Orange G degradation by heterogeneous peroxymonosulfate activation based on magnetic MnFe2O4/α-MnO2 hybrid.

Wastewater containing an azo dye Orange G (OG) causes massive environmental pollution, thus it is critical to develop a highly effective, environmental-friendly, and reusable catalyst in peroxymonosulfate (PMS) activation for OG degradation. In this work, we successfully applied a magnetic MnFe2O4/α-MnO2 hybrid fabricated by a simple hydrothermal method for OG removal in water. The characteristics of the hybrid were investigated by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller method, vibrating sample magnetometry, electron paramagnetic resonance, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The effects of operational parameters (i.e., catalytic system, catalytic dose, solution pH, and temperature) were investigated. The results exhibited that 96.8% of OG degradation was obtained with MnFe2O4/α-MnO2(1:9)/PMS system in 30 min regardless of solution pH changes. Furthermore, the possible reaction mechanism of the coupling system was proposed, and the degradation intermediates of OG were identified by mass spectroscopy. The radical quenching experiments and EPR tests demonstrated that SO4•̶, O2•̶, and 1O2 were the primary reactive oxygen species responsible for the OG degradation. The hybrid also displayed unusual stability with less than 30% loss in the OG removal after four sequential cycles. Overall, magnetic MnFe2O4/α-MnO2 hybrid could be used as a high potential activator of PMS to remove orange G and maybe other dyes from wastewater.

One-pot synthesis of manganese oxide/graphene composites via a plasma-enhanced electrochemical exfoliation process for supercapacitors.

In this work, a feasible one-pot approach to synthesize manganese oxide/graphene composites, the so-called plasma-enhanced electrochemical exfoliation process (PE3P), has been developed. Herein, a composite of graphene decorated with manganese oxide nanoparticles was prepared via PE3P from a KMnO4 solution and graphite electrode under a voltage of 70 V in an ambient environment. By controlling the initial KMnO4 concentration, we obtained distinct MnO2/graphene samples. The prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Raman spectroscopy. The electrochemical measurements of the MnO2/graphene composites revealed that the specific capacitance of the samples is approximately 320 F g-1 at a scan rate of 10 mV s-1, which is comparably very high for manganese oxide/carbon-based supercapacitor electrode materials. Considering the simple, low-cost, one-step and environmentally friendly preparation, our approach has the potential to be used for the fabrication of MnO2/graphene composites as the electrode materials of supercapacitors.

Facile synthesis of Mn-doped NiCo2O4 nanoparticles with enhanced electrochemical performance for a battery-type supercapacitor electrode.

We report the synthesis of manganese-doped nickel cobalt oxide (Mn-doped NiCo2O4) nanoparticles (NPs) by an efficient hydrothermal and subsequent calcination route. The material exhibits a homogeneous distribution of the Mn dopant and a battery-type behavior when tested as a supercapacitor electrode material. Mn-doped NiCo2O4 NPs show an excellent specific capacity of 417 C g-1 at a scan rate of 10 mV s-1 and 204.3 C g-1 at a current density of 1 A g-1 in a standard three-electrode configuration, ca. 152-466% higher than that of pristine NiCo2O4 or MnCo2O4. In addition, Mn-doped NiCo2O4 NPs showed an excellent capacitance retention of 99% after 1000 charge-discharge cycles at a current density of 2 A g-1. The symmetric solid-state supercapacitor device assembled using this material delivered an energy density of 0.87 µW h cm-2 at a power density of 25 µW h cm-2 and 0.39 µW h cm-2 at a high power density of 500 µW h cm-2. The cost-effective synthesis and high electrochemical performance suggest that Mn-doped NiCo2O4 is a promising material for supercapacitors.