논문현황

INSTITUTE FOR ADVANCED ENGINEERING

융합소재연구센터 Poly(methylmethacrylate) coating on quantum dot surfaces via photo-chemical reaction for defect passivation

· 저자

김도연, 주소영, 이찬기, 김범성, 김우병


An effective poly(methylmethacrylate) (PMMA) coating process via photo-chemical reaction for quantum dots (QDs) was investigated. Various concentrations of PMMA were tested and the optimal concentration was confirmed to be 0.1 mM. The quantum yield (QY%) of the 0.1 mM PMMA-coated sample showed a 27% increase in efficiency relative to the as-synthesized CdSe/ZnS QDs due to the passivation of defect states on the surface. The QY% enhanced by PMMA was further increased by light irradiation because of the strong interactions and bonding between the surface atoms and functional groups of PMMA (acrylic groups). The excitation and formation of electron-hole pairs generated by light irradiation lead to strong interactions and chemical bonding on the surface; this is applicable to other cadmium QDs. When the QDs were passivated by a photo-chemical method, the QY% increased by approximately 20% for CdSe, CdSe/ZnS, and CdSe/ZnSe QDs. In order to evaluate the long-term stability depending on the PMMA coating, the QDs were stored for 12 months. The efficiency of as-synthesized bare QDs, initially 90%, drastically decreased to 17% after 12 months, but the PMMA-coated QDs with our coating method maintained a high efficiency of over 75%.


융합소재연구센터 A Novel Synthetic Method for N Doped TiO2 Nanoparticles Through Plasma-Assisted Electrolysis and Photocatalytic Activity in the Visible Region

· 저자

김태형, 고광명, 조홍백, 송요셉, 이찬기, 좌용호


Nitrogen doped TiO2 (N-TiO2) nanoparticles were synthesized via a novel plasma enhanced electrolysis method using bulk titanium (Ti) as a source material and nitric acid as the nitrogen dopant. This method possesses remarkable merits with regard to the direct-metal synthesis of nanoparticles with its one-step process, eco-friendliness, and its ability to be mass produced. The nanoparticles were synthesized from bulk Ti metal and dipped in 5–15 mmol of a nitric acid electrolyte under the application of AC 500 V, the minimum range of voltage to generate plasma. By controlling the electrolyte concentration, the nanoparticle size distribution could be tuned between 12.1 and 24.7 nm using repulsion forces via variations in pH. The prepared N-TiO2 nanoparticles were calcined at between 100 and 300°C to determine their photocatalytic efficiency within the visible-light region, which depended on their crystal structure and N doping content. Analysis showed that the temperature treatment yielded an anatase TiO2 crystalline structure when the N doping content was varied from 0.4 to 0.54 at.%. In particular, the 0.4 at.% N doped TiO2 catalyst exhibited the highest catalytic performance with quadruple efficiency compared to the P-25 standard TiO2 nanoparticles, which featured a 91% degradation of methyl orange organic dye within 300 min. This solid-liquid reaction based on plasma enhanced electrolysis could open new pathways with regard to high purity mass producible ceramic nanoparticles with advanced properties.


융합소재연구센터 Facile Synthesis of Carbon-Coated LiFeBO 3 Microspheres by Spray Drying and Their Structural Properties

· 저자

강이승, 안혜란, 정승민, Nahm sahn, 이찬기


Spherical LiFeBO3 (LFB) powder was successfully synthesized by a commercially available spray drying process. The powders were coated with a layer of carbon through a calcination step. This simple method allowed for fabrication of the powder with spherical particles and a homogeneous carbon coating. The crystal configuration, microstructure, and nature of the carbon coating were investigated by Rietveld refinement, Mössbauer spectroscopy, scanning electron microscopy, and transmission electron microscopy. The characterized structure had a monoclinic phase and belonged to the C2/c space group. The synthesized particles had a radius of 5 μm and were covered by a 6.5-nm-thick carbon coating. The spherical geometry of LFB with a well-encapsulated carbon coating layer is expected to enhanced powder density and result in good electrical performance. This preliminary study are expected to contribute to a deeper understanding of the novel LFB and aid the development of an effective method to fabricate cathode materials for Li-ion batteries.


