A new azine-based ferrocenophane for azo dyes degradation in dark–ambient conditions

Abstract

In a novel approach, 1,1′-bis(2,3-diazabuta-l,3‑dien)ferrocenophane (Fc-azine) synthesized by self-condensation of 1,1′-Ferrocenedicarboxaldehyde hydrazone (FcDH) with the aid of Zn(OAc)2·2H2O or acetic acid at 120 °C under high pressure. Fc-azine as an insoluble compound was fully characterized by Fourier transform infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller analyses (BET), powder x-ray diffraction (XRD) and single crystal x-ray diffraction. The narrow band gap (Eg = 1.93 eV) and the presence of ferrocene and azine functional groups encouraged us to use Fc-azine as an advanced oxidation process (AOP) catalyst. Interestingly, the addition of Fc-azine (1 g L-1) to aqueous solutions of 50 ppm of Congo red (CR) and 10 ppm of methyl orange (MO) led to the fast degradation of CR (over 80 % in 5 min) and the slow degradation of MO (98 % in 48 h) in the dark, without additional energy sources or chemical reagents. It was found that Fc-azine can degrade CR in six cycles with high efficiency (over 80 %). CR degradation by Fc-azine can be performed in acid and basic environments (pH= 3–9), and effective MO degradation happens in slightly acidic and natural environments (pH= 5–7). Possible adsorption, reactive oxygen species production (·OH, O2·−), and the mechanism of CR and MO degradation were also studied.