Seungdu Kim

Compliment Graphene Oxide Coating on Silk Fiber Surface via Electrostatic Force for Capacitive Humidity Sensor Applications

Cylindrical silk fiber (SF) was coated with Graphene oxide (GO) for capacitive humidity sensor applications. Negatively charged GO in the solution was attracted to the positively charged SF surface via electrostatic force without any help from adhesive intermediates. The magnitude of the positively charged SF surface was controlled through the static electricity charges created on the SF surface. The GO coating ability on the SF improved as the SF’s positive charge increased. The GO-coated SFs at various conditions were characterized using an optical microscope, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and LCR meter. Unlike the intact SF, the GO-coated SF showed clear response-recovery behavior and well-behaved repeatability when it was exposed to 20% relative humidity (RH) and 90% RH alternatively in a capacitive mode. This approach allows humidity sensors to take advantage of GO’s excellent sensing properties and SF’s flexibility, expediting the production of flexible, low power consumption devices at relatively low costs.

A Gallium Oxide-Graphene Oxide Hybrid Composite for Enhanced Photocatalytic Reaction

Hybrid composites (HCs) made up of gallium oxide (GaO) and graphene oxide (GO) were investigated with the intent of enhancing a photocatalytic reaction under ultraviolet (UV) radiation. The material properties of both GaO and GO were preserved, even after the formation of the HCs. The incorporation of the GO into the GaO significantly enhanced the photocatalytic reaction, as indicated by the amount of methylene blue (MB) degradation. The improvements in the reaction were discussed in terms of increased surface area and the retarded recombination of generated charged carriers.

High-efficiency exfoliation of large-area mono-layer graphene oxide with controlled dimension

In this work, we introduce a novel and facile method of exfoliating large-area, single-layer graphene oxide using a shearing stress. The shearing stress reactor consists of two concentric cylinders, where the inner cylinder rotates at controlled speed while the outer cylinder is kept stationary. We found that the formation of Taylor vortex flow with shearing stress can effectively exfoliate the graphite oxide, resulting in large-area single- or few-layer graphene oxide (GO) platelets with high yields (>90%) within 60u2009min of reaction time. Moreover, the lateral size of exfoliated GO sheets was readily tunable by simply controlling the rotational speed of the reactor and reaction time. Our approach for high-efficiency exfoliation of GO with controlled dimension may find its utility in numerous industrial applications including energy storage, conducting composite, electronic device, and supporting frameworks of catalyst.

Toward Green Synthesis of Graphene Oxide Using Recycled Sulfuric Acid via Couette–Taylor Flow

Developing eco-friendly and cost-effective processes for the synthesis of graphene oxide (GO) is essential for its widespread industrial applications. In this work, we propose a green synthesis technique for GO production using recycled sulfuric acid and filter-processed oxidized natural graphite obtained from a Couette–Taylor flow reactor. The viscosity of reactant mixtures processed from Couette–Taylor flow was considerably lower (∼200 cP at 25 °C) than that of those from Hummers’ method, which enabled the simple filtration process. The filtered sulfuric acid can be recycled and reused for the repetitive GO synthesis with negligible differences in the as-synthesized GO qualities. This removal of sulfuric acid has great potential in lowering the overall GO production cost as the amount of water required during the fabrication process, which takes a great portion of the total production cost, can be dramatically reduced after such acid filtration. The proposed eco-friendly GO fabrication process is expected to promote the commercial application of graphene materials into industry shortly.

Preparation of Wrinkled Graphene Oxide Using Solution Method

Wrinkled graphene oxide (WGO) is formed using the solution method. The sub-μm-sized wrinkles are generated on the GO surface, with more wrinkles forming as the GaCl3 in the solution increases. The wrinkles are observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM) methods. The OH bonds connected to the GO surface are believed to cause the WGO, and these additional chemical bonds are detected via the Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. As with the wrinkled graphene, the wrinkled GO provides a much larger surface area and can expedite the production of advanced sensor and energy charging devices.

