Heterogeneous Photocatalytic Degradation of a Glucocorticoid in Aqueous Solution and Industrial Wastewater Using TiO2-Zn(II)-Clinoptilolite Catalyst

Abstract

Dexamethasone (DXM) is a glucocorticoid widely used in treating various diseases, but its extensive use raises environmental concerns due to poor absorption and rapid excretion, leading to its presence in aquatic environments. In this study, aqueous DXM was treated via heterogeneous solar photocatalysis (HSP) using a Zn-doped TiO2 catalyst supported on zeolite clinoptilolite (TiO2-Zn(II)-ZC), synthesized by electrodeposition. The catalyst was characterized by IR spectroscopy, SEM-EDS, XRD, atomic absorption spectroscopy, and Pzc determination. A Box–Behnken design was applied to evaluate the influence of initial DXM concentration (5–15 mg/L), hydraulic retention time (HRT: 30–60 min), and catalyst dose (0.5–1.5 g/L), using DXM (UV–Vis) and COD as response variables. Optimal conditions (12.5 mg/L DXM, 60 min HRT, 1.0 g/L catalyst) achieved 80% DXM removal (UV–Vis), 88.71% (HPLC), 85.29% COD removal, and 82.86% TOC reduction at 67 °C, 325.12 kJ/L, and 38.77 W/m2. Additionally, a treated sample of chocolate industry wastewater enriched with 12.5 mg/L DXM (DXM-WW) achieved 67.88% (HPLC), 93.02% (COD), and 92.38% (TOC) removal. The catalyst reduced the bandgap, enabling sunlight-driven generation of e−/h+ pairs and reactive oxygen species (•OH, H2O2, and O2•−), facilitating DXM degradation.