Low cost earthworm manure-derived carbon material for the adsorption of Cu²⁺ from aqueous solution: Impact of pyrolysis temperature

Earthworm manure, an emerging and abundant bio-waste from vermicomposting, was subjected to pyrolyze at 400–600 °C to prepare carbon material (EMBCs) for the removal of Cu²⁺ from aqueous solution. The adsorption capability and inherent mechanism were thoroughly investigated. All adsorption processes of Cu²⁺ by EMBCs were described through Langmuir isotherm model and pseudo-second-order model. The adsorption capacity of EMBCs was declined with the pyrolysis temperature, while the binding strength between EMBCs and Cu²⁺ was significantly enhanced accordingly. The adsorption process of Cu²⁺ by EMBCs was found to be dominated by precipitation, complexation, Cπ-cations interactions. Precipitation was mainly stimulated by silicates and phosphates leading to 35.12%–40.72% adsorption of Cu²⁺. The contribution of complexation to Cu²⁺ adsorption were decreased from 46.61% to 17.12% as the pyrolysis temperature was increased form 400 to 600 °C. Comparatively, the contribution of Cπ-cations interaction were increased from 18.27% to 42.16% with the increased temperature due to the abundant aromatic C[dbnd]C structure.