A self-corrugated surface of graphene oxide to enhance sensitivity and responsibility for various graphene oxide applications

P is a common chronic inflammatory skin disease, characterized by abnormal differentiation and proliferation of keratinocytes, angiogenesis and infiltration of inflammatory cells that secrete Th1 and Th17 associated cytokines in the skin lesion, such as TNF-α, IL-17 and IL-20. Although mRNAs that encode cytokines are short-lived mRNAs in eukaryotes, the premRNAs, which contain AU-Rich Elements (AREs) in their 3’-untranslated regions, are recognized and stabilized by Human Antigen R (HuR), an RNA-binding protein, for post-transcription. Previous studies have suggested that HuR is involved in the stabilization of mRNAs in the psoriatic skin. HuR binds to and regulates IL-20 mRNA and relocalizes to the cytoplasm of psoriatic keratinocytes. Furthermore, HuR can bind numerous transcripts involved in the pathogenesis of psoriasis. Therefore, HuR may be a potential therapeutic target for psoriasis. In the present study, we tested several novel oligopeptides that targeted the RNA binding site of HuR as therapeutic agents for psoriasis. A mouse model of imiquimod (IMQ)-induced psoriasis-like dermatitis was generated in BALB/c mice by daily topical application of IMQ cream on the ear from days 0 to 9. The mice were treated with oligopeptides from days 5 to 10. The pathological features of psoriasis were scored daily using the thickness gauge and clinical Psoriasis Area and Severity Index (PASI). We found that the oligopeptide JS-1 could significantly ameliorate psoriasis pathogenesis in a dose-dependent manner. The oligopeptide affected the HuR downstream signaling pathway. Collectively, this study may provide an alternative therapeutic strategy for psoriasis.W are looking forward to the simple but strong method to enhance a sensitivity and responsibility of Graphene Oxide (GO) by forming a self-corrugated surface of GO. The self-corrugated surface was formed by the reaction of graphene oxide with Gallium chloride. The surface of GO is more corrugated with the concentration of gallium hydroxide during the dry of GO powder. The graphene oxide structure was distorted due to the three hydroxyl groups of gallium hydroxide. The properties of wrinkled GO were investigated by scanning electron microscope, energy dispersive spectroscopy, X-ray diffraction, Raman spectroscopy and atomic force microscope, respectively. This self-corrugated GO have superior advantages over normal GO for a higher sensitivity and responsibility for sensor applications.I in developing alternative energy sources is increasing due to depletion of oil resources and global warming. Therefore, fuel cells, which are new energy conversion and storage devices with low emission of pollutants, are emerging as an alternative. The process of producing hydrogen as a fuel of fuel cells requires a great deal of cost. Therefore, researches are being studying on reforming catalysts for converting natural gas rich in reserved into hydrogen energy and for use in fuel cells. In general, a transition metal (Ni, Co, Cu) or a noble metal (Ru, Pd, Pt) is used as a methane steam reforming catalyst. The noble metal catalyst has excellent catalytic activity and resistance to carbon deposition. But it is becoming a stumbling block to commercialization due to expensive cost. Ni-based catalysts are less expensive than noble metals and have a simple manufacturing process, but the problem of degradation due to carbon deposition and grain growth is pointed out as a disadvantage. In this study, Ni/MgO composite reforming catalyst activated Ni catalyst by exsolution was manufactured to improve durability. The size and amount of precipitated Ni particles were controlled by the reducing temperature and time. The catalytic activity and durability of the catalysts prepared as above were evaluated. The conversion rate of methane was measured and evaluated in the temperature range of 250-750oC and methane:water vapor = 1:2 atmospheres with catalyst in fixed bed reactor. The microstructure and distribution of the produced catalyst were confirmed by XRD and SEM.A well-defined 3D bicontinuous network structure in nanoscopic regular array has attracted considerable attention because of its potential applications such as photonic crystals, meta-materials, energy devices and superconductor. In this study, the asymmetric polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) thin films on the two different substrate with highmolecular-weight were prepared to be exposed a neutral solvent vapor to generate a hexagonal (HEX) cylindrical morphology to