Hydrothermal Synthesis of MnO2 Microspheres and Their Degradation of Toluene

Various urchin-like MnO₂ materials were obtained with a facile hydrothermal method through controlling the Mn precursor, reaction time, and reaction temperature. The property of MnO₂ materials was characterized by scanning electron microscopy, X-ray diffraction, and H₂ temperature-programmed reduction. The results showed that the Mn precursor could significantly impact the morphology of as-prepared MnO₂. When the precursor was Mn(CH₃COO)₂·4H₂O, the MnO₂ morphology consisted of tennis-like microspheres assembled by nanorods. While the precursor was MnCl₂·4H₂O, the sample morphology was a chestnut shell, and the samples were sea urchin microspheres, as the precursor was MnSO₄·H₂O. At the same time, the morphology of MnO₂ was affected by hydrothermal time and temperature. The nanoneedles on the microsphere surface gradually lengthened with increasing hydrothermal time and hydrothermal temperature, until nanowires were formed. MnO₂ crystallinity was also influenced by hydrothermal temperature. It was γ-MnO₂ as the temperature was 50 and 80 °C while evolved to be α-MnO₂ and β-MnO₂ when the temperature increased to 140 °C. As MnO₂ (MnO₂-1 h, MnO₂-2 h, MnO₂-4 h, and MnO₂-6 h) was prepared to degrade toluene, all the samples could completely catalyze toluene at the temperature of 225 °C. However, the MnO₂-4 h showed the best catalytic effect at a lower temperature.