A dithizone-anchored silica gel surface, {SiO2}@DZ for the selective sample cleanup of Gd(iii) amidst Fe(iii), Th(iv), and Ce(iv) employing ion pair complexation

Abstract

The SG surface was functionalized with dithizone, R@-{SiO₂}_n, in a single step for selective sample clean-up and preconcentration of Gd(III) amidst Fe(III), Th(IV), and Ce(IV). Exploiting the differences in pH for extraction/or using selective eluents, the analytes were selectively separated. The sorbent brilliantly preconcentrates the dilute solutions of Gd(III), Fe(III), Th(IV), and Ce(IV) with a high level of enrichment factors at 183.2, 184.0, 184.1, and 182.1, respectively. The sorption process was found to be entropy gaining (ΔS: 0.033 ± 0.001 kJ mol⁻¹ K⁻¹), exothermic (ΔH: −0.098 ± 0.007 kJ mol⁻¹), and spontaneous (ΔG: −9.89 ± 0.31 kJ mol⁻¹). Systematic studies ensure the quantitative sorption of Gd(III), Th(IV), and Ce(IV) at their solution pH 5.75–6.5; while that for Fe(III) was found to be pH 2.25 ± 0.25. The hydroxy complexes [Gd₂(OH)₂(H₂O)₈]⁴⁺, [Fe₂(OH)₂(H₂O)₅]⁴⁺, [Ce(OH)₂(H₂O)₄]²⁺ and [Th(OH)₂(H₂O)₁₄]²⁺ exist at their respective sorption pH and being present in the vicinity of the electron-enriched ‘extractor-HOMO’ makes 1 : 1 ion-pair complexes, {extractor-HOMO} : {metal-hydroxy species}ⁿ⁺. The maximum sorption capacity (BTC) was determined from BTC = {amount of HOMO (μmol g⁻¹) × x} = 172 × x μmol g⁻¹ (where x, the degree of polymerization of a particular metal ion at its extraction pH is an integer and its numerical value(s) become(s) 2 for Gd(III)–Fe(III) and 1 for Th(IV)–Ce(IV)). The reusability (1600–1800 cycles) and the maximum sorption capacity (337.8, 331.1, 178.0, and 182.5 μmol g⁻¹, respectively, for Gd(III), Fe(III), Th(IV), and Ce(IV)) of the extractor with a durability of 18 months was outstanding.