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

Abstract

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.