Browsing by Author "Chen, Po-Chin"

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Alkali metal ion assisted synthesis of faceted anatase TiO2
(2013)
Yang, Min-Han
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Chen, Po-Chin
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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
;
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.
Bio-ingredient assisted formation of porous TiO2 for Li-ion battery electrodes
(2015-01-01)
Chang, Yi-Chun
;
Peng, Chih-Wei
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Chen, Po-Chin
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
Macroporous TiO2 was synthesized by using low-cost bio-ingredients as the pore forming templates. TiCl4 in C2H5OH(l) containing NH4OH(aq.) was polymerized in the presence of instant yeast and glucose. The organic-inorganic hybrid precursor was further processed to generate macroporous anatase TiO2 (pore size: 2.5-3 mu m) with mesopores (4-51 nm). The porous TiO2 was coated with a thin layer of carbon by chemical vapour deposition to generate the hierarchical C/TiO2 nanocomposite material. The porous products were investigated as anode materials for Li-ion batteries. The capacities of the hierarchical C/TiO2 electrode material remained 180 mA h g(-1) and 142 mA h g(-1) under high charge/discharge rates of 5 C and 10 C, respectively. It demonstrated good cycling stability of 318 mA h g(-1) at 0.1 C at various discharge-charge rates. The excellent performance is attributed to the high specific surface areas and open spaces of the C/TiO2 allowing effortless intercalation/deintercalation of Li ions.
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
;
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.
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
;
Tsai, Min-Chiao
;
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.
Nanosized MnO2 spines on Au stems for high-performance flexible supercapacitor electrodes
(2013)
Chen, Yu-Liang
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Chen, Po-Chin
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Chen, Tze-Lung
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
Electrodes composed of ultrathin MnO2 (thickness 5-80 nm) spines on Au nanowire (NW) stems (length 10-20 mu m, diameter 20-100 nm) were electrochemically grown on flexible polyethylene terephthalate (PET) substrates. The electrodes demonstrated high specific capacitance, high specific energy value, high specific power value, and long-term stability. In Na2SO4(aq.) (1 M), the maximum specific capacitance was determined to be 1130 F g(-1) by cyclic voltammetry (CV, scan rate 2 mV s(-1)) using a three-electrode system. From a galvanostatic (GV) charge/discharge test using a two-electrode system, a maximum capacitance of 225 F g(-1) (current density 1 A g(-1)) was measured. Even at a high charge/discharge rate of 50 A g(-1), the specific capacitance remained at an extremely high value of 165 F g(-1). The flexible electrodes also exhibited a maximum specific energy of 15 W h kg(-1) and a specific power of 20 kW kg(-1) at 50 A g(-1). After five thousand cycles at 10 A g(-1), 90% of the original capacitance was retained. A highly flexible solid-state device was also fabricated to reveal its supercapacitance performance.
One-Step Ge/Si Epitaxial Growth
(2011-07-01)
Wu, Hung-Chi
;
Lin, Bi-Hsuan
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Chen, Huang-Chin
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Chen, Po-Chin
;
Sheu, Hwo-Shuenn
Fabricating a low-cost virtual germanium (Ge) template by epitaxial growth of Ge films on silicon wafer with a Ge(x)Si(1-x) (0 < x < 1) graded buffer layer was demonstrated through a facile chemical vapor deposition method in one step by decomposing a hazardousless GeO(2) powder under hydrogen atmosphere without ultra-high vacuum condition and then depositing in a low-temperature region. X-ray diffraction analysis shows that the Ge film with an epitaxial relationship is along the in-plane direction of Si. The successful growth of epitaxial Ge films on Si substrate demonstrates the feasibility of integrating various functional devices on the Ge/Si substrates.
One-step vapor-solid reaction growth of Sn@C core-shell nanowires as an anode material for Li-ion batteries
(2012-10-28)
Hsu, Kai-Chieh
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Liu, Chia-Erh
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Chen, Po-Chin
;
Lee, Chi-Young
;
Chiu, Hsin-Tien
Sn@C core-shell nanowires (NWs) were synthesized by reacting SnO2 particles with a flowing mixture of C2H2 and Ar gases at elevated temperatures. The overall diameter of the core-shell nanostructure was 100-350 nm. The C shell thickness was 30-70 nm. The NW length was several micrometers. Inside the shell, a void space was found. The reaction is proposed to be via a vapor-solid reaction growth (VSRG) pathway. The NWs were investigated as a potential anode material for Li-ion batteries (LIBs). The half-cell constructed from the as-fabricated electrode and a Li foil exhibited a reversible capacity of 525 mA h g(-1) after one hundred cycles at a current density of 100 mA g(-1). At a current density as high as 1000 mA g(-1), the battery still maintained a capacity of 486 mA h g(-1). The excellent performance is attributed to the unique 1D core-shell morphology. The core-shell structure and the void space inside the shell can accommodate large volume changes caused by the formation and decomposition of LixSn alloys in the charge-discharge steps.
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
;
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.
Self-carbonized lamellar nano/micro hierarchical structure C/TiO2 and its Li-ion intercalation performance
(2012)
Chen, Po-Chin
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Tsai, Min-Chiao
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Chen, Huang-Chin
;
Lin, I-Nan
;
Sheu, Hwo-Shuenn
In this study, two new layered titanates, fibrillar TiO2 center dot(CH3COOH)(1.4) and chrysanthemum-like TiO2 center dot(CH3COOH)(0.9) (named as FT and CT) with acetic acid and acetate intercalation have been synthesized by reacting titanium isopropoxide (TTIP) with acetic acid at different temperatures. Furthermore, nano/micro hierarchical structure TiO2 with high TiO2-B/anatse ratio was obtained by annealing the titanate (CT). For use as an anode for lithium ion batteries, uniform carbon coated titanium dioxide with high TiO2-B content was obtained by "self-carbonizing'' CT under argon atmosphere at 350 degrees C, and the compound was named SC-CT350. The capacity of the anode made from SC-CT350 can reach 144 mA h g(-1) under a high charging/discharging rate (10 C) and showed excellent retention ability.
Simple chemical preparation of perovskite-based materials using alkali treatment
(2012)
Chen, Po-Chin
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Tsai, Min-Chiao
;
Huang, Yi-Jen
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Chiu, Hsin-Tien
;
Lee, Chi-Young
In this work, a simple alkali treatment process was introduced to synthesize ABO(3) perovskite related materials: CaTiO3 (CTO), SrTiO3 (STO), BaTiO3 (BTO) and BaxSr1-xTiO3 (BST). The perovskite materials, synthesized by using stoichiometric amounts of corresponding alkaline solutions Ba(OH)(2), Sr(OH)(2), Ca(OH)(2) and powdered TiO2, are pure phase and well-crystallized. The obtained powders are round, round-edged cubes and cubes with sharp edges for BaTiO3, SrTiO3 and CaTiO3 respectively. What's more, the Ba content (x) in BST can be directly and precisely modified to be any value between one and zero. And, the morphology of SrTiO3 can be manipulated by altering the reaction time. As time is prolonged, the morphology of the product changes from round to round-edged cubes to sharp-edged cubes. In the future, materials with such specific microstructure and morphologies may be used in electro-optical and photocatalytic applications.
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
;
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.