Photocatalytic degradation of diphenhydramine in aqueous solution by natural dolomite

Natural dolomite, an inexpensive and vastly available natural material, was demonstrated as a potential heterogeneous photocatalyst for the efficient removal of diphenhydramine (DP) from aqueous solution under simulated solar light in this study. About 65% DP removal and 14% mineralization were achieved with dolomite as a catalyst after 75 min irradiation. The electron spin resonance analysis and scavenger experiments verified that ¹O₂, ˙OH, and O₂ ^-˙ produced in the dolomite system were the main reactive species responsible for DP degradation. Furthermore, first-principle calculations combined with deoxygenation experiments were employed to elucidate the photocatalytic mechanism. The results revealed that the dolomite changed from an insulator to a semiconductor after partial substitution of Mg²⁺ by Fe²⁺, suggesting that natural dolomite could act as a semiconductor photocatalyst in photoreactions. Under irradiation, photo-excited electrons and holes separate and migrate to the surface of dolomite, and subsequently react to form reactive species resulting in the DP degradation. Product studies demonstrated that the main degradation pathways of DP included hydroxylation of the aromatic ring as well as hydroxyl radical mediated oxidation of the alkylamine side chain. This work indicated that natural dolomite could be applied in water and wastewater treatment as a promising photocatalyst.