Reactivity of iron-based nanoparticles by green synthesis under various atmospheres and their removal mechanism of methylene blue

In this study, iron-based nanoparticles (Fe NPs) were synthesized using tea extracts under various atmospheres (N-2, O-2 and air) to understand how atmospheres impact on the reactivity of Fe NPs, where Fe NPs were used for the degradation of methylene blue (MB). SEM and FTIR confirmed the morphology and change in size of iron-based nanoparticles before and after reaction with MB, indicating that different Fe composition, morphology and size were obtained under various atmospheres resulting in different reactivity of Fe NPs. In addition, various parameters impacting on removing MB by Fe NPs synthesized under various atmospheres show that the solution pH significantly affects the reactivity of Fe NPs. Furthermore, the data fitted well to the pseudo-second-order adsorption and pseudo-first-order reduction models, confirming that the removal of MB was based on both adsorption and reduction. Langmuir and Freundlich isotherms demonstrate that the removal of MB by Fe NPs synthesized under various atmospheres was different due to their composition, morphology and size. Finally, the degraded products such as benzothiazole were identified by gas chromatography-mass spectrometry (GC-MS) after the degradation of MB, and finally a feasible removal pathway is proposed.