Quantum Mechanical Modeling of CO₂ Interactions with Irradiated Stoichiometric and Oxygen-Deficient Anatase TiO₂ Surfaces: Implications for the Photocatalytic Reduction of CO₂

The conversion of CO₂ using light energy (CO₂ photoreduction) has the potential to produce useful fuels or valuable chemicals while decreasing CO₂ emissions from the use of fossil fuels. Identifying the mechanism and the active sites involved in the formation of negatively charged CO₂ species on TiO₂ surfaces represents a significant advance in our understanding of CO₂ photoreduction. To understand the role of the TiO₂ surface acting as a photocatalyst mediating CO₂ photocatalytic reduction, excited-state ab initio calculations of CO₂ adsorbed on clusters from the (010), (101), and (001) anatase surface planes were performed. Both post-Hartree−Fock calculations on small model surface clusters as well as density-functional theory (DFT) calculations on larger clusters indicate that conduction band electrons in irradiated, stoichiometric TiO₂ surfaces may not be transferred to CO₂. On the other hand, oxygen vacancies may act as the active sites for CO₂ photoreduction

Assessing the Depositional Environment of Cretaceous Ge-Rich Coals in the Wulantuga Mine, Shengli Coalfield, Northeastern China

To provide a new perspective on the formation of the Ge-rich coals, the depositional environment of the Wulantuga coals was studied with the incorporation of coal maceral and geochemistry-based indicators. The results show that the No.6 coal seam in the Wulantuga mine was formed in a mire with a succession of swamps, fens, and marsh. The average contents of Ge in coals formed in different mires, from high to low, are swamp (220 μg/g), marsh (205 μg/g), and fen (185 μg/g). The accumulation of the No.6 seam has been divided into four stages from bottom to top based on the identified coal facies types. The reducing condition and gelification of the ecosystem environment ranged from strong to weak, to strong, and back to weak. The variation of Ge concentrations also occurs in the same way. Strong reduction and gelification of the ecosystem environments can favor Ge enrichments in the Wulantuga coals. Sufficient sources and favorable conditions are essential for the unusual Ge enrichments in coals. This study provides a new perspective for the depositional environment of Ge-rich coals and is useful for the exploration of Ge-rich coal resources