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

A ditopic zwitterionic Schiff base modified silica gel adsorbent SG-H2L2 was prepared and it was characterized by Fourier transform infrared spectroscopy, elemental analysis, solid state NMR, thermogravimetry and porous structure analysis. SG-H2L2 could simultaneously adsorb metal ions and attendant anions from the aqueous solution of metal salts. SG-H2L2 exhibited a cooperative effect between the adsorption of metal cations and the attendant anions, and the adsorption efficiency decreased in the order MSO4 > M(NO3)(2) > MCl2 (M = Cu, Co, Ni, Mn, Cd). SG-H2L2 displayed good adsorption selectivity for Cu(II) and SO42- from the aqueous solutions containing mixed metal ions of Cu(II), Co(II), Ni(II), Mn(II) and Cd(II) or mixed anions of SO42-, NO3-, and CF. 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 SO42- on the simultaneous adsorption of Cu(II) and SO42- ions were investigated. The efficient adsorption of Cu(II) and SO42- could be achieved in neutral pH region and the maximum adsorption capacities for Cu(II) and SO42-, respectively, were the same of 0.42 mmol g(-1). at 25 degrees C. The adsorption isotherms for Cu(II) and SO42- fitted well with Langmuir model, while their adsorption kinetics followed the pseudo-second order model. Regeneration of SG-H2L2 was realized by adjusting the solution pH with diluted H2SO4 and ammonia solution, respectively. SG-H2L2 exhibited good recyclability and reusability for four cycles use without deterioration in its functionality. SG-H2L2 was also applied in different water samples and good recoveries and the selective adsorption of Cu(II) and SO42- were achieved. This study provides a new bifunctional adsorbent which may be used for the effective removal of Cu(II) and SO42- from water effluents containing mixed metal ions and anions.