Activated carbon derived from Azolla filiculoides fern: a high-adsorption-capacity adsorbent for residual ampicillin in pharmaceutical wastewater

In this study, the effectiveness of activated carbon prepared from the Azolla filiculoides fern (ACAF) in order to remove ampicillin from aqueous solution was examined. The preparation of the ACAF was performed through chemical and physical activation processes with the presence of ZnCl₂ and at a temperature of 450 °C. The ACAF yield was 44.7% of the fresh Azolla filiculoides. The results obtained from the characterization study indicate that the prepared ACAF has excellent surface and internal properties to be used as an adsorbent. The surface area, porosity, and pore volume were estimated to be 716.4 m²/g, 51.2%, and 0.621 cm³/g, respectively. The functional groups in ACAF that were responsible for the adsorption of ampicillin molecules were detected using FTIR analyses. The maximum efficiency (96.84%) and uptake (114.3 mg/g) of ACAF to remove ampicillin were achieved under the following conditions: ACAF dose = 0.8 g/L, pH = 7, concentration of ampicillin = 100 mg/L, contact time = 60 min, and temperature = 45 °C. It was found that the kinetic and isotherm data matched the pseudo-second-order and Langmuir models with high precision values, respectively. Considering the thermodynamics of the adsorption, the endothermic and spontaneous nature of the ampicillin adsorption onto ACAF was approved. The ampicillin adsorption capacity by ACAF was not significantly affected by the presence of different concentrations of NaNO₃ competitor ion. The considerably higher adsorption capacity of the ACAF for ampicillin (114.3 mg/g) than other previously used adsorbents with excellent regeneration level (five cycles) depicts the superior performance of ACAF in the adsorption systems.