Papers by Author: Shu Yin

Abstract: The oxidation of pentatitanium trisilicide (Ti₅Si₃) powder at high temperature was investigated in order to determine the suitability of this ceramic material for advanced application in an oxidation atmosphere at high temperature. Titanium silicide has been attracted for years as an engineering ceramics due to its high hardness, high melting point, and good chemical stability. The samples were oxidized from 300 to 1000 °C for 1 to 5 h in air. The mass changes were measured to estimate the oxidation resistance of the sample. The mass gain of the sample oxidized at 1000 °C for 5 h was about 26 % of the theoretical oxidation mass change. The commercial powder, Ti₅Si₃ showed an excellent oxidation resistance at 1000 °C, because the surface film of both titanium dioxide and silicon dioxide formed by oxidation acted as an oxidation resistant layer.

Abstract: Titanium carbide has been attractive for years an engineering ceramics due to its high hardness, high melting point, and good chemical stability. Similarly, titanium dioxide has excellent anti-microbial ceramic material by photon energy. In this study, the anatase type titanium dioxide layer prepared by oxidation of the titanium carbide powder by high temperature oxidation in air atmosphere was investigated in order to determine the possibility of its photocatalyst materials by radiant energy. TiC powder samples of different grain size were gained by ball mill. These samples were oxidized at room temperature to high temperature. The samples exhibited a steady mass gain with increasing oxidation temperature. Based on the results of the X-ray diffraction analysis, anatase type TiO₂ was detected on the titanium carbide samples. It is considered, the titanium carbide showed convension anatase type titanium dioxide layer produced by oxidation.

Abstract: The Ag₃PO₄ crystal with 200-600 nm in diameter was successfully synthesized using co-precipitation method with AgNO₃ and Na₂HPO₄^.12H₂O as starting materials. The product was characterized using XRD, DRS, FTIR and SEM. The photocatalytic activities were evaluated under blue light irradiation assisted by Fe²⁺. The 1 mL of Fe²⁺ aqueous solutions consisted of 1.00, 0.10, 0.01, 0.001 and 0.0001 mM Fe²⁺ was added into a 100 mL solution of Rhodamine B, and the photocatalytic oxidation of Rhodamine B was carried out under visible light irradiation. The highest photocatalytic activity was observed when 1 ml of 0.001 mM of Fe²⁺ aqueous solution was added in the Rhodamine B solution. The result inferred the possibility of in-situ peroxide generation during the photocatalysis reaction.

Abstract: The Bi₂O₃/Ag₃PO₄ composites consisting of the monoclinic α-Bi₂O₃ and body-centered cubic Ag₃PO₄ were successfully synthesized by grinding Ag₃PO₄ and Bi₂O₃ mixtures in ethanol using an agate mortar, followed by calcination at 500°C for 5 hours, where the Ag₃PO₄ was synthesized by co-precipitation method using AgNO₃ and NaH₂PO₄^.2H₂O as starting materials. The Bi₂O₃ content in the composite materials changed from 5 to 25 mol.%. The composites were characterized using XRD, DRS and BET specific surface area. The photocatalytic activities were evaluated using Rhodamin B degradation under visible light irradiation of blue LED (λ = 445 nm). The highest photocatalytic activities could be obtained at 5 mol.% Bi₂O₃ in Bi₂O₃/Ag₃PO₄ composite. The enhanced photocatalytic activity could be attributed to the effective separation of hole (h⁺) and electron (e^-) pairs in the Bi₂O₃/Ag₃PO₄ composite.

Abstract: Cr and La-codoped SrTiO₃ nanoparticles were successfully prepared by a microwave-assisted hydrothermal synthesis. The products were characterized by XRD, TEM, BET specific surface area, and UV-Vis absorption spectra. The photocatalytic activity was determined by deNO_x ability under irradiation of a 450 W high-pressure mercury lamp. The products could absorb the visible light and showed high photocatalytic ability for the decomposition of NO_x gas. All samples showed the photocatalytic activities superior to that of commercial titania (Degussa P25) in both UV and visible light regions.

