Crystallization behavior of 3D-structured OMS-2 under hydrothermal conditions

Abstract

Homogeneous flower-like OMS-2 particles were successfully prepared in a short time of merely 4 h using a hydrothermal method under a MnSO₄–K₂S₂O₈–K₂SO₄–H₂SO₄ system. The flower-like OMS-2 particles with a diameter of around 2 μm were composed of uniform slender cryptomelane rods several hundred nanometers in length when the pH of the precursor solution was 0.18 and the solution was treated at 443 K. XRD and SEM characterization techniques demonstrated that formation of flower-like OMS-2 involved three stages including formation of fiber-like OMS-2, flower-like pyrolusite-type MnO₂ and flower-like OMS-2 with decreasing pH value from 4.08 to 0.18. In the case of reaction time, the redox reaction between Mn²⁺ and S₂O₈²⁻ was accomplished within the initial 1 h, and the highly crystallized uniform flower-like particles were obtained at 4 h.