Se Woong Park

Selective positioning of organic dyes in a mesoporous inorganic oxide film

Although sequential adsorption of dyes in a single TiO(2) electrode is ideal to extend the range of light absorption in dye-sensitized solar cells, high-temperature processing has so far limited its application. We report a method for selective positioning of organic dye molecules with different absorption ranges in a mesoporous TiO(2) film by mimicking the concept of the stationary phase and the mobile phase in column chromatography, where polystyrene-filled mesoporous TiO(2) film is explored for use as a stationary phase and a Brønsted-base-containing polymer solution is developed for use as a mobile phase for selective desorption of the adsorbed dye. By controlling the desorption and adsorption depth, yellow, red and green dyes were vertically aligned within a TiO(2) film, which is confirmed by an electron probe micro-analyser. The external quantum efficiency (EQE) spectrum from a solar cell with three selectively positioned dyes reveals the EQE characteristics of each single-dye cell.

Electrospun chitosan nanofibers with controlled levels of silver nanoparticles. Preparation, characterization and antibacterial activity

The ideal wound dressing would have properties that allow for absorption of exudates, and inhibition of microorganism for wound protection. In this study, we utilized an electrospinning (ELSP) technique to design a novel wound dressing. Chitosan (CTS) nanofibers containing various ratios of silver nanoparticles (AgNPs) were obtained. AgNPs were generated directly in the CTS solution by using a chemical reduction method. The formation and presence of AgNPs in the CTS/AgNPs composite was confirmed by x-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV) and thermogravimetric analysis (TGA). The electrospun CTS/AgNPs nanofibers were characterized morphologically by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). These nanofibers were subsequently tested to evaluate their antibacterial activity against gram-negative Pseudomonas aeruginosa (P. aeruginosa) and gram-positive Methicillin-resistant Staphylococcus aureus (MRSA). Results of this antibacterial testing suggest that CTS/AgNPs nanofibers may be effective in topical antibacterial treatment in wound care.

Rapid Dye Adsorption via Surface Modification of TiO2 Photoanodes for Dye-Sensitized Solar Cells

A facile method for increasing the reaction rate of dye adsorption, which is the most time-consuming step in the production of dye-sensitized solar cells (DSSCs), was developed. Treatment of a TiO2 photoanode with aqueous nitric acid solution (pH 1) remarkably reduced the reaction time required to anchor a carboxylate anion of the dye onto the TiO2 nanoparticle surface. After optimization of the reaction conditions, the dye adsorption process became 18 times faster than that of the conventional adsorption method. We studied the influence of the nitric acid treatment on the properties of TiO2 nanostructures, binding modes of the dye, and adsorption kinetics, and found that the reaction rate improved via the synergistic effects of the following: (1) electrostatic attraction between the positively charged TiO2 surface and ruthenium anion increases the collision frequency between the adsorbent and the anchoring group of the dye; (2) the weak anchoring affinity of NO3(-) in nitric acid with metal oxides enables the rapid coordination of an anionic dye with the metal oxide; and (3) sufficient acidity of the nitric acid solution effectively increases the positive charge density on the TiO2 surface without degrading or transforming the TiO2 nanostructure. These results demonstrate the developed method is effective for reducing the overall fabrication time without sacrificing the performance and long-term stability of DSSCs.

Expanding the spectral response of a dye-sensitized solar cell by applying a selective positioning method

We have developed a facile method to position different dyes (N719 and N749) sequentially in a mesoporous TiO(2) layer through selective desorption and adsorption processes. From the selective removal of the only upper part of the first adsorbed dye, double-layered dye-sensitized solar cells have been successfully achieved without any damage to the dye. From the incident photon-to-current conversion efficiency (IPCE) measurement, the multi-layered dye-sensitized solar cell (MDSSC) was found to exhibit an expanded spectral response for the solar spectrum while maintaining the maximum IPCE value of each single-layered cell. The highest photocurrent density, 19.3 mA cm( - 2), was obtained from the MDSSC utilizing an N719/N749 bi-layered mesoporous TiO(2) film. The power conversion efficiency of 9.8% was achieved from the MDSSC, which is higher than that of single N719-or N749-based cells and cocktail-dyed (a mixture of N719 and N749) cells.

