Fern Dicranopteris linearis-derived biochars: Adjusting surface properties by direct processing of the silica phase

Abstract

This work specifically emphasizes the effect of the silica phase contained in the fern Dicranopteris linearis (D. linearis), a common shrub occurring widely throughout tropical and subtropical regions, on biochar surface properties. Slow pyrolysis was performed in the temperature range from 400 to 900 °C under various ambient reaction conditions, i.e., non-biochar-oriented conditions (open pyrolysis) and biochar-oriented conditions (closed and N2-supported pyrolysis). The resulting changes in micromorphology and different surface properties, specific surface area and surface charge, were elucidated. Open pyrolysis resulted in excessive decomposition of biomass and condensation of silica, while the closed and N2-supported pyrolysis methods showed notable enhancement of biochar yield. The presence of silica as an inter-embedded part of the fern D. linearis and the derived biochars likely supported a carbon-silica structural model in which these two components might be integrated or decomposed during pyrolysis. In general, joint processing of organic carbon and silica greatly altered the surface properties. At lower temperatures and during N2-supported pyrolysis, condensation of organic compounds limited the development of high surface charge densities. At higher temperatures and during open pyrolysis, intensification of the silica phase was accompanied with an increasing number of charged surface sites, thereby increasing the surface charge density. Based on the porous structure, large surface area (up to 701 m2 g−1) and high surface charge density (up to 0.5 μmol(−) m−2), D. linearis-derived biochars can be highlighted as potential agro-environmental materials.