With the increasing demand for electronic products, the amount of multilayer ceramic capacitor (MLCC) waste has also increased. Recycling technology has recently gained attention because it can simultaneously address raw material supply and waste disposal issues. However, research on recovering valuable metals from MLCCs and converting the recovered metals into high-value-added materials remains insufficient. Herein, we describe an electrospinning (E-spinning) process to recover nickel from MLCCs and modulate the morphology of the recovered nickel oxide particles. The nickel oxalate powder was recovered using organic acid leaching and precipitation. Nickel oxide nanoparticles were prepared via heat treatment and ultrasonic milling. A mixture of nickel oxide particles and polyvinylpyrrolidone (PVP) was used as the E-spinning solution. A PVP/NiO nanowire composite was fabricated via Espinning, and a nickel oxide nanowire with a network structure was manufactured through calcination. The nanowire diameters and morphologies are discussed based on the nickel oxide content in the E-spinning solution.

Energy storage systems should address issues such as power fluctuations and rapid charge-discharge; to meet this requirement, CoFe₂O₄ (CFO) spinel nanoparticles with a suitable electrical conductivity and various redox states are synthesized and used as electrode materials for supercapacitors. In particular, CFO electrodes combined with carbon nanofibers (CNFs) can provide long-term cycling stability by fabricating binder-free three-dimensional electrodes. In this study, CFO-decorated CNFs are prepared by electrospinning and a low-cost hydrothermal method. The effects of heat treatment, such as the activation of CNFs (ACNFs) and calcination of CFO-decorated CNFs (C-CFO/ACNFs), are investigated. The C-CFO/ACNF electrode exhibits a high specific capacitance of 142.9 F/g at a scan rate of 5 mV/s and superior rate capability of 77.6% capacitance retention at a high scan rate of 500 mV/s. This electrode also achieves the lowest charge transfer resistance of 0.0063 Ω and excellent cycling stability (93.5% retention after 5,000 cycles) because of the improved ion conductivity by pathway formation and structural stability. The results of our work are expected to open a new route for manufacturing hybrid capacitor electrodes containing the C-CFO/ACNF electrode that can be easily prepared with a low-cost and simple process with enhanced electrochemical performance.

The (Ga_1-xZn_x)(N_1-xO_x) solid solution is attracting extensive attention for photocatalytic water splitting and wastewater treatment owing to its narrow and controllable band gap. To optimize the photocatalytic performance of the solid solution, the key points are to decrease its band gap and recombination rate. In this study, (Ga_1-xZn_x)(N_1-xO_x) nanofibers with various Zn fractions are prepared by electrospinning followed by calcination and nitridation. The effect of the composition and crystallinity of electrospun oxide nanofibers on the morphology and optical properties of the obtained solid-solution nanofibers are systematically investigated. The results show that the final shape of the (Ga_1-xZn_x) (N_1-xO_x) material is greatly affected by the crystallinity of the oxide nanofibers before nitridation. The photocatalytic properties of (Ga_1-xZn_x)(N_1-xO_x) with different Ga:Zn atomic ratios are investigated by studying the degradation of rhodamine B under visible light irradiation.

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• Fabrication of Nanowire by Electrospinning Process Using Nickel Oxide Particle Recovered from MLCC
  Haein Shin, Jongwon Bae, Minsu Kang, Kun-Jae Lee
  journal of Korean Powder Metallurgy Institute.2023; 30(6): 502.     CrossRef

Bismuth vanadate (BiVO₄) is considered a potentially attractive candidate for the visible-light-driven photodegradation of organic pollutants. In an effort to enhance their photocatalytic activities, BiVO₄ nanofibers with controlled microstructures, grain sizes, and crystallinities are successfully prepared by electrospinning followed by a precisely controlled heat treatment. The structural features, morphologies, and photo-absorption performances of the asprepared samples are systematically investigated and can be readily controlled by varying the calcination temperature. From the physicochemical analysis results of the synthesized nanofiber, it is found that the nanofiber calcines at a lower temperature, shows a smaller crystallite size, and lower crystallinity. The photocatalytic degradation of rhodamine-B (RhB) reveals that the photocatalytic activity of the BiVO₄ nanofibers can be improved by a thermal treatment at a relatively low temperature because of the optimization of the conflicting characteristics, crystallinity, crystallite size, and microstructure. The photocatalytic activity of the nanofiber calcined at 350°C for the degradation of RhB under visible-light irradiation exhibits a greater photocatalytic activity than the nanofibers synthesized at 400°C and 450°C.

