Highly efficient oxidative degradation of organic dyes by manganese dioxide nanoflowers

MnO2 nanoflowers were synthesized using one pot chemical precipitation method. The MnO2 nanoflowers consisted of intersected nanosheets. XRD, HRTEM and BET analyses indicate that the MnO2 nanoflowers contained amorphous structure with surface area of 253 m2/g and pores size of 79.3 Å. The catalytic performance of MnO2 nanoflowers to degrade Rhodamine (RhB) without optical light source was examined. It performed well under acidic condition (pH 3) with 99.0% of removal efficiency in 10 min. The oxidative degradation mechanism of RhB by MnO2 nanoflowers was proposed based on a few findings. First, the crystal defects in the amorphous structure facilitated a series of oxidative degradation process. Second, the formation of Mn2+ in acidic condition catalysed the formation of hydroxyl free radicals for the degradation of RhB. Third, the high surface area-to-volume ratio of nanoflowers provided large area for the absorption of RhB dye. From practical perspectives, the MnO2 nanoflowers showed excellent repeatability on its removal performance by recording 98.4% removal efficiency even after 5 repeated cycles. The MnO2 nanoflowers also showed good removal efficiency on industrial dye waste sample. This catalyst is envisioned to hold great promise for organic wastewater treatment with virtues of high efficiency and excellent repeatability performance.