pH-Dependent Degradation of Methylene Blue via Rational-Designed MnO2 Nanosheet-Decorated Diatomites

Hierarchical MnO 2 -modified diatomite (MnO 2 -D) nanostructures are synthesized through a one-pot hydrothermal method. By adjusting the preparative parameters, the morphology and surface pore size distribution of MnO 2 -D composites can be well-controlled. Their nanostructures are examined by focused-ion-beam scanning electron microscopy (FIB/SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), and Fourier transform infrared (FT-IR) spectroscopy. The results show that birnessite-type MnO 2 nanosheets are observed to grow vertically on the internal and external surfaces of purified diatomite, thus building a hierarchical architecture. Furthermore, the degradation ability of MnO 2 -D composites toward MB solution is fully investigated. It was found that MnO 2 -D composite degraded 97.7% of MB solution (0.02 g L –1, 100 mL) by oxidation within only 5 min in acid solution (pH 2); moreover, in neutral solution (pH 6–7), this composite catalyzed the oxidation decomposition reaction of MB (0.02 g L –1, 100 mL) by H 2 O 2 with a high removal percentage of 92.4% in 2 h, and it also represented a high adsorption capacity of 714.3 mg g –1 for the removal of MB in alkaline solution (pH 11), respectively. In principle, these MnO 2 -D composites provided an appropriate way for the degradation of complex and various dye wastewater in practical applications.