Utilizing ferrocene for doping iron into graphitic carbon nitride (FeIII/g-C3N4): an internal dual photocatalyst for tandem oxidation/cyclization of toluene to benzimidazoles under visible light conditions

Abstract

Recently, doping metals into graphitic carbon nitride (g-C₃N₄) is considered for environmental applications and organic reactions. In this study, we used ferrocene as a source of Fe³⁺ to dope iron onto g-C₃N₄. The scaffold of the internal electric field is presented as an impressive strategy to increase photocatalytic activities. Fe³⁺ was doped onto graphitic carbon nitride (Fe^III/g-C₃N₄) by the calcination method, which was well characterized by FT-IR, Raman, XRF, XRD, XPS, UV-visible DRS, photo-luminescence (PL), photocurrent, SEM, HR-TEM, EDX, BET, EIS, and cyclic voltammetry analyses. The synthesis of benzimidazole derivatives as pharmaceutically active compounds was introduced by using a suitable method under mild reaction conditions without using a base, oxidant, and other reagents or additives. The modification by using iron had a considerable effect on the optical and electronic characteristics in contrast to g-C₃N₄. The nanocomposite Fe^III/g-C₃N₄ could be employed as a multifunctional photocatalyst to perform the tandem process, oxidation of toluene, and then cyclization with o-phenylenediamines to prepare benzimidazoles under visible light conditions. The existence of the dynamic equilibrium of Fe³⁺/Fe²⁺ helped in significantly improving the activity. By changing the reaction conditions and different control experiments as well as Mott–Schottky plot analysis, the superoxide ion (O₂˙⁻) can be obtained as the reactive species in this reaction. The photocatalytic activity of Fe^III/g-C₃N₄ for this one-pot reaction is also investigated in detail.