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

In this study, (GaN)_1-x(ZnO)_x solid solution nanoparticles with a high zinc content are prepared by ultrasonic spray pyrolysis and subsequent nitridation. The structure and morphology of the samples are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The characterization results show a phase transition from the Zn and Ga-based oxides (ZnO or ZnGa₂O₄) to a (GaN)_1-x (ZnO)_x solid solution under an NH3 atmosphere. The effect of the precursor solution concentration and nitridation temperature on the final products are systematically investigated to obtain (GaN)_1-x(ZnO)_x nanoparticles with a high Zn concentration. It is confirmed that the powder synthesized from the solution in which the ratio of Zn and Ga was set to 0.8:0.2, as the initial precursor composition was composed of about 0.8-mole fraction of Zn, similar to the initially set one, through nitriding treatment at 700°C. Besides, the synthesized nanoparticles exhibited the typical XRD pattern of (GaN)_1-x(ZnO)_x, and a strong absorption of visible light with a bandgap energy of approximately 2.78 eV, confirming their potential use as a hydrogen production photocatalyst.

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

In this study, ultrasonic spray pyrolysis combined with salt-assisted decomposition, a process that adds sodium nitrate (NaNO₃) into a titanium precursor solution, is used to synthesize nanosized titanium dioxide (TiO₂) particles. The added NaNO₃ prevents the agglomeration of the primary nanoparticles in the pyrolysis process. The nanoparticles are obtained after a washing process, removing NaNO₃ and NaF from the secondary particles, which consist of the salts and TiO₂ nanoparticles. The effects of pyrolysis temperature on the size, crystallographic characteristics, and bandgap energy of the synthesized nanoparticles are systematically investigated. The synthesized TiO₂ nanoparticles have a size of approximately 2–10 nm a bandgap energy of 3.1–3.25 eV, depending on the synthetic temperature. These differences in properties affect the photocatalytic activities of the synthesized TiO₂ nanoparticles.

Current synthesis processes for titanium dioxide (TiO₂) nanoparticles require expensive precursors or templates as well as complex steps and long reaction times. In addition, these processes produce highly agglomerated nanoparticles. In this study, we demonstrate a simple and continuous approach to synthesize TiO₂ nanoparticles by a salt-assisted ultrasonic spray pyrolysis method. We also investigate the effect of salt content in a precursor solution on the morphology and size of synthesized products. The synthesized TiO₂ nanoparticles are systematically characterized by X-ray diffraction, transmission electron micrograph, and UV-Vis spectroscopy. These nanoparticles appear to have a single anatase phase and a uniform particle-size distribution with an average particle size of approximately 10 nm. By extrapolating the plots of the transformed Kubelka-Munk function versus the absorbed light energy, we determine that the energy band gap of the synthesized TiO₂ nanoparticles is 3.25 eV.

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• Effect of Pyrolysis temperature on TiO₂ Nanoparticles Synthesized by a Salt-assisted Ultrasonic Spray Pyrolysis Process
  Jae-Hyun Yoo, Myeong-Jun Ji, Woo-Young Park, Young-In Lee
  Journal of Korean Powder Metallurgy Institute.2019; 26(3): 237.     CrossRef

Despite numerous advances in the preparation and use of GaN, and many leading-edge applications in lighting technologies, the preparation of high-quality GaN powder remains a challenge. Ammonolytic preparations of polycrystalline GaN have been studied using various precursors, but all were time-consuming and required high temperatures. In this study, an efficient and low-temperature method to synthesize high-purity hexagonal GaN powder is developed using sub-micron Ga₂O₃ powder as a starting material. The sub-micron Ga₂O₃ powder was prepared by an ultrasonic spray pyrolysis process. The GaN powder is synthesized from the sub-micron Ga₂O₃ powder through a nitridation treatment in an NH₃ flow at 800°C. The characteristics of the synthesized powder are systematically examined by X-ray diffraction, scanning and transmission electron microscopy, and UV-vis spectrophotometer.

The structural formation of inorganic nanoparticles dispersed in polymer matrices is a key technology for producing advanced nanocomposites with a unique combination of optical, electrical, and mechanical properties. Barium titanate (BaTiO₃) nanoparticles are attractive for increasing the refractive index and dielectric constant of polymer nanocomposites. Current synthesis processes for BaTiO₃ nanoparticles require expensive precursors or organic solvents, complicated steps, and long reaction times. In this study, we demonstrate a simple and continuous approach for synthesizing BaTiO₃ nanoparticles based on a salt-assisted ultrasonic spray pyrolysis method. This process allows the synthesis of BaTiO₃ nanoparticles with diameters of 20-50 nm and a highly crystalline tetragonal structure. The optical properties and photocatalytic activities of the nanoparticles show that they are suitable for use as fillers in various nanocomposites.

