NEXAFS and XPS characterisation of carbon functional groups of fresh and aged biochars

作者：Singh Balwant^*; Fang Yunying; Cowie Bruce C C; Thomsen Lars

来源：Organic Geochemistry, 2014, 77: 1-10.

DOI：10.1016/j.orggeochem.2014.09.006

• Biochar
• Black carbon
• NEXAFS
• XPS
• C functional groups
• C mineralisation
• Light fraction
• Carbohydrates
• Amino acids
• Carboxylic acids

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 degrees C (B450) and 550 degrees C (B550), were incubated separately in each of the four contrasting soils for up to 2 years at 20 degrees C, 40 degrees C and 60 degrees C. Carbon functional groups of the light fraction (< 1.8 g/cm(3)) of the control and biochar amended soils (fresh and aged for 1 and 2 years at 20 degrees C, 40 degrees C and 60 degrees 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 similar to 285.1 eV and 288.5 eV, which were attributed to the C1s-pi*(C=C) transitions of aromatic C and C1s-pi(C=O)* 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.

• 出版日期2014-12