Removal of Ciprofloxacin and Norfloxacin from Aqueous Solution with Activated Carbon from Cupuaçu (Theobroma grandiflorum) Bark

The widespread use of antibiotics such as fluoroquinolones (FQs) has raised environmental and health concerns. This study is innovative as we investigate the removal of ciprofloxacin (CIP) and norfloxacin (NOR) from water using activated carbon derived from cupuaçu bark (CAC). This previously discarded biomass is now a low-cost raw material for the production of activated carbon, boosting the local economy. CAC was physiochemically characterized, and adsorption experiments were designed using the Box-Behnken design to assess the effects of contact time, adsorbate concentration, and adsorbent dosage on the removal efficiency and adsorption capacity. The optimal conditions were determined using the desirability function, and kinetic, isothermal, and thermodynamic experiments were performed. CAC showed a 50.22% yield, low humidity (4.81%), and low ash content (4.27%), with acidic functional groups dominating. The surface area was 1335.66 m²/g, with an average pore volume of 0.753 cm³/g and a pore diameter of 2.206 nm. Adsorption was most effective at pH 5.0 due to electrostatic interactions between the basic adsorbent and cationic forms of CIP and NOR. Optimal conditions yielded adsorption capacities of 6.02 mg/g for CIP and 5.70 mg/g for NOR, with the Langmuir model suggesting monolayer adsorption. The regeneration with NaOH was effective, but the adsorption efficiency decreased below 50% after two cycles. These findings demonstrate that CAC is a sustainable, low-cost adsorbent for treating antibiotic-contaminated water.