Atomic scale insight into the decomposition of nanocrystalline zinc hydroxynitrate toward ZnO using Mn2+ paramagnetic probes

Ioana D Vlaicu; Mariana Stefan; Cristian Radu; Daniela C Culita; Dana Radu; Daniela Ghica

doi:10.3389/fchem.2023.1154219

Atomic scale insight into the decomposition of nanocrystalline zinc hydroxynitrate toward ZnO using Mn²⁺ paramagnetic probes

Front Chem. 2023 Apr 6:11:1154219. doi: 10.3389/fchem.2023.1154219. eCollection 2023.

Authors

Ioana D Vlaicu¹, Mariana Stefan¹, Cristian Radu^{1

2}, Daniela C Culita³, Dana Radu¹, Daniela Ghica¹

Affiliations

¹ National Institute of Materials Physics, Magurele, Romania.
² Faculty of Physics, University of Bucharest, Magurele, Romania.
³ Ilie Murgulescu Institute of Physical Chemistry, Romanian Academy, Bucharest, Romania.

Abstract

Layered zinc hydroxynitrate (ZHN), with the chemical formula Zn₅ (OH)₈ (NO₃)₂·2H₂O, exhibits a range of special properties such as anion-exchange and intercalation capacity, as well as biocompatibility, making it attractive for a large variety of applications in fields from nanotechnology to healthcare and agriculture. In this study nanocrystalline ZHN doped with 1,000 ppm Mn²⁺ was prepared by two synthesis methods (coprecipitation and solid state reaction) using similar environment-friendly precursors. The complex morpho-structural [X-ray diffraction, scanning and transmission electron microscopy, textural analysis] and spectroscopic [Fourier transform infrared and electron paramagnetic resonance (EPR)] characterization of the two ZHN nanopowders showed similar crystalline structures with Mn²⁺ ions localized in the nanocrystals volume, but with differences in their morphological and textural characteristics, as well as in the doping efficiency. ZHN obtained by coprecipitation consists of larger nanoplatelets with more than two times larger specific surface area and pore volume, as well as a dopant concentration than in the ZHN sample obtained by solid state reaction. The thermal stability and the on-set of the structural phase transformation have been investigated at atomic scale with high accuracy by EPR, using Mn²⁺ as paramagnetic probes. The on-set of the ZHN structural phase transformation toward ZnO was observed by EPR to take place at 110°C and 130°C for the samples prepared by coprecipitation and solid state reaction, respectively, evidencing a manganese induced local decrease of the transformation temperature. Our results contribute to the selection of the most appropriate ZHN synthesis method for specific applications and in the development of new green, cost-effective synthesis routes for Mn²⁺ doped nano-ZnO.

Keywords: Mn2+ paramagnetic probe; electron paramagnetic resonance; morpho-structural analysis; nanocrystals; structural phase transformation; zinc hydroxynitrate.

Grants and funding

This work is funded by the Core Program of the National Institute of Materials Physics, granted by the Romanian Ministry of Research, Innovation and Digitalization through the Project PC1- PN23080101. The fee for open access publication was supported from the project 35PFE/2021, funded by the Romanian Ministry of Research, Innovation and Digitization.