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• Design, synthesis, and characterization of a porous ceramic-supported CeO2 nanocatalyst for CO -free H2 evolution
  Jimin Lee, Minseob Lim, Tae Sung Kim, Kee-Ryung Park, Jong-Sik Lee, Hong-Baek Cho, Joo Hyun Park, Yong-Ho Choa
  Applied Surface Science.2021; 548: 149198.     CrossRef

Magnetic 0-D Nd₂Fe₁₄B powders are successfully fabricated using 1-D Nd₂Fe₁₄B nanowire formed by an efficient and facile electrospinning process approach. The synthesized Nd-Fe-B fibers and powders are investigated for their microstructural, crystallographic, and magnetic properties according to a series of subsequent heat treatments. Each heat-treatment process leads to the removal of organic impurities and the formation of the respective oxides/composites of Nd, Fe, and B, resulting in the formation of Nd₂Fe₁₄B powders. Nd-Fe-B fibers exhibit the following magnetic properties: The coercivity (H_ci) of 3260 Oe, a maximum magnetization at 3T of 109.44 emu/g, and a magnetization remanence (M_r) of 44.11 emu/g. This process easily mass produces hard magnetic Nd₂Fe₁₄B powders using a 1-D synthesis process and can be extended to the experimental design of other magnetic materials.

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• Nd2Fe14B/FeCo Core–Shell Nanoparticle Synthesis Using Galvanic Substitution Based Electroless Plating
  Muhammad Aneeq Haq, Han-Saem Lee, Mi Hye Lee, Da-Woon Jeong, Eom Nu Si A, Bin Lee, Yoseb Song, Bum Sung Kim
  Coatings.2022; 12(3): 389.     CrossRef

To meet the current demand in the fields of permanent magnets for achieving a high energy density, it is imperative to prepare nano-to-microscale rare-earth-based magnets with well-defined microstructures, controlled homogeneity, and magnetic characteristics via a bottom-up approach. Here, on the basis of a microstructural study and qualitative magnetic measurements, optimized reduction conditions for the preparation of nanostructured Sm-Co magnets are proposed, and the elucidation of the reduction-diffusion behavior in the binary phase system is clearly manifested. In addition, we have investigated the microstructural, crystallographic, and magnetic properties of the Sm-Co magnets prepared under different reduction conditions, that is, H₂ gas, calcium, and calcium hydride. This work provides a potential approach to prepare high-quality Sm-Co-based nanofibers, and moreover, it can be extended to the experimental design of other magnetic alloys.

To meet the current demand in the fields of permanent magnets for achieving a high energy density, it is imperative to prepare nano-to-microscale rare-earth-based magnets with well-defined microstructures, controlled homogeneity, and magnetic characteristics via a bottom-up approach. Here, on the basis of a microstructural study and qualitative magnetic measurements, optimized reduction conditions for the preparation of nanostructured Sm-Co magnets are proposed, and the elucidation of the reduction-diffusion behavior in the binary phase system is clearly manifested. In addition, we have investigated the microstructural, crystallographic, and magnetic properties of the Sm-Co magnets prepared under different reduction conditions, that is, H₂ gas, calcium, and calcium hydride. This work provides a potential approach to prepare high-quality Sm-Co-based nanofibers, and moreover, it can be extended to the experimental design of other magnetic alloys.

