title: Controllable synthesis of α- and β-MnO(2): cationic effect on hydrothermal crystallization.
abstract: α- and β-MnO(2) were controllably synthesized by hydrothermally treating amorphous MnO(2) obtained via a reaction between Mn(2+) and MnO(4)(-), and cationic effects on the hydrothermal crystallization of MnO(2) were investigated systematically. The crystallization is believed to proceed by a dissolution-recrystallization mechanism; i.e. amorphous MnO(2) dissolves first under hydrothermal conditions, then condenses to recrystallize, and the polymorphs formed are significantly affected by added cations such as K(+), NH(4)(+) and H(+) in the hydrothermal systems. The experimental results showed that K(+)/NH(4)(+) were in competition with H(+) to form polymorphs of α- and β-MnO(2), i.e., higher relative K(+)/NH(4)(+) concentration favoured α-MnO(2), while higher relative H(+) concentration favoured β-MnO(2).
authors.affiliation: State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, Xiamen University, Xiamen 361005, People's Republic of China.
authors.forename: Xingkang
authors.initials: X
authors.lastname: Huang
authors.forename: Dongping
authors.initials: D
authors.lastname: Lv
authors.forename: Hongjun
authors.initials: H
authors.lastname: Yue
authors.forename: Adel
authors.initials: A
authors.lastname: Attia
authors.forename: Yong
authors.initials: Y
authors.lastname: Yang