Characteristics and mechanisms of cadmium adsorption from aqueous solution using lotus seedpod-derived biochar at two pyrolytic temperatures

Abstract

Herein, biochar derived from lotus seedpods, as an effective adsorbent, was prepared by pyrolysis method at 300 and 600 °C. The physicochemical characteristics and cadmium adsorption properties were studied systematically by batch adsorption experiments, FTIR, SEM–EDX, XRD, and XPS. Cd adsorption onto lotus seedpod-derived biochar was better fitted using Freundlich isotherm and pseudo-second-order model. Adsorption capacity of biochar produced at 300 and 600 °C was 31.69 and 51.18 mg g⁻¹, respectively. The Cd adsorption capacity of biochar was related to its characteristics determined by pyrolysis temperature, including carbonization, surface area, surface morphology, and surface functional groups. Cd adsorption on lotus seedpod-derived biochar revealed that adsorption was controlled by multiple mechanisms including surface complexation, ion exchange, surface precipitation, and Cd–π interaction. This study showed that lotus seedpod-derived biochar is an effective and environmentally friendly adsorbent for water treatment.