Degradation of bromothymol blue by ‘greener’ nano-scale zero-valent iron synthesized using tea polyphenols

Application of green zero-valent iron nanoparticles to the remediation of soils contaminated with ibuprofen

“…A 30-mL volume of extract and the iron(III) solution (1.5; 6.0; and 9.0 mL for black tea leaves, grape marc, and vine leaves, respectively) were added to the flask simultaneously, achieving in-situ production of nZVI. Considering the results of the antioxidant ca-pacity of the extracts (Machado et al, 2013) and the results of Hoag et al (2009) it was assumed that all iron(III) was reduced. Final nZVI concentrations of 2.7, 9.8 and 14 mmol L −1 for black tea leaf-, grape marc-, and vine leaf extracts, respectively, were obtained.…”

“…These methods are generally expensive and require specific equipment. In one of the most widely used bottom-up processes sodium borohydride is used to reduce iron(III) or iron(II) to zero-valent iron nanoparticles (Hoag et al, 2009). This chemical process presents disadvantages related to safety issues associated with the use of a toxic reagent (sodium borohydride) and the formation of a flammable gas (hydrogen) during the process (Li et al, 2006).…”

“…This chemical process presents disadvantages related to safety issues associated with the use of a toxic reagent (sodium borohydride) and the formation of a flammable gas (hydrogen) during the process (Li et al, 2006). However, in the last years several authors have been developing a greener bottom-up method that involves the utilization of extracts from natural products (usually leaves or peels) (Hoag et al, 2009;Machado et al, 2013). These extracts have high reductive capacities and assure the reduction of the iron(III)/(II), producing nZVI.…”

“…fruit peels or tree leaves) and non-toxic solvents, in this case water. This 'green' method also enhances the stability of the nZVIs through the capping action of the polyphenols present in the extract, which delays the agglomeration process and increases the reactivity and efficiency of the remediation (Hoag et al, 2009). However, this method is not yet universally accepted because of the lack of knowledge of the production method as well as of the nZVIs' characteristics, namely size, agglomeration, and, mainly, their reactivity.…”

Characterization of green zero-valent iron nanoparticles produced with tree leaf extracts

“…This method uses aqueous extracts with high reduction capacities which are obtained from natural products, such as tea leaves (Hoag et al, 2009) or tree and bush leaves (Machado et al, 2013b). The use of these extracts provides several advantages when compared to the traditional method: i) the polyphenolic matrix can act as a capping agent that protects the iron nanoparticles from premature oxidation (Hoag et al, 2009) and agglomeration, ii) it can be used as a source of nutrients and microorganisms for a possible bioremediation action after the chemical treatment (Machado et al, 2013b) and iii) the valorization of natural products, such as tree leaves, that, in some cases, are considered wastes or do not have any added value (Machado et al, 2013b). Martins et al (unpublished results) used life cycle assessment to evaluate the environmental performance of the two synthesis methods (traditional using the sodium borohydride and the green using natural extracts) and concluded that the green synthesis method presents lower environmental impacts than the traditional method.…”