Identification of the surface structure of nanoparticles is important for understanding the catalytic mechanism and improving the properties of the particles. Here, we provide a detailed description of the coordination modes of ethylenediaminetetraacetate (EDTA) on Mn3O4 nanoparticles at the atomic level, as obtained by advanced electron paramagnetic resonance (EPR) spectroscopy. Binding of EDTA to Mn3O4 leads to dramatic changes in the EPR spectrum, with a 5-fold increase in the axial zero-field splitting parameter of Mn(II). This indicates significant changes in the coordination environment of the Mn(II) site; hence, the binding of EDTA causes a profound change in the electronic structure of the manganese site. Furthermore, the electron spin echo envelope modulation results reveal that two 14N atoms of EDTA are directly coordinated to the Mn site and a water molecule is coordinated to the surface of the nanoparticles. An Fourier transform infrared spectroscopy study shows that the Ca(II) ion is coordinated to the carboxylic ligands via the pseudobridging mode. The EPR spectroscopic results provide an atomic picture of surface-modified Mn3O4 nanoparticles for the first time. These results can enhance our understanding of the rational design of catalysts, for example, for the water oxidation reaction.
Bibliographical noteFunding Information:
This research was supported by Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) funded by Ministry of Science and ICT (NRF-2017M3D1A1039377 to K.T.N. and 2017M3D1A1039380 to S.H.K.) and NRF grant funded by Ministry of Science and ICT (NRF-2017R1A2B4008691 to S.H.K.). K.T.N. appreciates the support from Institute of Engineering Research, Research Institute of Advanced Materials (RIAM) and Soft Foundry at Seoul National University.
Copyright © 2020 American Chemical Society.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry