Adsorptive removal of tetracycline by sulfur and nitrogen co-doped modified sludge biochar

Background The presence of antibiotics like tetracycline (TC) in aquatic environments poses serious risks to ecosystems and public health, primarily by contributing to antibiotic resistance. As a response to this challenge, biochar-based adsorbents have gained attention for their sustainability and efficiency. Methods This study introduces sulfur and nitrogen co-doped modified sludge biochar (NSBC), synthesized using thiourea, urea, and ammonium bisulfate, as a novel adsorbent for TC removal. Its performance was compared to unmodified sludge biochar (SBC), sulfur-doped (SSBC), and nitrogen-doped (NBC) variants. NSBC showed superior adsorption capacity (83.01 mg/g) and removal efficiency (83.01 %). Key parameters—temperature, dosage, and pH—were optimized, with pH 5 and elevated temperature yielding the best results. Adsorption followed a pseudo-second-order kinetic model and fit best with the Freundlich and Sips isotherms, indicating chemisorption on a heterogeneous surface. Significant Findings NSBC demonstrated enhanced affinity for TC due to its surface characteristics, confirmed by electrostatic potential and HOMO-LUMO analyses, which showed active electron-donating and accepting regions. These findings highlight NSBC as a promising, low-cost, and sustainable option for antibiotic removal in water treatment, offering a viable solution to mitigate pharmaceutical pollution in aquatic systems.