Browsing by Author "Yang, Min-Han"

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Alkali metal ion assisted synthesis of faceted anatase TiO2
(2013)
Yang, Min-Han
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Chen, Po-Chin
;
Tsai, Min-Chiao
;
Chen, Ting-Ting
;
Chang, I-Chun
This work reports on a simple hydrothermal method for tuning the shape and exposed face of TiO2 nanocrystal by using sodium titanate as a precursor in the presence of different alkali metal ion salts. The {101}-exposed anatase TiO2 was synthesized in lithium salt solution. The formation of anatase TiO2 with exposed high-index {301} facet, obtained in the presence of sodium ions, has never before been reported upon. When the reaction proceeded in potassium salt solution, the obtained anatase TiO2 with a high aspect ratio was elongated in the < 001 > direction. Anatase TiO2 with a high aspect ratio was obtained in hydrothermal process in the presence of low charge density high atomic number alkali metal ions, which were not easily absorbed by the {001} planes of anatase, so the growth along this direction was not restrained. The photodegradation of methylene blue, assisted by anatase TiO2 with various exposed faces reveals that the photoactivity of anatase {101} planes is larger than that of {301} planes.
Anatase and brookite TiO2 with various morphologies and their proposed building block
(2014)
Yang, Min-Han
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Chen, Po-Chin
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Tsai, Min-Chiao
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Chen, Ting-Ting
;
Chang, I-Chun
In this work, brookite TiO2 has been synthesized by a simple hydrothermal approach using sodium titanate as a precursor in the presence of a sodium fluoride aqueous solution. The ratio of brookite and anatase TiO2 can be tailored by the NaF concentration. In a concentrated NaF solution, high quality brookite TiO2 was acquired. Pure anatase nanoparticles were obtained in only deionized water. Moreover, the morphology and size of brookite TiO2 can be tailored by using various acid treated titanates which influence the stability of the building blocks and nucleation points of TiO2. Micro-sized flower-like brookite, submicro-sized urchin-like brookite and brookite nanorods with anatase nanoparticles were obtained. The micro-sized flower-like brookite remains the same shape and phase even at 800 degrees C, whereas obvious grains were formed on the matrix with brookite, rutile and anatase mixture phases at 900 degrees C. On the other hand, as the submicro-sized urchin-like brookite was heated, a rutile phase appeared at 750 degrees C and 100% grain-like rutile was obtained at 900 degrees C.
Considerable humidity response of a well-aligned SOMS micro-wire flexible sensor by moisture-induced releasing of trapped electrons
(2017-09-07)
Chan, Kuei-Lin
;
Yang, Min-Han
;
Chiu, Hsin-Tien
;
Lee, Chi-Young
;
應用化學系
Sandia Octahedral Molecular Sieves micro-wires (SOMS MWs) that exhibit ultra-high response to moisture and a short response time can be produced easily in an environmentally friendly mass production process. They are excellent candidate materials for use in humidity sensors. SOMS MWs were synthesized using niobium pentoxide as a precursor in concentrated sodium hydroxide solution. To fabricate humidity-sensing devices, electrophoresis was utilized to align the SOMS MWs on a polyethylene terephthalate (PET) substrate. The degree of alignment of SOMS MWs can be tuned by controlling the electric field during electrophoresis. Both well-aligned SOMS MWs (S-1.00) and randomly distributed SOMS MWs (S-0.00) exhibit maximum sensitivities to humidity (RRH/RDRY) of almost 10(4) and 10(7) respectively, and both exhibit short response times (34 and 38 s) and recovery times (7 and 10 s); these MWs outperform metal oxide ceramic-based materials in sensing humidity. Furthermore, the humidity response of S-1.00 exceeds that of S-0.00 by three orders of magnitude, and this result cannot be explained with reference to the Grotthuss mechanism. Therefore, the moisture-induced carriers from trapped electrons contribute significantly to the humidity response of SOMS MWs. In addition, with outstanding humidity sensing-performance under extreme bending conditions and superior durability after being bent hundreds of times, the well-aligned SOMS MW sensor is a favorable candidate for emerging multifunctional electronic-skin.
