Ji Sun Im

The effect of carbon nanotubes on drug delivery in an electro-sensitive transdermal drug delivery system

An electro-sensitive transdermal drug delivery system was prepared by the electrospinning method to control drug release. A semi-interpenetrating polymer network was prepared as the matrix with polyethylene oxide and pentaerythritol triacrylate polymers. Multi-walled carbon nanotubes were used as an additive to increase the electrical sensitivity. The release experiment was carried out under different electric voltage conditions. Carbon nanotubes were observed in the middle of the electrospun fibers by SEM and TEM. The amount of released drug was effectively increased with higher applied electric voltages. These results were attributed to the excellent electrical conductivity of the carbon additive. The suggested mechanism of drug release involves polyethylene oxide of the semi-interpenetrating polymer network being dissolved under the effects of carbon nanotubes, thereby releasing the drug. The effects of the electro-sensitive transdermal drug delivery system were enhanced by the carbon nanotubes.

Fluorination of electrospun hydrogel fibers for a controlled release drug delivery system

Electrospinning and fluorination were carried out in order to obtain a controlled release drug delivery system to solve the problem of both an initial burst of the drug and a limited release time. Poly(vinyl alcohol) was electrospun with Procion Blue as a model drug and heat treated in order to obtain cross-linked hydrogel fibers. Two different kinds of electrospun fibers of thin and thick diameters were obtained by controlling the electrospinning conditions. Thin fibers offer more available sites than thick fibers for surface modification during fluorination. Fluorination was conducted to control the release period by introducing hydrophobic functional groups on the surface of fibers. With an increase in the reaction pressure of the fluorine gas hydrophobic C-F and C-F(2) bonds were more effectively introduced. Over-fluorination of the fibers at higher reaction pressures of fluorine gas led to the introduction of C-F(2) bonds, which made the surface of the fibers hydrophobic and resulted in a decrease in their swelling potential. When C-F bonds were generated the initial drug burst decreased dramatically and total release time increased significantly, by a factor of approximately 6.7 times.

Carbon Doping of TiO 2 for Visible Light Photo Catalysis - A review

The field of photocatalysis is one of the fastest growing areas both in research and commercial fields. Titanium dioxide is the most investigated semi-conductor material for the photocatalysis applications. Research to achieve TiO2 visible light activation has drawn enormous attentions because of its potential to use solar light. This paper reviews the attempts made to extend its visible photocatalytic activity by carbon doping. Various approaches adopted to incorporate carbon to TiO2 are summarized highlighting the major developments in this active research field. Theoretical features on carbon doping are also presented. Future scenario in the rapidly developing and exciting area is outlined for practical applications with solar light. Keywords : Titania, Carbon doping, Solar light, Semi-conductor photocatalysis, Environmental applications

Improved capacitance characteristics of electrospun ACFs by pore size control and vanadium catalyst

Nano-sized carbon fibers were prepared by using electrospinning, and their electrochemical properties were investigated as a possible electrode material for use as an electric double-layer capacitor (EDLC). To improve the electrode capacitance of EDLC, we implemented a three-step optimization. First, metal catalyst was introduced into the carbon fibers due to the excellent conductivity of metal. Vanadium pentoxide was used because it could be converted to vanadium for improved conductivity as the pore structure develops during the carbonization step. Vanadium catalyst was well dispersed in the carbon fibers, improving the capacitance of the electrode. Second, pore-size development was manipulated to obtain small mesopore sizes ranging from 2 to 5 nm. Through chemical activation, carbon fibers with controlled pore sizes were prepared with a high specific surface and pore volume, and their pore structure was investigated by using a BET apparatus. Finally, polyacrylonitrile was used as a carbon precursor to enrich for nitrogen content in the final product because nitrogen is known to improve electrode capacitance. Ultimately, the electrospun activated carbon fibers containing vanadium show improved functionality in charge/discharge, cyclic voltammetry, and specific capacitance compared with other samples because of an optimal combination of vanadium, nitrogen, and fixed pore structures.

Improved photodegradation properties and kinetic models of a solar-light-responsive photocatalyst when incorporated into electrospun hydrogel fibers.

The capacity of a photocatalyst system to degrade water pollutants was optimized using solar-light-sensitive TiO(2) and the swelling behavior of a hydrogel. TiO(2) synthesized via a sol-gel process was modified by multielement doping to change its solar-light-responsive properties. A hydrogel was used for the rapid absorption of both anionic and cationic water pollutants. TiO(2) particles were immobilized in/on hydrogel fibers by an electrospinning method for the easy recovery of TiO(2), and the ability of the hydrogel/TiO(2) composite to degrade dye molecules was studied. The TiO(2) particles were observed to have maintained their original anatase-type crystallinity in/on the electrospun hydrogel fibers. The dye degradation capacity of the hydrogel/TiO(2) composite was investigated using both anionic and cationic dyes under sunlight. Two mechanisms were suggested by which the hydrogel/TiO(2) composite can remove dye particles from the water: (1) the absorption of dyes by the hydrogel and (2) the degradation of the dye by the TiO(2) in the hydrogel. Both of these mechanisms were investigated in this study. We found that the dye was effectively absorbed by the hydrogel fibers as demonstrated by the swelling behavior of the hydrogel and the nano-size effects. The dye was then introduced to the TiO(2) particles for degradation.

