Relative proportions of organic carbon functional groups in biochars as influenced by spectral data collection and processing

Authors: MUNIRA, SIRAJUM - University Of Manitoba; DYNES, JAMES - University Of Saskatchewan; ISLAM, MOFIZUL - University Of Manitoba; KHAN, FAHAD - University Of Manitoba; ADESANYA, THERESA - University Of Manitoba; REGIER, TOM - University Of Saskatchewan; Spokas, Kurt; FARENHORST, ANNEMIEKE - University Of Manitoba

Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/22/2021
Publication Date: 6/7/2021
Citation: Munira, S., Dynes, J.J., Islam, M., Khan, F., Adesanya, T., Regier, T.Z., Spokas, K.A., Farenhorst, A. 2021. Relative proportions of organic carbon functional groups in biochars as influenced by spectral data collection and processing. Chemosphere. 283. Article 131023. https://doi.org/10.1016/j.chemosphere.2021.131023.
DOI: https://doi.org/10.1016/j.chemosphere.2021.131023

Interpretive Summary: Biochar is a material that could serve as a media for removal of agrochemicals and nutrients from agricultural impacted waters. However, before fully utilizing this media for this purpose there is a critical need to properly characterize biochar for knowledge into what the potential mechanisms are for sorption processes in order to optimize its use. This research examined two of the potential analytical methods for characterizing the surface chemistry of the biochar [nuclear magnetic resonance (NMR) and synchrotron-based X-ray adsorption near-edge structure (XANES)]and observed that there are significant differences in the resulting quantification that are a function both of settings during the collection of the instrumentation data as well as the post-processing algorithms applied to the data. There is an urgent need to develop standardized guidance of how to collect and analyze data on biochar’s carbon compositional arrangement. These results are significant to assist scientists, engineers, farmers, as well as supplying guidance for utilizing biochar as a remediation tool for removing water contaminants.

Technical Abstract: The relative proportion of organic C functional groups in biochars influences the interactions of biochars with inorganic and organic chemicals, and hence biochar practical applications such as in water treatment technologies. The objective of this study was to examine the impact of spectral data collection and data processing on the estimated relative proportions of organic C functional groups in biochars. Spectral data were obtained for 15 biochars using synchrotron-based X-ray Absorption Near-Edge Structure (XANES) versus solid-state 13C Nuclear Magnetic Resonance (NMR) and subsequently processed by integration (INTEG) versus deconvolution (DECONV). Significant positive associations were observed between NMR-INTEG and XANES-INTEG only for aromatic-C (r=0.63) and O-alkyl C (r=0.58), whereas NMR-DECONV and XANES-DECONV showed no associations. The influence of data processing on the estimated relative proportions of organic C functional groups was less for NMR than XANES because NMR-INTEG and NMR-DECONV showed good agreement for aromatic, alkyl, O-alkyl, and phenolic C (r=0.74-0.91). In contrast, XANES-INTEG and XANES-DECONV only showed significant positive associations for aromatic C (r=0.68). Regardless of the type of data collection or processing, aromatic C accounted for about 45% of organic C in biochars. Differences between NMR and XANES in aromatic C percentages for the same biochar were as large as 24% and 35% using INTEG and DECONV, respectively. We conclude that spectral data collection and processing influence the quantification of C functional groups in a given biochar to the extent that the differences observed are as large as differences observed between biochars when analyzed using the same spectral data collection and processing technique.