title: Generalized two-dimensional perturbation correlation infrared spectroscopy reveals mechanisms for the development of surface charge and recalcitrance in plant-derived biochars.
abstract: Fundamental knowledge of how biochars develop surface-charge and resistance to environmental degradation is crucial to their production for customized applications or understanding their functions in the environment. Two-dimensional perturbation-based correlation infrared spectroscopy (2D-PCIS) was used to study the biochar formation process in three taxonomically different plant biomass, under oxygen-limited conditions along a heat-treatment-temperature gradient (HTT; 200-650 °C). Results from 2D-PCIS pointed to the systematic, HTT-induced defragmenting of lignocellulose H-bonding network and demethylenation/demethylation, oxidation, or dehydroxylation/dehydrogenation of lignocellulose fragments as the primary reactions controlling biochar properties along the HTT gradient. The cleavage of OH(...)O-type H-bonds, oxidation of free primary hydroxyls to carboxyls (carboxylation; HTT ≤ 500 °C), and their subsequent dehydrogenation/dehydroxylation (HTT > 500 °C) controlled surface charge on the biochars; while the dehydrogenation of methylene groups, which yielded increasingly condensed structures (R-CH(2)-R →R═CH-R →R═C═R), controlled biochar recalcitrance. Variations in biochar properties across plant biomass type were attributable to taxa-specific transformations. For example, apparent inefficiencies in the cleavage of wood-specific H-bonds, and their subsequent oxidation to carboxyls, lead to lower surface charge in wood biochars (compared to grass biochars). Both nontaxa and taxa-specific transformations highlighted by 2D-PCIS could have significant implications for biochar functioning in fire-impacted or biochar-amended systems.
authors.affiliation: Water Management and Hydrologic Sciences, Texas A&M University, College Station, Texas 77843, United States. Omar.Harvey@usm.edu
authors.forename: Omar R
authors.initials: OR
authors.lastname: Harvey
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Herbert
authors.forename: Li-Jung
authors.initials: LJ
authors.lastname: Kuo
authors.forename: Patrick
authors.initials: P
authors.lastname: Louchouarn
mesh_terms: D018533:Biomass; D002606:Charcoal / Q000737:chemistry*; D006860:Hydrogen Bonding; D008031:Lignin / Q000737:chemistry; D010084:Oxidation-Reduction; D010944:Plants / Q000737:chemistry*; D006109:Poaceae / Q000737:chemistry; D013055:Spectrophotometry, Infrared / Q000379:methods; D013499:Surface Properties; D013696:Temperature; D014934:Wood / Q000737:chemistry
chemical_list: C540010:biochar; C036909:lignocellulose; D002606:Charcoal; D008031:Lignin