Sang Kyoo Lim

Titania nanofibers as a photo-antenna for dye-sensitized solar hydrogen

Directionally grown TiO(2) nano-architectures can serve as effective platforms for photogenerated charges to flow vectorially through the architecture framework, promising an unexpectedly high efficiency. This study demonstrates that directionally aligned TiO(2) nanofibers (TNF) obtained via a simple rearrangement of randomly scattered TiO(2) nanoparticles (TNP) exhibit significantly enhanced activity in terms of hydrogen production from water under visible light (λ > 420 nm). It has been found that Eosin Y (EY)-sensitized hydrogen production with TNF is greater than those with TNP and commercial TiO(2) samples (Degussa P25 and Hombikat UV-100) by a factor of 7 and >140, respectively, in the presence of triethanolamine (TEOA) as an electron donor. The annealing of TNF at elevated temperatures reduces the amount of H(2) produced and changes various physicochemical properties. Attempts have been made to find correlation factors between hydrogen production and reaction parameters (e.g., pH-dependent EY adsorption, surface area, pore size, particle size, and anatase-to-rutile ratio), none of which have provided an apparent correlation. It was suggested that the interparticle electron transfer is facilitated when TiO(2) nanoparticles are physically interconnected, and TNF might work as a robust photo-antenna for efficiently collecting the photogenerated electrons. The photocurrent measurements in visible light-irradiated EY/TiO(2) suspensions indicate that the photocurrent of TNF is 50% higher than that of TNP, supporting the photo-antenna mechanism of TNF.

Effect of TiO2 Nanoparticle Modification on Ultraviolet Photodetection Properties of Al-Doped ZnO Nanowire Network

This study was conducted in order to observe the changes in the ultraviolet (UV) photodetection characteristic when TiO2 nanoparticles are modified on the surface of an aluminum-doped zinc oxide (AZO) nanowire in an AZO nanowire network with enhanced conductivity. According to the experiment results, the UV photosensitivity under a bias of 5 V was 52-fold in a bare AZO network, and it increased to 147-fold in the case when TiO2 nanoparticles were modified. The UV reset time decreased from 9 to 5 s. The AZO nanowire onto which TiO2 nanoparticles were adsorbed showed an approximately 2-fold faster response time and an approximately 3-fold higher UV photosensitivity than the existing bare AZO nanowire. The faster UV photoresponse time of the AZO nanowire network with adsorbed TiO2 nanoparticles is because the adsorbed TiO2 nanoparticles serve as recombination sites for electrons excited by UV illumination. In addition, with enhanced UV photosensitivity, adsorbed TiO2 nanoparticles serve as electron donation sites that provide additional electrons to the AZO nanowire when UV light is turned on.

Formation of Macropore and Three-Dimensional Nanorod Array in p-Type Silicon

We carried out a study on the change in pore wall thickness depending on the current density in p-type silicon. We attempted the formation of a uniform macropore or nanorod array with a high aspect ratio in p-type silicon by electrochemical etching through the optimization of the hydrogen fluoride (HF)/organic electrolyte composition and the design of the mask pattern. The electrochemical etching of p-type silicon in the HF: dimethylsulfoxide (DMSO): deionized (DI) water = 1:5:5 electrolyte can control the velocity of a reaction between an electrolyte and a hole necessary for the electrochemical etching of silicon through the mixing of the protic property of DI water and the aprotic property of DMSO. In this study, we fabricated a p-type silicon nanorod array of three-dimensional structures with an approximately 350 nm diameter from macroporous Si by applying two-step currents (40 mA, 200 s + 38 mA, 1600 s) to a 1.8 cm2 circular area using an optimized HF: DMSO: DI water = 1:5:5 electrolyte composition.