long-range ordered Gyroid (GYR). The interfacial interaction by different substrate interaction induced the two distinct GYR, [211] and [111] planes, which were directed from cylinders, like the parallel and perpendicular orientation on the selective and neutral substrate, respectively. Moreover, we further performed coarse-grained simulations of a block copolymer model to provide the molecular mechanisms. Our results based on experiments and simulations suggest a simple route for the controlled and well-defined GYR structures.T Fe-Mo based double perovskites have attracted much attention in the field of materials science due to their multiverse fascinating physical properties which make them suitable candidates for several technological applications. In the present work, the Sr2-xNdxFeMoO6 (0.0≤x≤0.3) samples have been investigated for their structural, magnetic and magnetocaloric properties. Polycrystalline Sr2-xNdxFeMoO6 (0.0≤x≤0.3) samples were prepared by using the conventional solid-state reaction method. To achieve the target double perovskite phase and to minimize the undesirable secondary phases, the samples were sintered in a reducing atmosphere, created by a gas mixture of 5% H2/95% Ar. The structure, microstructure and phase purity of the samples were investigated by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD study confirmed the formation of tetragonal structure with Fm3m space group in all the synthesized samples. The Arrott plots and magnetization measurements showed a second order of ferromagnetic phase transition in all the fabricated samples. All the samples went through a paramagnetic to ferromagnetic phase transition at the Curie temperature (TC). A magnetocaloric effect was calculated in terms of isothermal magnetic entropy change. The value of the Relative Cooling Power (RCP) was observed to decrease with the increasing Nd content. A significant variation in the magnetocaloric properties of the samples was observed with the increasing Nd concentration. This investigation suggests that Sr2-xNdxFeMoO6 samples can be used as potential magnetic refrigerants for magnetocaloric applications.Purpose: Vorinostat (SAHA) is the most representative histone deacetylase inhibitor and a widely used anticancer drug, SAHA is applied in the treatment of hematological malignancies and most solid tumors. SAHA is challenging due to poor water solubility, low bioavailability and rapid elimination of drugs in vivo. In this study, we will prepare SAHA-Pluronic F127 Nanoparticles and investigated whether this could improve drug solubility, the effect of sustained release and inhibitory effect on cancer cells.C nanotube/polytetrafluoroethylene composite polymer targets (abbreviated as composite target) are proposed for use in the fabrication of plasma polymer fluorocarbon (abbreviated as PPFC) thin films using the mid-range frequency sputtering process. Large-area PPFC thin films were fabricated on roll-type PET substrate (polyethylene terephthalate, width 700 mm, thickness 100 μm) by a pilot-scale roll-to-roll sputtering system. The PPFC thin films exhibit an amorphous phase with a smooth surface and show a high water contact angle, optical transmittance and bendability. Mechanical property of PPFC thin films were studied using nanoindentation method and analyzed using X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. As the carbon nanotube concentration in the composite target increases, a carbon cross-linked structure was formed which enhanced the film hardness and the modulus of the PPFC thin films.T monolayer graphene-Ag nanoparticles hybrids system is fabricated as the electro-optical coordinated controlled substrate of Surface-Enhanced Raman Scattering (SERS) spectroscopy. Plasmon-exciton coupling interactions of this hybrid system are systemically investigated and applied in the field of surface catalytic reactions, manipulated by the electrooptical synergy. Our experimental results demonstrate that plasmon-exciton coupling interaction co-driven surface catalytic reactions can not only be controlled via plasmon-exciton coupling, but also by gate voltages and electric current (or bias voltage). The gate voltage can tune the Density of State (DOS) of hot electrons and electric current can make the hot electrons with higher kinetic energy. Both of them can significantly promote plasmon-exciton co-driven surface catalytic reaction. Our electro-optical device based on plasmon-exciton coupling can be potentially applied in the fields of sensor, catalysis, energy and environment.C thin film coatings present unique optical properties. In this study, structural, chemical bonding