융합소재연구센터 Synthesis and Characterization of TiO2/CuS Nanocomposite Fibers as a Visible Light-Driven Photocatalyst

· 저자

안혜란, 강이승, 안효진, 좌용호, 이찬기


TiO2/CuS nanocomposites were fabricated by precipitation of nanosized CuS via sonochemical method on electrospun TiO2 nanofibers, and their structure, chemical bonding states, optical properties, and photocatalytic activity were investigated. In the TiO2/CuS nanocomposite, the position of the conduction band for CuS was at a more negative than that of TiO; meanwhile, the position of the valence band for CuS was more positive than those for TiO, indicating a heterojunction structure belonging to type-II band alignment. Photocatalytic activity, measured by decomposition of methylene blue under visible-light irradiation (λ > 400 nm) for the TiO2/CuS nanocomposite, showed a value of 85.94% at 653 nm, which represented an improvement of 52% compared to that for single TiO2nanofiber (44.97% at 653 nm). Consequently, the photocatalyst with TiO2/CuS nanocomposite had excellent photocatalytic activity for methylene blue under visible-light irradiation, which could be explained by the formation of a heterojunction structure and improvement of the surface reaction by increase in surface area.


융합소재연구센터 Valorization of cobalt from waste lib cathode through cobalt oxalate and cobalt oxide synthesis by leaching-solvent extract-precipitation stripping

· 저자

Basudev swain, LEE, J. C., 이찬기


An ecoefficient, economical and sustainable valorization process for the synthesis of Co3O4 from waste lithium-ion battery (LIB) by leaching-solvent extract-scrubbing-precipitation stripping route has been developed. Through an optimization, the waste LIB cathode was leached using 2000 mole/m3 of H2SO4 and 5 Vol. % of the H2O2 at a pulp density of 100 kg/m3 under leaching time 60 minutes and temperature 75°C. From the separated leach liquor, cobalt was purified by saponified Cyanex 272. From cobalt, loaded Cyanex 272 impurities were scrubbed and the CoC2O4·2H2O was recovered through precipitation stripping. Finally, the precipitate was calcined to synthesize Co3O4, which is a precursor for LIB cathode materials manufacturing. From TGA-DTA, followed by XRD analysis it was confirmed that at 200°C the CoC2O4·2H2O can be converted to anhydrous CoC2O4 and at 350°C the anhydrous can be converted to Co3O4 and at 1100°C the Co3O4 can be converted to CoO. Through reported route waste LIB can back to LIB manufacturing process through a versatile and flexible industrial approach.


융합소재연구센터 An investigation into the effective surface passivation of quantum dots by a photo-assisted chemical method

· 저자

주소영, 박현수, 김도연, 김범성, 이찬기, 김우병


In this study, we have developed an effective amino passivation process for quantum dots (QDs) at room temperature and have investigated a passivation mechanism using a photo-assisted chemical method. As a result of the reverse reaction of the H2O molecules, the etching kinetics of the photo-assisted chemical method increased upon increasing the 3-amino-1-propanol (APOL)/H2O ratio of the etching solution. Photon-excited electron-hole pairs lead to strong bonding between the organic and surface atoms of the QDs, and results in an increase of the quantum yield (QY%). This passivation method is also applicable to CdSe/ZnSe core/shell structures of QDs, due to the passivation of mid-gap defects states at the interface. The QY% of the as-synthesized CdSe QDs is dramatically enhanced by the amino passivation from 37% to 75% and the QY% of the CdSe/ZnSe core/shell QDs is also improved by ∼28%.


