Soo Wohn Lee

Exalted photocatalytic activity of tetragonal BiVO4 by Er3+ doping through a luminescence cooperative mechanism

Er-doped BiVO4 are synthesized by means of a surfactant free microwave assisted hydrothermal method having good photoactivities under sun-like excitation for the degradation of methylene blue. From the structural and morphological characterization, it has been stated that the presence of Er(3+) induces a slight stabilization of the tetragonal phase, probably due to its incorporation in the BiVO4 lattice. The best photocatalytic performances were attained for the samples with Er(3+) content higher than 3 at%. The occurrence of the Er(3+) doped tetragonal BiVO4 clearly induces higher photocatalytic activities. The existence of a luminescence process has been related with the enhanced photoactivity observed.

UV, visible and near-infrared lights induced NOx destruction activity of (Yb,Er)-NaYF4/C-TiO2 composite

Titanium dioxide (TiO2) is a well-known photocatalyst for environmental cleaning and energy conversion. However, it can only be excited by ultraviolet light for photocatalysis due to its wide band gap (3.2 eV). In this paper, we present a novel (Yb,Er)-NaYF4/C-TiO2 composite which can be perfectly induced not only by ultraviolet light but also weak visible and near infrared lights, owing to the increased carbon doping contents and optimal energy transfer between up-conversion phosphor and C doped TiO2 compared with that of solely C-TiO2. Consequently, the (Yb,Er)-NaYF4/C-TiO2 composite can present the outstanding continuous NOx gas destruction ability under the irradiation of ultraviolet, weak visible and infrared lights much superior to pure C-TiO2, P25 titania and even that of (Yb,Er)-NaYF4/N-TiO2 composite, due to the nice synergetic effect of (Yb,Er)-NaYF4 and C-TiO2, indicating a promising potential in the photocatalyst application with high efficiency of ultraviolet, visible and infrared lights induced photocatalysis simultaneously.

Wear of plasma-sprayed nanostructured zirconia coatings against stainless steel under distilled-water conditions

The friction and wear properties of plasma-sprayed nanostructured and traditional zirconia coatings against stainless steel were investigated with a sliding, reciprocating and vibrating test machine under water-lubricated conditions. The counterface was a 10-mm diameter AISI316 stainless steel ball. It was found that the plasma-sprayed nanostructured zirconia coating possessed better wear resistance than traditional zirconia coating. The wear rates of the nanostructured zirconia coatings are in the range from one-fourth to four-fifths of the traditional zirconia coating under loads ranging from 20 to 50 N. The plasma-sprayed nanostructured zirconia coating also reduces wear rate of the friction pair materials. The higher wear resistance of the plasma-sprayed nanostructured zirconia coating is attributed to its enhanced cohesion, improved microhardness and homogenous microstructure. The wear mechanisms of nanostructured and traditional zirconia coatings under water-lubricated conditions are discussed.

Study on porosity of plasma-sprayed coatings by digital image analysis method

The porosities of plasma-sprayed Al2O3, ZrO2, and TiO2 coatings deposited on 304 stainless steel plates were evaluated by the digital image analysis method. As the accuracy of this method depends significantly on metallographic preparation and metallography procedure for coating specimens, the effects of cross-surface roughness, magnification, and number of fields of view on the porosity were studied. The results indicate that the porosity value from polished specimen with cross-surface roughness no more than 0.1 µm is acceptable. The porosity value obtained at higher magnification is a little bit higher, especially when the real porosity is higher; more fields of view have to be considered in this case. Both experimental results and statistic analysis suggest that 15 fields of view at 1000× magnification can be implemented to evaluate porosity of plasma-sprayed coating considering both the domain size and the resolution at the same time.

Green phosphorescence-assisted degradation of rhodamine B dyes by Ag3PO4

Here we report a new photocatalytic system of the Ag3PO4 semiconductor coupled with Sr4Al14O25:(Eu,Dy) long afterglow phosphor, which can harvest persistent phosphorescence to decompose organic contaminants in aqueous solution after turning off the lamp irradiation. This suggests a strategy to design new photocatalysts as a practical photofunctional material for wastewater cleaning.

Sonochemical synthesis of solar-light-driven Ag̊-PbMoO4 photocatalyst

Ag°-PbMoO4 photocatalysts were synthesized by facile sonochemical method with different mol.% of Ag nanoparticles dispersed on the surface of PbMoO4. The synthesized powders were characterized by X-ray Diffraction (XRD) Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), and Diffuse Reflectance Spectroscopy (UV-vis DRS) to investigate the crystal structure, morphology, chemical composition, and optical properties of the photocatalyst. Photocatalytic activities of the Ag°-PbMoO4 samples were evaluated by the degradation of Indigo Carmine (IC) dye under simulated solar light irradiation. It has been observed that the sample containing 0.3 mol.% of Ag showed the best photocatalytic activity as compared to other samples. The results suggest that the dispersion of Ag nanoparticles on the surface of PbMoO4 significantly enhances the photocatalytic activity of PbMoO4. Increase in photocatalytic activity of Ag°-PbMoO4 photocatalyst has been explained on the basis of surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the photocatalyst.

