(716b) Systematic Investigation of Pore Structure Changes of Activated Biochar Using Small Angle X-Ray Scattering (SAXS)

Conversion of biomass to biochar develops a complex porous network that has numerous applications in industry, such as carbon capture and environmental remediation. The pore structure and surface area are extremely important for controlling the effectiveness of biochar in all potential applications. This study is using small-angle x-ray scattering (SAXS) and electron microscopy to compare the pore size and shape distributions for activated biochar materials synthesized from model compounds (cellulose and lignin) and biomass from agricultural waste streams. The biomass will be converted to biochar using hydrothermal carbonization at 300 °C and 1300 psi, which are the optimal conditions to achieve high carbon content in biochar. The so-formed biochar is then thermally activated (in an inert nitrogen atmosphere) at various temperatures, ranging from 400-1000°C. Thermal activation induces re-organization of the amorphous carbon layers as well as the removal of oxygen-containing functional groups within the pore structure. Both of these processes result in nanoscale re-organization of the pores within the biochar (both size and morphology). Small angle X-ray scattering (SAXS) coupled with scanning electron microscopy (SEM) has been employed to monitor changes in the pore network and linked to the bulk characteristics of the biomass and activated biochar. We use these techniques to explore the hypothesis that the pore structure, pore evolution kinetics, and amounts/types of oxygen-containing groups in the activated biochar will be strongly affected by the activation temperature. Understanding the pore network development, especially the transition from micropore to mesopore, based on operating conditions can help guide the synthesis of the required activated biochar for specific applications.