융합소재연구센터 Bulk-Direct Synthesis of TiO 2 Nanoparticles by Plasma-Assisted Electrolysis with Enhanced Photocatalytic Performance

· 저자

김태형, 정승재, 임효령, 조홍백, 이찬기, 좌용호


A new plasma-assisted electrolysis method has been developed to synthesize amorphous TiO2 nanoparticles and exploited for the enhanced photocatalytic performance. The method is simple, environmentally friendly, produces nanoparticles directly from bulk metal, and is suitable for mass production. The process was conducted in low-concentration nitric acid electrolyte under a voltage of 450 V, the minimum necessary to produce plasma on the anode surface. The average nanoparticle size was tuned between 16 and 28 nm by controlling electrolyte concentration within the range of 5 to 15 mM. The production rate increased with time, with the maximum of 11.27 g/h. The amorphous TiO2 nanoparticles were calcined at various temperatures to determine the crystalline structures and to compare their photocatalytic effects. The structure ranged from pure anatase to rutile under various calcination temperatures; the anatase–rutile mixed phase produced at 600°C showed the highest catalytic performance, with 94% degradation of methylene blue within 30 min owing to a synergetic effect between the phases. This liquid-phase plasma-assisted electrolysis method can pave the way for large-scale synthesis of highly pure metal-based ceramic nanoparticles with narrow size distributions.


융합소재연구센터 Structural and Optical Properties of ZnSe:Eu/ZnS Quantum Dots depending on Interfacial Residual Europium

· 저자

박지영, 이찬기, 서한욱, 정다원, 김민영, 김우병, 김범성


A multimodal emitter comprising of ZnSe:Eu/ZnS (core/shell) quantum dots (QDs) by adding a ZnS precursor in situ during synthesis. ZnSe/Eu2+/Eu3+/ZnS actives both core and core/shell. QDs prepared with the ZnS precursor displayed a luminescence intensity three times that of ZnSe QDs due to the passivation effect of the Shell. While the core QDs display the 450–550 nm emission of Eu2+ (4F65D1 → 4F7), the core/shell system showed no Eu2+ emission but only the sharp peaks in the red at 579, 592, 615, 651, and 700 nm due to the electronic transitions of 5D0 → 7Fn (n = 0–4) depending on leisurely decreased with increased reaction time. These results are in agreement with Eu 3d spectra of XPS analysis results. Microscopic analyses show that the core and core/shell QDs both have a zinc blende structure, and their respective sizes were about 3.19 and 3.44 nm. The lattice constant in the central portion of the core/shell QDs are around d111 = 3.13 Å, which is between the outside and inside ring patterns (d111 = 3.27 and 3.07 Å, respectively). This shows the effective over-capping of shell onto the core QDs. The core/shell structure may contain Eu2O3 bonding the over-coated ZnS surface on the Eu3+-doped ZnSe core.


융합소재연구센터  Size-Distribution Effects of TiO2 Nanopowders Synthesized by Chemical Vapor Condensation Method for Dye-Sensitized Solar Cells

· 저자

주소영, 박현수, 이찬기, 김우병


The size distribution effects of TiO2 nanoparticles synthesized by chemical vapor condensation (CVC) have been investigated. Nanoparticles of sizes 3–5 nm, 10–400 nm and 30–400 nm were synthesized at synthesis pressures of 5 kPa, 40 kPa and 100 kPa, respectively. Anodes of the dye-sensitized solar cell (DSSC), when doped with 3–5 nm nanoparticle (synthesized at 5 kPa) exhibited the highest photoconversion efficiency (5.04%), which is attributed to (1) narrow size-distribution of nanoparticle and pore, (2) high specific surface area and (3) high transmission of the dye absorption wavelength. However, anodes fabricated with 10–400 nm TiO2 nanoparticles (synthesized at 40 kPa) produced the lowest photo-current. This could be due to sintering of bi-size nanoparticle, because the bi-size of nanoparticles produced the smaller pore size and lower concentration of pore volume during sintering and which results in the poor penetration of electrolyte into the porous TiO2.


