Polydopamine modified coconut shell biochar decorated with ZIF-8 for improved adsorption of malachite green and...

Although various biochars from different biomass materials have been developed to remediate dye-contaminated environments, the removal capabilities of pristine biochar for dyes urgently require further enhancement due to insufficient surface adsorption sites. To introduce more adsorption sites, this work proposes a simple approach to fabricate coconut shell biochar (CSB) based adsorbent by anchoring zeolitic imidazolate framework-8 (ZIF-8) via the active sites provided by polydopamine (PDA)-coated CSB. The nucleation sites provided by the PDA layer promote the dispersion of ZIF-8 on the surface of CSB, resulting in sufficient adsorption sites for removing malachite green (MG) and rhodamine B (RB) from wastewater. The resulting CSB/PDA/ZIF-8 demonstrates a large specific surface area (749.54 m² g^-1) and outstanding adsorption capacities for MG (1568 mg g^-1) and RB (1496 mg g^-1). Furthermore, CSB/PDA/ZIF-8 adsorbents can maintain a satisfactory removal rate for MG (91%) and RB (77%) even after five reuses. The analysis of the adsorption mechanism exhibits that electrostatic interactions, hydrogen bonds, coordination bonds, and π-π stacking are of significance for adsorbing MG and RB. Therefore, CSB/PDA/ZIF-8 is a promising candidate for dye wastewater treatment, while this work provides guidance for the high-quality utilization of biomass materials.