Green synthesis of carbon nanomaterials from Chondrus crispus and Palmaria palmata algae biomass for ciprofloxacin and malachite green uptake from water

Carbon-based nanomaterials were prepared using a simple microwave-assisted hydrothermal carbonization method, with Chondrus crispus and Palmaria palmata algae as a sustainable feedstock. These materials were thoroughly characterized by FTIR spectroscopy, elemental microanalysis, and XPS analysis. The resulting hydrochars effectively removed ciprofloxacin (CIP), an antibiotic, and malachite green (MG), an organic dye, both of which are pollutants posing threats to ecosystems and public health. The hydrochar derived from Chondrus crispus (HC-Cho-MW) demonstrated superior performance, following a cooperative adsorption process well-described by the Dubinin–Radushkevich isotherm. It exhibited maximum adsorption capacities of 350 mg.g⁻¹ for CIP and 136 mg.g⁻¹ for MG, at 25ºC and pH 6. These values surpass those of previously reported hydrochars and are competitive with certain activated carbons. The pseudo-second-order model provided the best fit for the kinetic data, with film diffusion predominant at specific intervals. The adsorption of CIP and MG was exothermic and entropically favorable for both hydrochars. The small ΔH values (-9.85 to -23.26 kJ.mol⁻¹) suggest that physisorption predominantly governed the overall adsorption mechanism, although electrostatic interactions may also contribute. The hydrochars could be regenerated and reused to remove CIP and MG over three consecutive cycles. These results highlight the potential of using renewable and readily available algae biomass as a precursor for sorbents to remove pollutants from environmental water. This approach utilizes highly efficient microwave heating and avoids costly activation processes.