Browsing by Author "Wang, Han-Yi"

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Combination of electrophoresis and electro-flocculation for the formation of adhering IrO2 pH sensing films
(2019-07-20)
Wang, Han-Yi
;
Hsieh, Yi-Chieh
;
Tso, Kuang-Chih
;
Chang, Chung-Kai
;
Cheng, Yu-Ting
We demonstrate a simple scheme to produce dense and adhering IrO2 thin films on ITO substrates via a bipolar pulsing process combining both electrophoresis and electro-flocculation. Our fabrication steps entail the synthesis of negatively-charged IrO2 nanoparticles in size of 3.5 nm using NaClO as an oxidizer in conjunction with Na3IrCl6, citric acid, and NaOH. Subsequently, multiple bipolar potentiostatic pulses are imposed in which alternating positive and negative potentials engender the electrophoresis of IrO2 nanoparticles, followed by their immediate coalescence facilitated by proton-catalyzed electro-floccu-lation. The resulting IrO2 thin films reveal impressive physical properties in surface uniformity, robust structural integrity, and strong adhesion to the substrate. The as-synthesized IrO2 thin film exhibits an amorphous nature with a pH sensing slope between -73.6 and -71.5 mV/pH, characteristic of super-Nernstian behavior. In contrast, the annealed IrO(2 )sample demonstrates a crystalline rutile phase with a pH sensing slope between -49.5 and -54.7 mV/pH, consistent with typical Nernstian response. Our approach provides a new route for the formation of strong and adhering oxide films from their colloidal constituents. (C) 2019 Elsevier Ltd. All rights reserved.
Development of IrO2 bio-ink for ink-jet printing application
(2019-09-01)
Hsieh, Yi-Chieh
;
Wang, Han-Yi
;
Tso, Kuang-Chih
;
Chang, Chung-Kai
;
Chen, Chi-Shih
We develop a chemical formulation to synthesize stable IrO2 colloidal solution as a bio-ink for ink-jet printing purpose. This wet chemical process entails Na3IrCl6 and NaClO as the Ir precursor and oxidizer, respectively. In addition, citric acid and sodium hydroxide are employed as the complex agent and pH adjuster. The pH value of the IrO2 colloidal solution could be readily adjusted over a broad range without incurring undesirable precipitation. Their respective zeta potential decreases from positive to negative with increasing pH values. The IrO2 colloidal solution demonstrates impressive chemical stability over extended storage at 5 and 65 degrees C. Images from transmission electron microscope indicate the average size for the IrO2 nanoparticles to be 3.5 nm. The X-ray diffraction pattern from the heat-treated IrO2 sample shows a polycrystalline rutile phase. The IrO2 colloidal solution undergoes repeated filtering and washing to retrieve the IrO2 nanoparticles. After an annealing at 450 degrees C for 2 h in air, the crystalline IrO2 nanoparticles are resuspended in a 0.5 wt% aqueous medium as the bio-ink for ink-jet printing on an ITO substrate. Our method enables the synthesis of stable IrO2 nanoparticles in a neutral solution at 25 degrees C, which provides a facile and effective approach over conventional ones that require alkaline environment at elevated temperature.
Synthesis of IrO(2)decorated core-shell PS@PPyNH(2)microspheres for bio-interface application
(2020-09-11)
Hsieh, Tsung-Lin
;
Hung, Pei-Sung
;
Wang, Chuan-Jyun
;
Tso, Kuang-Chih
;
Wang, Han-Yi
In this paper, an effective approach is demonstrated for the fabrication of IrO2-decorated polystyrene@functionalized polypyrrole (core@shell; PS@PPyNH2) microspheres. The synthesis begins with the preparation of monodispersive PS microspheres with a diameter of 490 nm, by a process of emulsifier-free emulsion polymerization, followed by a copolymerization process involving pyrrole and PyNH(2)monomers in a PS microsphere aqueous suspension, to produce uniform PS@PPyNH(2)microspheres with a diameter of 536 nm. The loading of 2 nm IrO(2)nanoparticles onto the PS@PPyNH(2)microspheres can be easily adjusted by tuning the pH value of the IrO(2)colloidal solution and the PS@PPyNH(2)suspension. At pH 4, we successfully obtain IrO2-decorated PS@PPyNH(2)microspheres via electrostatic attraction and hydrogen bonding simultaneously between the negatively-charged IrO(2)nanoparticles and the positively-charged PS@PPyNH(2)microspheres. These IrO2-decorated PS@PPyNH(2)microspheres exhibit a characteristic cyclic voltammetric profile, similar to that of an IrO(2)thin film. The charge storage capacity is 5.19 mA cm(-2), a value almost five times greater than that of PS@PPyNH(2)microspheres. In addition, these IrO2-decorated PS@PPyNH(2)microspheres exhibit excellent cell viability and biocompatibility.