2020同步年報

072 ACTIVITY REPORT 2020 Fig. 1 : (a) µFTIR spectra of BC, ADE and adjacent soil: The absorption line of Fe-aromatic C complex- ation at 1380−1384 cm -1 and the line of aryl−OH at 1241 cm -1 are highlighted with red and orange arrows, respectively. Integral map of the selected spectral range, showing the distri- bution of aromatic C over 1625−1595 cm -1 (b) carbonyl C=O over 1730−1650 cm -1 (c) lattice water O−H over 3750−3550 cm -1 in clay minerals (d) and aryl−OH over 1260−1220 cm -1 (e). The scale bar is 40 μm. [Reproduced from Ref. 3] L inear combination fitting of k- spacing in the X-ray absorption spectra (XAS) revealed that ferrihydrite contributed to 81.1% of the Fe-minerals in black carbon (BC, biochar), acquired by using TPS 21A and TLS 16A1 . A small but distinct signal was observed at 5.7 Å -1 in the extended X-ray absorption fine structure (EXAFS) k oscillation of BC acquired by using TLS 17C1 , revealing the presence of Fe-C (including Fe−O−C) covalent bonds. No Fe−C path was yield- ed by the XAS fitting when an obvious signal downshift of the first (Fe-Fe 1 ) shell was observed, indicating that the availability of inner-sphere Fe−C com- plexation was limited to the BC surface and interphase region. The main minerals for organo-mineral complexation were short-range-order (SRO) ferrihydrite on BC instead of corner-sharing FeO 6 octa- hedra. The coordination number of the first (Fe−Fe 1 ) and second (Fe−Fe 2 ) shell was greater in BC than for Amazonian Dark Earth (ADE), revealing a higher degree of order in coordination between the neighboring Fe mineral crystals. Black C limited the progressive aging of amor- phous Fe phases and greatly enriched SRO ferrihydrite in the redox-fluctuating and high-leaching environment. The transformation of SRO ferrihydrite into the more crystalline Fe oxides was con- trolled with the local pH environment. A strong signal from the complexed phenolic group (aryl−OH, 1241 cm -1 ) and a distinct line of inner-sphere complex- ation (Fe−aryl C, 1380−1384 cm -1 ) were identified in the micro-Fourier transform infrared (µFTIR) spectra. The enrichment of poorly crystalline minerals can have a positive feedback on the enduring stabi- lization of BC. The scale-up application of Black Carbon Enriches Short-Range-Order Ferrihydrite in Amazonian Dark Earth This study underpins the mechanism of organo-mineral interaction between BC and associated minerals in the historical BC-rich ADE using synchrotron-based microscopic (TXM) at TLS 01B1 , microspectroscopic (μFTIR) and spectroscopic (XAS and μ-diffraction) approaches. The BC-rich ADE contained over 100% more poorly crystalline minerals than the adjacent tropical soil.