Chromium(III/VI) binding to magnetite, hausmannite, and jacobsite nanomaterials
Chromium is a very versatile metal that is used for many applications in the world. Two of the most common ions of chromium that occur naturally are Cr(III) and Cr(VI). These two oxidation states have very different heath effects in living organisms. Cr(III) is relatively non-toxic to living organisms; however, Cr(VI) is very toxic to most living organisms This study was conducted to find a simple and cost effective method to sequester these two common ionic species of chromium from sources of water that are adjacent to or that are affected by other water sources contaminated by these two ions. In this study an investigation was conducted to observe the binding between three different engineered nanomaterials (Magnetite, Hausmannite and Jacobsite) to both hexavalent and trivalent chromium. A traditional synthesis was used to make these nanomaterials, which consisted of a titration of iron(II) chloride for the Magnetite, manganese sulfate for the Hausmannite, and a combination of the two previous salts in a 2:1 ratio for the Jacobsite. Magnetite (Fe3O4) and Hausmannite (Mn3O4) were synthesized using two different aging processes and Jacobsite (MnFe2O4) was synthesized using only one process. The first aging process involves a traditional heating source in an open vessel at 90°C for 60 minutes. The second ageing technique used was a microwave assisted hydrothermal synthesis method using a closed vessel at 90°C for 30 minutes. The Jacobsite was aged using only the microwave technique. The batch studies showed that the binding to the three different materials were pH dependent. The studies showed that Cr(III) and Cr(VI) bind to the nanomaterials differently at different pHs. In addition, the binding of the Cr(III) to the nano-Magnetite showed identical behavior binding to both the open vessel and the hydrothermally synthesized nanoparticles with pH. But the Cr(VI) showed differences in the binding to the open vessel and the closed vessel nano-Magnetite, with higher binding at lower pHs observed with the open vessel nanomaterials compared to the closed vessel nanomaterials. The Hausmannite micro-waved aged material had a better affinity for the hexavalent chromium then the open aged system. The studies with Cr(III) showed that the ion had greater affinity with the Hausmannite material than with Cr(VI). The Jacobsite showed favorable binding to Cr(VI) then it did to Cr(III) at higher pHs. The studies showed that all the materials exhibited the majority of their binding to chromium at around pH 4. Further data was obtained from batch studies included time dependency, isotherm capacities and interference studies. Overall the nanomaterials adsorbed both chromium species, and two of them (Magnetite and Hausmannite) reduced the hazardous Cr(VI) to Cr(III) determined by X-ray absorption spectroscopy. The materials were effective at removing both chromium ions from solution ns containing competing anions.
Analytical chemistry|Environmental science
Hernandez, Jeffrey, "Chromium(III/VI) binding to magnetite, hausmannite, and jacobsite nanomaterials" (2010). ETD Collection for University of Texas, El Paso. AAI1479558.