Adsorption Characteristics and Mechanisms of Oxytetracycline on Nano Biochar: Effects of Environmental Conditions and Particle Aggregation

Physical disintegration of macro biochars in natural environments produces nano biochars, thus affecting environmental processes (e.g., adsorption, migration) of antibiotic contaminants. However, knowledge about the relationships between adsorption behaviors of antibiotics and unique physicochemical colloidal properties of nano biochar are relatively limited. In this study, a nano biochar (NSD700) was prepared from sawdust-derived biochar (SD700) by a combination method of ball milling, sonication, and centrifugation to contrastively investigate their adsorption for oxytetracycline (OTC). NSD700 had similar chemical structure properties of carbon fraction with SD700, whereas NSD700 possessed greater surface area and porosity. The maximal sorption capacity of OTC on NSD700 was 30.7 mg/g, similar to 3 times greater than that of SD700 (10.4 mg/g), primarily benefiting from more exposed surfaces and pores. OTC adsorption on NSD700 was inhibited under acidic and alkaline condition, and the inhibiting effect was more significant in comparison with that on SD700. OTC sorption onto NSD700 gradually decreased with increasing concentration of Na+, but was not observed for SD700. Aggregation kinetic of NSD700 varying with Na+ concentration