Search

Your search keyword '"Kim, Yoon Hwa"' showing total 127 results
Start Over Author "Kim, Yoon Hwa"
127 results on '"Kim, Yoon Hwa"'

15. Confinement of Ultrasmall Bimetallic Nanoparticles in Conductive Metal–Organic Frameworks via Site‐Specific Nucleation (Adv. Mater. 38/2021)

Author

Park, Chungseong, primary, Koo, Won‐Tae, additional, Chong, Sanggyu, additional, Shin, Hamin, additional, Kim, Yoon Hwa, additional, Cho, Hee‐Jin, additional, Jang, Ji‐Soo, additional, Kim, Dong‐Ha, additional, Lee, Jiyoung, additional, Park, Seyeon, additional, Ko, Jaehyun, additional, Kim, Jihan, additional, and Kim, Il‐Doo, additional

Published
2021
Full Text
View/download PDF

18. Sacrificial Template‐Assisted Synthesis of Inorganic Nanosheets with High‐Loading Single‐Atom Catalysts: A General Approach.

Author

Shin, Hamin, Ko, Jaehyun, Park, Chungseong, Kim, Dong‐Ha, Ahn, Jaewan, Jang, Ji‐Soo, Kim, Yoon Hwa, Cho, Su‐Ho, Baik, Hionsuck, and Kim, Il‐Doo

Subjects
INORGANIC synthesis, NANOSTRUCTURED materials, CATALYSTS, METALLIC oxides, HEAT treatment, ACETONE
Abstract

Single‐atom catalysts (SACs) supported on inorganic materials have attracted much attention in numerous research fields for their high catalytic performance. However, such SACs have been limited by the low metal loading, especially on different types of inorganic supports. Herein, a general approach is presented for preparing SACs on metallic, metal oxide, and perovskite nanosheet (NS) supports to reach a high metal loading of up to 3.94 wt%, by utilizing N‐doped graphene as a sacrificial template that spatially confines the single atoms (SAs). Specifically, the target support material precursors are adsorbed onto the SAs‐stabilized sacrificial template, followed by subsequent heat treatment to transfer the SAs to the support material and to remove the graphene layer. Pt SAs on oxide support exhibits little to no aggregation throughout >10 000 min of annealing at 275 °C, demonstrating high thermal stability, as also supported by ex situ post‐anneal electron microscopy and X‐ray absorption fine structure studies. As a proof‐of‐concept, Pt SACs on SnO2 NSs exhibit high catalytic activity toward chemiresistive sensing of acetone gas (response = 95.4 at 10 ppm, 7.6‐fold enhancement compared with pristine SnO2 NSs) and unprecedented stability under highly humid conditions (27.4% response deterioration at 95% relative humidity). [ABSTRACT FROM AUTHOR]

Published
2022
Full Text
View/download PDF

35. A zero-thermal-quenching phosphor

Author

Kim, Yoon Hwa, primary, Arunkumar, Paulraj, additional, Kim, Bo Young, additional, Unithrattil, Sanjith, additional, Kim, Eden, additional, Moon, Su-Hyun, additional, Hyun, Jae Young, additional, Kim, Ki Hyun, additional, Lee, Donghwa, additional, Lee, Jong-Sook, additional, and Im, Won Bin, additional

Published
2017
Full Text
View/download PDF

39. Single-Atom Pt Stabilized on One-Dimensional Nanostructure Support viaCarbon Nitride/SnO2Heterojunction Trapping

Author

Shin, Hamin, Jung, Wan-Gil, Kim, Dong-Ha, Jang, Ji-Soo, Kim, Yoon Hwa, Koo, Won-Tae, Bae, Jaehyeong, Park, Chungseong, Cho, Su-Ho, Kim, Bong Joong, and Kim, Il-Doo

Abstract

Catalysis with single-atom catalysts (SACs) exhibits outstanding reactivity and selectivity. However, fabrication of supports for the single atoms with structural versatility remains a challenge to be overcome, for further steps toward catalytic activity augmentation. Here, we demonstrate an effective synthetic approach for a Pt SAC stabilized on a controllable one-dimensional (1D) metal oxide nano-heterostructure support, by trapping the single atoms at heterojunctions of a carbon nitride/SnO2heterostructure. With the ultrahigh specific surface area (54.29 m2g–1) of the nanostructure, we obtained maximized catalytic active sites, as well as further catalytic enhancement achieved with the heterojunction between carbon nitride and SnO2. X-ray absorption fine structure analysis and HAADF-STEM analysis reveal a homogeneous atomic dispersion of Pt species between carbon nitride and SnO2nanograins. This Pt SAC system with the 1D nano-heterostructure support exhibits high sensitivity and selectivity toward detection of formaldehyde gas among state-of-the-art gas sensors. Further ex situTEM analysis confirms excellent thermal stability and sinter resistance of the heterojunction-immobilized Pt single atoms.

Published
2020
Full Text
View/download PDF

40. Hydrogen Sensors Based on MoS2Hollow Architectures Assembled by Pickering Emulsion

Author

Park, Chan Ho, Koo, Won-Tae, Lee, Young Jun, Kim, Yoon Hwa, Lee, Jiyoung, Jang, Ji-Soo, Yun, Hongseok, Kim, Il-Doo, and Kim, Bumjoon J.

