Hydrothermal Synthesis and Crystal Structure of a Mixed-Valence Bismuthate, Na3Bi3O8

Md Saiduzzaman; Shuhei Akutsu; Nobuhiro Kumada; Takahiro Takei; Sayaka Yanagida; Hisanori Yamane; Yoshihiro Kusano

doi:10.1021/acs.inorgchem.0c00213

Hydrothermal Synthesis and Crystal Structure of a Mixed-Valence Bismuthate, Na₃Bi₃O₈

Inorg Chem. 2020 Apr 6;59(7):4950-4960. doi: 10.1021/acs.inorgchem.0c00213. Epub 2020 Mar 26.

Authors

Md Saiduzzaman¹, Shuhei Akutsu¹, Nobuhiro Kumada¹, Takahiro Takei¹, Sayaka Yanagida¹, Hisanori Yamane², Yoshihiro Kusano³

Affiliations

¹ Center for Crystal Science and Technology, University of Yamanashi, 7-32 Miyamae-cho, Kofu 400-8511, Japan.
² Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
³ Department of Applied Chemistry and Biotechnology, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan.

PMID: 32212697
DOI: 10.1021/acs.inorgchem.0c00213

Abstract

Four types of bismuth oxides, Na₃Bi₃O₈, NaBiO₃, α-Bi₂O₃, and ε-Bi₂O₃, were obtained by hydrothermal reactions using NaBiO₃·nH₂O in NaOH solution. The crystal structure of a new phase (Na₃ Bi³⁺)Bi₂⁵⁺O₈ ((Na_0.75Bi_0.25)₂BiO₄) was determined by using single crystal X-ray diffraction data, and this compound was found to show a Na₂MnCl₄-related structure with a monoclinic system (space group, Pm) with the following lattice parameters: a = 5.990 (2) Å, b = 3.335 (2) Å, c = 10.108 (2) Å, and β = 91.08 (3)°. The final R-factors R₁ and wR₂ were 0.041 and 0.090 (all data), respectively. The new phase was composed of mixed valence states of Bi (Bi³⁺ and Bi⁵⁺, with a mean Bi valence of 4.30) with five distinct Bi sites, where two Bi⁵⁺ (Bi1 and Bi2) fully occupied the distorted octahedral sites and three Bi³⁺ (Bi3, Bi4, and Bi5) were statistically distributed at the split sites with Na⁺ (Na3, Na4, and Na5). The Na6 site is fully occupied. The distorted Bi⁵⁺O₆ octahedra formed one-dimensional chains via edge-sharing along the b-axis, with the chains held by Bi³⁺/Na⁺ split sites. The structural feature except for the split distribution of Bi³⁺/Na⁺ was classified as a Na₂MnCl₄-type structure. DFT calculations based on a model discounting the split distribution of Bi³⁺/Na⁺ indicated that Bi 6s and O 2p orbitals form sp hybridization at the conduction band. This new mixed valence bismuth oxide exhibited photocatalytic activity for phenol degradation under visible light irradiation. In addition to Na₃Bi₃O₈, the hydrothermal reaction using NaBiO₃·nH₂O in NaOH solution yielded micrometer-sized single crystals of an ilmenite-type NaBiO₃ and two polymorphs of bismuth oxides with monoclinic (α-Bi₂O₃) and orthorhombic (ε-Bi₂O₃) structures, depending on the reaction temperature and NaOH concentration.