Photoreduction of inorganic carbon(+IV) by elemental sulfur: Implications for prebiotic synthesis in terrestrial hot springs

摘要

Terrestrial hydrothermal systems have been proposed as alternative birthplaces for early life but lacked reasonable scenarios for the supply of biomolecules. Here, we show that elemental sulfur (Ssup0/sup), as the dominant mineral in terrestrial hot springs, can reduce carbon dioxide (COsub2/sub) into formic acid (HCOOH) under ultraviolet (UV) light below 280 nm. The semiconducting Ssup0/sup is indicated to have a direct bandgap of 4.4 eV. The UV-excited Ssup0/sup produces photoelectrons with a highly negative potential of ?2.34 V (versus NHE, pH 7), which could reduce COsub2/sub after accepting electrons from electron donors such as reducing sulfur species. Simultaneously, UV light breaks sulfur bonds, benefiting the adsorption of charged carbonates onto Ssup0/sup and assisting their photoreduction. Assuming that terrestrial hot springs covered 1% of primitive Earth’s surface, Ssup0/sup at 10 μM could have produced maximal 10sup9/sup kg/year HCOOH within 10-cm-thick photic zones, underlying its remarkable contributions to the accumulation of prebiotic biomolecules.