Adsorption studies of Cu(II) ions on dendrimer-grafted silica-based materials

Abstract

Globally observed increase in water contamination has prompted the search for novel, efficient adsorbents, in particular those capable of adsorbing heavy metals. A group of novel hybrid materials composed of silica-gel functionalized with dendritic structures was synthesized. Firstly, four poly(amidoamine) dendrimers (PAMAM) were synthesized in a two-step synthesis: (1) Michael addition between amine core – tris(2-aminoethyl)amine - and methyl acrylate; (2) amidation with the use of four structurally diverse amines: ethylenediamine, triethylenetetramine, tris(2-aminoethyl)amine and 4,7,10-trioxa-1,13-tridecanediamine. Obtained dendrimers were characterized with NMR and MS analysis, and subsequently used as grafting agents dedicated to isocyanate-functionalized silica particles. The obtained hybrid materials (SiO2-dendrimers) were subjected to IR spectroscopic study and tested for their adsorptive properties towards Cu2+ ions. Adsorption studies included obtaining of adsorption isotherms and kinetic and thermodynamic studies, using spectrophotometric measurements. Adsorption capacity values of the materials fluctuated between 19.8 and 104.6 mg g−1. Also, other coefficients, such as adsorption rate constants, standard enthalpies or standard Gibbs free energies, describing chelating ability of adsorbents were considerably various for different materials. According to the results, incorporation of structurally diverse amines as amino-terminal components of dendritic structure had a significant influence on adsorptive properties of silica-dendrimer hybrid materials.