Ultrahigh adsorption of tetracycline on willow branche-derived porous carbons with tunable pore structure: Isotherm, kinetics, thermodynamic and new mechanism study

The problem of tetracycline (TC) antibiotic pollution in aquatic environment has attracted wide attention and research. It is still meaningful to develop high-efficiency separation materials and investigate their adsorption behavior and mechanism. In this research, porous carbons were prepared using the renewable willow branches as carbon source, via pre-carbonization and alkali activation. The activation temperature and alkali usage played important roles in the pore structure, which was mainly microporous. The WBAC-850-4 obtained at 850 °C and alkali/biochar ratio of 4:1 exhibited the largest specific surface area (3342 m 2 /g) and total pore volume (1.912 cm 3 /g), displaying the ultrahigh TC adsorption capacity of 1300 mg/g at 298 K. which was higher than that of the reported TC-adsorbents. WBAC-850-4 kept high adsorption ability with a minor impact in the broad pH range of 3.0–8.0. Thermodynamic analysis implied the physisorption dominated the spontaneous adsorption process. The structure-activity relationship between the TC adsorption capacity and porosity properties was established for the first time. Notably, the adsorption capacity of TC had a positive linear correlation with specific surface area, total pore volume, micropore surface area and micropore pore volume, and the correlation coefficient were higher than 0.97. It was first revealed that micropore filling was the main mechanism for porous carbons to bind TC, which meaningfully provided new insight for designing advanced TC-adsorbents in future.