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 center dot degraded about 16.4%-25.5% SMX and center dot OH degraded about 49.8%-63.9% SMX in the pH range of 4-6 while center dot 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 center dot 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.

Automated summary

This study employed a green synthesis method to prepare zero-valent iron (ZVI) with improved dispersity and stability. The use of tannins (TA) as reducing agents resulted in ZVI with a higher specific surface area and reactive sites compared to chemically prepared ZVI. TA also enhanced the adsorption and degradation of pollutants and provided an oxidative degradation continuous source. The presence of TA accelerated the conversion of Fe and delayed the formation of passivation layer, thereby enhancing the antioxidant capacity of ZVI.