Hybrid Mn3O4–NiO nanocomposites as efficient photoelectrocatalysts towards water splitting under neutral pH conditions

Dual oxide Mn₃O₄–NiO nanocomposites synthesised by seed-mediated epitaxial growth have been exploited as electrocatalysts towards water splitting at an applied overpotential of 280 mV under neutral pH conditions.

The effect of lanthanum(III) and cerium(III) ions between layers of manganese oxide on water oxidation

Manganese oxide structure with lanthanum(III) or cerium(III) ions between the layers was synthesized by a simple method. The ratio of Mn to Ce or La in samples was 0.00, 0.04, 0.08, 0.16, 0.32, 0.5, 0.82, or 1.62. The compounds were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction studies, and atomic absorption spectroscopy. The compounds show efficient catalytic activity of water oxidation in the presence of cerium(IV) ammonium nitrate with a turnover frequency of 1.6 mmol O2/mol Mn.s. In contrast to the water-oxidizing complex in Photosystem II, calcium(II) has no specific role to enhance the water-oxidizing activity of the layered manganese oxides and other cations can be replaced without any significant decrease in water-oxidizing activities of these layered Mn oxides. Based on this and previously reported results from oxygen evolution in the presence of H 2 (18) O, we discuss the mechanism and the important factors influencing the water-oxidizing activities of the manganese oxides.

Manganese oxides supported on gold nanoparticles: new findings and current controversies for the role of gold

We synthesized manganese oxides supported on gold nanoparticles (diameter <100 nm) by the reaction of KMnO4 with gold nanoparticles under hydrothermal conditions. In this green method Mn oxide is deposited on the gold nanoparticles. The compounds were characterized by scanning electron microscopy, energy-dispersive spectrometry, high-resolution transmission electron microscopy, X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. In the next step, the water-oxidizing activities of these compounds in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant were studied. The results show that these compounds are good catalysts toward water oxidation with a turnover frequency of 1.0 ± 0.1 (mmol O2/(mol Mn·s)). A comparison with other previously reported Mn oxides and important factors influencing the water-oxidizing activities of Mn oxides is also discussed.

Carbon for engineering of a water-oxidizing catalyst

Herein we report that the reaction of KMnO4 with cobalt nanoparticles coated with multiple graphene layers forms a promising catalyst toward water oxidation. The compound was characterized by scanning electron microscopy, energy-dispersive spectroscopy, high resolution transmission electron microscopy, X-ray diffraction, electronic spectroscopy, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. In addition to the Mn oxide-based characteristics of the catalyst, it is a conductive, self-healing, recycling, highly dispersible, magnetically separable, environmentally friendly, and nano-sized catalyst for water oxidation. The turnover frequency for the catalyst toward water oxidation is 0.1 and 0.05 (mmol O2 per mol Mn s) in the presence of cerium(iv) ammonium nitrate and photo-produced Ru(bpy)3(3+).

A very simple and high-yield method to synthesize nanolayered Mn oxide

Nanolayered Mn oxides have been prepared by a very simple, low-cost and high-yield method using soap, KOH, MnCl2 and H2O2. Scanning electron microscopy, transmission electron microscopy, dynamic light scattering, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray diffraction spectrometry have been used to characterize the phase and the morphology of the nanolayered Mn oxide. The nanolayered Mn oxide shows good catalytic activity toward water oxidation in the presence of cerium(iv) ammonium nitrate.

Gold nanorods or nanoparticles deposited on layered manganese oxide: new findings

Our results show that nano-sized gold has no significant effect on the water-oxidation activity of the Mn oxide phase in the presence of Ce(iv).

Nano-sized Mn oxides on halloysite or high surface area montmorillonite as efficient catalysts for water oxidation with cerium(iv) ammonium nitrate: support from natural sources

We used halloysite, a nano-sized natural mineral and high surface area montmorillonite as supports for nano-sized Mn oxides to synthesize efficient water-oxidising catalysts.