¹²⁹Xe NMR Studies of Pecan Shell-Based Biochar and Structure-Process Correlations

Abstract

Pecan shell-based biochar is utilized as a filtration medium, sequestrant for metallic ions, soil conditioner, and other applications. One process for creating the biochar involves the use of phosphoric acid at high temperature in a partial oxygen atmosphere to produce a highly porous carbonaceous material. In this work, we found ¹²⁹Xe NMR to be an excellent technique to study micropores in biochar. Thus, the ¹²⁹Xe chemical shift in biochar was found to vary linearly with the xenon pressure; from the data an estimate of about 8–9 Å could be proposed for the average pore diameter in pecan shell-based biochar. Through saturation recovery and 2-D NMR exchange experiments, information on the exchange between free versus bound xenon was obtained. Furthermore, correlations of ¹²⁹Xe NMR data with the carbonization process conditions were made.

Keywords:

• ¹²⁹Xe NMR
• Activated carbon
• Agricultural by-products
• Biochar
• Pecan shells

ACKNOWLEDGEMENTS

The authors thank Professor Cecil Dybowski of the University of Delaware for helpful discussions and Lynda H. Wartelle for the samples of pecan shell biochar. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.