New insights for titanium(iv) speciation in acidic media based on UV-visible and 31P NMR spectroscopies and molecular modeling. Issue 43 (9th August 2021)

• Record Type: Journal Article
• Authors: Mangold, Lucas; Halleux, Hubert; Leclerc, Sébastien; Moncomble, Aurélien; Cote, Gérard; Chagnes, Alexandre
• Is Part Of: RSC advances. Volume 11:Issue 43(2021)
• Page Start: 27059
• Page End: 27073
• Publication Date: 2021-08-09
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1ra04284j
• Languages: English
• ISSNs: 2046-2069

Abstract

Abstract : A spectroscopic study of titanium(iv ) speciation in diluted nitric acid (model of non-complexing medium) and 0.1–12.7 mol L −1 phosphoric acid aqueous solutions. Evidence for the presence of polynuclear species is supported by molecular modeling. Abstract : Titanium chemistry in aqueous acidic media has been extensively investigated over the last decades. Hydrolyzed species such as Ti(OH) 3+, TiO 2+, Ti(OH)2 2+ or Ti(OH)3 + have been identified and their equilibria have been studied in nitric and perchloric acid. A predominance of the divalent cations was found for low pH ( i.e., pH <2). Nonetheless, recent literature reports the existence of small titanium oxo-clusters in aqueous acidic media for large titanium(iv ) concentration (typically., >0.1 mol L −1 ), as stable precursors for the formation of condensed titanium dioxide. The present paper reconsiders firstly previous knowledge about the speciation of titanium(iv ) in non-complexing acidic media by giving evidence for the presence of polynuclear hydrolyzed species, even at very low Ti(iv ) concentration ( i.e., typically <0.1 mmol L −1 ). UV-visible absorbance spectra recorded for diluted nitric acid solutions (a model of non-complexing acidic medium) containing titanium(iv ) were compared to time-dependent density functional theory (TD-DFT) predicted excitation energies. Experimental and predicted maximal absorbance wavelengths showed significantly improved matches when polynuclear species were considered in TD-DFT calculation. Then, 0.1–12.7 mol L −1 phosphoric acid solutions containing titanium(iv ) were studied by means of spectroscopic techniques (UV-visible, NMR) in order to identify qualitatively the presence of titanium(iv ) complexes and to link this speciation to the acid concentration. Two different titanium(iv ) orthophosphate complexes, potentially polynuclear, were detected, and the presence of free titanium(iv ) is also expected for low phosphoric acid concentration ( i.e., <0.1 mol L −1 ). A general complexation scheme for a large range of H3 PO4 concentration was thus formulated.