Effects of size and shell thickness of TiO2 hierarchical hollow spheres on photocatalytic behavior: An experimental and theoretical study
(2014-04-05)
Tsai, Min-Chiao
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Lee, Jeng-Yi
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Chen, Po-Chin
;
Chang, Yuan-Wei
;
Chang, Ya-Chen
Through a self-sacrificing template method, highly uniform hollow-spheres of TiO2 anatase are synthesized with controllable diameter from 365 nm to 930 nm. Compared to large hollow spheres, a large enhancement in the photocatalytic activity is reported for the small hollow spheres (with a thickness of 50 nm). By extending Mie\'s scattering theory from solid- to hollow-spheres, for a spherical scatter with a diameter of 300-900 nm, theoretical calculation reveal that each singular hollow sphere has absorption power equivalent to a solid sphere as the shell thickness parameter reaches a critical value of 0.3-0.6. This critical thickness parameter is independent to the size of a single hollow sphere, demonstrating that hollow spheres have quantitative advantages over solid spheres of the same weight. Moreover, calculation supported that small hollow spheres have stronger absorption power than large hollow spheres due to higher thickness. This greatly enhance the performance of small hollow spheres under a photocatalytic test. Our theoretical results showed good agreement to the experimental measurements, and provided a framework for the design of hollow-sphere nano-particles for optimized absorption power. (C) 2013 Elsevier B.V. All rights reserved.
Electrochromism of rutile nanowires, vertically aligned along the [001] direction, due to alkali metal ion intercalation
(2011)
Yang, Min-Han
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Chen, Ting-Ting
;
Wang, Yu-Shiuan
;
Chiu, Hsin-Tien
;
Lee, Chi-Young
Rutile nanowires were grown along the [001] direction and perpendicular to the fluorine doped tin oxide coated glass substrate (R(perpendicular to)) by a solvothermal process using titanium isopropoxide as the precursor in acidic solution. The edge length of the nanowires obtained in isopropyl alcohol is ten times less than that of the nanowires obtained in water. Due to the high ionic diffusion rate along the rutile [001] direction and good optical transmittance, R(perpendicular to) was used as an electrochromism electrode. When -2 V was applied, the color of the electrode became blue with a 60% change in the transmittance for 30 s due to the cathodic polarization potential in LiClO(4)/PC electrolyte (where PC is propylene carbonate). The lithium ion intercalated/extracted densities of R(perpendicular to), P25-coated and rutile nanowires-coated electrodes are 138.6/129.1 mC cm(-2), 93.6/83.2 mC cm(-2) and 31.7/15.9 mC cm(-2) respectively. After 50 cycles, the R(perpendicular to) electrode still performs very well. Furthermore, a large amount of sodium cation intercalation into TiO(2) was observed for the first time at -1.0 V. According to these results, the R(perpendicular to) electrode is a promising candidate to be a multi-function device.
Large-scale synthesis of uniform Cu2O nanocubes with tunable sizes by in-situ nucleation
(2013)
Chang, I-Chun
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Chen, Po-Chin
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Tsai, Min-Chiao
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Chen, Ting-Ting
;
Yang, Min-Han
Uniform Cu2O nanocubes with various sizes were synthesized by reducing Cu(OH)(2) using ascorbic acid in the presence of various amounts of sodium citrate. The monodispersed nanocubes with an edge length of approximately 80 nm used as an anode exhibit excellent lithium storage behavior.
Photo-induced nucleation of rutile nanorods-an ignored parameter in crystallization
(2011)
Ke, Tsung-Ying
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Chen, Po-Chin
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Yang, Min-Han
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Chiu, Hsin-Tien
;
Lee, Chi-Young
This work presents a surfactant-free and economical sol-gel method to synthesize multi-branched rutile TiO(2) nano-trees. Simple illumination by incandescent light during synthesis causes numerous branches to grow from the sides of nanorods, this process is accompanied by hydroxylation of the crystal surface. A {101} twin is demonstrated to connect the trunk to the branches. The extents of branching and surface hydroxylation are controlled by either photo-illumination or the addition of an exciton scavenger (H(2)O(2)). The relationship between the quantity of the branches and the excitons can be elucidated by considering photo-induced defects.
