Joon Yeob Lee

Heterojunction-based two-dimensional N-doped TiO2/WO3 composite architectures for photocatalytic treatment of hazardous organic vapor.

Two-dimensional nanosheet structures of N-doped TiO2/WO3 composites (WO3-N-TNSs) with varying WO3 loadings were synthesized by incorporating WO3 and N sources into sonochemically prepared TiO2 nanosheets (TNSs). These nanostructures were employed as photocatalysts, and their efficacy in the decomposition of hazardous hexane vapor was investigated. The photocatalytic efficiencies of the WO3-N-TNS composites were higher than those of N-doped TNS (N-TNS), which in turn were higher than the corresponding values for un-doped TNS. These variations were ascribed to the different light absorbance efficiencies, adsorption abilities, and charge carrier separations between the samples. An optimal WO3 loading for the performance of WO3-N-TNS was determined. Interestingly, the photocatalytic efficiency for hexane mixed with isopropyl alcohol (IPA) was lower than that for pure hexane, whereas the degradation efficiency for IPA did not vary with the feed method. Also investigated were the hexane conversion into CO2 over a representative WO3-N-TNS sample, the durability of the photocatalyst, and potential byproduct formation. Based on measurements of the hydroxyl radical population, a heterojunction-type mechanism was considered more plausible than a direct Z-scheme-type mechanism for the photocatalytic decomposition of hexane over the WO3-N-TNS photocatalysts.

The Effect of the Melt Viscosity and Impregnation of a Film on the Mechanical Properties of Thermoplastic Composites

Generally, to produce film-type thermoplastic composites with good mechanical properties, high-performance reinforcement films are used. In this case, films used as a matrix are difficult to impregnate into tow due to their high melt viscosity and high molecular weight. To solve the problem, in this paper, three polypropylene (PP) films with different melt viscosities were used separately to produce film-type thermoplastic composites. A film with a low melt viscosity was stacked so that tow was impregnated first and a film with a higher melt viscosity was then stacked to produce the composite. Four different composites were produced by regulating the pressure rising time. The thickness, density, fiber volume fraction (Vf), and void content (Vc) were analyzed to identify the physical properties and compare them in terms of film stacking types. The thermal properties were identified by using differential scanning calorimetry (DSC) and dynamical mechanical thermal analysis (DMTA). The tensile property, flexural property, interlaminar shear strength (ILSS), and scanning electron microscopy (SEM) were performed to identify the mechanical properties. For the films with low molecular weight, impregnation could be completed fast but showed low strength. Additionally, the films with high molecular weight completed impregnation slowly but showed high strength. Therefore, appropriate films should be used considering the forming process time and their mechanical properties to produce film-type composites.

Influence of Interleaved Films on the Mechanical Properties of Carbon Fiber Fabric/Polypropylene Thermoplastic Composites

A laminated composite was produced using a thermoplastic prepreg by inserting an interleaved film with the same type of matrix as the prepreg during the lay-up process to improve the low interlaminar properties, which is a known weakness of laminated composites. Carbon fiber fabric (CFF) and polypropylene (PP) were used to manufacture the thermoplastic prepregs. Eight prepregs were used to produce the laminated composites. Interleaved films with different thicknesses were inserted into each prepreg. The physical properties of the composite, such as thickness, density, fiber volume fraction (Vf), and void content (Vc), were examined. The tensile strength, flexural strength, interlaminar shear strength (ILSS), impact property, and scanning electron microscopy (SEM) were used to characterize the mechanical properties. Compared to the composite without any inserted interleaved film, as the thickness of the inserted interleaved resin film was increased, Vc decreased by 51.45%. At the same time, however, the tensile strength decreased by 8.75%. Flexural strength increased by 3.79% and flexural modulus decreased by 15.02%. Interlaminar shear strength increased by 11.05% and impact strength increased by 15.38%. Fracture toughness of the laminated composite was improved due to insertion of interleaved film.