BaTiO₃-coated Fe nanofibers are synthesized via a three-step process. α-Fe₂O₃ nanofibers with an average diameter of approximately 200 nm are first prepared using an electrospinning process followed by a calcination step. The BaTiO₃ coating layer on the nanofiber is formed by a sol-gel process, and a thermal reduction process is then applied to the core-shell nanofiber to selectively reduce the α-Fe₂O₃ to Fe. The thickness of the BaTiO₃ shell is controlled by varying the reaction time. To evaluate the electromagnetic (EM) wave-absorbing abilities of the BaTiO₃@Fe nanofiber, epoxy-based composites containing the nanofibers are fabricated. The composites show excellent EM wave absorption properties where the power loss increases to the high frequency region without any degradation. Our results demonstrate that the BaTiO₃@Fe nanofibers obtained in this work are attractive candidates for electromagnetic wave absorption applications.

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• Research on Electromagnetic Wave Absorption Based on Electrospinning Technology†
  Baoding Li, Jing Qiao, Yue Liu, Haoyuan Tian, Wei Liu, Qilei Wu, Zhou Wang, Jiurong Liu, Zhihui Zeng
  Chinese Journal of Chemistry.2024; 42(7): 777.     CrossRef
• Design, synthesis, and characterization of a porous ceramic-supported CeO2 nanocatalyst for CO -free H2 evolution
  Jimin Lee, Minseob Lim, Tae Sung Kim, Kee-Ryung Park, Jong-Sik Lee, Hong-Baek Cho, Joo Hyun Park, Yong-Ho Choa
  Applied Surface Science.2021; 548: 149198.     CrossRef
• Electromagnetic wave absorption properties of Fe/MgO composites synthesized by a simple ultrasonic spray pyrolysis method
  Hyo-Ryoung Lim, Seung-Jae Jung, Tae-Yeon Hwang, Jimin Lee, Ki Hyeon Kim, Hong-baek Cho, Yong-Ho Choa
  Applied Surface Science.2019; 473: 1009.     CrossRef
• Study on the Optimization of Reduction Conditions for Samarium-Cobalt Nanofiber Preparation
  Jimin Lee, Jongryoul Kim, Yong-Ho Choa
  Journal of Korean Powder Metallurgy Institute.2019; 26(4): 334.     CrossRef

Perforated polygonal cobalt oxide (CO₃O₄) is synthesized using electrospinning and a hydrothermal method followed by the removal of a carbon nanofiber (CNF) template. To investigate their formation mechanism, thermogravimetric analysis, field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Xray photoelectron spectroscopy are examined. To obtain the optimum condition of perforated polygonal CO₃O₄, we prepare three different weight ratios of the Co precursor and the CNF template: sample A (Co precursor:CNF template- 10:1), sample B (Co precursor:CNF template-3.2:1), and sample C (Co precursor:CNF template-2:1). Among them, sample A exhibits the perforated polygonal CO₃O₄ with a thin carbon layer (5.7-6.2 nm) owing to the removal of CNF template. However, sample B and sample C synthesized perforated round CO₃O₄ and destroyed CO₃O₄ powders, respectively, due to a decreased amount of Co precursor. The increased amount of the CNF template prevents the formation of polygonal CO₃O₄. For sample A, the optimized weight ratio of the Co precursor and CNF template may be related to the successful formation of perforated polygonal CO₃O₄. Thus, perforated polygonal CO₃O₄ can be applied to electrode materials of energy storage devices such as lithium ion batteries, supercapacitors, and fuel cells.

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• Synthesis of Nitrogen Doped Protein Based Carbon as Pt Catalysts Supports for Oxygen Reduction Reaction
  Young-geun Lee, Geon-hyeong An, Hyo-Jin Ahn
  Korean Journal of Materials Research.2018; 28(3): 182.     CrossRef
• Electrochemical Behavior of Well-dispersed Catalysts on Ruthenium Oxide Nanofiber Supports
  Geon-Hyoung An, Hyo-Jin Ahn
  Journal of Korean Powder Metallurgy Institute.2017; 24(2): 96.     CrossRef

