Isosteric Heats of Adsorption of Carbon Dioxide on Commercially Available Biochar Samples

Author

Nathanial Smith, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2025

Degree Name

Master of Science

Department

Physics

First Advisor

Talapatra, Saikat

Abstract

This thesis explores the surface properties of commercially-available, highly-porous biochar materials. More specifically, our goal was to investigate how biochar, a material with a growing market, high scalability, and low cost, could help mitigate the release of carbon dioxide (CO2) into the atmosphere. To achieve this goal, we first tested the effective specific surface areas (ESSA) available for the commercially-available biochar sample using volumetric gas adsorption measurements, using Nitrogen as the adsorbate gas and the biochar as the substrate at liquid nitrogen temperature (77K). The nitrogen adsorption data provide a good baseline for what the material can achieve under ideal conditions while the carbon dioxide is the adsorbate that we want to focus on. Broadly speaking, we looked at the efficacy of the biochar surfaces by utilizing the principles of physical adsorption (physisorption) measurements using an Extended Pressure Adsorption Analyzer (ASAP 2050) from Micromeritics. Two different biochar samples were tested, which we classified as flake biochar and granular biochar by examining the physical texture of the biochar samples acquired. The specific surface area (ESSA) for the flake biochar was ~446 m2/g and for the granular biochar materials was ~645 m2/g.The adsorption behavior of carbon dioxide was also investigated on both these samples. Volumetric adsorption isotherms using CO2 as the gas adsorbate on the flake biochar were measured at various temperatures between 273 and 315 K. The isosteric heat of adsorption for carbon dioxide on the flake biochar was determined from these isotherms. We found that the isosteric heat of adsorption for carbon dioxide on the flake biochar is of the order of 260 meV. Similarly, we measured the CO2 adsorption on the granular biochar at 273, 293, 298, 303, 308, and 318 K. Using these isotherms, the isosteric heat of adsorption for carbon dioxide on the granular biochar was found to be on the order of 260 meV. In conclusion, the flake biochar has a lower ESSA than the granular, 446 ± 12 m2/g to 645 ± 14 m2/g, while having a higher heat of adsorption 300 meV to 260 meV. As the climate continues to change, the use of Carbon Capture and Utilization (CCU) to reduce the amount of carbon dioxide emitted each year seems to be a viable way to slow the emissions. These values for biochar suggest that it could be a strong candidate for such technologies. Biochar itself offers a unique dual role: not only serving as a functional capture medium but also sequesters the carbon in a stable solid form.