Titania Nanotubes Grown on Carbon Fibers for Photocatalytic Decomposition of Gas-Phase Aromatic Pollutants

This study aimed to prepare titania (TiO2) nanotube (TNT) arrays grown on un-activated carbon fibers (UCFs), with the application of different TiO2 loadings based on the coating-hydrothermal process, and to evaluate their photocatalytic activity for the degradation of sub-ppm levels of aromatic pollutants (benzene, toluene, ethyl benzene, and o-xylene (BTEX)) using a plug-flow photocatalytic reactor. The characteristics of the prepared photocatalysts were determined by scanning electron microscopy (SEM),energy-dispersive X-ray (EDX), transmission electron microscopy (TEM), UV-visible absorption spectroscopy (UV-Vis) and X-ray diffraction (XRD) analyses. Spectral analysis showed that the prepared photocatalysts were closely associated with the characteristics of one-dimensional nanostructured TiO2 nanotubes for TNTUCFs and spherical shapes for TiO2-coated UCF (TUCF). The photocatalytic activities of BTEX obtained from TNTUCFs were higher than those obtained from a reference photocatalyst, TUCF). Specifically, the average degradation efficiencies of BTEX observed for TNTUCF-10 were 81%, 97%, 99%, and 99%, respectively, while those observed for TUCF were 14%, 42%, 52%, and 79%, respectively. Moreover, the photocatalytic activities obtained for TNTUCFs suggested that the degradation efficiencies of BTEX varied with changes in TiO2 loadings, allowing for the optimization of TiO2 loading. Another important finding was that input concentrations and air flow rates could be important parameters for the treatment of BTEX, which should be considered for the optimization of TNTUCFs application. Taken together, TNTUCFs can be applied to effectively degrade sub-ppm levels of gas-phase aromatic pollutants through the optimization of operational conditions.

Simplified sonochemical preparation of titania embedded with selected metals for purification of benzene and toluene

Titania (TiO2) photocatalysts, each embedded with one of six metals (Ag, Ce, Co, Fe, Mg, and Mn), were prepared using a simplified ultrasonic process. The characteristics of the prepared metal-embedded TiO2 (metal-TiO2) were determined using transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, photoluminescence emission spectroscopy, UV-visible spectroscopy, and nitrogen adsorption-desorption. Except for Co-TiO2, the metal-TiO2 photocatalysts showed improved performance for the decomposition of gaseous benzene and toluene, which are two of the most problematic indoor air pollutants that can cause a variety of adverse health symptoms, under daylight lamp irradiation. Photocatalytic activity was greatest for the Mg-TiO2 sample, followed by, in order, the Ag-TiO2, Ce-TiO2, Fe-TiO2, Mn-TiO2, unmodified TiO2, and Co-TiO2 samples. Although Mg-TiO2 showed the least redshift in its light absorption and the highest electron-hole recombination rate among the metal-TiO2 photocatalysts, it yielded the highest photocatalytic activity, likely because of its increased adsorption capacity and anatase composition. The degradation of benzene and toluene over Mg-TiO2 improved as ultrasound treatment amplitude increased from 20 to 37 μm, then decreased gradually as amplitude was further increased to 49 μm. Degradation efficiency also improved as ultrasound operation time increased from 30 to 60 min, then decreased gradually as amplitude was further increased to 90 min. Overall, this process could be utilized to prepare metal-TiO2 photocatalysts with improved performance for the decomposition of gas phase pollutants under daylight lamp irradiation.

Iron-impregnated titania composites for the decomposition of low-concentration aromatic organic pollutants under UV and visible light irradiation

Abstract Fe-TiO2 photocatalysts with different ratios of Fe to Ti were prepared by a sol-gel process using tetra-n-butyl titanium and iron(III) nitrate as Ti and Fe sources, respectively. The photocatalytic function of the prepared composites was examined for the decomposition of low-concentration (0.1 ppm) airborne benzene, toluene, ethyl benzene, and o-xylene (BTEX). The Fe-TiO2 composites were characterized by energy dispersive X-ray spectroscopy, X-ray diffraction, UV-visible spectroscopy, and Fourier transform infrared spectroscopy. The time-series ratios of outlet to inlet concentrations of toluene, ethyl benzene, and o-xylene target chemicals, as determined by the Fe-TiO2 composites under visible light exposure, were lower than or similar to those of the reference TiO2 photocatalyst. Moreover, the time-series ratios of outlet to inlet concentrations of the three compounds, as determined for the Fe-TiO2 composites, increased as the ratio of Fe to Ti increased from 0.001 to 0.010. In contrast, under UV exposure, the time-series ratios of outlet to inlet concentrations of BTEX, determined for the Fe-TiO2 composites, were similar to or higher than those obtained from the reference TiO2 photocatalyst. Fe-TiO2 composites with an optimal Fe to Ti ratio could effectively be applied for the purification of low-concentration aromatic organic pollutants.