NEXAFS and XPS characterisation of carbon functional groups of fresh and aged biochars |
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| Institution: | 1. Divisão de Metrologia de Materiais, Instituto Nacional de Metrologia, Qualidade e Tecnologia, Duque de Caxias, RJ 25250-020, Brazil;2. Austrian Cooperative Research, Centre for Electron Microscopy and Nanoanalysis, Graz, Austria;3. Electron Microscopy Centre, AIIM, University of Wollongong, Wollongong, NSW 2519, Australia;4. Geomicrobiology, Center for Applied Geoscience, University of Tuebingen, Germany;5. Faculty of Environment and Earth Sciences, Thai Nguyen University of Sciences, Thai Nguyen, Vietnam;6. Graham Centre for Agricultural Innovation, Charles Sturt University, North Wagga, NSW 2678, Australia;7. Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Minneapolis, MN 55455, United States;8. School of Physics and Institute for Superconducting and Electronic Materials, University of Wollongong, Wollongong, NSW 2522, Australia;9. Discipline of Chemistry University of Newcastle, Callaghan, NSW 2308, Australia;10. NSW Department of Primary Industries, Wollongbar Primary Industries Institute, Wollongbar, NSW 2477, Australia;11. Department of Crop and Soil Sciences, Cornell University, Ithaca, NY 14853, United States;12. School of Materials Science and Engineering, University of New South Wales, NSW 2052, Australia;13. Escuela Superior Politécnica del Litoral, ESPOL, Facultad de Ingeniería Mecánica y Ciencias de la Producción, Campus Gustavo Galindo Km 30.5 Vía Perimetral, P.O. Box 09-01-5863, Guayaquil, Ecuador |
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| Abstract: | The oxidation of surface functional groups on biochar increases its reactivity and may contribute to the cation exchange capacity of soil. In this study, two Eucalyptus wood biochars, produced at 450 °C (B450) and 550 °C (B550), were incubated separately in each of the four contrasting soils for up to 2 years at 20 °C, 40 °C and 60 °C. Carbon functional groups of the light fraction (< 1.8 g/cm3) of the control and biochar amended soils (fresh and aged for 1 and 2 years at 20 °C, 40 °C and 60 °C) were investigated using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS). The spectra of biochar and light fractions of the control and biochar amended soils showed two distinct peaks at ～285.1 eV and 288.5 eV, which were attributed to the C1s-π1C C transitions of aromatic C and C1s-π1CO transitions of carboxylic C, carboxyamide C and carbonyl C. The proportion of aromatic C was substantially greater in the light fraction of the biochar amended soils than the corresponding light fraction of the control soils. Also, the proportion of aromatic C was much higher in the light fraction of the B550 amended soils than in the corresponding B450 amended soils. Neither NEXAFS nor XPS results show any consistent change in the proportion of aromatic C of biochar amended soils after 1 year ageing. However, XPS analysis of hand-picked biochar samples showed an increase in the proportion of carboxyl groups after ageing for 2 years, with an average value of 8.9% in the 2 year aged samples compared with 3.0% in the original biochar and 6.4% in the control soil. Our data suggest that much longer ageing time will be needed for the development of a significant amount of carboxyl groups on biochar surfaces. |
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| Keywords: | Biochar Black carbon NEXAFS XPS C functional groups C mineralisation Light fraction Carbohydrates Amino acids Carboxylic acids |
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