantum yield of 4.22% at 420 nm, is achieved for Au-CdS with the largest void size. The enhancement in photocatalytic performance with increase in void size is mostly attributed to improved mass transport kinetics, with additional gains from more efficient charge transfer and stronger surface plasmon resonance-mediated near-field effects. This comprehensive study demonstrates that void size is a critical structural parameter in optimizing the performance of yolk-shell nanostructures for photocatalysis or other mass-transport related applications.
ZnO-Au-SnO2 Z-scheme photoanodes for remarkable photoelectrochemical water splitting
(2016)
Li, Jing-Mei
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Cheng, Hao-Yun
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Chiu, Yi-Hsuan
;
Hsu, Yung-Jung
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材料科學與工程學系
For the first time a ZnO nanorod-based Z-scheme heterostructure system was proposed and realized for efficient photoelectrochemical water splitting. The samples were prepared by depositing a thin layer of SnO2 on the Au surface of Au particle-decorated ZnO nanorods. For ZnO-Au-SnO2 nanorods, the embedded Au can mediate interfacial charge transfer by promoting electron transfer from the conduction band of SnO2 to the valence band of ZnO. This vectorial charge transfer resulted in the situation that the photoexcited electrons accumulated at ZnO while the photogenerated holes concentrated at SnO2, giving ZnO-Au-SnO2 substantially high redox powers. Time-resolved photoluminescence spectra suggested that the interfacial charge transfer across the ZnO/Au/SnO2 interface was significantly improved as a result of the Z-scheme charge transfer mechanism. With the substantially high redox powers and significantly improved interfacial charge transfer, ZnO-Au-SnO2 nanorods performed much better as a photoanode in photoelectrochemical water splitting than pristine ZnO, plasmonic Au-decorated ZnO and type-II SnO2-coated ZnO nanorods did. The present study has provided a viable approach to exploit Z-scheme photoanodes in the design of efficient artificial photosynthesis systems for solar energy conversion.
ZnO-graphene composites as practical photocatalysts for gaseous acetaldehyde degradation and electrolytic water oxidation
(2015-01-25)
Chen, Yu-Chih
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Katsumata, Ken-ichi
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Chiu, Yi-Hsuan
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Okada, Kiyoshi
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Matsushita, Nobuhiro
A facile, green one-pot hydrothermal method has been developed to prepare ZnO-reduced graphene oxide (rGO) composites with controllable rGO content. Time-resolved photoluminescence spectra revealed that an increased electron-transfer rate constant was observed for ZnO-rGO with increasing rGO contents, suggesting that an increased number of photoexcited charge carriers were separated and available for photocatalysis utilization. The photocatalytic properties of the ZnO-rGO composites were investigated by using gaseous acetaldehyde (CH3CHO), a typical volatile organic compound (VOC), as the test pollutant. This is the first time that ZnO-rGO composites have been used as photocatalysts for gaseous CH3CHO degradation. Compared to pure ZnO, ZnO-rGO composites with suitable rGO contents (1.0 and 3.0 wt%) displayed significantly enhanced photocatalytic activity in both CH3CHO degradation and CO2 generation. This enhancement was ascribed to the rGO support that can promote the carrier utilization efficiency of ZnO by readily accepting the photoexcited electrons from ZnO. As a result, abundant photogenerated holes remained on the ZnO and were available for participation in the CH3CHO photodegradation. Furthermore, the photoactivity of ZnO-rGO toward electrolytic water oxidation was evaluated. The results showed that ZnO-rGO composites achieved 50% increase in water oxidation current over pure ZnO under white light illumination. The demonstration from this work may facilitate the use of ZnO-rGO composites in photodegradation of VOCs as well as for photoelectrochemical applications, which is imperative from the environmental and energetic points of view. (C) 2014 Elsevier B.V. All rights reserved.