Removal of Fe(III) from ethanol by silica-gel supported ester-terminated PAMAM dendrimers: experimental and DFT calculation

Silica-gel supported ester-terminated polyamidoamine (PAMAM) dendrimers (SG-G0.5, SG-G1.5, and SG-G2.5) were utilized as adsorbents for the removal of Fe(III) from fuel ethanol. The adsorption property was systematically investigated by determining the effects of dendrimer generation, contact time, temperature, initial Fe(III) concentration, and adsorbent dosage on the adsorption. Static saturated adsorption indicates the adsorption capacity increases with the increasing of dendrimer generation by following the sequence of SG-G2.5 > SG-G1.5 > SG-G0.5. Adsorption kinetic shows that the adsorption equilibrium can reach within 200 min for all the adsorbents. The adsorption kinetic can be well fitted by pseudo-second-order model and is controlled by film diffusion process. Adsorption isotherm demonstrates the adsorption favors high temperature and initial Fe(III) concentration. The adsorption isotherm follows Langmuir model and carries out by monolayer chemical ion-exchange mechanism. Thermodynamic parameters imply the adsorption process of Fe(III) by SG-G0.5, SG-G1.5 and SG-G2.5 is a spontaneous, endothermic and entropy increased process. The regeneration property shows the adsorbents exhibit good reusability and maintain excellent adsorption capacity after three adsorption-desorption cycles. Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculation indicate the interaction of carbonyl oxygen and amine nitrogen groups with Fe(III) mainly dominate the adsorption process.