Co-Adsorption Capabilities and Mechanisms of Bentonite Supported Sludge Biochar for De-Risking Norfloxacin and Cu2+ Contaminated Water

Abstract

Various bentonite-sludge biochar composites were fabricated by a sequence of loading and pyrolysis for the simultaneous removal of norfloxacin (NOR) and copper (Cu 2+ ) from an aqueous solution. The morphology and characteristics of obtained composites were reflected through cation exchange capacity (CEC), BET specific surface area (S BET ), SEM, XRD, FTIR and XPS. The Sips adsorption model fitted better for the adsorption of NOR and Cu 2+ during singular adsorption and co-adsorption. The theoretical maximum adsorption capacity of BT:2SB (the ratio of bentonite to sludge is 1:2) for NOR and Cu 2+ was 89.36 mg·g -1 and 104.10 mg·g -1 at 25 ℃ in the co-adsorption system, which was 6.50 and 6.58 times higher than bentonite and also higher than sludge biochar. The thermodynamic results showed the capture of NOR and Cu 2+ was spontaneous, accompanied by an endothermic reaction with different randomness. The mechanism of Cu 2+ adsorption was related to the electrostatic attraction and precipitation, as well as the interaction of complexation. And π-π interaction, hydrogen bonding and electrostatic attraction were responsible for NOR adsorption due to the surface oxygen-containing functional groups of bentonite-sludge biochar composites. This study suggests that using natural minerals as a carrier for biochar can improve the adsorption capability of biochar for both organic and metal contaminants.

Keywords: Co-adsorption, Bentonite, Sludge, Norfloxacin, Cu2+