Scalable magnetic biochar-based thin films for efficient multi-contaminant water remediation: Overcoming the limitations of powdered adsorbents

The presence of pharmaceutical residues and industrial dyes, such as ciprofloxacin (CIP) and crystal violet (CV), in water bodies poses environmental and human health risks. Despite the development of numerous adsorbents for their removal, the majority exist in powdered form, making their practical application inefficient and technically challenging. In this study, we aimed to develop and evaluate a reusable thin film adsorbent based on magnetic biochar for the efficient removal of CIP and CV. Biochar was synthesized from sunflower husk and functionalized with polyethyleneimine and Fe 3 O 4 nanoparticles. The composite was embedded in a chitosan–polyvinyl alcohol matrix to form magnetic thin films. We evaluated its sorption behaviour through kinetic, isotherm, thermodynamic, and competitive adsorption studies. Characterization confirmed successful functionalization and the presence of a mesoporous structure. Batch adsorption studies revealed up to 91% removal of CV and 87% of CIP, following pseudo-second-order kinetics and Freundlich isotherms, indicating multilayer chemisorption on heterogeneous surfaces. Thermodynamic analysis revealed endothermic behaviour for CV adsorption and exothermic behaviour for CIP. Competitive adsorption experiments indicated faster initial uptake of CIP than CV under the tested binary conditions, although this behaviour should be interpreted as a concentration- and time-dependent competitive adsorption trend rather than as evidence of true selectivity. These findings provide a scalable strategy for water remediation, combining easy recoverability, reusability, and high efficiency in one platform. The thin-film format offers a promising route toward sustainable water remediation technologies by combining ease of use, mechanical stability, and high adsorption efficiency in multi-contaminant environments.