Visible light-induced degradation of indigo carmine over ZnFe2O4/Tannin/ZnO: Role of tannin as a modifier and its degradation mechanism

Design and usage of efficient visible light photocatalytic systems for wastewater treatment and degradation of organic dyes are of remarkable interest in the fields of environmental protection. In this study, magnetic ZnFe₂O₄, ZnFe₂O₄/ZnO, Tannin/ZnFe₂O₄ and Tannin/ZnFe₂O₄/ZnO nanocomposites with interfacial contact have been synthesized. The photocatalytic efficiencies of as-obtained samples are analyzed by the degradation of indigo carmine in aqueous solution under UV and visible-light. The degradation ratios of IC are 82% and 99% of IC over the Tannin/ZnFe₂O₄/ZnO under the both of UV light and visible light for 90 min, respectively. And after five times recycling, the photocatalytic performance of IC presence the Tannin/ZnFe₂O₄/ZnO can even reach nearly 89.79%. The results demonstrate that the Tannin/ZnFe₂O₄/ZnO exhibits great photocatalytic efficiency for indigo carmine (IC) compared to their constituent photocatalysts and easy separation from dye solution by magnet. The synergistic interactions between ZnFe₂O₄, tannin and ZnO prolonged lifetime of photoexcited carriers leading to greater absorption in both UV and visible light. This nanocomposite was beneficial for separating the photogenerated charge carriers and facilitating electron transfer. Tannin has a decisive role for increasing the photocatalytic performance of ZnFe₂O₄ due to the abundant units of phenolic groups in tannin molecules. ZnFe₂O₄ makes the Tannin/ZnFe₂O₄/ZnO magnetically separable in a system. This work presents new insights that tannin molecules function as great modifier to improve very impactful tannin-modified magnetic photocatalysts in removing environmental contamination.