ZnO rods rooted on manifold carbon nanofiber paper as a scalable photocatalyst platform: the effects of ZnO morphology

Crystalline ZnO rods rooted on manifold carbon nanofiber (CNF) paper were synthesized via electrodeposition of ZnO onto electrospun CNF paper (∼300 μm thick) followed by oxidative annealing. The morphology of the ZnO deposited on the conductive CNF paper can be tailored to be polycrystalline rods with convex-shaped ends at a high Zn2+ precursor concentration (0.5 mM) upon annealing (denoted CZ-a-0.5, where “a” refers to annealing), whereas the sample electrodeposited at a low Zn2+ precursor concentration (0.25 mM) results in single crystalline rods with concave-shaped ends (denoted CZ-a-0.25). In order to systematically examine the photocatalytic activity, the annealed and non-annealed CNF/ZnO samples (CZ-a and CZ, respectively) were compared for the oxidation of phenol (one-electron transfer reaction), the production of H2 via water splitting and H2O2 production via oxygen reduction (both two-electron transfer reactions). Irrespective of the type of reaction, the CZ-a samples exhibit superior photocatalytic activities than the CZ samples in the following order: CZ-a-0.25 > CZ-a-0.5 > CZ-0.5 > CZ-0.25. The observed activity order is consistent with the trend observed in the XRD intensity ratio between the (100) and (002) planes (i.e., I100/I002 ratio) of the corresponding samples. The time-resolved photoluminescence decay spectra further reveal that the average lifetime of charge carriers is the shortest for CZ-a-0.25, followed by CZ-a-0.5, CZ-0.5 and CZ-0.25, which is consistent with the trends in the I100/I002 ratio and the photocatalytic activity. The growth mechanism of the samples and the key factors determining the photocatalytic activity are discussed. Finally, the detailed surface characterization of the samples is described.

Metal nanoparticles decorated PET/PET-TiO2 bi-component filaments by photocatalytic deposition

Gold, silver, and platinum nanoparticles were immobilized on the surface of TiO2 in the sheath part of bi-component filaments. The processes involved include the spinning process used to prepare polyethylene terephthalate (PET)/PET-TiO2 bi-component filaments and the photocatalytic deposition process of gold, silver and platinum nanoparticles. The core part and the sheath part consist of virgin PET and 4 wt.% of TiO2 compounded PET, respectively. The sheath: core ratio of the filament was 50:50. For the photo-deposition of metal nanoparticles, adsorption of the metal ions on the surface of the fabrics was performed by immersing them in AgNO3, HAuCl4, and H2PtCl6 aqueous solutions, with simultaneous addition of methanol as a sacrificial agent. Photo-deposition was then carried out under UV light with an irradiation time of 60 seconds. The structural and antibacterial properties of the bi-component filaments were characterized. The nano-sized noble metal particles in a polka dot form were observed around the surface of the TiO2 particles in sheath region of bi-component filaments after photocatalytic deposition. Ag, Au, and Pt metal photo-deposited fabrics showed excellent antimicrobial effect against the two types of bacteria Staphylococcus aureus and Klebsiella pneumoniae under dark conditions.

Antimicrobial Properties of PET/(Nano-TiO 2 ) Composite Films Prepared by Photocatalytic Deposition of Silver

Nanocomposite films of poly(ethylene terephthalate)(PET) and nano titania() were prepared by melt compounding with a twin-screw extruder followed by hot pressing for the purpose of investigating antibacterial activity. FE-SEM, EDS and XRD measurements confirmed that nano was successfully dispersed at the level of individual particles in the PET matrix. Silver was introduced through photocatalytic reduction by nano under UV (254 nm) irradiation to the nanocomposite films after being immersed in aqueous solution (100 ppm Ag ion). Even at 1 wt% of content, the nanocomposite with silver photodeposition exhibited strong antimicrobial activity against Klebsiella pneumoniae and Staphylococcus aureus in measurement by shaking flask method.

