A facile one-pot synthesis of three-dimensional microflower birnessite (δ-MnO2) and its efficient oxidative degradation of rhodamine B

Abstract

High purity birnessite (δ-MnO₂) was obtained by a facile one-pot method using MnSO₄·H₂O as a Mn resource, ethylenediamine tetraacetic acid disodium salt (EDTA-Na) as a complexing agent and oxygen in the air as an oxidant under alkaline conditions. The as-prepared birnessite presented three-dimensional microflowers composed of two-dimensional ultrathin nanosheets. Degradation results indicated that the prepared δ-MnO₂ possessed excellent abilities for removal of rhodamine B (RhB). Typically, 50 mL of RhB (10 mg L⁻¹) could be degraded completely with a 10 mg sample in 5 min without any additives such as hydrogen peroxide, peroxysulphate or any supplementary means such as microwaves or ultrasound. The samples were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and N₂ gas adsorption–desorption and thermogravimetry analysis (TGA) techniques. The mechanism of the degradation process was proposed and it was discussed that a redox reaction between birnessite and RhB occurred in an acidic environment. Clearly, the as-prepared birnessite provides great potential for the rapid degradation of dyes and organic pollutants. As it has easily available starting materials, a simple method for synthesis and undemanding degradation conditions, the as-prepared birnessite has high practical value in treating environmental pollutants.