Photocatalytic performance of bipyramidal anatase TiO2 toward the degradation organic dyes and its catalyst poisoning effect
(1970-01-01)
Chan, Kuei-Lin
;
Lin, Wei-Hsiang
;
Chen, Fu-Jung
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Yang, Min-Han
;
Jiang, Cheng-Han
It has been reported that bipyramidal anatase TiO2 with {101}-exposed facets (AT170) results in outstanding photocatalytic performance. However, its activity decayed significantly and comparatively lower than that of commercial P25 after 20 min. Further studies and calculations showed that the methylene blue (MB) degradation rate constants for AT170 were time dependent and decrease of k values with time. Besides, the results of XPS, EA and TEM could clearly elucidate that the active sites of catalysts were blocked by the carbon buildup and covered on the surface creating the metal-carbon bonding on the catalysts. These observation strongly implied the existence of the poisoning effect of AT170 during photocatalytic processes. Also, the surface area values of P25 and AT170 were found to be 46.83 and 3.56 m(2)/g respectively. It was suggested that the catalyst poisoning effect could be prevented or controlled by increasing the surface area of the catalyst. Besides of surface area, zeta potential was also found to be served as the important factor determining the photocatalytic performance toward organic dyes due to the attraction/repulsion of electrostatic interaction. The zeta potential values of P25 and AT170 were found to be - 3.8 and - 32.9 mV respectively, which can adsorb cationic MB dyes on the negative charged surface through attraction of electrostatic interaction successively enhancing the degradation performance. It strongly indicates that both surface area and zeta potential play vital roles in photocatalytic degradation toward organic dyes and affect the rate constants.
Photodegradation by a Heterogeneous Mixture of Micro-Sized Anatase and Truncated Rhomboid Anatase Hollow Spheres
(2013-07-01)
Yang, Min-Han
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Tsai, Min-Chiao
;
Chang, Yuan-Wei
;
Chang, Ya-Chen
;
Chiu, Hsin-Tien
Highly uniform hollow spheres were assembled from truncated rhomboid anatase TiO2 nanoparticles (HS), which were synthesized from the hydrothermal treatment of a NaF solution by using amorphous TiO2 spheres as a precursor and template. The submicron hollow spheres with highly photocatalytic active surfaces exhibited excellent photocatalytic behavior. In this investigation, the factors that enhanced the photocatalytic performance were examined in terms of light harvesting, photoefficiency, and reaction activity. The photocatalytic performance was increased by a factor of approximately 1.5 for the scattering structure of submicron hollow spheres than that of nanofragments of submicron hollow sphere powder. The rate constant of anatase TiO2 with specific photoactive surfaces at {001} and {101} was approximately six times higher than that of randomly exposed TiO2 particles. Furthermore, a heterogeneous mixture of the submicron hollow spheres and micro-sized anatase TiO2 (HS@micro-sized TiO2) prohibited electron-hole recombination in the catalyst during the degradation reaction. The rate constant for the heterojunction system was 3.4times greater than that of the individual constituents. The rate constant for HS@micro-sized TiO2 (k=0.175min-1) was 1.8times larger than that of commercial P25 (k=0.099min-1). HS@micro-sized TiO2 is a promising photocatalytic material.
Porous titanium oxynitride sheets as electrochemical electrodes for energy storage
(2014)
Chen, Ting-Ting
;
Liu, Hsiao-Ping
;
Wei, Yen-Ju
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Chang, I-Chun
;
Yang, Min-Han
A flexible, porous TiOxNy sheet consisting of numerous conductive fibers was synthesized by nitridation of titanate and further used as an electrochemical electrode. The high surface area and mixed-oxidation state of titanium make TiOxNy sheets to be promising candidates for a good supercapacitor.
Rutile TiO2 Nanorod arrays grown on graphite foil as binder-free flexible electrode for sodium-ion batteries
(2017-04-02)
Tai, Yeh Ching
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Yang, Min-Han
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Chiu, Hsin-Tien
;
Lee, Chi-Young
;
應用化學系
Scattering resonance enhanced dye absorption of dye sensitized solar cells at optimized hollow structure size
(2014-12-05)
Tsai, Min-Chiao
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Lee, Jeng-Yi
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Chang, Ya-Chen
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Yang, Min-Han
;
Chen, Tin-Tin
This study elucidates the size effect on dye-sensitized solar cells (DSSCs) by synthesizing highly uniform hierarchical hollow sphere TiO2 samples, with the diameters from 220 nm to 800 nm. Experimental results indicate that the optimum conversion efficiency using N719 dye can be achieved around 5.5%, as the diameter of hierarchical hollow spheres is 450-550 nm. According to the incident photon-to-current conversion efficiency (IPCE) spectra, large-sized hierarchical hollow spheres significantly enhance the light harvesting by scattering; whereas small-sized hallow spheres (<360 nm) improve negligibly. Additionally, mesoporous and solid spheres with an identical diameter, 440 nm in this study, are also studied as a comparison. Our results demonstrate that hollow spheres perform the same conversion efficiency as that of mesoporous spheres owing to the equivalent adsorption of dye molecules in both hierarchical structures - regardless of the surface area of the interior of mesoporous structure, which shows that hollow spheres have higher conversion efficiency per unit volume than that of mesoporous spheres. (C) 2014 Elsevier B.V. All rights reserved.
