Useful aminoalcohol molecules incorporated in an epoxide silylating agent for silica organofunctionalization and thermodynamics of copper removal

Abstract

Ethanolamine (E) and diethanolamine (D) molecules were incorporated onto a precursor 3-glycidoxypropyltrimethoxysilane (G) agent, followed by organofunctionalization of the silica gel through homogeneous (A) and heterogeneous (B) routes, to yield SiEA, SiDA, SiEB and SiDB hybrids. These chemically organofunctionalized silicas were characterized by several techniques, including infrared spectroscopy (FTIR), solid-state nuclear magnetic resonance (¹³C and ²⁹Si NMR using CP/MAS), thermogravimetry and elemental analysis. Based on the obtained nitrogen percentages, the amount of pendant organic groups attached to the inorganic matrices SiEB, SiEA, SiDB and SiDA were calculated as 0.22 ± 0.04, 1.05 ± 0.03, 0.29 ± 0.02 and 0.89 ± 0.01, respectively. The infrared spectra presented characteristic bands attributed either to the inorganic framework or to the immobilized chains. Solid-state ¹³C NMR results clearly demonstrated that the organic moieties are covalently bonded to the inorganic framework, while ²⁹Si NMR revealed the silicon atoms with distinct environments, Q and T, in agreement with the covalent attachment of organic moieties. The basic centers attached on the pendant groups have the ability to sorb copper from aqueous solution. This process was adjusted to the Langmuir model, to obtain maximum sorption values of 0.28 ± 0.02, 0.40 ± 0.02, 0.29 ± 0.03, 0.76 ± 0.02 mmol g⁻¹ for SiEB, SiEA, SiDB and SiDA hybrids, respectively, from the isotherms. Thermodynamic data obtained from calorimetric titrations reflected the spontaneity of the reactions, which are also enthalpically and entropically favorable for the proposed cation/basic center interactions for these chelating processes at the solid/liquid interface.