Papers by Author: Yan Hong Li

Abstract: Selective laser sintering (SLS) of Si3N4 and Al2O3 powders were investigated in this work. Copolymer was synthesized through monomer MMA and BMA. Infrared spectrum was employed to characterize the as-synthesized copolymer. Results show that the main compositions of the copolymer are PMMA and PBMA. The binders were prepared by mixing the copolymer and the inorganic NH4H2PO4 with certain ratio. Binders were used to coat the Si3N4 and Al2O3 powders by spray drying. The coated powders were sintered successfully by SLS to make cubic part and rotor part.

Abstract: Nitrogen-doped TiO2 has been prepared by calcining technical grade guanidine hydrochloride and commercial anatase TiO2 powders. XRD patterns indicate that the prepared powders are composed of anatase. XPS results show that N atoms have been incorporated into the lattice of anatase. UV-Vis reflectance spectra show that the light absorption of the synthesized N-doped anatase powders has red-shifted well into visible-light region. Degradation of methylene blue (MB) aqueous solution by N-doped anatase has been investigated by UV-Vis light spectrophotometer. The 400-mL 10 mg/L aqueous solution of MB could be degraded with 4 g N-doped TiO2 within 4.5 hrs of visible light irradiation. Photocatalytic paint was prepared by adding the synthesized N-doped nanocrystalline anatase TiO2 powders into self-engineered oxidation resistance latex paint system. The effects of the amount and types of the TiO2 in the paints on the sterilization were systematically investigated. The colony counting method was used to study its sterilization performance under visible light irradiation. The sterilization experiments show that the rate of sterilizing E. coli by the N-doped TiO2 modified paint can exceed more than 99% after irradiation by the visible light for 2 to 4 hours.

Abstract: Nanosize anatase TiO2 powders have been synthesized by hydrothermal synthesis by using technical grade TiOSO4 as precursor and urea as precipitating agent. The initial pressure of the reaction system was set at 6 MPa. Stirring speed was fixed at 300r/min. The reaction system reacted at the temperature ranged from 110 to 150°C for holding 2hrs to 8hrs and the concentration of the precursor was ranged from 0.25M to1.5M. XRD patterns show that the synthesized powders are in the form of anatase phase. Calculated grain size is ranged from 6.7 to 8.9nm by Scherrer method from the line broadening of the (101) diffraction peak of anatase. The specific surface area of the powders synthesized under different conditions is ranged from 124 to 240m2/g. The grain size of the powders increases with the increase of the reaction temperature, holding time and precursor concentration, respectively. The specific surface area decreases with the increase of reaction temperature and holding time, and does not obviously change with the change of precursor concentration when the concentration of the precursor is less than 1M. However, when the concentration is higher than 1M, the specific surface area will decrease quickly with the increase of the precursor concentration. XRD and DSC-TG analysis shows that the synthesized anatase TiO2 will begin to transform to rutile TiO2 at about 840°C. When heated to 1000°C for holding 1h, the anatase powders will transform to rutile completely.

Abstract: N-doped TiO2 powders with high photocatalytic activity under visible-light irradiation have been prepared by calcining anatase nanocrystalline TiO2 powders and guanidine hydrochloride at 350 °C, 450 °C, 550 °C and 650 °C with the holding time ranged from 1.5 h to 3 h, respectively. The guanidine hydrochloride content was varied from 1 to 6 M for the experiments. XRD patterns indicate that all the powders are anatase crystalline phase. The specific surface area is 25~45 m2/g measured by BET method. XPS results show that N atoms were incorporated into the lattice of TiO2 and the amount of N doped in TiO2 is reached up to 8.26 at%. UV-Vis absorption spectra show that the absorption edge of the synthesized N-doped TiO2 powders, calcined at 350 °C for 2.5 h, has red-shifted well into visible region up to 700 nm. Degradation of methylene blue (MB) aqueous solution has been investigated by UV-Vis light spectrophotometer. The 400-mL 10 mg/L aqueous solution of methylene blue could be degraded completely with 4 g N-doped TiO2 within 4.5 h of visible light irradiation.

Abstract: A new functional photocatalytic paint was prepared by adding N-doped nanocrystalline anatase TiO2 powders into self-engineered oxidation resistance latex paint system. The property of the UV-Vis light absorbance of the paint was characterized. The effects of the amount, types, and the introducing methods of the TiO2 in the paints on the behavior of the UV absorption, photocatalytic properties of the paint were systematically investigated. UV-Vis absorption spectra reveal that the ultraviolet light can strongly be absorbed by the paints. The absorption edge of the N-doped nanocrystalline anatase powders modified paint has red-shifted to visible light region. The colony counting method is used to study its sterilization performance under visible light irradiation. The sterilization experiments show that the rate of sterilizing staphylococcal bacteria by the N-doped TiO2 modified paint can exceed more than 99% after the paint has been irradiated by the visible light for 2 to 4 hours.