Magnetic porous cobalt-embedded nitrogen-doped biochar derived from natural loofah cellulose for efficient adsorption of tetracycline from water

Carbon-based composite materials with high specific surface areas can provide favorable conditions for wastewater treatment. Nevertheless, it remains challenging to sustainably synthesize high-adsorption performance carbon materials on a large scale. Here, we report a facile green method for the scalable synthesis of magnetic porous adsorbents using inexpensive and widely available natural loofah (L) biomass as the carbon precursor. Polydopamine (P) and zeolitic imidazolate framework-67 (ZIF-67) were introduced into the biochar via an in situ self-assembly approach to enable heteroatom doping and increase the specific surface area. After carbonization under a N₂ atmosphere, the nitrogen-doped adsorbent of C-(ZIF-67@P@L) retained a highly interconnected honeycomb-like 3D porous structure with a high specific surface area of 444.59 m²/g. Adsorption kinetics and thermodynamics conformed to the pseudo-second-order kinetic and Langmuir isotherm model, with the maximum adsorption capacity estimated at 662.25 mg/g on the basis of the Langmuir isotherm equation. The adsorption mechanism investigation revealed that the adsorption mechanism mainly included electrostatic interactions, ππ interactions, hydrogen bonding, and pore filling. Additionally, the adsorbent had good cycle stability and the ability to be magnetically separated from water, making it highly promising for practical wastewater treatment applications.