Sustainable enhancement of biochar and biochar composite properties through temperature-controlled pyrolysis of agricultural biomass and marble waste

This study explores the utilization of cocoa pod husk, coconut shell, and marble waste as raw materials to prepare biochar and biochar/marble composites adsorbents. The influence of pyrolysis temperatures 500, 600, and 700 °C was evaluated to obtain more information about the thermal behavior of these adsorbents and to precisely engineer the physicochemical properties of biochar and its composites, facilitating the development of highly efficient and sustainable materials, while maximizing process efficiency and resource utilization. The adsorbent samples were analyzed using elemental analysis, surface area and porosity measurements, infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermogravimetry, and point of zero charge analysis. Results indicated that higher pyrolysis temperatures enhanced porosity, aromaticity, and surface functional groups. Increasing the temperature from 500 to 700 °C led to a decrease in biochar yields, with coconut biochar yields declining from 31.7 % to 28.5 % and cocoa biochar from 36.1 % to 31.2 %. In contrast, composite yields exceeded 50 % due to marble content. The addition of marble significantly improved the specific surface area (SSA) and porosity, with the SSA values of biochar ranging from 12.0 m² g⁻¹ to 29.1 m² g⁻¹ and the SSA of the biochar composite ranging from 47.3 m² g⁻¹ to 95.1 m² g⁻¹. Ca(OH)₂ and MgO phases were identified on the surfaces of the biochar composites, demonstrating the capacity to facilitate cation exchange with adsorbates (e.g., herbicides), thereby enhancing the adsorption process. These properties contribute to the development of strategic, eco-friendly, and highly efficient adsorbent materials.