Ball milling and phosphoric acid hydrothermally co-functionalized sludge biochar for efficiently adsorptive removal of environmental concentration sulfamethoxazole: Experimental, characterization and DFT study

Efficiently eliminating environmental concentration sulfamethoxazole (SMX) from water has become a great challenge because its undesirable removal efficiencies/rates by the present sewage treatment technologies. In this study, various pyrolysis temperatures (400–700 °C), ball milling parameters (speed (300–700 rpm) and time (30–120 min)) and acids (CH3COOH, H3PO4 and HNO3) hydrothermal activation were studied to optimize the preparation of modified sludge biochar (SBC) with the greater adsorption capacity. As expected, ball milling and H3PO4 hydrothermally co-functionalized SBC (BPSBC) showed the optimum adsorption performance for SMX, and its maximum adsorption capacity (4.61 × 104 μg/g) calculated from Langmuir model was 6.30 times that of SBC. The adsorption behaviors and mechanism were investigated by kinetics, isotherms model fitting, thermodynamics, characterization, and density functionalization theory (DFT) calculation etc. Pore filling, π-π conjugation, H-bonding and P-O complexation were proved to be the main contributors to SMX adsorption by BPSBC. BPSBC showed the favorable sustainable adsorption performance for SMX by NaOH regeneration and stability over a broad pH value with the low leaching risk of phosphorus. This work developed a promising adsorbent of BPSBC for environmental concentration SMX removal, in addition to that the resource utilization of sludge was simultaneously achieved.