Investigation of multielemental catalysts based on decreasing the band gap of titania for enhanced visible light photocatalysis

Novel photocatalysts based on carbon-, nitrogen-, boron-, and fluorine-codoped TiO(2) have been successfully prepared from a single precursor in order to obtain titania with a decreased band gap. Three kinds of catalytic mechanisms are suggested. Initially, boron acts as an initiator to lead the movement of electrons in the valence band, and then nitrogen and fluorine provide electrons in the valence band. Eventually, electrons in the valence band can travel to the conduction band through a carbon bridge. The effect of the calcination temperature was also evaluated for the photodegradation of dyes. Excellent photoactivity results were obtained in the case of samples treated at 400 degrees C and the phase transformation from anatase to rutile did not occur up to calcination temperatures of 800 degrees C. The photodegradation followed the pseudo-first-order kinetic expression. The exceptional visible photoactivities of the prepared catalysts can be predominantly attributed to the effects of doping on titania, reducing its band gap.

Effects of fluorination modification on pore size controlled electrospun activated carbon fibers for high capacity methane storage

Electrospun carbon fibers were prepared as a methane storage medium. Chemical activation was carried out using potassium carbonate to develop the pore structure, which can provide sites for the uptake of methane, and then fluorination surface modification was conducted to enhance the capacity of storage. Chemical activation provided a highly microporous structure, which is beneficial for methane storage, with a high specific surface area greater than 2500m(2)/g. The pore size distribution showed that the prepared samples have pore sizes in the range of 0.7-1.6nm. The effect of fluorination surface modification was also investigated. The functional groups, which were confirmed by XPS analysis, played an important role in guiding methane gas into the carbon silt pores via the attractive force felt by the electrons in the methane molecules due to the high electronegativity of fluorine. Eventually, the methane uptake increased up to 18.1wt.% by the synergetic effects of the highly developed micropore structure and the guiding of methane to carbon pores by fluorine.

Influence of oxyfluorination on activated carbon nanofibers for CO 2 storage

The oxyfluorination effects of activated carbon nanofibers (OFACFs) were investigated for CO2 storage. Electrospun CFs were prepared from a polyacrylonitrile/N,N-dimethylformamide solution via electrospinning and heat treatment. The electrospun CFs were chemically activated in order to generate the pore structure, and then oxyfluorination was used to modify the surface. The samples were labeled CF (electrospun CF), ACF (activated CF), OFACF-1 (O2:F2 = 7:3), OFACF-2 (O2:F2 = 5:5) and OFACF-3 (O2:F2 = 3:7). The functional group of OFACFs was investigated using X-ray photoelectron spectroscopy analysis. The C-F bonds formed on surface of ACFs. The intensities of the C-O peaks increased after oxyfluorination and increased the oxygen content in the reaction gas. The specific surface area, pore volume and pore size of OFACFs were calculated by the Brunauer–Emmett–Teller and density functional theory equation. Through the N2 adsorption isotherm, the specific surface area and pore volume slightly decreased as a result of oxyfluorination treatment. Neverthe less, the CO2 adsorption efficiency of oxyfluorinated ACF improved around 16 wt% due to the semi-ionic interaction effect of surface modificated oxygen functional groups and CO 2 molecules.

X-ray Photoelectron Spectroscopic Analysis of Modified MWCNT and Dynamic Mechanical Properties of E-beam Cured Epoxy Resins with the MWCNT

The surface treatment effects of reinforcement filler were investigated based on the dynamic mechanical properties of mutiwalled carbon nanotubes (MWCNTs)/epoxy composites. The as-received MWCNTs(R-MWCNTs) were chemically modified by direct oxyfluorination method to improve the dispersibility and adhesiveness with epoxy resins in composite system. In order to investigate the induced functional groups on MWCNTs during oxyfluorination, X-ray photoelectron spectroscopy was used. The thermo-mechanical property of MWCNTs/epoxy composite was also measured based on effects of oxyfluorination treatment of MWCNTs. The storage modulus of MWCNTs/epoxy composite was enhanced about 1.27 times through oxyfluorination of MWCNTs fillers at 25 C. The storage modulus of oxyfluorinated MWCNTs (OF73-MWCNTs) reinforced epoxy composite was much higher than that of R-MWCNTs/epoxy composite. It revealed that oxygen content led to the efficient carbon-fluorine covalent bonding during oxyfluorination. These functional groups on surface modified MWCNTs induced by oxyfluorination strikingly made an important role for the reinforced epoxy composite.

Graphene-based carbon materials for electrochemical energy storage

Because of their unique 2D structure and numerous fascinating properties, graphene-based materials have attracted particular attention for their potential applications in energy storage devices. In this review paper, we focus on the latest work regarding the development of electrode materials for batteries and supercapacitors from graphene and graphene-based carbon materials. To begin, the advantages of graphene as an electrode material and the existing problems facing its use in this application will be discussed. The next several sections deal with three different methods for improving the energy storage performance of graphene: the restacking of the nanosheets, the doping of graphene with other elements, and the creation of defects on graphene planes. State-of-the-art work is reviewed. Finally, the prospects and further developments in the field of graphene-based materials for electrochemical energy storage are discussed.