Iron sulfur (Fe–S) phases have been implicated in the emergence of life on early Earth due to their catalytic role in the synthesis of prebiotic molecules. Similarly, Fe–S phases are currently of high interest in the development of green catalysts and energy storage. Here we report the synthesis and structure of a nanoparticulate phase (FeSnano) that is a necessary solid-phase precursor to the conventionally assumed initial precipitate in the iron sulfide system, mackinawite. The structure of FeSnano contains tetrahedral iron, which is compensated by monosulfide and polysulfide sulfur species. These together dramatically affect the stability and enhance the reactivity of FeSnano.

We have investigated the adsorption stability of ruthenium N749 dye [black dye (BD)], a highly efficient dye for dye-sensitized solar cells (DSCs), through protonated and deprotonated carboxyl group anchors on a TiO2 anatase (101) surface by using first-principles calculations. Geometry optimizations of the surface system with a supercell and the UV-visible spectrum calculation of the optimized dye structure were carried out. Among the configurations with one and two anchors, the BD adsorption anchored with one protonated carboxyl group was found to be the most stable, in contrast to most previous reports. Hydrogen bonding between the proton retained in BD and the surface oxygen is responsible for the stability of the protonated anchor. We confirmed that the calculated UV-visible spectrum of the most stable dye structure shows the best consistency with the experimental data. It is also demonstrated that the electronic density of states largely depends on the proton position. This novel aspect of adsorption via a protonated carboxyl anchor gives a new perspective for interfacial electronic processes of DSCs.

We have used DFT calculations to investigate the binding of catechol, one of the smallest sensitizing chromophores, to the rutile TiO2(100) surface. On the clean surface, we find that monodentate adsorption is favored over molecular adsorption. An oxygen defective site strongly favors the fully dissociative bidentate adsorption, which is otherwise found not to be stable. Regardless of the protonation form of catechol, however, occupied molecular states are introduced into the band gap of rutile (100). The lowest unoccupied levels are localized exclusively on the substrate.