One-step versus two-step UV-CH2O2 treatment of tramadol and ornidazole using NiFe-LDH@biochar: competitive adsorption and reuse stability

Maximizing water decontamination efficiency remains a global industrial priority. Supporting functional nanomaterials such as layered double hydroxides (LDHs) on biochar (BC) offers a practical route to improve catalyst handling and photocatalytic performance in water treatment. This study evaluates Ni/Fe-LDH supported on biochar (Ni/Fe-LDH@BC) for the removal of tramadol (TMD) and ornidazole (ONZ) from an equimolar bicomponent solution through coupled adsorption and UV-driven oxidation. The synthesized composite exhibits a specific surface area of 671 m 2 g -1 , representing a 13-fold increase over pristine Ni/Fe-LDH (51 m 2 g -1 ). Adsorption kinetics and equilibrium were best described by the Elovich and the Freundlich models, respectively, with approximately 70% removal of TMD and 90% removal of ONZ during the dark adsorption stage. A conventional two-step route (system A) combined optimized adsorption with UV-C/H 2 O 2 photocatalysis, achieving >95% TMD and >99% ONZ removal within 120 min. One-step configurations without the preliminary adsorption stage (systems B and C, with and without stirring, respectively) accelerated treatment, reaching >97% (TMD) and >99% (ONZ) within 60 min. System C exhibited the highest operational stability, maintaining photocatalytic activity over 12 consecutive reuse cycles. Scavenger tests identified hydroxyl radicals (•OH) and photogenerated holes (h+) as the dominant reactive species under UV-C/H 2 O 2 . Acute toxicity screening with Artemia salina showed >50% survival after 24 h for treated samples, supporting the environmental relevance of the proposed process. These results highlight the potential of Ni/Fe-LDH@BC as a reusable photocatalyst and demonstrate the advantages of one-step UV-C/H 2 O 2 treatment for pharmaceutical wastewater remediation.