New Insights on the UV/TiO2 Photocatalytic Treatment of Thiomersal and its 2-Sulfobenzoic Acid Product

DE LA FOURNIÈRE, EMMANUEL M.; MEICHTRY, JORGE M.; CUSTO, GRACIELA S.; GAUTIER, EDUARDO A.; LITTER, MARTA I.

Journal of Photocatalysis

Bentham Science

Año: 2021 vol. 2 p. 223 - 233

2665-976X

Background: Thiomersal (TM), a complex between 2-mercaptobenzoic acid (2-MBA) andethylmercury (C2H5Hg+), is an antimicrobial preservative used in immunological, ophthalmic, cosmeticproducts, and vaccines.Objective: TM has been treated by UV/TiO2 photocatalysis in the presence or absence of oxygen atacidic pH. C2H5Hg+, 2-MBA, and 2-sulfobenzoic acid (2-SBA) were found as products. A 2-SBAphotocatalytic treatment was undertaken to study sulfur evolution.Methods: Photocatalytic runs were performed using a UVA lamp (λmax = 352 nm), open to air or underN2. A suspension of the corresponding TM or 2-SBA salt and TiO2 was prepared, and pH was adjusted.Suspensions were stirred in the dark for 30 min and then irradiated. TM, 2-MBA, 2-SBA, andC2H5Hg+ were quantified by HPLC, sulfur by TXRF, and the deposits on the photocatalyst were analyzedby chemical reactions. The mineralization degree was followed by TOC. Sulfate was determinedusing BaCl2 at 580 nm.Results: Photocatalytic destruction of TM and total C2H5Hg+ was complete under N2 and air, but TMdegradation was much faster in air. The evolution of TM and the products followed a pseudo-first orderkinetics.Conclusion: TiO2-photocatalytic degradation is a suitable technique for the treatment of TM and itsdegradation products. In contrast to other organomercurial compounds, TM degradation is faster in thepresence of O2, indicating that the oxidative mechanism is the preferred pathway. A significant TMmineralization (> 60%, NPOC and total S) was obtained. TM was more easily degraded than 2-SBA.Sulfate was the final product.