Removal of Ni(II) from fuel ethanol by PAMAM dendrimers/silica hybrid materials: Combined experimental and theoretical study

Abstract The adsorption of Ni(II) from fuel ethanol by polyamidoamine (PAMAM) dendrimers/ silica hybrid materials (SG-G0.5–SG-G3.0) was performed combining experimental and theoretical method. The influences of terminal functional group, dendrimer generation, adsorption time, temperature, and initial concentration of Ni (II) on the adsorption were demonstrated. Equilibrium adsorption shows that the adsorption capacity of amino-terminated product is higher than their counterpart ester-terminated product. Adsorption kinetic indicates the adsorption equilibration can be reached at 350 and 270 min for amino- and ester-terminated products, respectively. Adsorption kinetic can be described by pseudo-second-order model. Boyd film diffusion model demonstrates film diffusion process is the rate limiting step during the adsorption process. Adsorption isotherm implies the adsorption can be promoted by increasing initial Ni(II) concentration and temperature. Langmuir model is more suitable than Freundlich model to describe the isotherm adsorption, indicating the adsorption proceeds by monolayer behavior. The results of D–R model indicate the adsorption is chemical adsorption process. The uptake of Ni (II) is proved to be spontaneous, endothermic, and entropy increasing by thermodynamic parameters. FTIR demonstrates the chemical nature of the adsorption process with the participation of nitrogen and carbonyl oxygen atoms. Density functional theory (DFT) calculation indicates the formation of tetra-coordination chelates by carbonyl O atoms and secondary amine N atoms dominates the adsorption for both ester- and amino-terminated PAMAM dendrimer. This work may provide promising adsorbents for the effective removal of Ni(II) from fuel ethanol with practical values.