Preparation of hydrophobic fabric using cross-linked fluorinated poly methacryalte copolymer nanobeads

In this study, we synthesized cross-linked poly methyl methacrylate beads and cross-linked fluorinated poly methacryalte copolymer (F-cPMMA) beads by the dispersion polymerization method with methyl methacrylate monomer, ethylene glycol dimethacrylate, and 2,2,2-trifuloroethyl methacrylate. The size of cross-linked PMMA and F-cPMMA beads was about 100 nm. Then we developed a new geometrical high-hydrophobic film by embedding the F-cPMMA nanobeads on polyurethane (PU) film. The PU film containing fluorinated poly methacryalte copolymer beads showed a greater hydrophobic property than the non-fluorinated one in the range of 1–10 wt.%. For the purpose of industrial application of the PU films, we applied 0.1–1 wt.% of beads on the fabric by the laminating method. The PU film containing 1 wt.% of fluorinated poly methacryalte copolymer beads, which was laminated onto nylon fabric, showed the best performance of hydrophobic property (water contact angle, 79°) and moisture vapor transmission rate (8797 g·m–2·24 h).

Colorimetric hydrogen gas sensor based on PdO/metal oxides hybrid nanoparticles

We have synthesized new colorimetric hydrogen-sensing materials, PdO/metal oxide hybrid nanoparticles, in which palladium oxide was loaded upon surface of substrate materials via an acid-base reaction between a H2PdCl4 solution and substrate materials, ZnO, MgO, TiO2, and SiO2 respectively at 25 °C. The colorimetric hydrogen gas sensing properties of all the samples, PdO/ZnO, PdO/MgO, PdO/TiO2 and PdO/SiO2, were characterized and compared in order to investigate how hydrogen gas sensitivity would be affected by surface property of substrate materials. It was confirmed that the amount of the loaded PdO, which was thought to be closely related with the colorimetric hydrogen sensitivity, was quite different according to the substrate materials and was increased with increasing of the basicity of substrate materials (ZnO > MgO > TiO2 > SiO2). Consequently, among the PdO/metal oxide hybrid nanoparticles, the largest amount of PdO was observed to be loaded on ZnO substrate nanoparticles due to its highest basicity. The best colorimetric hydrogen gas sensing properties (color difference, ΔE = 71.57) was observed in PdO/ZnO hybrid nanoparticles, showing the most prominent color change from brown to black, when the sample was exposed to hydrogen gas of 4 vol% balanced with nitrogen for 2 min.

Anti-bacterial activity of tetragonal and cross-pillar-shaped polyester/TiO2 filaments with photo-deposited silver and platinum nanoparticles

In this work, we tried to enhance anti-bacterial activity of fabric fibers by controlling the shape of filaments, such as tetragonal and cross-pillar, which led to an increase of the surface portion of filaments. With this purpose, silver and platinum nanoparticles were immobilized on the surface of TiO2 nanoparticles within tetragonal and cross-pillar-shaped polyester (PET) filaments. The process consists of preparing 4 wt.% of TiO2 compounding PET chips, melt-spinning of them and photo catalytic deposition of nanoparticles in sequence. To obtain tetragonal and cross-pillar-shaped morphologies of filaments, two different nozzles were used in the melt-spinning process. For the photo-deposition of metal nanoparticles, adsorption of the metal ions on the surface of the filaments was performed by immersing them in AgNO3 and H2PtCl6 aqueous solutions, respectively, with simultaneous addition of methanol as a sacrificial agent. Photo-deposition was then carried out under ultraviolet light with an irradiation time of 300 s. The structural and antimicrobial properties of the tetragonal and cross-pillar-shaped PET/TiO2 filaments with noble metal loaded were systematically characterized. Ag and Pt metal photo-deposited filaments showed excellent antimicrobial effect against the two types of bacteria, Staphylococcus aureus and Klebsiella pneumonia, under the dark condition.

Synthesis and Characterization of Poly(Ethylene Terephthalate) /Al2O3 Nanocomposites

Poly (ethylene terephthalate)(PET)/Al2O3 nanocomposites via in situ polymerization were studied. The nanoparticle loading was varied from 0.3 to 1 wt.%. From the DSC results, no significant differences were recorded for melting temperatures. However, simple added PET/Al2O3 nanocomposites slightly changed to the lower melting temperature. Morphology of the nanocomposites has been examined by SEM. From the SEM results revealed that dispersed Al2O3 nanoparticles in the EG (ethylene glycol) during the polymerization can be well dispersed in PET matrix.