Solid-phase extraction, separation and preconcentration of titanium(iv) with SSG-V10 from some other toxic cations: a molecular interpretation supported by DFT

Abstract

The present work reports the separation and preconcentration of titanium(IV) with functionalized silica gel (SSG-V10). A density functional theory (DFT) calculation has been performed to analyze the structure of both the extractor and the titanium(IV)-extractor complex to rationalize the sorption pathway. The systematic studies on the solid phase extraction of titanium(IV) ensured its quantitative sorption at solution pH: 5.0–6.0, influent volume: 1000 mL, analyte concentration: 23.95–35.92 μg mL⁻¹, flow rate: 2.5 mL min⁻¹, temperature: 27 °C, time of equilibration: 1.5 minutes and stress of foreign ions concentration (Cl⁻, SO₄²⁻, ClO₄⁻ and NO₃⁻): 200 μg mL⁻¹. The extractor, i.e., SSG-V10 (29 567.465 eV; η = 3.671 eV), has a high BET surface area (149.46 m² g⁻¹), a good value of exchange capacity (2.54 meq. of H⁺ g⁻¹ of dry SSG-V10), break-through capacity (Q₀ = 37.4–40.7 μg mg⁻¹) and column efficiency (N: 108) with respect to titanium(IV). The +ve ΔH (0.048 kJ mol⁻¹), ΔS (5 J K⁻¹ mol⁻¹) and −ve ΔG (−1.1488 kJ mol⁻¹) indicate that the sorption process was endothermic, entropy-gaining and spontaneous in nature. The DFT calculations reveal that the guest, [(OH)(H₂O)Ti(-μO)₂(OH)(H₂O)]⁺² (15 531.185 eV; η = 3.39 eV), is stabilized as a syn isomer. This syn isomer was then placed at the exchange site and a second DFT calculation was performed. It was found that the hydrogen bonded anti complex gets stabilized by 0.286 eV over the syn isomer as the extracted species. The loading of titanium(IV) has been confirmed by EDX. The sorbed titanium(IV) was eluted as a distinct and detectable color with 1 M HCl containing H₂O₂. The preconcentration factor has been optimized at 60.8 ± 0.5. Titanium(IV) amid congeners and other metal ions, associated with it in ores and alloy samples, have been separated from synthetic mixtures. Moreover, the method was found effective for alloy samples.