Carbon foams derived from biomass with ultra-high adsorption capacity for the removal of tetracycline

Abstract

This study investigates the development and application of carbon foams (CF) derived from carbohydrate-based precursors for the adsorptive removal of organic pollutants from water. The effect of various metal nitrate catalysts—cobalt, zinc, iron, magnesium, and chromium—as well as carbon precursors such as cellulose, agar, sucrose, and starch, was evaluated to determine optimal combinations for CF synthesis. Tetracycline was selected as the model pollutant for assessing adsorptive performance. CFs were synthesized using different precursor–catalyst combinations, with zinc nitrate–catalyzed agar-based CF identified as the most effective and subsequently studied in detail. Batch adsorption experiments were carried out to evaluate the influence of key operational parameters, including initial tetracycline concentration (25–500 mg L-1), CF loading (0.25–1.00 g L-1), solution pH (4.5–9.8), and temperature (20–35 °C). The maximum adsorption capacity achieved was 1822 mg g-1 at an initial concentration of 500 mg L-1 and a CF loading of 0.25 g L-1. The adsorption behavior was best described by the Freundlich isotherm, indicating a heterogeneous surface with multilayer adsorption. Kinetic analysis revealed that the process followed a pseudo-second-order model, suggesting chemisorption as the dominant mechanism. Thermodynamic parameters confirmed the process to be endothermic and spontaneous, accompanied by increased system disorder (positive entropy change). Furthermore, the CF exhibited excellent reusability, retaining significant adsorption efficiency over three successive cycles.