Valuable polar moieties on cereal-derived biochars

Abstract The application of biochar (BC) in various fields of engineering, agriculture and environmental protection demands the task-specific adjustment of the surface characteristics of the carbon material. Polar moieties are those elements which distinguish BC from regular carbon black. The knowledge of polar moieties on the surface of the BC is crucial for its application for polar pollutants removal and resistance of nutrients. In this paper several techniques were applied for the verification of polar moieties of crop-derived biochars (both straw and grain) by several techniques (SBET, FTIR, SEM, EDS, pH PZC , elemental analysis). The characterization was also made for washed BCs. It was found that this carbon material is rich in polar moieties, mostly hydroxyl groups and oxides, the latter being washed away together with salts. The high oxygen content decreased after washing (>15%). The values of pH ZPC do not differ between the tested BCs, were in the range of 2.2 to 2.0, and were not changed after the washing of BCs. Thanks to the SBET isotherm analysis, irreversible changes in the material structure by water adsorption were proven. The oxygen content in the surface of BCs can be changed after a very brief time of exposition to natural water or soil with no change in the surface charge. Still, the biochar derived from cereals is a useful material for application in environmental protection purposes.