Microporous assembly of MnO2 nanosheets for malachite green degradation

•Microporous MnO2 material with large surface area was prepared.•The material comprised of spherical soft aggregates of MnO2 nanosheets.•Malachite green (MG) degradation was carried out using the MnO2 nanomaterial.•MG degradation was performed under room temperature stirring.•About 99% decolorization and 40% mineralization of MG was achieved in 1 h.

Porous assembly of MnO2 nanosheets has been prepared via a simple redox co-precipitation method using Mn(OAc)2 and KMnO4. The material has been characterized by XRD, XPS, FESEM, TEM, FTIR, and N2-adsorption–desorption analyses. The as-prepared MnO2 nanomaterial is microporous (average pore diameter: 0.8 nm; surface area: 162 m2/g) and poorly crystalline. The TEM and SEM images reveal the formation of spherical assembly of fine nanosheets. The oxidation state of manganese is determined by XPS analysis. The porous nature and the oxidizing property of the nano MnO2 has been exploited for MG degradation in aqueous media under ambient condition. The effects of various parameters (such as pH, MnO2 dose, initial MG concentration, air/O2, and organic acids) on MG degradation are evaluated. The mineralization of MG is monitored through TOC analyses. About 99% decolorization and ∼44% mineralization of MG (conc.: 50 mg/L) is achieved in 120 min with MnO2 (dose: 0.5 g/L). The decolorization follows first order kinetics. During the oxidative degradation, slight leaching of Mn2+ is observed. The reusability of the material has been shown for three consecutive cycles with good performance.

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