Abstract
The molecular form of nitrogen, N2, is universally available but is biochemically inaccessible for life due to the strength of its triple bond. Prior to the emergence of life, there must have been an abiotic process that could fix nitrogen in a biochemically usable form. The UV photo-catalytic effects of minerals such as pyrite on nitrogen fixation have to date been overlooked. Here we show experimentally, using X-ray photoemission and infrared spectroscopies that, under a standard earth atmosphere containing nitrogen and water vapour at Earth or Martian pressures, nitrogen is fixed to pyrite as ammonium iron sulfate after merely two hours of exposure to 2,3 W/m 2 of ultraviolet irradiance in the 200–400 nm range. Our experiments show that this process exists also in the absence of UV, although about 50 times slower. The experiments also show that carbonates species are fixed on pyrite surface.
Highlights
The molecular form of nitrogen, N2, is universally available but is biochemically inaccessible for life due to the strength of its triple bond
Previous ultra-high vacuum experiments to investigate the capability of pyrite to fix nitrogen, have been discouraging as they found that N2 does not dissociate on FeS2{100} under conditions where it would dissociate on Fe surfaces[12]
Previous studies have confirmed that iron and sulfur from pyrite surface are highly sensitive to chemical changes due to UV irradiation, even after very short times of 2 or 5 hours of UV exposition it has been confirmed that there exists an increase of iron oxidized species and the appearance of new oxidized and sulfates species[26]
Summary
The molecular form of nitrogen, N2, is universally available but is biochemically inaccessible for life due to the strength of its triple bond. Recent experimental work has shown that nitrogen may have been fixed on Mars by bolide impacts in CO2‐N2 atmospheres as nitrogen oxide NO, with a high fixation rate when this is done in the presence of hydrogen (H2)[6]. Materials with enhanced performance in terms of both adsorption capacity and strength of retention of ammonia are still needed, and it has been described that sulfur plays a role as sulfate ions can react with ammonia to form ammonium sulfate[14] It is the purpose of this work to investigate the role of pyrite (iron-sulphur) on the fixation of molecular nitrogen on terrestrial planets like Mars and the Earth. Taking these cases as examples, in this work, we will investigate the enhanced catalytic properties of pyrite under exposure to UV radiation
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