Mechanistic Insight for the Sorption of Cd(II) and Cu(II) from Aqueous Solution on Magnetic Mn-Doped Fe(III) Oxide Nanoparticle Implanted Graphene

The sorption behaviors of M(II) (M = Cu, Cd) were investigated from their aqueous solution by magnetic Mn-doped Fe(III) oxide nanoparticle implanted graphene (GMIO) at varying pH, contact times, and concentrations. Kinetically, the pseudo-second-order equation governed the overall sorption process at optimized pH (5.1 +/- 0.1). Redlich-Peterson (R-P) (0.97 < R-2 < 1.00, 0.84 < g < 1.00) and Langmuir (0.96 < R-2 < 1.00) isotherms described sorption equilibriums better than Freundlich (0.86 < R-2 < 0.96). Monolayer sorption capacity values of GMIO for M(II) increased (88 mg.g(-1) to 127 mg.g(-1) for Cd; 130 mg.g(-1) to 144 mg.g(-1) for Cu) with increasing temperature from 288 K to 333 K. Negative Delta G(0) values indicated spontaneous sorption nature despite positive Delta H-0 values owing to an entropy increase (positive Delta S-0) at the solid-liquid interface. Relatively less regeneration (similar to 70%) of M-II-GMIO by 0.1 M HCl possibly stemmed the chemisorption of metal ions, and this is well-corroborated by the nature of Stern-Volmer plot of fluorescence quenching data with reaction time.