Effects of pH, dissolved humic acid and Cu2+ on the adsorption of norfloxacin on montmorillonite-biochar composite derived from wheat straw

A montmorillonite-biochar (MT-BC) composite was prepared from wheat straw heating at 400 °C. Adsorption isotherms and effects of pH, dissolved humic acid (DHA) and Cu2+ on norfloxacin (NOR) sorption to biochar and MT-BC composite were carried out. Montmorillonite modified biochar showed higher adsorption affinity for NOR. The qmax value increased from 10.58 mg g−1 to 25.53 mg g−1 after surface modified by montmorillonite. MT-BC composite had rich pore structure, with specific surface area (SSA) and pore volume values of 112.6 m2 g−1 and 0.604 cm3 g−1, respectively. The optimum pH range for NOR adsorption on MT-BC composite is 5–11. The presence of DHA (20–150 mg L−1) greatly suppressed the NOR adsorption. The decrease of NOR sorption is attributed to the “competitive adsorption” of DHA with NOR and “pore blockage” by sorbed DHA. Similarly, reduced NOR sorption with Cu2+ was probably due to the competition for sorption sites on biochar surface. Compared to DHA, Cu2+ resulted to a smaller decrease in NOR sorption. This is because the formation of NOR-Cu2+ complexes can slightly increase NOR sorption capacity. The dominant adsorption mechanisms of NOR on MT-BC composite are electrostatic interaction, H-bond and pore-filling. This study provided valuable guidance and effective method for the removal of NOR from aquatic environments.