and optical properties of the thin films in relation to the composition of reaction gas via sputtering process were investigated. All the thin films exhibited a polycrystalline character with cubic fluorite-structure for cerium dioxide along (111), (200) and (222) orientations. XPS analysis revealed that two oxidation states of CeO2 and Ce2O3 are present in the films prepared at lower argon-oxygen flow ratios, whereas the films are totally oxidized into CeO2 as the aforementioned ratio increases. Optical parameters (α, ε1, ε2, n and k) derived from UV-Vis reflectance data indicate that the thin films have indirect optical band gaps in the range of 2.25-3.1 eV. Density Functional Theory (DFT+U) implemented in the Cambridge Serial Total Energy Package (CASTEP) has been employed to model some optical properties of CeO2 cluster at ground state. The simulated electronic Density of State (DOS) of the relaxed structure of CeO2 demonstrates a band gap, agrees well with the measured optical band gap. The experimental and calculated absorption coefficient (α), have analogous trends and to some extent a similar range of values in the wave length. All in all, our theoretical findings consistently support the experimental results.A neuronal growth underlies the prefrontal cortical (PFC) pathology of many neurodegenerative disorders. Current treatments are inadequate and commonly cause severe side effects. Importantly, conventional pharmacotherapy strategies have limited efficacy in treating PFC dis-regulation in neurodegenerative disorders. Electrical stimulation is a modern treatment method which can include electroconvulsive therapy, Deep-Brain Stimulation (DBS) and epidural stimulation, etc. Previous studied showed that the application of electrical stimulations promotes neuritis outgrowth resulted to inter neuronal networking. Wide range of metallic microelectrodes composed of gold, steel, platinum etc. have been previously utilized to perform electrical stimulation however, rigidity, incompatible mechanical properties, high initial impedance and low chargetransfer capacity limit their application. Graphene and its derivatives are an exciting class of materials, which are utilized in microelectrodes due to having excellent mechanical stability, electrical conductivity, biocompatibility, flexibility and ability to fabricate and scale up. This work develops three-dimensional (3D) flexible electrode composed of 3D printed Reduced Liquid Crystalline Graphene Oxide (rLCGO) on a polyurethane (PU) substrate. The flexible conducting electrode is used as Host Template for Human Neural Stem Cells (hNSCs) development during proliferation and differentiation. The application of electrical stimulation on hNSC using graphene/PU electrodes revealed promising results to improve neurites guidance through 3D printed lines and enhanced cell-cell communication and networking.P method is superior in the fabrication of ultra-high-temperature ceramics with the designable composition and structure, low sintering temperature and easy densifying process. In this study, three kinds of hybrid precursors for ZrC/C, ZrC/SiC and ZrC/SiBNC multinary ceramics were synthesized via radical polymerization. ZrC/C ceramic precursor was synthesized using Cp2Zr (CH2CH=CH2) as monomer ZrC/SiC or ZrC/SiBNC precursor is obtained by further adding low molecular weight polycarbosilane (LPCS) or polyborosilazane (LPBSZ) for copolymerization. By controlling the preparation procedure, these hybrid polymers can dissolve in most organic solvent, which is essential to construct CMCs in complicated shapes and large sizes. After pyrolyzing at 1400oC, the synthesized precursors can convert into Zr-containing multinary ceramics, with ZrC nanoparticles finely dispersed in C, SiC or SiBNC matrix depending on the hybrid polymer. All of the three Zr-containing multinary ceramics can remain finely phase distribution at 1600oC, especially for ZrC/C and ZrC/SiC multinary ceramics, which can have a stabilized microstructure and little mass loss (less than 1.5 wt%) up to 2000oC in inert atmosphere. As for ZrC/SiBNC, the introduction of ZrC phase can restrict the decomposition of SiBNC matrix at 1800oC. Although the SiC and SiBNC components improve the oxidation resistance of ZrC, the oxidation weight increase of these multinary ceramics at about 500oC is still up to 5%.W synthesized cationic, one-dimensional fibril assemblies formed from coil-sheet poly(L-lysine)-block-poly(Lthreonine) (PLL-b-PLT) block co-polypeptides as anticancer agents. The 1D fibril assemblies can efficiently interact with negatively charged cellular and mitochondrial membranes via