Effects of whisker distribution and sintering temperature on friction and wear of Si3N4-whisker-reinforced Si3N4-composites

Abstract Friction and wear behaviors of Si 3 N 4 -whisker-reinforced Si 3 N 4 -composites have been studied in different sliding directions with respect to the orientation of the Si 3 N 4 -whiskers by using a ball-on-disk reciprocating sliding apparatus. These ceramic samples were sintered by the gas press sintering (GPS) technique at 1875 and 2000°C for 4 h in 2.4 MPa of N 2 gas, where the whiskers were controlled to have unidirectional orientation with different alignments or orientation (0°/90°) with a cross-structure by tape-casting and stacking. The results show that for the unidirectionally orientated composites, wear rate in the direction parallel to the whiskers is much greater than in perpendicular direction. With decreasing alignment of the whiskers, the wear rate decreases in the parallel sliding direction and increases in the perpendicular direction. Wear rate of the bidirectionally oriented (BD) composites is between those of unidirectionally oriented composites in the two sliding directions. With increasing sintering temperature, the wear rate increases in both parallel and perpendicular directions. Wear process occurs periodically during sliding.

Young's modulus and residual stress of plasma-sprayed boron carbide coatings

Abstract This paper addresses the application of nondestructive evaluation techniques, such as the use of ultrasonic and X-ray techniques, for characterizing the quality of plasma-sprayed boron carbide coatings. The Youngs modulus and shear modulus of plasma-sprayed boron carbide coatings were measured by an ultrasonic echo technique. The residual stresses of coatings were determined by X-ray diffraction technique. The relationship between Youngs modulus and microstructure of the coatings is discussed. The results showed that the spraying distance has a significant effect on the phase composition and microstructure of boron carbide coatings. The elastic modulus of boron carbide coatings decreases with increasing spraying distance. This is explained by the increasing content of B2O3 and pores in the boron carbide coatings. The residual stresses of the coatings show a polynomial relationship with the spraying distance.

Ag-BaMoO4: Er3+/Yb3+ photocatalyst for antibacterial application

Silver loaded and Er3+/Yb3+ doped BaMoO4 octahedron microcrystals were fabricated by microwave hydrothermal process. The synthesized samples were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDS), and Ultraviolet-visible diffuse reflection spectroscopy (UV-Vis DRS). The antibacterial application of samples were investigated by visible light irradiation and disk-diffusion method towards representative Gram-negative pathogen (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive pathogen (methicillin resistant Staphylococcus aureus). The complete inactivation of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were observed by Ag-BaMoO4: Er3+/Yb3+ photocatalyst within 1h, 4h, and 5h, respectively, under visible light irradiation. The high killing percentage and superior zone of inhibition revealed the excellent antibacterial performance. The FESEM images were used to visualize the morphology with the extent of damage in the phospholipid layer present in the cell membrane of bacteria. The synergistic effect of loaded silver particles and doped Er3+/Yb3+ ions in BaMoO4 contributed for efficient antibacterial performance in visible light as well as in the dark. The excellent antibacterial performance of Ag-BaMoO4: Er3+/Yb3+ photocatalyst makes the material suitable for smart weapon for multidrug-resistant microorganisms and disinfectants in biomedical application.

Electrodeposition and characterization of Ni-TiB2 composite coatings

Nickel-titanium diboride (Ni-TiB2) composite coatings were successfully fabricated by pulse electrodeposition techniques from nickel sulfamate bath containing dispersed submicron TiB2 particles. The effect of TiB2 codeposition on the morphological, microstructural, microhardness and anti-corrosive properties of the composite coatings have been investigated by using scanning electron microscopy coupled with energy dispersive spectroscopy system, X-ray diffraction (XRD), vickers microhardness, and electrochemical impedance spectroscopy (EIS) techniques. Incorporation of TiB2 particles into the nickel matrix has modified the regular crystal growth of nickel. The XRD patterns revealed that the preferred (100) crystallite orientation of pure nickel has been modified into mixed orientations by the enhancement of (111) and attenuation of (200) diffraction intensities by the incorporation of TiB2 particles into the nickel matrix. Vickers microhardness of the Ni-TiB2 composite coating is found to be increased which is nearly 3 times higher than pure nickel coating. The results obtained by polarization curves and EIS analysis in 3.5 wt% NaCl solution have shown the improved corrosion resistance properties of Ni-TiB2 composite coating over pure nickel electrodeposit.