Fabrication of sodium alginate-biochar-graphene oxide composite for sulfadiazine adsorption from aquatic environment: Performance and mechanisms.

The effective removal of sulfadiazine (SDZ), an emerging and persistent aquatic contaminant, remains a significant environmental challenge. In this study, a novel sodium alginate-biochar-graphene oxide composite (SA-BC-GO) was synthesized via crosslinking for efficient SDZ adsorption removal in aqueous environments. Characterization revealed a hierarchically porous architecture with a 2.6-fold increase in specific surface area compared to pristine SA, along with reinforced pore walls and enhanced mechanical stability. Batch adsorption experiments demonstrated a Langmuir maximum capacity of 51.91 mg/g at 308 K and 97.3 % SDZ removal efficiency within 7 h. Adsorption kinetics adhered to the pseudo-second-order model, while thermodynamic analysis indicated spontaneous and endothermic characteristics. Fixed-bed column studies further confirmed practical feasibility, achieving 98.7 % SDZ removal efficiency, with Thomas-model-described breakthrough behavior. Mechanistic investigations via XPS and FTIR analyses revealed that SDZ adsorption was governed by multiple interactions, including electrostatic attraction, π-π electron interaction, hydrogen bonding, and hydrophobic partitioning. Notably, SA-BC-GO retained 77.7 % of its adsorption capacity after five regeneration cycles, underscoring remarkable reusability. These findings established SA-BC-GO as a robust, reusable adsorbent, providing mechanistic insights and scalable potential for SDZ and other sulfonamide contaminants in aquatic environments.