Self-powered electrochemical deposition of Cu@Ni(OH)(2) nanobelts for high performance pseudocapacitors
(2014)
Chang, I-Chun
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Chen, Ting-Ting
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Yang, Min-Han
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Chiu, Hsin-Tien
;
Lee, Chi-Young
Two aluminum-driven spontaneous electrochemical reactions are developed for depositing Cu@Ni(OH)(2) nanobelts on carbon/aluminum electrodes. The Cu@Ni(OH)(2) NBs function as pseudocapacitor electrodes, which exhibit a high specific capacitance of 2426 F g(-1) and a remarkable rate performance.
Size-controlled wurtzite zinc oxide spheres with the characteristics of visible absorption and Mie scattering
(2014)
Chen, Ting-Ting
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Chang, I-Chun
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Tsai, Min-Chiao
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Chang, Yi-Chun
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Yang, Min-Han
The enhancement of the light harvesting efficiency over a metal oxide is crucial to optic-related applications which can convert solar energy into chemical energy. Here, we demonstrated a method to develop the characteristics of visible light absorption and visible Mie scattering over wurtzite ZnO microspheres. Size-controlled ZnO microspheres were successfully prepared in the thermal decomposition of amorphous/ layered basic zinc salt (LBZ) spheres. Firstly, trisodium citrate was employed as the chelating agent to synthesize amorphous/LBZ microspheres in a nucleation-controlled method. The sphere size was controlled by the nuclei number, which depends on the competition between hydroxyl ions and citrate to the ligand with Zn2+. Secondly, visible-active wurtzite ZnO spheres were obtained by thermal decomposition. The uniform sized microspheres exhibited Mie scattering in the visible range due to the interaction with specific incident electromagnetic radiation, and the full absorption spectrum was easily obtained by tuning the size of the spheres. Such uniform spheres exhibited superior visible absorption and scattering effects and thus are expected to be good candidates for the optic-related applications.
The "cascade effect" of nano/micro hierarchical structure: A new concept for designing the high photoactivity materials - An example for TiO2
(2013-10-01)
Chen, Po-Chin
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Tsai, Min-Chiao
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Yang, Min-Han
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Chen, Ting-Ting
;
Chen, Huang-Chin
The chrysanthemum-like TiO2 (CT800) was synthesized. It exhibited excellent photoactivity, which greatly exceeded that of conventional P25. To discover the key factors that governed the photocatalytic properties, the specific reduction of Ag+ ions was carried out and EPR spectra of CT800 were obtained. Both an HADDF image and EDX mapping indicated that the Ag+ ions tended to be reduced close to the center of the micro matrix of CT800. Moreover, the EPR spectra strongly suggest that the excited electrons tended to migrate toward the center of the micro matrix, resulting from a multiple junction, cascade effect, which efficiently reduces the recombination of excited electrons and holes and greatly increases the photoactivity. Additionally, the special morphology of CT800 was responsible for the hot spots at the surface of nano sheets and then contributing to its outstanding photocatalytic activity. Furthermore, the unidirectional electron transfer, because of the cascade effect, by materials of different sizes provides a new avenue for the design of electronic and photoelectrochemical devices. (c) 2013 Elsevier B.V. All rights reserved.
The exceptional photo-catalytic activity of ZnO/RGO composite via metal and oxygen vacancies
(2013-10-01)
Chen, Ting-Ting
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Chang, I-Chun
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Yang, Min-Han
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Chiu, Hsin-Tien
;
Lee, Chi-Young
ZnO/reduced graphene oxide (RGO) nanocomposite with many zinc and oxygen vacancies, synthesized in a simple solvothermal reaction exhibits significant photocatalytic activity. Photoluminescence and electron paramagnetic resonance measurements indicate that the zinc vacancies and oxygen vacancies were generated on the ZnO surface, and were crucial to that photocatalytic behavior. The photodegradation of methylene orange was significantly reduced by the addition of h(+) and (OH)-O-center dot scavengers. Both zinc and oxygen vacancies cause effective charge separation in the photodegradation of methylene orange, which markedly inhibits the recombination of charges. The advanced photocatalytic behavior of the ZnO/RGO composite is discussed in detail herein. (c) 2013 Elsevier B.V. All rights reserved.