Crystal structure control of nanosized MnO₂ particles synthesized by a hydrothermal process using different Mn precursors

Abstract

Single-phase α-,β-, and γ-MnO₂ nanoparticles with high crystallinity were successfully synthesized by a hydrothermal process using different Mn precursors, such as Mn(OAc)₂, MnSO₄, MnCl₂, and Mn(NO₃)₂. The crystal structure and morphology of the MnO₂ particles could be effectively controlled by changing the Mn source. The use of Mn(OAc)₂ and MnSO₄ as precursors resulted in rod-shaped α- and β-MnO₂ particles, whereas MnCl₂, and Mn(NO₃)₂ yielded aggregated angular nanoparticles of γ-MnO₂. X-ray photoelectron spectroscopic analysis revealed that β-MnO₂ had a high ratio of Mn4+ and Olatt on the particle surface, whereas α- and γ-MnO₂ sample had a lower valence state of Mn, such as Mn3+ and Mn2+, on the surface, and the ratio of Olatt was also relatively low.