The photogeochemical cycle of Mn oxides on the Earth's surface

Manganese (Mn) oxides have been prevalent on Earth since before the Great Oxidation Event and the Mn cycle is one of the most important biogeochemical processes on the Earth's surface. In sunlit natural environments, the photochemistry of Mn oxides has been discovered to enable solar energy harvesting and conversion in both geological and biological systems. One of the most widespread Mn oxides is birnessite, which is a semiconducting layered mineral that actively drives Mn photochemical cycling in Nature. The oxygen-evolving centre in biological photosystem II (PSII) is also a Mn-cluster of Mn4CaO5, which transforms into a birnessite-like structure during the photocatalytic oxygen evolution process. This phenomenon draws the potential parallel of Mn-functioned photoreactions between the organic and inorganic world. The Mn photoredox cycling involves both the photo-oxidation of Mn(II) and the photoreductive dissolution of Mn(IV/III) oxides. In Nature, the occurrence of Mn(IV/III) photoreduction is usually accompanied with the oxidative degradation of natural organics. For Mn(II) oxidation into Mn oxides, mechanisms of biological catalysis mediated by microorganisms (such as Pseudomonas putida and Bacillus species) and abiotic photoreactions by semiconducting minerals or reactive oxygen species have both been proposed. In particular, anaerobic Mn(II) photo-oxidation processes have been demonstrated experimentally, which shed light on Mn oxide emergence before atmospheric oxygenation on Earth. This review provides a comprehensive and up-to-date elaboration of Mn oxide photoredox cycling in Nature, and gives brand-new insight into the photochemical properties of semiconducting Mn oxides widespread on the Earth's surface.

Thermodynamics of the S2-to-S3 state transition of the oxygen-evolving complex of photosystem II

The S2 to S3 transition in the OEC of PSII changes the structure of the Mn cluster. Monte Carlo sampling finds a Ca terminal water moves to form a bridge to Mn4 and the Mn1 ligand E189 can be replaced with a hydroxyl as a proton is lost.

A Mn13-cluster based coordination polymer as a co-catalyst of CdS for enhanced visible-light driven H2 evolution

A Mn cluster-based polymer has been applied as a noble-metal-free co-catalyst of CdS, showing enhanced photocatalytic H2-production activity under visible light.

A novel 2-D Mn selenidostannate(iv) incorporating high-nuclear Mn clusters with spin canting behavior

The incorporation of a hepta-nuclear Mn cluster [Mn7(ea)6]8+ into a selenidostannate(iv) framework leads to a novel 2-D Mn selenidostannate(iv) with spin canting behavior.