Theoretical Calculation, Molecular Dynamics Simulation and Experimental Investigation for Adsorption of Cadmium (II) on Amidoxime-chelating Cellulose
Amidoxime-chelating cellulose (ACCS) was obtained through comprehensive modification, i.e. alkalization, etherification, amination and chelating, and then the adsorption of cadmium (II) was investigated by batch experiments, characterization, and computational theoretical calculations and molecular dynamics simulation. Isothermal adsorption showed that the Freundlich equation fitted for describing the adsorption data at pH 5.0 and 7.0, whereas the Langmuir model was in good accordance at pH 1.0 and 3.0. As confirmed, ACCS exhibited best Cd (II) adsorption capacity (134.13 mg g-1) at pH 5.0, even remained considerable adsorption performance at extremely acidic condition. Additionally, it still maintained excellent adsorbability and little weight loss after 5 cycles. Further, adsorption structure of 2662 type was determined by quantum molecular (QM) and molecular orbital (MO). On the basis of this structure, amidoxime group (-C(NH2) = NOH) was proved to be the key in the adsorption process by analysis of Muliken charge and molecular dynamics simulation. Furthermore, binding energy values stated clearly that Cd (II) favored to bind with the C-NH2 over C=N-OH in amidoxime group. In summary, interpretation of the entire adsorption mechanism was well quantified by efficient calculation and simulation.