Constructing chelating organic macrocycles inside the pores of hybrid mesoporous silica to intensify the toxic metal recovery ability

Abstract

Inorganic–organic hybrid mesoporous silicas have been considered some of the most effective matrices for the adsorption of potentially toxic species from aqueous and non-aqueous media. Among them, SBA-15 porous silica is superior due to its all-connected large pores associated with the intrinsic high surface area of this class of materials. Herein, we take advantage of the high pore volume of SBA-15 and form large organic macrocycles containing basic centres inside the mesopores to potentialize the toxic metal adsorption ability from aqueous waste water. The construction of the macrocycles was carried out through controlled sequential reactions of the silica matrix with 3-iodopropyltriethoxysilane, diethyl iminodiacetate, cysteamine and 1,3-tribromopropane, resulting in a final chelating conformation containing nitrogen, oxygen and sulfur basic centres. The enclosed configuration intensified the complexing effect of the moieties and boosted the ability of toxic metal recovery from aqueous media. Especially for lead cation adsorption, the sequential functionalization led to uptake values of (1.09 ± 0.13), (2.96 ± 0.24), and (5.74 ± 0.07) mmol g⁻¹ for diethyl iminodiacetate, cysteamine and macrocycle-containing hybrids, respectively. The maximum adsorption capacities of Cd²⁺ and Cu²⁺ were (0.12 ± 0.01) and (1.10 ± 0.07) mmol g⁻¹, respectively. Calorimetric measurements provided further insight into the nature of the interactions of the metal cations with the pendant basic centres, indicating intensified adsorption effects according to the progress of the sequential modification processes.