Removal mechanism of di-n-butyl phthalate and oxytetracycline from aqueous solutions by nano-manganese dioxide modified biochar.

In this work, nano-manganese dioxide (nMnO2)-modified biochar (BC) was synthesized in order to improve BC's adsorption capacity for di-n-butyl phthalate (DBP) and oxytetracycline (OTC). The results showed that nMnO2 on the BC surface exhibited a poor crystallinity and oxidation state (Mn (IV)). Sorption experiments showed that, compared to BC, DBP sorption capacity of nMnO2-BC (1:20) and OTC sorption capacity of nMnO2-BC (1:10) were 0.0364 and 0.0867 mmol/g, respectively, which are significantly higher than that of BC (0.0141 and 0.0151 mmol/g). Kinetics and isotherm experiments indicated that physical adsorption and chemical interactions have both exerted their impacts on the adsorption process. Further X-ray photoelectron spectroscopy (XPS) analysis showed that part of the Mn (IV) in nMnO2-BC was reduced to Mn (III) and Mn (II) after DBP or OTC adsorption. Therefore, we suggest the nMnO2 also acted as an oxidizer on modified BC, which may accelerate the degradation of DBP and OTC.