Abstract EANA2025-57

The alteration of sulphide minerals under ultraviolet (UV) radiation provides an important source of chemical species such as oxides, hydroxides, sulphates and carbonates. Furthermore, sulphide minerals, due to their chemical complexity, have been proposed as a key process in the formation of prebiotic molecules such as ammonia, one of the necessary building blocks in amino acids, nucleic acids and proteins [1,2]. In addition, UV-induced photocatalysis process on sulphide minerals such as pyrite, promotes the fixation of nitrogen from the atmosphere. This process has been proposed as abiotic mechanism providing a source of fixed nitrogen in a biochemically available form [3]. However, the influence of characteristic mineral parameters, such as metal composition and crystalline structure, on the mechanism of nitrogen fixation is not yet fully understood [4].  

The aim of this work is to analyse the structure of different minerals, in order to probe whether the presence of iron bonded to sulphur as disulphide or monosulphide is critical in the nitrogen adsorption process under UV conditions. For this purpose, we exposed different metal sulphides present in early Earth -pyrite (FeS2), chalcopyrite (CuFeS2), pyrrhotite (Fe7S8) and millerite (NiS)- to UV radiation under ambient conditions. The samples were irradiated with UV for short (2 hours) and long (27 hours) periods of time. The characterization was performed by the techniques X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), focusing on the role of the metal cation of each sulphide as a parameter to be studied in the nitrogen fixation process from the atmosphere.

Preliminary results indicate a higher nitrogen fixation in pyrite and, to a minor extend, also in chalcopyrite compared to the monosulphides, pyrrhotite and millerite. It is proposed that the coordination of iron with sulphur and the crystalline structure of each mineral may serve as parameters favouring or inhibiting the nitrogen adsorption process. The formation of oxides and sulphates after different UV irradiation times was also identified. In the case of chalcopyrite, after exposure to UV radiation, local patches of CN compounds have been identified on the surface observed by SEM and characterized by XPS and EDX; in these, nitrogen is associated with three different chemical groups.

The present study contribute to the understanding of the reactivity of different sulphide mineral surfaces in the process of nitrogen fixation from the atmosphere. These surfaces facilitate the natural fixation of atmospheric nitrogen, catalysing it into functional groups that are then accessible for polymerization reactions. Unravelling these mechanisms provides a better understanding of the prebiotic chemistry and the origins of life on early Earth.

[1] Laura E. Rodriguez, Thiago Altair, Ninos Y. Hermis, Tony Z. Jia et al, “Chapter 4: A Geological and Chemical Context for the Origins of Life on Early Earth” Astrobiology 24(S1), 76-106 (2024).

[2] C. Felipe Garibello, Daniel S. Eldridge, Francois Malherbe and Rosalie K. Hocking, “Abiotic transformations of nitrogen mediated by iron sulfides and related species from early Earth to catalyst design” Inorg. Chem. Fron. 10, 6792-6811 (2023).

[3] E. Mateo-Marti, S. Galvez-Martinez, C. Gil-Lozano and María-Paz Zorzano, “Pyrite-induced uv-photocatalytic abiotic nitrogen fixation: implications for early atmospheres and Life” Scientific Reports 9, 15311-15321 (2019).

[4] Yamei Li , Norio Kitadai and Ryuhei Nakamura, “Chemical Diversity of Metal Sulfide Minerals and Its Implications for the Origin of Life” Life 8(4), 46-72 (2018).