electrostatic interactions, leading to cell necrosis through membrane lysis and apoptosis via the lytic effect of mitochondria. This effect is similar to that of one-dimensional drug carriers that exhibit enhanced cell penetration. Compared to free PLL chains, PLL-b-PLT fibril assemblies exhibited more selective cytotoxicity against cancer cells, lower hemolytic activity, higher membranolytic activity and a different apoptotic pathway, which may be due to differences in the peptide-membrane interactions. The fibril assemblies significantly inhibited tumor growth, improved survival and suppressed tumor metastasis to the lung in C57BL/6 mice bearing syngeneic LL2 lung tumors. An additive antitumor activity was also observed when the tumor bearing mice were treated with PLL-b-PLT in combination with the common chemotherapeutic drug cisplatin. Collectively, these results support the feasibility of using one-dimensional fibril assemblies as potential anticancer therapeutics.C Vapor Deposition (CVD) synthesis of Carbon Nanotubes (CNTs) was carried out in a self-assembled apparatus consisting of a hot tube furnace. Magnesium oxide supported iron catalyst samples, containing varied proportions of iron loadings were prepared using impregnation method and spread uniformly over copper strips. Ceramic boats were placed in the furnace so as to expose the catalyst-loaded copper strips to industrial gases such as nitrogen, methane and hydrogen. Usage of horizontal tube furnace instead of conventional CVD reactor not only reduced the cost but also added to the simplicity of the apparatus. Additionally, ceramic boats are at least 50% cheaper than the commonly used quartz boats. FESEM tests on the resultant samples revealed that the CNTs ranged between 19.78 nm and 30.36 nm in diameter, which validates the nanotube structures. We demonstrate that increasing the iron loading in the catalyst samples enhanced the probability of CNT formation: 0% iron loading yielded no CNTs, while increasing the loading to 6.5% gave way to formation of Multi-Walled Carbon Nanotubes (MWCNTs). This study opens up an economical route for the mass production of MWCNTs.H structured materials consist of a bimodal structure with a periodic or harmonic distribution of fine and coarse grains allowing optimum combination of high strength and ductility to be attained. Harmonic structured materials have potential in variety of applications, where high wear and corrosion resistance are required. Therefore, effect of harmonically distributed fine and coarse grains on the corrosion and wear behavior of a SUS304L austenitic stainless steel was studied and compared with a non-harmonic structured SUS304L and a conventional 304 stainless steel. The corrosion study was performed using linear, potentiodynamic and cyclic polarization techniques as well as salt fog exposure test for 30 days in 3.5% NaCl solution. Improved pitting corrosion resistance was found in case of the harmonic structured steel as compared to that of the non-harmonic and the conventional 304 stainless steel. Harmonically distributed fine grained structure, less porosity and higher fraction of passive α-FeOOH are attributed to the improvement in corrosion resistance of the harmonic structured steel. The wear study was performed using fretting wear tests at varying loads under ball-on-flat contact configuration. Coefficient of friction and wear volume were found to be minimum at intermediate normal load of 5 N, whereas maximum at 10 N in case of the harmonic stainless steel compared to other two steels. Harmonically distributed fine grained structure attributes to the higher wear rate of the harmonic structured steel because of hard and soft interaction of the ball with the harmonically distributed fine and coarse grains.A Solid Oxide Electrolyzer Cells (SOECs) is an electrochemical device for producing hydrogen by electrolysis water vapor at a high temperature. SOEC is that they can operate reversibly as solid oxide fuel cells, producing electricity with high efficiency by consuming stored hydrogen. It can also be used in next-generation power generation and storage systems that produce hydrogen using surplus power. SOEC have disadvantage to provide high temperature/high-pressure water vapor to the hydrogen electrode and since oxygen is released very quickly at the air electrode, deterioration of cells and stacks is larger than SOFC and it is a stumbling block to commercialization. In this study, the effect of operating conditions on hydrogen electrode performance and deterioration of SOEC was investigated. To improve the durability of the hydrogen electrode the material technology