Mid-Infrared Spectroscopy of Biochars and Spectral Similarities to Coal and Kerogens: What Are the Implications?

Biochar is the solid residue produced by the pyrolysis of any bio-organic material under low, or no, oxygen conditions and has generated considerable interest as a means to sequester carbon in, and improve the quality of, soils. However, the exact properties of biochar depend on its composition, which in turn depends on the composition of the starting material and the temperature and conditions under which the biochar is produced. Mid-infrared spectroscopy offers an excellent and rapid method for characterizing both the starting materials and the resulting biochar. Results using diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) have shown that spectral changes can be easily correlated with the production temperature and that DRIFTS offers a rapid method for biochar characterization. It was demonstrated that as the temperature increases biochars become increasingly more aromatic and carbonaceous in nature. We also showed that biochars are spectrally very similar to kerogens and coals; therefore, the methods and knowledge developed from decades of studies on these materials should greatly improve our understanding of biochar composition and effects in soil. This work indicates that rapid characterization using DRIFTS can be used to predict the nature of biochar and to determine the production conditions needed to produce a so-called “Designer Biochar” which will have properties of benefit to soil quality as well as sequestering carbon.