Elucidating the Mechanisms of N2O and CH4 Retention via Biochars Opens a New Direction in the Development of Fertilizers With Better Environmental Performance

Abstract

Significant reductions in emissions of greenhouse gases, particularly N and C oxides, following the incorporation of biochar into soil have been repeatedly and independently reported over the past two decades. However, the underlying mechanisms responsible for these effects remain poorly understood. In this study, advanced computational chemistry methods are employed to address fundamental questions concerning the surface structures of biochar (such as the role of edge functional groups, polyaromatic sheet architecture, and sheet size) and their influence on molecular interactions with N₂O and CH₄. It is first revealed that, for individual biochar particles, both CH₄ and N₂O are considerably more attracted to the central aromatic sheet than to edge CC bonds and functional groups, such as carboxyl, alcohol, aldehyde, and methoxy. The nature of the oxygenated functional groups does not appear to be a key driving element, with alcohol, aldehyde, and methoxy generating quite a similar response. However, at high concentrations of biochar particles in the aqueous phase, stacking of biochar sheets happens through ππ interactions, considerably reducing attraction to aromatic rings. These findings provide new insights into the sorption behavior of crucial greenhouse gases, contributing to a deeper mechanistic understanding of biochar's role in mitigating greenhouse gas emissions. The results show that increasing the ionic strength of the solution significantly enhances N₂O interaction with biochar, with the enhancement being approximately 1.4 times greater for smaller biochar models (composed of 7 benzene rings) compared to larger ones (17 benzene rings).