Adsorption of two antibiotics on biochar prepared in air-containing atmosphere: Influence of biochar porosity and molecular size of antibiotics

The porous biochar was prepared by pyrolysis of wood at 600–800 °C in the air-containing atmosphere, so as to enhance the biochar's capacity for adsorption of antibiotics from water. The analytical results obtained from N 2 adsorption/desorption indicated that air addition in pyrolysis atmosphere improved significantly the biochar's porosity, especially the development of mesopores. The mesoporous biochars showed high adsorption of antibiotics, and the highest adsorption was observed on the A 1/5 C800 biochar prepared at the air/gas ratio of 1/5 and heat treatment temperature (HTT) of 800 °C. The adsorption isotherm data were well fitted to the Langmuir model, and the maximum adsorptions ( Q m ) of tetracycline and sulfadiazine on the A 1/5 C800 sample are 163 and 261 mg/g respectively, which are 18.8 and 52.8 folds of those on the microporous NC800 biochar prepared at the same HTT but in total nitrogen atmosphere. The outstanding performance of mesoporous biochar was linked to the utilization of more inner pore surface for adsorption, which favors the adsorption of smaller-sized sulfadiazine molecules. While the stronger interactions between tetracycline and biochar contributed to the relatively higher adsorption of tetracycline on the microporous biochar. The mesoporous biochar retained most of the adsorption capacity (>50%) in a wide pH range (3.5–10) and with the co-existence of humic acid (10 mg/L). In general, this research provides a simple and green method to enhance the biochar's efficiency as an adsorbent for remediation of water contaminated by antibiotics.