Green synthesis of zero valent iron using tannins to activate persulfate for sulfamethoxazole degradation

Majority zero-valent iron (ZVI) materials are prepared by reducing agents in liquid phase, resulting in the high environmental pollution and poor particle size distribution uniformity. Therefore, this study employed a green synthesis method to prepare ZVI. Tannins (TA) with phenolic hydroxyl groups that are characterized by strong reducing capacity were employed to synthesize ZVI (TA@ZVI). The dispersity and stability of ZVI was improved by TA, which inhibited the agglomeration of ZVI. Meanwhile, the specific surface area of TA@ZVI was higher than chemical prepared ZVI, increasing the reactive sites. The organic matter components enriched on TA could promote the adsorption of pollutants and complex with Fe(II/III) to enhance the reactivity of TA@ZVI. Also, the polyphenol structure in TA was oxidized to quinone, which facilitated electron transport. In order further test the performance of TA@ZVI, SMX was chosen as a target pollutant to study the oxidative degradation performance of TA@ZVI. SO₄^•- degraded about 16.4%-25.5% SMX and •OH degraded about 49.8%-63.9% SMX in the pH range of 4-6 while •OH played a dominant role in the neutral and alkaline conditions. Moreover, the presence of TA reduced Fe(III) to Fe(II) and promoted the release of Fe(II), providing a continuous source of •OH for the oxidative degradation of SMX. Besides, the conversion of Fe(II/III) was accelerated due to TA, which delayed the formation of passivation layer. Thus, TA enhanced the antioxidant capacity of ZVI. Generally, this study provided an environmental-friendly technology to synthesize and improve the reactivity of ZVI.