Cu/Fe co-doped Sphagnum palustre-derived biochar for the synergistic adsorption and photocatalytic removal of tetracycline hydrochloride

A Cu/Fe co-doped S. palustre -derived biochar composite with an S-scheme heterojunction enables synergistic adsorption and photocatalytic removal of tetracycline hydrochloride under visible-light irradiation, achieving an overall efficiency of 94.56 %. • Sustainable Cu–Fe oxide photocatalyst synthesized from S. palustre biochar. • Cu–Fe co‑doping enhanced charge transfer and intermediate desorption. • CFO/S‑10 removed 94.6 % of TCH via adsorption–photocatalysis synergy. • Heterojunction promoted charge separation and ROS generation. The widespread presence of antibiotic pollutants, such as tetracycline hydrochloride (TCH), cause significant environmental and public health concerns. Biochar-based photocatalysts derived from renewable biomass have attracted increasing attention due to their low cost, structural tunability, and environmental sustainability. However, their photocatalytic performance is often limited by poor charge separation and a lack of active sites. This study aims to construct a visible-light-responsive Cu/Fe co-doped biochar composite using Sphagnum palustre as a biomass precursor for the synergistic adsorption and photocatalytic removal of TCH from aqueous environments. The Cu/Fe co-doped photocatalyst (CFO/S) was synthesized via a hydrothermal method by integrating Cu–Fe oxides with Sphagnum -derived biochar. The composite was comprehensively characterized, and its visible-light performance was evaluated. The photocatalytic mechanism was elucidated through radical trapping experiments and DFT + U simulations. The CFO/S-10 composite achieved a TCH removal efficiency of 94.56 % within 60 min under visible-light irradiation. Adsorption was identified as the primary removal mechanism, while photocatalysis contributed to the degradation of adsorbed molecules. A layered FeO/CuFe 2 O 4 /S structure promoted charge separation and intermediate desorption. Multiple degradation products were detected, involving demethylation, hydroxylation, and ring-opening reactions. The Cu/Fe co-doped biochar composite exhibited excellent removal performance through a synergistic adsorption-photocatalysis mechanism. Photogenerated electrons were the dominant reactive species, supported by •OH, •O 2 − , and h + . An S-scheme charge transfer mechanism was proposed to explain the enhanced redox capability. These findings demonstrate the potential of CFO/S as a promising candidate for visible-light-driven removal of antibiotic contaminants in water.