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

Abstract

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 (S0), as the dominant mineral in terrestrial hot springs, can reduce carbon dioxide (CO2) into formic acid (HCOOH) under ultraviolet (UV) light below 280 nm. The semiconducting S0 is indicated to have a direct bandgap of 4.4 eV. The UV-excited S0 produces photoelectrons with a highly negative potential of −2.34 V (versus NHE, pH 7), which could reduce CO2 after accepting electrons from electron donors such as reducing sulfur species. Simultaneously, UV light breaks sulfur bonds, benefiting the adsorption of charged carbonates onto S0 and assisting their photoreduction. Assuming that terrestrial hot springs covered 1% of primitive Earth’s surface, S0 at 10 μM could have produced maximal 109 kg/year HCOOH within 10-cm-thick photic zones, underlying its remarkable contributions to the accumulation of prebiotic biomolecules.

Investigating the viability of sulfur polymers for the fabrication of photoactive, antimicrobial, water repellent coatings

“…It is expected that intense UV exposure not only promotes photocatalysis but also degradation of the polymer and/or S–S bonds, leading to the production of organic contaminates that change the wettability and result in the UV-induced hydrophilicity that was observed. 40 As previously reported by Liu et al , the suspected photocatalysis mechanism of elemental sulfur liberates OH˙ radicals – though sulfur can retain its intrinsic hydrophobicity, the presence of radical species could contribute towards the degradation of the organic crosslinker. 40 Despite this, when compared to our past work using coatings composed of titanium dioxide nanoparticles functionalised with a monolayer of fluoroalkyl silane molecules (TiO2-FAS), which turned superhydrophilic after only 12 minutes of irradiation, PER_60–60 displayed greatly enhanced UV stability.…”

“…40 As previously reported by Liu et al , the suspected photocatalysis mechanism of elemental sulfur liberates OH˙ radicals – though sulfur can retain its intrinsic hydrophobicity, the presence of radical species could contribute towards the degradation of the organic crosslinker. 40 Despite this, when compared to our past work using coatings composed of titanium dioxide nanoparticles functionalised with a monolayer of fluoroalkyl silane molecules (TiO2-FAS), which turned superhydrophilic after only 12 minutes of irradiation, PER_60–60 displayed greatly enhanced UV stability. It is expected that the presence of sulfur decelerated the rate of photodegradation due to its stability against UV induced changes in wettability.…”

An assumption of in situ resource utilization for “bio-bricks” in space exploration

“…More economically, the magnetite-assisted in situ microbial oxidation of H 2 S to S 0 has been recently reported (Jung et al, 2020). Furthermore, elemental sulfur S 0 can reduce CO 2 into formic acid under ultraviolet light below 280 nm (Li et al, 2020a). Thus, state-of-the-art of physical/chemical and biological technology requires more research on the application of sulfate reduction in bioconcrete.…”

Carbon dioxide photoreduction in prebiotic environments

“…Simultaneously, UV light breaks sulfur bonds, allowing the adsorption of charged carbonates onto S 0 and assisting their photoreduction. Assuming that terrestrial hot springs covered 1% of primitive Earth's surface, S could have produced up to 10 9 kg/year HCOOH within 10-cm-thick photic zones, underlying its remarkable contributions to the accumulation of prebiotic biomolecules [61].…”