Studies of the kinetics and isotherms of copper ions adsorption on APTES-modified silica materials

In the present study, the potential of hydrophilic fumed silica Asil300 functionalized with 3-aminopropyltriethoxysilane for the adsorption of copper ions from aqueous solution was investigated. The modification of the silica surface with two amounts of APTES (0.3 and 0.6 mmol/g), resulting in materials named NH 2 -Asil300 (0.3) and NH 2 -Asil300 (0.6), respectively was carried out. Asil300, as an example of a fumed oxide (amorphous form) and in the form of aggregates or agglomerates forming a developed surface, is a promising material for the preparation of porous adsorbents. Both the equilibrium and kinetics adsorption of Cu(II) ions were investigated. The pseudo-first order, pseudo-second order, as well as Boyd's and Bangham's models were used to describe the adsorption kinetics. The results displayed that the adsorption kinetics followed the pseudo-second order model and most likely controlled by film diffusion. The isotherms of equilibrium adsorption of Cu(II) were analyzed using the Freundlich, Langmuir and Temkin isotherms. The best fit was obtained for the Freundlich isotherm. The adsorption capacities for Cu(II) were found to be 36.90 mg/g, 56.82 mg/g and 70.42 mg/g for Asil300, NH 2 -Asil300 (0.3) and NH 2 -Asil300 (0.6), respectively. This study shows that the NH 2 functionalization of nanoporous silica improves its adsorption capacity and makes it possible to obtain an effective adsorbent for the removal of copper ions from the water environment. • Modification of silica with APTES shows high adsorption capacity towards Cu(II) ions. • The increase in the adsorption capacity of the adsorbent is correlated with the degree of modification (the number of functional groups attached to its surface). • The dominant mechanism of copper ion adsorption on the tested material is film diffusion. • Copper is an important trace element, but when present in higher concentrations it is one of the most toxic heavy metals.