Abstract: Silver orthophosphate semiconductor was synthesized by the ion-exchange method using AgNO₃ and Na₂HPO₄.12H₂O as starting materials. The molar ratio of AgNO₃ and Na₂HPO₄.12H₂O was designed as 3:1. The product was characterized using XRD, SEM and DRS. The photocatalytic activity was determined using phenol oxidation under LED lamps with various wavelengths of visible lights such as 627nm (red), 530 nm (green) and 445 nm (blue). The body-centered cubic structure of silver orthophosphate with 1-10 μm in diameter was successfully synthesized. The band gap energy of the material could be found as 2.42 eV. The excellent photocatalytic activities of silver orthophosphate for phenol oxidation could be obtained under blue light (λ= 445nm) irradiation. The photocatalytic ability of Ag₃PO₄ under blue light irradiation was not lost even after heat treatment at 700°C.

Abstract: The hybrid materials consisting of plate-like potassium lithium titanate (K0.81Li0.27Ti1.73O4) micro particles coated with calcia-doped ceria (Ce0.8Ca0.2O1.8) nano particles were prepared by the co-precipitation method and sol-gel method. Broad-spectrum UV-shielding composite materials with good comfort and low oxidation catalytic activity were successfully synthesized. The comfort when applied on skin and UV-shielding ability of the composites prepared by the sol-gel method were superior to those by the co-precipitation method.

Abstract: Different valences of metal ions such as Fe3+ and Nb5+ were co-doped with nitrogen ion into titanium dioxide by hydrothermal method using metal chlorides and hexamethylenetetramine as the sources of metal ions and nitrogen ion, respectively. The co-doping of low-content metal ion showed no noticeable influence on the crystalline phases and specific surface area (S.S.A.) of the samples. Doping with Fe ion could significantly enhance the absorption in visible light region, but doping with Nb ion showed almost no effect. The photocatalytic activities of the samples were determined for the oxidative destruction of NO gas under various wavelengths. Co-doping with Nb ion improved the deNOx ability, but co-doping with Fe ion depressed it, indicating that co-doping with higher valence metal ion was effective in reducing the vacancy in the lattice which acts as the recombination center of the photo-induced electrons and holes, and achieving higher photocatalytic activity.

Abstract: Niobium and nitrogen co-doped SrTiO3 possessing excellent visible light responsive photocatalytic activity was successfully synthesized by microwave-assisted solvothermal reaction using SrCl2.6H2O, Ti(OC3H7)4, NbCl5 and hexamethylenetetramine in KOH aqueous solution. The photocatalytic activity was determined by DeNOx ability using LED lamps with the wavelengths of 627 nm (red), 530 nm (green), 445 nm (blue) and 390 nm (UV). The photocatalytic activity of SrTiO3 for DeNOx ability in visible light region could be improved by co-doping Nb5+ and N3-. The excellent visible light photocatalytic activity of this substance may be due to the generation of a new band gap that enables to absorb visible light and decrease in the lattice defects which acts as a recombination center of photoinduced electrons and holes.

Abstract: Monodispersed plate-like CeO2 particles were successfully synthesized by a mild solution process followed by calcination in air at 400oC. During the solution processing, monodispersed orthorhombic single-crystal of plate-like Ce2(CO3)3.8H2O was obtained by using Ce(NO3)3.6H2O as cerium source, and NaHCO3 aqueous solution as precipitation reagent and carbon source. The concentration of NaHCO3 solution affects the morphologies and particle size of the cerium carbonate compounds. High concentration of NaHCO3 led to a decrease in the particle size of Ce2(CO3)3.8H2O effectively. The CeO2 particles synthesized by the decomposition of carbonate precursors possessed similar morphologies and slightly smaller particle size. The plate-like ceria particles possessed good UV-shielding properties and low oxidation catalytic activities, indicating the potential application as cosmetics materials