융합소재연구센터 Carbon Co-Deposition during Gas Reduction of Water-Atomized Fe-Cr-Mo Powder

· 저자

Basit ali, 최상훈, 서석준, 맹덕영, 이찬기, 김택수, 박경태


The water atomization of iron powder with a composition of Fe-3Cr-0.5Mo (wt.%) at 1600°C and 150 bar creates an oxide layer, which in this study was reduced using a mixture of methane (CH4) and argon (Ar) gas. The lowest oxygen content was achieved with a 100 cc/min flow rate of CH4, but this also resulted in a co-deposition of carbon due to the cracking of CH4. This carbon can be used directly to create high-quality, sinter hardenable steel, thereby eliminating the need for an additional mixing step prior to sintering. An exponential relationship was found to exist between the CH4 gas flow rate and carbon content of the powder, meaning that its composition can be easily controlled to suit a variety of different applications.


융합소재연구센터 Room-temperature processing of CdSe quantum dots with tunable sizes

· 저자

주소영, 정다원, 이찬기, 김범성, 박현수, 김우병


In this work, CdSe quantum dots (QDs) with tunable sizes have been fabricated via photo-induced chemical etching at room temperature, and the related reaction mechanism was investigated. The surface of QDs was oxidized by the holes generated through photon irradiation of oxygen species, and the obtained oxide layer was dissolved in an aqueous solution of 3-amino-1-propanol (APOL) with an APOL:H2O volume ratio of 5:1. The generated electrons promoted QD surface interactions with amino groups, which ultimately passivated surface defects. The absorption and photoluminescence emission peaks of the produced QDs were clearly blue-shifted about 26 nm with increasing time, and the resulting quantum yield for an 8 h etched sample was increased from 20% to 26%, as compared to the initial sample.


융합소재연구센터 Optical Properties of Nano–Structured ZnO : Sn Powders Prepared in a Micro Drop Fluidized Reactor

· 저자

유동준, 임대호, 강용, 이찬기, 강경민


Optical properties of nano–structured ZnO : Sn powders prepared by means of a one–step micro drop fluidized reactor continuously were investigated. The band–gap edge of ZnO : Sn powder was extended to the visible region due to the formation of the extrinsic levels of interstitial oxygen and oxygen vacancy in the band structure of ZnO. The BET surface area of ZnO : Sn powders increased by up to 300%. The fluidization of micro drops of precursors during thermal decomposition contributed to the formation of porous surface morphology and modification of band gap structure of the ZnO : Sn powders by generating micro shear force and strain at the surface of micro drops. The doping of Sn4+ ions into ZnO reduced the electrical resistivity by generating extra free electrons at the surface of ZnO : Sn powders.


융합소재연구센터 Effect of controlled Mn doping on transition of oxygen vacancies in Bi2Ti2O7 thin films: An electrochemical study

· 저자

강이승, 안혜란, 김태형, 이덕희, 박경수, Basudev swain, 이찬기, Nahm sahn


Crystalline pyrochlore Bi2Ti2O7 (B2T2) thin films were well formed at 300 °C under 740 mTorr of oxygen partial pressure using pulsed laser deposition. In order to improve the electrical properties of the dielectric B2T2 films, Mn ions were doped into the films and their influence was investigated. Improvement in electrical behavior, especially leakage current density were revealed via impedance spectroscopy and electrochemical studies. Mn doping at an appropriate level improved the electrical properties of the films by affording extrinsic oxygen vacancies that reduced the number of intrinsic oxygen vacancies acting as electron trap sites at the interface between the Pt electrode and the B2T2 film. Schottky emission was posited as the leakage current mechanism in the 10 mol% Mn doped B2T2 (Mn:B2T2) films. The barrier height between the Pt electrode and the Mn:B2T2film was approximately 1.46 eV, but decreased to 0.51 eV for the non-doped film due to large numbers of intrinsic oxygen vacancies.


