Development of biochar molecular models with controlled porosity

Abstract: Biochars are an exciting class of environmental materials with a wide range of applications, including carbon storage and sequestration, soil enhancement, and pollution remediation. However, the limited knowledge of their molecular structures and compositions and the lack of comprehensive understanding of the relationship between these structures and biochars' diverse functionality, is hindering advancements in their development. In this work, we further advance the approach, first introduced by Wood et al. (2023), to constructing biochar molecular models; and now include control of microporosity (pores < 2 nm size) within the developed models. We construct biochar models representative of woody biochars which are experimentally produced at 600 -- 650 oC highest heating temperatures. Our models reproduce experimental H/C and O/C atomic ratios, percentage aromatic carbon, true density, cumulative porosity, and pore size distribution. The development of microporous biochar molecular models allows us to identify the importance of chemical structures involved in the assembly of biochar materials, and describe the relationship between these structures and obtained micropores. To facilitate other researchers integrating our approach into their work, we detail the steps taken, including the tests and reasons for each decision, in the construction of the biochar models. Furthermore, we share our developed molecular models in a format that can be easily integrated into other group's work in the form of molecular dynamics simulations.