Peroxidation and photo-peroxidation of pantoprazole in aqueous solution using silver molybdate as catalyst

Abstract

In this study, silver molybdate was used as a catalyst in different oxidation processes to degrade pantoprazole (PAN) from aqueous suspension. The catalyst was synthesized using a controlled precipitation method and characterized by XRD, FTIR spectroscopy, BET analysis, Zeta potential, FEG-SEM/EDS, DRS and EPR. The α- and β-phases of Ag₂MoO₄ were identified as crystalline structure of the butterfly-shaped particles. The metastable α-phase could be completely converted into β-Ag₂MoO₄ by thermal treatment at 300 °C. The band gap energy of β-Ag₂MoO₄ (E_g = 3.25 eV) is slightly higher than for as-prepared catalyst (α-Ag₂MoO₄ + β-Ag₂MoO₄) (E_g = 3.09 eV), suggesting that as-prepared catalyst should be active under visible light. PAN is sensible to UV light irradiation, and the addition of H₂O₂ as electron acceptor enhanced the mineralization rate. In the catalytic UV-based reactions, high PAN oxidation efficiencies were obtained (>85%) but with low mineralization (32-64%). Catalytic peroxidation and photo-catalytic peroxidation under visible light showed the highest PAN oxidation efficiency, leading to its almost complete mineralization (>95%), even under dark conditions (98% in 120 min). Several degradation byproducts were identified and three mechanistic routes of PAN decomposition were proposed. The identified byproducts are less toxic than the parent compound. EPR coupled with the spin trapping method identified ^•OH radicals as the main ROS species in both photocatalytic and catalytic peroxidation reactions. Ag₂MoO₄ showed to be a promising catalyst to promote the decomposition of hydrogen peroxide into ROS.¹.

Keywords: Advanced oxidation processes; Ag(2)MoO(4); Pharmaceuticals; Photocatalysis.