Substitution of Ca2+ in Calcite by Sn2+ and Sr2+ cations through ion exchange characterized by X-ray absorption and photoelectron spectroscopies

Abstract

Tin (Sn2+) and strontium (Sr2+), two potential alternatives to lead (Pb2+) in perovskite formation, were explored in transforming calcium carbonate (CaCO3) into a leaving group in a cation exchange reaction. This is the first part of a sequential ion exchange process in transforming calcite into a Pb-free perovskite material for perovskite solar cell applications. Calcite, a polymorph of CaCO3, was successfully transformed into strontianite (SrCO3) through a cation exchange reaction. In the Sn substitution reaction on the other hand, no SnCO3 formation was noted. Instead, oxides of Sn were formed. The wider spaces in between Ca2+ cations in (100) orientation account for the higher atomic Sn2+ and Sr2+ concentrations as compared to (001) orientation, where the cation movement is restricted. X-ray absorption and photoelectron spectroscopies were used to investigate the ion-exchange transformation of calcite towards the formation of an intermediate carbonate material. Graphic abstract

Sn-rich tourmaline from the Land’s End granite, SW England

“…Similarly, Weck and Kim (2016) predicted that Sn 2+ may be substituted for Ca as a major element in hydroxylapatite. Contrary to the theoretical studies mentioned above, experiments trying to incorporate Sn 2+ into carbonates were unsuccessful (Junio et al 2021), and feldspars from tin granites have very low Sn contents (Müller et al 2006;Chen et al 2021).…”

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Mineralogy, geochemistry, and depositional environment of phosphates in the Pabdeh Formation, Khormuj anticline, SW of Iran

“…al. 2021) and the activity of bacteria that reduce sulfate to sul de(Zarasvandi et al 2021); Eu 2+ replaces Ca 2+ in francolite and calcium carbonate due to their similar ionic radius (1.01 Å)(Junio et al 2021). Consequently, a positive Eu anomaly is created in carbonate and phosphate sediments.…”