An alternative synthesis of magnetic biochar from green coconut husks and its application for simultaneous and individual removal of caffeine and salicylic acid from aqueous solution

Efficient remediation of water pollutants requires the continuous development of new technologies. Magnetic biochars offer a sustainable solution by combining the high adsorptive capacity of biochar with easy adsorbent recovery. However, the main existing methods for synthesizing magnetic carbons have some disadvantages, such as obtaining materials with a poor magnetic response or with less surface area available for the adsorption of contaminants. Thus, there is an evident need to develop new methods for the synthesis of magnetic carbons. This study presents an innovative approach to obtaining a magnetic nanocomposite (MNC). Initially, chemically activated biochar (ACP) was produced from the pyrolysis of green coconut husks (GCH). Subsequently, an oleic acid-coated magnetite colloid was employed to incorporate magnetic nanoparticles into the porous structure of ACP. Two additional magnetic carbons were prepared using co-pyrolysis of GCH or GCH biochar, both impregnated with FeCl3 solution, for performance comparison. Characterization of MNC revealed a high BET surface area (1019 m2·g−1) and favorable magnetism (11.2 ± 1.1 emu·g−1). The MNC exhibited similar or superior adsorption capacities for caffeine (153 mg·g−1) and salicylic acid (203 mg·g−1) when compared to the other materials. These findings highlight the ability of this innovative process to provide a material with good magnetic properties and concomitantly high surface area, resulting in a promising adsorbent for the removal of contaminants from water.