Biochars have been recognized as an important material to improve soil properties. In a number of studies their beneficial properties have been found to increase with residence time in soil and during the composting process. The beneficial properties have been correlated with surface functional groups resulting from the interactions between char particles, inorganic and organic matter in the soil and soil biota. These interactions result in the formation of organo-mineral phases on the internal and external surfaces of the biochar. A paucity of information exists, particularly from longer-term field trials, on organo-mineral phases present on both the internal and external surfaces of the biochar. To characterize the structure of, and interface between, the carbon and mineral phases, we examined biochars recovered from two field trials and after composting from different countries using high resolution scanning electron microscopy (SEM), atomic resolution transmission electron microscopy (TEM) and scanning TEM (STEM), energy electron loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS) at resolutions of 1–20 nm. The work revealed the formation of porous agglomerates of different minerals/inorganic compounds bound together with organic compounds on the surfaces of the biochar. In some cases, these agglomerates were bound together to form organo-mineral associations. The analyses also showed that the organic compounds containing both N and C functional groups and mixed valence iron oxide nanoparticles are possibly interacting with the organic compounds. The analysis also showed the formation of pores at the interface of the carbon matrix and organo-mineral aggregates.
Bibliographical noteFunding Information:
B.S.A., M.E.M., C.A.A. and J.R.A. would like to thank CNPq, FINEP and FAPERJ for financial support. S.J., P.M. and S.D. would like to acknowledge funding from the Australia Government and Renewed Carbon Pty. through the ARC Linkage Grant and through DAFF Carbon Farming Futures Filling the Research Gap (RG134978) and the support of the Electron Microscope Units at the University of Newcastle Australia and NSW. M.A. acknowledges the financial support from European Union Seventh Framework Programme under Grant Agreement 312483 ? ESTEEM II (Integrated Infrastructure Initiative?I3). WC was produced during a ?Short Term Scientific Mission? (STSM) granted to N.H. by the EU COST Action TD1107 ?Biochar as option for sustainable resource management?. We identify certain commercial equipment, instruments, or materials in this article to specify adequately the experimental procedure. In no case does such identification imply recommendation or endorsement, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.
- Carbon and nitrogen functional groups
- Electron microscopy
- Organo-mineral associations