The Role of Titanium Species in Ti-SBA-15 Materials for the UV–Photocatalytic Degradation of Acetaminophen in Water

Abstract

Water contamination by acetaminophen, a compound di����cult to remove via conventional treatments, has become a growing environmental concern due to its excessive consumption in recent years. Among emerging methods for removing this pollutant, heterogeneous photocatalysis is a promising option that enables catalyst recovery and reuse. In this research, Ti-SBA-15 materials with di����erent Si/Ti molar ratios were synthesized by a onestep sol–gel method to improve Ti dispersion within the SBA-15 silica framework. A detailed characterization of the materials was carried out using XRD, SEM, ICP-OES, N2 physisorption, UV-Vis-DRS, XPS, and zeta potential techniques. The results showed that the characteristic hexagonal mesoporous structure of SBA-15 was largely preserved at high Si/Ti ratios, while ICP-OES analysis showed that the synthesis method allowed Ti incorporation close to the theoretical Si/Ti molar ratio for most synthesized materials. As the Ti content increased, the speci����c surface area decreased, whereas the band gap energy increased. The UV-Vis-DRS spectrum showed an absorption band around 230 nm, which is commonly associated with ligand-to-metal charge transfer transitions in isolated Ti species with tetrahedral coordination. Together with the XPS results, these ����ndings suggest that the Ti incorporated into the silica framework is predominantly in tetrahedral coordination. Small amounts of Ti in Ti-SBA-15 materials are su����cient to promote photocatalytic acetaminophen degradation, without requiring signi����cant anatase formation. Catalyst dosage and solution pH signi����cantly in����uenced system performance, with higher degradation rates observed under acidic conditions. However, the rapid disappearance of acetaminophen did not directly translate into high mineralization, as aromatic intermediates are di����cult to break down into carboxylic acids. Consequently, the maximum mineralization achieved was 50%, obtained with a catalyst concentration of 50 mg/L at pH 6. The proposed reaction scheme successfully predicted the experimental data. These results show that the Ti-SBA-15 system possesses a high capacity for degrading acetaminophen; however, complete mineralization is limited by the slow oxidation rate of aromatic intermediates, making the control of subsequent degradation stages a key factor in improving the overall e����ciency of the photocatalytic process.