A bifunctional adsorbent of silica gel-immobilized Schiff base derivative for simultaneous and selective adsorption of Cu(II) and SO42−

Abstract A ditopic zwitterionic Schiff base modified silica gel adsorbent SG-H 2 L 2 was prepared and it was characterized by Fourier transform infrared spectroscopy, elemental analysis, solid state NMR, thermogravimetry and porous structure analysis. SG-H 2 L 2 could simultaneously adsorb metal ions and attendant anions from the aqueous solution of metal salts . SG-H 2 L 2 exhibited a cooperative effect between the adsorption of metal cations and the attendant anions, and the adsorption efficiency decreased in the order MSO 4  > M(NO 3 ) 2  > MCl 2 (M = Cu, Co, Ni, Mn, Cd). SG-H 2 L 2 displayed good adsorption selectivity for Cu(II) and SO 4 2− from the aqueous solutions containing mixed metal ions of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) or mixed anions of SO 4 2− , NO 3 − , and Cl − . The preliminary mechanism for simultaneous and selective adsorption of the metal ions and attendant anions were discussed. The effect of different parameters including pH, contact time and initial concentrations of Cu(II) and SO 4 2− on the simultaneous adsorption of Cu(II) and SO 4 2− ions were investigated. The efficient adsorption of Cu(II) and SO 4 2− could be achieved in neutral pH region and the maximum adsorption capacities for Cu(II) and SO 4 2− , respectively, were the same of 0.42 mmol g −1 at 25 °C. The adsorption isotherms for Cu(II) and SO 4 2− fitted well with Langmuir model, while their adsorption kinetics followed the pseudo-second order model. Regeneration of SG-H 2 L 2 was realized by adjusting the solution pH with diluted H 2 SO 4 and ammonia solution, respectively. SG-H 2 L 2 exhibited good recyclability and reusability for four cycles use without deterioration in its functionality. SG-H 2 L 2 was also applied in different water samples and good recoveries and the selective adsorption of Cu(II) and SO 4 2− were achieved. This study provides a new bifunctional adsorbent which may be used for the effective removal of Cu(II) and SO 4 2− from water effluents containing mixed metal ions and anions.