Structural Characterization of Biomass Derived Biochar Using Electron Energy Loss Spectroscopy

Biochar was previously considered as a low-valued solid fuel, which is the side product from biomass pyrolysis process. However, recent researches figured out the potential application of biochar as a renewable resource for selective adsorption medium, electrode material, and carbon fiber fillers. For the successful utilization of biochar, it is imperative to characterize the biochar structure. Many spectroscopic techniques, for example FT-IR, XPS, FT-Raman, NMR and XRD, partially revealed the structure. However, most spectroscopic techniques only provide qualitative information of specific functional groups in biochar. Without quantitative chemical bonding information, it is difficult to figure out the detailed structure of biochar. In this study, electron energy loss spectroscopy is used, which can quantitatively analyze chemical bonding states (sp² and sp³ bonding) of biochar produced from loblolly pine under different temperature, atmosphere, and activation conditions. Two different gas atmospheres, nitrogen (100% nitrogen) and partial oxygen (7% oxygen + 93% nitrogen), were applied to different pyrolysis temperatures at 300°C, 350°C, 500°C, and 700°C. In addition, NaOH activation was applied to the selected biochar samples. Electron energy loss spectra analysis showed biochar carbon sp² bonding percent as 54.69% for O-300 (partial oxygen atmosphere and 300°C pyrolysis temperature) sample and 75.48% for O-700 (partial oxygen atmosphere and 700°C pyrolysis temperature) sample. The relationship between biochar structure and the production conditions will be presented in detail and its potential application will be discussed.