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• Sr doping effects on La(1-x)SrxMnO3-BaTiO3 nanocomposites: A comprehensive analysis of structural, optical, magnetic, and dielectric properties
  Milad Karamzadeh-Jahromi, Morteza Izadifard, Mohammad Ebrahim Ghazi
  Journal of Alloys and Compounds.2024; 1006: 176272.     CrossRef

Noncontact direct-printed conductive silver patterns with an enhanced electrical resistivity are fabricated using a silver ink with a mixture of silver nanoparticles and nanoplates. The microstructure and electrical resistivity of the silver pattern are systematically investigated as a function of the mixing ratio of the nanoparticles and nanoplates. The pattern, which is fabricated using a mixture with a mixing ratio of 3(nanoparticles):7(nanoplates) and sintered at 200°C shows a highly dense and well-sintered microstructure and has a resistivity of 7.60 μΩ·cm. This originates a mutual synergistic effect through a combination of the sinterability of the nanoparticles and the packing ability of the nanoplates. This is a conductive material that can be used to fabricate noncontact direct-printed conductive patterns with excellent electrical conductivity for various flexible electronics applications, including solar cells, displays, RFIDs, and sensors.

TiOF₂, which has remarkable electrochemical and optical properties, is used in various applications such as Li-ion batteries, electrochemical displays, and photocatalysts. In addition, it is possible to utilize the template which is allowed to synthesize fluorine doped TiO₂ powders with hollow or faceted structures. However, common synthesis methods of TiOF₂ powders have some disadvantages such as the use of expensive and harmful precursors and batchtype processes with a limited production scale. In this study, we report a synthetic route for preparing TiOF₂ powders by using an inexpensive and harmless precursor and a continuous ultrasonic spray pyrolysis process under a controlled atmosphere to address the aforementioned problems. The synthesized powder has an average size of 1 μm, a spherical shape, a pure TiOF₂ phase, and exhibits a band-gap energy of 3.2 eV.

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• Photocatalytic activity of rutile TiO2 powders coupled with anatase TiO2 nanoparticles using surfactant
  Jong Min Byun, Chun Woong Park, Young In Kim, Young Do Kim
  journal of Korean Powder Metallurgy Institute.2018; 25(3): 257.     CrossRef

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

Vertically oriented nickel nanowire arrays with a different diameter and length are synthesized in porous anodic aluminium oxide templates by an electrodeposition method. The pore diameters of the templates are adjusted by controlling the anodization conditions and then they are utilized as templates to grow nickel nanowire arrays. The nickel nanowires have the average diameters of approximately 25 and 260 nm and the crystal structure, morphology and microstructure of the nanowires are systematically investigated using XRD, FE-SEM and TEM analysis. The nickel nanowire arrays show a magnetic anisotropy with the easy axis parallel to the nanowires and the coercivity and remanence enhance with decreasing a wire diameter and increasing a wire length.

Much research into fuel cells operating at a temperature below 800°C. is being performed. There are significant efforts to replace the yttria-stabilized zirconia electrolyte with a doped ceria electrolyte that has high ionic conductivity even at a lower temperature. Even if the doped ceria electrolyte has high ionic conductivity, it also shows high electronic conductivity in a reducing environment, therefore, when used as a solid electrolyte of a fuel cell, the powergeneration efficiency and mechanical properties of the fuel cell may be degraded. In this study, gadolinium-doped ceria nanopowder with Al₂O₃ and Mn₂O₃ as a reinforcing and electron trapping agents were synthesized by ultrasonic pyrolysis process. After firing, their microstructure and mechanical and electrical properties were investigated and compared with those of pure gadolinium-doped ceria specimen.

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• High growth-rate atomic layer deposition process of cerium oxide thin film for solid oxide fuel cell
  Jin-Geun Yu, Byung Chan Yang, Jeong Woo Shin, Sungje Lee, Seongkook Oh, Jae-Ho Choi, Jaehack Jeong, Wontae Noh, Jihwan An
  Ceramics International.2019; 45(3): 3811.     CrossRef
• Atomic-layer-deposited ZrO2-doped CeO2 thin film for facilitating oxygen reduction reaction in solid oxide fuel cell
  Byung Chan Yang, Dohyun Go, Seongkook Oh, Jeong Woo Shin, Hyong June Kim, Jihwan An
  Applied Surface Science.2019; 473: 102.     CrossRef