for inhibiting oxidation of Ni/YSZ was studied. The polarization resistance and J-V characteristics are evaluated in both SOFC/SOEC. The partial pressure of water vapor is changed to 10, 30 and 50%. The change of voltage is observed under the condition of applying current density of 0.1 mA/cm2 to the cell. And the durability of the cell is evaluated by measuring the voltage change according to the SOFC-SOEC switching operation. In addition, to suppress the oxidation of the hydrogen electrode (Ni/YSZ) in a steam atmosphere, a composite hydrogen electrode was fabricated by applying anticorrosion technology and the possibility of oxidation suppression is examined.Methods: Morphology was studied by Transmission Electron Microscopy (TEM). 5 μl of freshly prepared micellar dispersions were placed on Formvar and allowed to dry for 5 min. To unveil the usefulness of such formulations concerning physical stability, formulations FM1-FM5 and meloxicam were dissolved in enteric and gastric medium. After 1 and 2 h we quantified meloxicam in gastric medium and after 3 and 4 h we quantified meloxicam in enteric medium. Quantification was performed using an UV spectrophotometer and absorbance taken at 363 nm. To determine encapsulation efficiency, FM1-FM5 was quantified immediately after preparation. Later on, micellar suspensions were centrifuged at 3000 g for 15 min using Amicon® Ultra 4 Centrifugal filter units, the supernatant was quantified and EE calculated based on the following equation: Finally, cytotoxicity of formulations was assessed in Caco-2 cells by Alamar Blue assay, performing a screening of crescent concentrations (0.625%, 1.25%, 2.5%, 5% and 10%) for each formulation.G Multiforme (GBM) is an aggressive brain tumor with poor prognosis, mainly because standard treatment is not always effective enough in reaching tumor cells. Blood-Brain Barrier (BBB) is pointed out as one of great challenges in this field. Considering the negative charge of BBB surface and its restricted permeability to small compounds, positively-charged nanoparticles have been developed to facilitate the transport of drugs through the BBB. This work aimed at studying the interaction of different cationic surfactants used in Lipid Nanoparticle (LN) formulations with BBB, using atomistic simulations. Surfactants incorporating natural structural motifs, specifically serine, were chosen instead of the conventional synthetic surfactants, due to the lower cytotoxicity and higher biodegradability, thus being environmental friendly. Molecular dynamics simulations were performed on 4 systems containing different serine-based surfactants, two of them are monomeric (16SerTFA and 12SerTFA) and the other two are dimeric ((12ser)2CON12 and (12ser)2N5), in a fully hydrated palmitoyloleoylphosphatidylcholine (POPC) lipid model, intended to mimic cell membranes of both the BBB and tumor. The systems were evaluated in terms of effects induced by the surfactants in this type of membranes and rationalize the interactions at molecular level. The results showed an integration of all surfactants into the POPC membrane. Longer chain length surfactants tended to induce the highest membrane stabilization, as evidenced by 16serTFA. Conversely, the dimeric (12ser)2CON12 led to the greater disturbance in the membrane structure, probably due to bridging phenomena. This may anticipate a better BBB cross ability of LN containing (12ser)2CON12. Overall, this computational study suggests the viability of cationic serine-based surfactants as appealing compounds in LN formulations for targeted GBM therapy.

Impedance Spectroscopy Analysis and Equivalent Circuit Modeling of Graphene Oxide Solutions

The optical and electrical characteristics of a graphene oxide solution (GS) with different graphene oxide (GO) concentrations in de-ionized water are investigated via the electrochemical impedance spectroscopy (EIS) method. The measurement results produced by the EIS for the GS are represented with both Bode and Nyquist plots in a frequency range from 1 kHz to 10 MHz. Using these results, we develop an equivalent circuit model as a function of the GO concentration, representing the GS as a mixed circuit of two-dimensional (2D) GO dispersed in parallel in de-ionized (DI) water. The underlying physics of the current-flowing behavior in the GS are explained and interpreted using empirical circuit models; the circuit model also shows that highly resistive GO becomes conductive in GS form in the DI water. The findings in this work should draw new attention toward GSes and related applications, including functional composite materials, catalysts, and filter membranes.