융합소재연구센터 A validation experiment on indium recovery by electrowinning of aqueous electrolytes: Optimization of electrolyte composition

· 저자

이성규, 이수영, Basudev swain, 조성수, 이찬기


A batch-type and lab-scale indium recovery method was developed via electrowinning (EW) to prove mass production-capability and economic recovery of indium from InCl3 crystals precipitated from the solvent extraction using a suitable phosphoric acid-based extractant. More precisely, the InCl3 crystals thus precipitated were further dissolved in three different aqueous electrolyte mixtures for subsequent electrowinning experiments: 0.05 M InCl3 – 0.7 M LiCl; 0.05M InCl3; 0.05 M InCl3 – 0.7 M NaCl. The effect of adding LiCl and NaCl supporting electrolytes to InCl3 on overall EW efficiency was thus comprehensibly investigated. Direct electroreduction of InCl3 using 0.05 M InCl3 aqueous electrolyte resulted in the highest indium metal purity of 99.996 % deposited on the copper cathode. Thus, metallic contents obtained from the validation experiments were further characterized using various analytical tools such as inductively coupled plasma/atomic emission spectroscopy (ICP/AES), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF).


융합소재연구센터 Opto-electrical properties of ZnO:Al powders prepared in a micro drop fluidized reactor

· 저자

유동준, 임대호, 강용, 이찬기, 강경민


Optical and electrical properties of ZnO:Al powders prepared in a continuous and one-step micro drop fluidized reactor were investigated. The shift of main peaks in XRD patterns and crystallite size of ZnO:Al powders increased with increasing flow rate of micro bubbles (UMB), indicating that the fluidization of micro drops during the formation of powders could help the doping of Al3+ ions into the lattice of ZnO. The band gap energy of ZnO:Al powders became narrow by forming the extrinsic donor levels to the conduction band more easily, with increasing UMB. The surface morphology of ZnO:Al powders became more wrinkled and furrowed with increasing UMB, due to the increase of micro shear force and strain acting on the surface of ZnO:Al during the formation in the fluidization field of the reactor. The room temperature photoluminescence indicated that the doping effects of as-prepared ZnO:Al powders were getting better with increasing UMB. The electrical resistivity of ZnO:Al decreased considerably due to the active generation of extra free electrons at the surface of the powder, with increasing UMB.


융합소재연구센터 Understanding the isothermal growth kinetics of CdSe quantum dots through the microfluidic reactor assisted combinatorial synthesis

· 저자

Basudev swain, 홍명환, 강이승, 이찬기


With the use of a microfluidic-assisted combinatorial reactor, the synthesis of CdSe quantum dots was optimized by varying one parameter at a time, and the isothermal growth kinetics of CdSe quantum dots using various models was analyzed. To understand precisely the nucleation and growth characteristics of CdSe quantum dots (QDs), we synthesized the CdSe QDs using various experimental conditions. Different model equations, like acceleratory growth-time curves, sigmoidal growth-time curves or Johnson-Mehl-Avrami-Kolmogorov (JMAK), acceleratory growthtime curves based on diffusion, geometric model growth-time curves, and nth order growth-time curves were fitted. Among all growth models, the JMAK model with α=1−e−(kt)nα=1−e−(kt)n, and n = 1 was the best fitting model with the MATLAB interactive curve-fitting procedure were used. Errors associated with the best-fitting model and statistics for the goodness of fit were analyzed. Most of the models were not as good as the other than the proposed model. The errors associated with the proposed model were minimal, and the growth kinetics and other associated statistical factors are very similar, for all the variables investigated. The minimal error associated with the reproducibility and the similar data for growth kinetics for all studied parameters indicated that microfluidic-assisted combinatorial synthesis can be used in the industrial production of QDs. By using the proposed model to obtain an understanding of growth of QDs, their size and properties can be managed and simulated.


융합소재연구센터 Optimization of CdSe nanocrystals synthesis with a microfluidic reactor and development of combinatorial synthesis process for industrial production