Abstract

For rapid hydrogen gas (H2) sensing, we propose the facile synthesis of the hollow structure of Pt-decorated molybdenum disulfide (h-MoS2/Pt) using ultrathin (mono- or few-layer) two-dimensional nanosheets. The controlled amphiphilic nature of MoS2surface produces ultrathin MoS2NS-covered polystyrene particles viaone-step Pickering emulsification. The incorporation of Pt nanoparticles (NPs) on the MoS2, followed by pyrolysis, generates the highly porous h-MoS2/Pt. This hollow hybrid structure produces sufficiently permeable pathways for H2and maximizes the active sites of MoS2, while the Pt NPs on the hollow MoS2induce catalytic H2spillover during H2sensing. The h-MoS2/Pt-based chemiresistors show sensitive H2sensing performances with fast sensing speed (response, 8.1 s for 1% of H2and 2.7 s for 4%; and recovery, 16.0 s for both 1% and 4% H2at room temperature in the air). These results mark the highest H2sensing speed among 2D material-based H2sensors operated at room temperature in air. Our fabrication method of h-MoS2/Pt structure through Pickering emulsion provides a versatile platform applicable to various 2D material-based hollow structures and facilitates their use in other applications involving surface reactions.

Published
2020
Full Text
View/download PDF

41. Color tunable single-phase Eu2+ and Ce3+ co-activated Sr2LiAlO4 phosphors.

Author

Ha, Jungmin, Kim, Yoon Hwa, Novitskaya, Ekaterina, Wang, Zhenbin, Sanchez, Maritza, Graeve, Olivia A., Ong, Shyue Ping, Im, Won Bin, and McKittrick, Joanna

Abstract

High purity Eu2+ and Ce3+ singly and co-activated Sr2LiAlO4 phosphors were successfully synthesized through a facile combustion reaction. Fabrication of color tunable, single-phase phosphors was achieved by varying the Eu2+/Ce3+ ratio that utilized the energy transfer between Ce3+ and Eu2+. For the singly activated compositions, the highest quantum efficiencies were 25% and 40% for Sr1.998Eu0.002LiAlO4 and Sr1.998Ce0.002LiAlO4, respectively. The emission of Sr2LiAlO4:Ce3+ and the excitation of Sr2LiAlO4:Eu2+ overlap in the range of 400 nm–500 nm, so that energy transfer from Ce3+→ Eu2+ takes place. The emission color of Eu2+ and Ce3+ co-activated Sr2LiAlO4 changes from blue, to cool-white, to green depending on the activator concentrations. The maximum quantum efficiency of Eu2+ and Ce3+ co-activated Sr2LiAlO4 was 55%, a 40% increase over the singly activated phosphors, which demonstrates that the quantum efficiency improves by co-activation. [ABSTRACT FROM AUTHOR]

Published
2019
Full Text
View/download PDF

42. Cobalt-Doped Ceria Sensitizer Effects on Metal Oxide Nanofibers: Heightened Surface Reactivity for High-Performing Chemiresistive Sensors

Author

Baek, Jong Won, Han, Seunghee, Lee, Sang Eun, Ahn, Jaewan, Park, Chungseong, Nam, Jong Seok, Kim, Yoon Hwa, Shin, Euichul, Kim, Minhyun, Jang, Ji-Soo, Kim, Jihan, Park, Hee Jung, and Kim, Il-Doo

Abstract

Chemiresistive gas sensors based on semiconducting metal oxides typically rely on noble metal catalysts to enhance their sensitivity and selectivity. However, noble metal catalysts have several drawbacks for practical utilization, including their high cost, their propensity for spontaneous agglomeration, and poisoning effects with certain types of gases. As such, in the interest of commercializing the chemiresistive gas sensor technology, we propose an alternative design for a noble-metal-free sensing material through the case study of Co-doped ceria (Co–CeO2) catalysts embedded in a SnO2matrix. In this investigation, we utilized electrospinning and subsequent calcination to prepare Co–CeO2catalyst nanoparticles integrated with SnO2nanofibers (NFs) with uniform particle distribution and particle size regulation down to the sub-2 nm regime. The resulting Co–CeO2@SnO2NFs exhibited superior gas sensing characteristics toward isoprene (C5H8) gas, a significant biomarker for monitoring the onset of various diseases through breath diagnostics. In particular, we identified that the Co–CeO2catalysts, owing to the transition metal doping, facilitated the spillover of chemisorbed oxygen species to the SnO2sensing body. This resulting in the sensor having a 27.4-fold higher response toward 5 ppm of C5H8(compared to pristine SnO2), exceptionally high selectivity, and a low detection limit of 100 ppb. The sensor also exhibited high stability for prolonged response–recovery cycles, attesting to the strong anchoring of Co–CeO2catalysts in the SnO2matrix. Based on our findings, the transition metal-doped metal oxide catalysts, such as Co–CeO2, demonstrate strong potential to completely replace noble metal catalysts, thereby advancing the development of the commercially viable chemiresistive gas sensors free from noble metals, capable of detecting target gases at sub-ppm levels.

Published
2024
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results