Cr(VI) removal with green iron-based nanoparticles

I.E. LÓPEZ; E.R. NEIS; G.P. SCIPIONI; H.D. TRAID; M.L. VERA; M.I. LITTER

Congreso; WCCE11- 11th world Congress of Chemical Engineering; 2023

Chromium is a heavy metal used in many industrial processes, mainly in the metallurgical industry for metal finishing and in the forestry industry for wood preservation. The most abundant chromium species in water are Cr(III) and Cr(VI), the latter being the most dangerous, as it is a well-known human carcinogen. The most widely used process for the treatment of Cr(VI) in water is its reduction to less toxic and mobile Cr(III) species [1].A promising alternative for Cr(VI) removal from water is the use of iron (Fe)-based nanoparticles (NPs), such as nanoscale zerovalent iron (nZVI) NPs, or Fe nano-oxides such as nanomagnetite (nFe3O4) or nanomaghemite (nγ-Fe2O3), which promote oxidation-reduction reactions combined with adsorption and coprecipitation processes.The most commonly used method for the synthesis of nZVI is the chemical reduction of Fe(II) or Fe(III) salts with sodium borohydride (NaBH4), a toxic and flammable compound. However, in recent times, safer and environmentally friendly methods have been reported to obtain Fe-based nanoparticles by a green chemistry method (g-FeNPs) from natural plant extracts with high polyphenol content. In the present work, g-FeNPs were synthesized using Yerba Mate (YM) extract and FeCl3 at acid pH. The NPs were thoroughly characterized, and the efficiency of Cr(VI) removal from aqueous solutions has been tested. The extraction process of the YM powder was made in water at 80 °C. The extract was centrifuged and filtered. The total polyphenol content was determined by the Folin-Ciocalteu method (ISO, 2005). Then, a 0.1 M FeCl3.6H2O solution was added to the extract at room temperature obtaining g-FeNPs dispersed in the extract. Subsequently, to obtain a nanoparticulate powder of g-FeNPs (free of extract), the suspension was centrifuged at 3500 rpm, and the sedimented g-FeNPs were washed with distilled water and dried in a forced convection oven at 50 °C for 8 h. The obtained NPs were characterized by UV-Vis spectroscopy, scanning electron microscopy, and X-ray diffraction, confirming the presence of Fe-based nanoparticles. The efficiency for Cr(VI) transformation (300 μM) of the YM extract, the g-FeNPs water suspension (with the extract), and the powder of g-FeNPs suspended in water was evaluated. With the YM extract, 58% Cr(VI) transformation was obtained in 2 h of reaction; with the water suspension of the g-FeNP powder, the removal was slightly higher, reaching 62% at 2 h and 71% at 4 h of reaction. On the other hand, with the g-FeNPs extract suspension, an excellent transformation (100%) of Cr(VI) was achieved in only 5 min of reaction. In conclusion, Fe-based nanoparticles were synthesized by a rapid, easy, and environmentally friendly method. Both, the YM extract and the nanoparticulate powder were shown to have a good Cr(VI) removal activity, but the removal was higher and faster with the suspension of g-FeNPs in the extract, which would indicate a synergistic effect between the polyphenols of YM and the nanoparticles.