WS₂-W-WC embedded carbon nanofiber composites were fabricated by using electrospinning method for use in high-performance supercapacitors. In order to obtain optimum electrochemical properties for supercapacitors, WS₂ nanoparticles were used as precursors and the amounts of WS₂ precursors were controlled to 4 wt% (sample A) and 8 wt% (sample B). The morphological, structural, and chemical properties of all samples were investigated by means of field emission photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. These results demonstrated that the embedded phases of samples A and B were changed from WS₂ to WS₂-W-WC through carbothermal reaction during carbonization process. In particular, sample B presented high specific capacitance (~119.7 F/g at 5 mV/s), good high-rate capacitance (~60.5%), and superb cycleability. The enhanced electrochemical properties of sample B were explained by the synergistic effect of the using 1-D structure supports, increase of specific surface area, and improved conductivity from formation of W and WC phases.

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• WS2 Nanoparticles Embedded in Carbon Nanofibers for a Pseudocapacitor
  Ki-Wook Sung, Jung Soo Lee, Tae-Kum Lee, Hyo-Jin Ahn
  Korean Journal of Materials Research.2021; 31(8): 458.     CrossRef

SnO₂-CoO/carbon-coated CoO core/shell nanowire composites were synthesized by using electrospinning and hydrothermal methods. In order to obtain SnO2-CoO/carbon-coated CoO core/shell nanowire composites, SnO₂-Co₃O₄ nanowire composites and SnO₂-Co₃O₄/polygonal Co₃O₄ core/shell nanowire composites are also synthesized. To demonstrate their structural, chemical bonding, and morphological properties, field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out. These results indicated that the morphologies and structures of the samples were changed from SnO₂-Co₃O₄ nanowires having cylindrical structures to SnO₂-Co₃O₄/Co₃O₄ core/shell nanowires having polygonal structures after a hydrothermal process. At last, SnO₂-CoO/carbon-coated CoO core/shell nanowire composites having irregular and high surface area are formed after carbon coating using a polypyrrole (PPy). Also, there occur phases transformation of cobalt phases from Co₃O₄ to CoO during carbon coating using a PPy under a argon atmosphere.

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• Co-Embedded Graphitic Porous Carbon Nanofibers for Pt-Free Counter Electrode in Dye-Sensitized Solar Cells
  혜란 안, 혜린 강, 효정 선, 지호 한, 효진 안
  Korean Journal of Materials Research.2015; 25(12): 672~677.     CrossRef
• Synthesis of Perforated Polygonal Cobalt Oxides usinga Carbon Nanofiber Template
  Dong-Yo Sin, Geon-Hyoung An, Hyo-Jin Ahn
  Journal of Korean Powder Metallurgy Institute.2015; 22(5): 350.     CrossRef

Flake-like LiCoO₂ nanopowders were fabricated using electrospinning. To investigate their formation mechanism, field-emssion scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out. Among various parameters of electrospinning, we controlled the molar concentration of the precursor and the PVP polymer. When the molar concentration of lithium and cobalt was 0.45 M, the morphology of LiCoO₂ nanopowders was irregular and round. For 1.27 M molar concentration, the LiCoO₂ nanopowders formed with flake-like morphology. For the PVP polymer, the molar concentration was set to 0.011 mM, 0.026 mM, and 0.043 mM. Irregular LiCoO₂ nanopowders were formed at low concentration (0.011 mM), while flake-like LiCoO₂ were formed at high concentration (0.026 mM and 0.043 mM). Thus, optimized molar concentration of the precursor and the PVP polymer may be related to the successful formation of flake-like LiCoO₂ nanopowders. As a results, the synthesized LiCoO₂ nanopowder can be used as the electrode material of Li-ion batteries.

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• Electrochemical Behavior of Well-dispersed Catalysts on Ruthenium Oxide Nanofiber Supports
  Geon-Hyoung An, Hyo-Jin Ahn
  Journal of Korean Powder Metallurgy Institute.2017; 24(2): 96.     CrossRef
• Synthesis and Characterization of SnO2-CoO/carbon-coated CoO Core/shell Nanowire Composites
  Yu-Jin Lee, Bon-Ryul Koo, Hyo-Jin Ahn
  Journal of Korean Powder Metallurgy Institute.2014; 21(5): 360.     CrossRef