Removal of Co(II) from fuel ethanol by silica-gel supported PAMAM dendrimers: Combined experimental and theoretical study

- Experimental and DFT methods were used for the removal of Co(II) from ethanol.
- SiO2-G0 ∼ SiO2-G3.0 were promising adsorbents for the removal of Co(II).
- The pseudo-second-order model best describe the adsorption kinetics.
- The adsorption processed chemically with charge transfer from ligands to Co(II).

Silica-gel supported PAMAM dendrimers (SiO2-G0.5 ∼ SiO2-G3.0) were used for the removal of Co(II) from fuel ethanol by batch method. The adsorption mechanism was revealed by combining the results of experiment and density functional theory (DFT) calculation. Results indicated the adsorption capacity was closely related with the generation number of PAMAM dendrimer, contact time, Co(II) concentration, and temperature. Amino-terminated PAMAM dendrimers exhibited better adsorption performance than the corresponding ester-terminated ones. Kinetic adsorption followed pseudo-second-order model and dominated by film diffusion. Isotherm adsorption can be well depicted by Langmuir isotherm model and proceeded by chemical mechanism. Thermodynamic parameters implied the adsorption was spontaneous, endothermic, and randomness incremental process. DFT calculation demonstrated that ester-terminated PAMAM tended to chelate with Co(II) by secondary amine nitrogen atoms and carbonyl oxygen atoms in a quadri-coordinated manner, while amino-terminated PAMAM preferred to act as tetradentate and pentadentate ligand to bind Co(II) with secondary amine nitrogen atom, carbonyl oxygen atom, and primary amine nitrogen atom. Charge transfer of the adsorption process mainly occurred from PAMAM dendrimer to Co(II).

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