TY - JOUR
T1 - Subnano-transformation of molybdenum carbide to oxycarbide
AU - Wakizaka, Masanori
AU - Atqa, Augie
AU - Chun, Wang Jae
AU - Imaoka, Takane
AU - Yamamoto, Kimihisa
N1 - Funding Information:
The authors acknowledge Dr Ken Albrecht (Kyushu Univ.) for his support with the synthesis of the TPM-DPAG4, Dr Ken Motokura (Tokyo Tech.) for his support with the XAFS measurements, and Suzukakedai Materials Analysis Division (Tokyo Tech.) for PXRD measurement. This study was performed under the approval of the Photon Factory Program Advisory Committee (proposal no. 2018G042), of the Japan Synchrotron Radiation Research Institute (proposal no. 2018B1550), and of the Kyushu Synchrotron Light Research Center (proposal no. 1904027F and 1910084F). This study was supported by JST ERATO Grant Number JPMJER1503 and JSPS KAKENHI Grant Numbers JP15H05757 and JP18K14237, Japan.
Publisher Copyright:
© The Royal Society of Chemistry.
PY - 2020/8/7
Y1 - 2020/8/7
N2 - Ultrasmall particles exhibit structures and/or properties that are different from those of the corresponding bulk materials; in this context especially ultrasmall precious-metal particles have been extensively investigated. In this study, we targeted the transition base-metal Mo and succeeded in systematically producing Mo oxycarbide/carbide particles with diameters of 1.7 ± 0.7, 1.4 ± 0.5, 1.3 ± 0.4, 1.2 ± 0.3, 1.0 ± 0.3, and 0.8 ± 0.2 nm on a carbon support using the carbothermal hydrogen reduction method at 773 K and a diphenylazomethine-type dendrimer as a template. The formation and properties of the particles were confirmed using X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, and X-ray absorption fine structure (XAFS) studies. We found that Mo particles with a diameter of 1.3 nm or greater formed carbides such as β′-Mo2C, whereas smaller particles formed oxycarbides, indicating a size-dependent transformation in the phase or composition of the particles. Thus, this work demonstrated a new concept, subnano-transformation, which would be a new class of phase transformation based on the concept of the size dependence in such an ultrasmall scale. In addition, the movement of Mo atoms within a cluster and on the fringes of a nanoparticle was also demonstrated during continuous time-course high-resolution HAADF-STEM observation. This journal is
AB - Ultrasmall particles exhibit structures and/or properties that are different from those of the corresponding bulk materials; in this context especially ultrasmall precious-metal particles have been extensively investigated. In this study, we targeted the transition base-metal Mo and succeeded in systematically producing Mo oxycarbide/carbide particles with diameters of 1.7 ± 0.7, 1.4 ± 0.5, 1.3 ± 0.4, 1.2 ± 0.3, 1.0 ± 0.3, and 0.8 ± 0.2 nm on a carbon support using the carbothermal hydrogen reduction method at 773 K and a diphenylazomethine-type dendrimer as a template. The formation and properties of the particles were confirmed using X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, and X-ray absorption fine structure (XAFS) studies. We found that Mo particles with a diameter of 1.3 nm or greater formed carbides such as β′-Mo2C, whereas smaller particles formed oxycarbides, indicating a size-dependent transformation in the phase or composition of the particles. Thus, this work demonstrated a new concept, subnano-transformation, which would be a new class of phase transformation based on the concept of the size dependence in such an ultrasmall scale. In addition, the movement of Mo atoms within a cluster and on the fringes of a nanoparticle was also demonstrated during continuous time-course high-resolution HAADF-STEM observation. This journal is
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U2 - 10.1039/d0nr04495d
DO - 10.1039/d0nr04495d
M3 - Article
C2 - 32691809
AN - SCOPUS:85089125253
VL - 12
SP - 15814
EP - 15822
JO - Nanoscale
JF - Nanoscale
SN - 2040-3364
IS - 29
ER -