Generation of functionalized polymer nanolayer on implant surface via initiated chemical vapor deposition (iCVD)

Initiated chemical vapor deposition (iCVD) was utilized to generate a 200nm thick, uniform, functionalized polymer nanolayer comprised of glycidyl methacrylate (GMA) on the surface of titanium implants as a means to improve cellular attachment. Dot-patterned GMA-coated specimens were prepared as well as fully coated specimens. In vitro cellular responses, including cell morphology, protein adsorption, cell proliferation assays, alkaline phosphate activity (ALP) assays, and calcium deposition assays were studied using adipose derived stem cells. The mechanical stability of the thin film was investigated by XPS and FE-SEM analysis of the GMA-coated implant after implantation to an extracted bone from a pig. The GMA-coated specimens displayed increased protein adsorption, higher alkaline phosphatase activities, and higher calcium deposition as compared to control sample with no cytotoxicity. Additionally, no defect was observed in the test of mechanical stability. Notably, dot-patterned GMA-coated samples displayed higher alkaline phosphatase activities than others. Functionalized polymer nanolayer deposition via iCVD is a flexible and robust technique capable of mass production of biocompatible layers. These properties make this technique very suitable for implant applications in a variety of ways.

Influence of solvent and bridge structure in alkylthio-substituted triphenylamine dyes on the photovoltaic properties of dye-sensitized solar cells.

Three new triphenylamine dyes that contain alkylthio-substituted thiophenes with a low bandgap as a π-conjugated bridge unit were designed and synthesized for organic dye-sensitized solar cells (DSSCs). The effects of the structural differences in terms of the position, number, and shape of the alkylthio substituents in the thiophene bridge on the photophysical properties of the dye and the photovoltaic performance of the DSSC were investigated. The introduction of an alkylthio substituent at the 3-position of thiophene led to a decrease in the degree of redshift and the value of the molar extinction coefficient of the charge-transfer band, and the substituent with a bridged structure led to a larger redshift than that of the open-chain structure. The introduction of bulky and hydrophobic side chains decreased the short-circuit photocurrent (J(sc)), which was caused by the reduced amount of dye adsorbed on TiO(2). This resulted in a decrease in the overall conversion efficiency (η), even though it could improve the open-circuit voltage (V(oc)) due to the retardation of charge recombination. Furthermore, the change in solvents for TiO(2) sensitization had a critical effect on the performance of the resulting DSSCs due to the different amounts of dye adsorbed. Based on the optimized dye bath and molecular structure, the ethylene dithio-substituted dye (ATT3) showed a prominent solar-to-electricity conversion efficiency of 5.20%.

Biofunctionalized titanium with anti-fouling resistance by grafting thermo-responsive polymer brushes for the prevention of peri-implantitis

In the last decade, titanium has been effectively used in the dental field for oral surgery as an implant material. However, disinfected Ti can be easily re-infected by the surrounding environment. Thus, a novel anti-fouling treatment for Ti implants is currently necessary. In this study, we designed an anti-fouling surface comprised of poly N-isopropylacylamide (PIPAAM) grafted Ti by introducing poly glycidyl methacrylate (pGMA) coating via an initiated chemical vapor deposition (iCVD) system to prevent bacterial infection. The results indicate that pristine Ti was well coated with pGMA with a film thickness of approximately 60 nm and uniformly grafted with PIPAAM. The bacteria were effectively detached after rinsing with a buffer solution at room temperature, while hADSCs were well attached on the surface treated Ti surface at oral temperature. All tests clearly confirm that our strategy may be a useful means of imparting anti-fouling characteristics to Ti in order to prevent bacterial adhesion and resultant peri-implantitis.