Effect of Camellia sinensis Origin and Heat Treatment in the Iron Oxides Nanomaterials Composition and Fenton Degradation of Methyl Orange

Sustainable and environmentally friendly methods for nanomaterials synthesis have been emerging recently. The use of extracts of polyphenol-rich plants with high reducing and chelating power is advantageous because the polyphenol can protect the nanomaterial from agglomeration and deactivation. Green nanomaterials have been applied in several areas, including remediation of toxic organic pollutants from contaminated effluents. Herein, we describe the preparation of green iron oxide nanoparticles (IONPs) with extracts of the plant Camellia sinensis as black tea for dye removal application. The as-prepared IONPs were composed of amorphous FeOOH and FeII/III-polyphenol complexes. To obtain crystalline and pure iron-based nanomaterials, the amorphous precursor was annealed at 900 ºC. Samples of black tea from different regions were used to verify the reproducibility of the iron phases formed. The same iron phases were obtained for all black tea samples, α-Fe2O3 (hematite), FePO4, and Fe3PO7, but in different proportions. The materials were applied as heterogeneous-Fenton catalysts for the removal of the dye methyl orange. The amorphous as-prepared IONPs were more active than the respective annealed IONPs due to the proton release from the polyphenol into the reaction medium, setting the pH to around 3, which is the optimum pH for the Fenton system.近年来，可持续且环境友好的纳米材料合成方法层出不穷。选取还原与螯合能力优异的富多酚植物提取物具备显著优势，因多酚可有效保护纳米材料免受团聚与失活侵扰。绿色纳米材料已被广泛应用于诸多领域，其中涵盖受污染废水中毒性有机污染物的修复治理。本文报道以红茶（即茶树Camellia sinensis提取物）为原料制备绿色氧化铁纳米颗粒（iron oxide nanoparticles, IONPs）的方法，该材料可用于染料脱除场景。所制备的IONPs由无定形FeOOH与FeⅡ/Ⅲ-多酚复合物组成。为获得结晶态、高纯度的铁基纳米材料，将该无定形前驱体置于900℃下进行退火处理。选取不同产地的红茶样品开展重复性验证实验，以确认所生成铁相的可重现性。所有红茶样品均可得到一致的铁相组分：α-Fe₂O₃（赤铁矿，hematite）、FePO₄以及Fe₃PO₇，仅各相占比存在差异。将所制备的材料作为非均相Fenton催化剂，应用于甲基橙染料的脱除处理。所制备的无定形IONPs催化活性优于经退火处理的IONPs，其原因在于多酚可向反应介质中释放质子，将体系pH值调节至3左右——这正是Fenton体系的最优pH条件。