Octahedral morphology of NiO with (111) facet
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Among environmental air pollutants, Nitrogen Oxides, also refers as NOx, are particularly generated from fuel cell combustion of industrial processes or vehicle engine. Moreover, the massive use of non-renewable energy has made NOx concentration in air increases in recent years based on previous evidence. They are heavily toxic to humans, causing severe health problems include short breath, headaches, respiratory malfunction, eye irritation and so on. On that account, many scientist are urged to develop responsive sensing and active photocatalyst materials to detect and degrade NOx for saving humanity.
On the other hand, Nickel Oxide (NiO), a transition metal oxide semiconductor with a rock-type structure, has shown its potentiality towards NOx sensing and removal. Their performance, however, is far from satisfaction due to a low surface-gas molecules interaction. A conceptual design has been proposed to explore facet formation in a typical rock-salt type material, and (111)-faceted NiO is particularly promising due to adsorption site abundancy and high polarity, yet practically difficult to design for its thermodynamic unfavorability
Recently, the group of Prof. Shu Yin at the Institute Multidisciplinary Research on Advanced Materials (IMRAM) of Tohoku University and collaborators, Prof. Ryo Maezono of the Japan Advanced Institute of Science and Technology have successfully demonstrated the promising strategy to synthesize NiO with a dominantly (111) surface facet using a layered nickel hydroxychlorides (NiOHCl) as shown in Figure 1. The morphological structure showed (111) facet of octahedron nanostructure of NiO was parallel to (111) surface plane, in an fcc crystal system.
Fig. 1 (a-c) Detail morphological observation and (d) morphological transformation of octahedral morphology of (111)-faceted NiO
The group has shown that the obtained NiO exhibited the best NOx gas sensing response (16.5 %) to 300 ppb level and deNOx photocatalytic ability over 50% under UV irradiation compared to another crystal facet such as (110) (Figure 2). Using DFT calculation, the group has revealed that that the abundance of Ni atoms in the clean (111) surface layer enables the favorable adsorption of N adatoms, forming the Ni-N bond. The charge transfer from NiO to NO orbital has proven to be a cause of bond weakening and stretching from 1.1692 Å to 1.2231 Å, leading to NOx molecular decomposition.
Figure 2 (a) NOx sensing response and (b) deNOx ability of NiO samples
It is interesting to highlight several key points of this finding. First, ionic chlorine in NiOHCl may be helpful for (111) facet formation during the transformation process. Second, (111) crystal facet exhibited the lowest adsorption energy for NOx molecules, led to the best surface-gas interaction and charge transfer-induced redox reaction. Third, NOx gas is likely to be highly adsorbed on Ni terminated surface with N adatom rather than O, led to high selectivity compared to other organic vapors (containing only C, H, and O).
The above combination of experimental and calculation results demonstrates that the surface-engineering approach offers the potential to design high-performance gas sensing and photocatalyst materials.
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Octahedral morphology of NiO with (111) facet synthesized from the transformation of NiOHCl for NOx detection and degradation: Experiment and DFT calculation
Angga Hermawan, Adie Tri Hanindriyo, Erland Rachmad Ramadhan, Yusuke Asakura, Takuya Hasegawa, Kenta Hongo, Miki Inada, Ryo Maezono and Shu Yin
Inorg. Chem. Front., 2019, Advance Article
http://dx.doi.org/10.1039/D0QI00682C
*文中图片皆来源上述文章
通讯作者简介
Professor Shu Yin
Tohoku University IMRAM
Dr. Shu Yin is a full professor in IMRAM, Tohoku University. He received a B. S. degree in inorganic chemical engineering from the Dalian University of Technology in 1987. He received a M. S. degree in chemical metallurgy from the Institute of Chemical Metallurgy (ICM, latterly Institute of Process and Engineering, IPE), Chinese Academy of Science in 1990, then worked as a research associate for 2 years at ICM. He came to Japan and worked as a research fellow in the Hydrothermal Chemistry Research Laboratory (Prof. N.Yamasaki’s Group), Kochi University in 1992, then became a research assistant at the Institute for Chemical Reaction Science (ICRS, Prof. T.Sato’s group), Tohoku University during 1995–1997. He received a Ph.D. degree in applied chemistry from Tohoku University (research period shortened) in 1999. He has been a research assistant at the ICRS in 1999, then a lecture and associate professor at the Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University in 2005, and then a fulltime professor in 2016.
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