· 저자

Basudev swain, 홍명환, 강이승, 김범성, 김남훈, 이찬기


A lab scale microfluidic reactor with computer-controlled programmable isocratic pumps and online detectors was employed to syntheses CdSe nanocrystal and operational parameters for lab scale microfluidic reactor were optimized. Three reaction parameters, viz. the reaction time, the [Cd]/[Se] molar concentration ratio, and the precursor concentrations, were optimized for optical characteristics, the particle diameter, and product yield. The average time corresponding to each reaction condition for obtaining the ultraviolet–visible (UV–vis) absorbance and photoluminescence spectra was approximately 10 min. Based on lab scale microfluidic reactor a combinatorial reactor for synthesis CdSe on commercial interest has been redesigned and reproducibility of the CdSe synthesis, diameter size, and product yield were verified at the obtained condition from the lab scale synthesis. Using the data from the combinatorial synthesis system, the effects of the reaction conditions on the synthesized CdSe nanocrystals and their yield were elucidated. Further, the data were used to determine the relationships between the reaction conditions, the CdSe particle diameter, and the product yield. Advantages of reported synthesis are, unlikely, other reported processes instead of batch scale operation, the combinatorial synthesis system can be used for continuous production, if required. Through the process, controlling the precursor concentration, flow rate, and other physical and instrumental parameter, desired sized NCs can be synthesized precisely, which is a remarkable aspect of the combinatorial synthesis reported here. Depending upon the requirement, automation can be done for preciseness, reproducibility and mass production of the NCs.


융합소재연구센터 Effect of Amine Additive for the Synthesis of Cadmium Selenide Quantum Dots in a Microreactor

· 저자

정다원, Basudev swain, 성태연, 박경태, 이찬기, 김범성


The effect of octylamine flow rate on the structure and morphology of CdSe quantum dots synthesized in a microreactor was studied. The flow rate of octylamine was varied from 0.005 ml/min to 0.030 ml/min, and the optical properties of the synthesized particles were analyzed by UV–vis and photoluminescence spectroscopy. The particle size of the quantum dots was found to increase with an increasing octylamine flow rate. Further, UV–vis and photoluminescence bands were found to be red‐shifted with an increasing flow rate. We determined that, by controlling octylamine flow rate, the particle size of the quantum dots could be controlled. This method will help to determine the optimal octylamine flow conditions for synthesizing nanoparticles for use in a diverse range of applications.


융합소재연구센터 Fischer-Tropsch Synthesis of the Promoted Co/ZSM-5 Hybrid Catalysts for the Production of Gasoline Range Hydrocarbons

· 저자

강석환, 류재홍, 김진호, 김효식, 이찬기, 이연조, 전기원


Fischer-Tropsch synthesis (FTS) reaction for the direct production of gasoline range hydrocarbons (C5-C9) from syngas was investigated on Ru, Pt, and La promoted Co/ZSM-5 (Si/Al = 25) catalysts. The hybrid catalysts were characterized by BET surface area, XRD, H2-TPR, NH3-TPD and XPS analyses. These physico-chemical properties were correlated with activity and selectivity of the catalysts. The promoted Co/ZSM-5 hybrid catalysts were found to be superior to the unpromoted Co/ZSM-5 catalyst in terms of better C5-C9 selectivity. Pt-Co/ZSM-5 exhibited the highest catalytic activity because of the small cobalt particle size.


융합소재연구센터 Bubble and Heat Transfer Phenomena in Viscous Slurry Bubble Column

· 저자

김효식, 김진호, 이찬기, 강석환, 우광재, 정호진, 김동욱


Heat transfer and bubble phenomena were investigated by adopting the drift flux model in a viscous slurry bubble column reactor (SBCR), having a diameter of 0.0508 m (ID) and height 1.5 m. The effects of superficial gas velocity (0.002 - 0.164 m/s), solid concentration (0 - 20 wt%) and liquid viscosity (paraffin oil; 16.9 mPa∙s and squalane; 25.9 mPa∙s) on the gas holdup and heat transfer characteristics were examined. It was observed that the gas holdup increased with increasing superficial gas velocity (UG), but decreased with increasing solid concentration (SC) or slurry viscosity. The degree of non-uniformity in a SBCR could be determined by the modified drift flux model at the heterogeneous flow regime. The local heat transfer coefficient (h) between the immersed heater and the bed decreased with increasing liquid viscosity and SC, but it increased with increasing UG. The modified Nusselt number including the gas holdup and local heat transfer coefficient was well correlated in terms of dimensionless groups such as Reynolds and Prandtl numbers.