Fabrication of carboxymethyl cellulose and chitosan modified Magnetic alkaline Ca-bentonite for the adsorption of hazardous doxycycline

Abstract To obtain an effective, cheap and recyclable adsorbent for refractory pollutants removal, carboxymethyl cellulose (CMC) and chitosan (CS) modified magnetic Fe3O4/alkaline Ca-bentonite (MACB-CC) was successfully fabricated by modifying magnetic Fe3O4/alkaline Ca-bentonite (MACB) with both CMC and CS via the Schiff base reaction. The designed adsorbent exhibited stable magnetic separation ability and excellent adsorption for doxycycline (DC) (96%) as compared to the pristine MACB (84%). DC adsorption efficiency increased with increasing time from 0 to 2 h for MACB and MACB-CC and then reached to equilibrium. The optimum pH value/range for DC adsorption were achieved at pH 7.0 and 4.0 ∼ 8.0 for MACB and MACB-CC respectively. DC adsorption was boosted by the presence of humic acid in low concentration (20 ∼ 40 mg L−1 and 0 ∼ 40 mg L−1 for MACB and MACB-CC respectively). The mechanism of DC adsorption on MACB-CC mainly included complexation, electrostatic attraction and deposition. The adsorption data of DC both on MACB and MACB-CC fitted well with the pseudo-second-order kinetic model and Langmuir adsorption isotherm model. MACB-CC achieved 1.2 times higher uptake for DC (643 mg g−1) than that of MACB. The enhanced adsorption of DC could be ascribed to the synergistic organic modification by CMC and CS. In addition, MACB-CC exhibited good magnetic separation ability and magnetic stability during the recycling process, and hence could be deemed as a promising alternative for DC adsorption from wastewater on industrial level.