Ex Cathedra Immobilization of 8-Hydroxyquinoline to Inorganic Carriers via a New Silane Coupling Reagent for Extractive Sample Cleanup of Iron(III)

Abstract

By the use of a new silane coupling reagent, dimethyldichlorosilane (DMDCS), effective and instantaneous immobilization of 8-hydroxyquinoline (HQ) on an inorganic carrier (silica gel, SG) has been carried out for the facile synthesis of an extractor material (composition: {Si(OSi)p=4(H2O)x=0.16}n=11[−Si(CH3)2–NH–C6H4–N═N–HQ]z=4·25H2O; molar mass: 4010.3 g/mol). The material (thermal stability: ≤100 °C; chemical stability: ≤8 M HNO3) possesses a high Brunauer–Emmett–Teller surface area (BET-SAFe(III): 1170 m2·g–1), an appreciable preconcentration factor (PFFe(III): 145.1), and high breakthrough capacity (BTCFe(III): column exchange capacity, 269 μmol·g–l; Langmuir Q0, 278.6 μmol·g–1) for Fe(III). Along with these discernible analytical qualities, a high level of reusability (<800 cycles @ 95% recovery) reflects the material warranty. Fe(III), present as [Fe(OH)(H2O)5]2+ at the recommended pH (1.90 ± 0.15), binds at the highest occupied molecular orbital (HOMO) of the sorbent (η = 7.69 eV) through hard–soft binding with an appreciable binding energy (−14.2 eV). The breakthrough capacity (BTC: 269–278.6 μmol·g–1) was found to be the product of the amount of extractor HOMO (280 μmol·g–1) and the degree of polymerization of the adsorbed metal ion, x (i.e., BTC = [amount of HOMOextractor (μmol·g–1)] × x for monomeric (x = 1) and polymeric (x > 1) species). The findings reveal substantial improvement of Weetall–Hill immobilization of chelating ligands on inorganic carriers.