Facile synthesis of MnOx‐loaded biochar for the removal of doxycycline hydrochloride: effects of ambient conditions and co‐existing heavy metals

BACKGROUND In this study, manganese oxide (MnOx) nanoparticle loaded biochar (BC) was applied for doxycycline hydrochloride (DOX) removal from water. Biochar composites were synthesized by either pre‐treating biomass using MnCl2/KMnO4/NaOH (PMBC) or inserting MnOx ultrafine particles after pyrolysis of biomass (AMBC). In complex water environments, the presence of heavy metals may affect the removal of antibiotics. Cu(II) and Cr(VI) were used to study their effect on DOX removal. RESULTS The BC loaded with MnOx exhibited superior adsorption properties for DOX. The adsorption capacity of AMBC and PMBC was ≈93 mg/g and 104 mg g−1, respectively, which was about nine‐ and ten‐fold higher than that of raw BC (11.48 mg g−1). The characterization indicated that AMBC and PMBC had better surface structure and more surface functional groups than raw BC. The main mechanisms for DOX adsorption onto PMBC were surface complexation, H‐bond, π–π interaction and electrostatic interaction. DOX removal by PMBC also involved its degradation effect on DOX. Adsorption experiments were carried out with the influence of pH, ionic strength and background electrolyte. The presence of Cu(II) obviously enhanced the DOX adsorption capability through Cu(II) bridging effect, whereas the presence of Cr(VI) significantly inhibited DOX adsorption through competitive adsorption and electrostatic repulsion. CONCLUSIONS The results suggested that PMBC could be implemented as a cost‐effective and environmentally friendly adsorbent for DOX removal from water. Heavy metal ions can obviously enhance or weaken the adsorption ability of PMBC for DOX. © 2019 Society of Chemical Industry