Cr3+ incorporation into an Al3+ Keggin-type oligomer to form the Al25.7Cr6.3S216+ polycation

Keggin-type aluminum polycations are an important class of compounds from metal-oxo family that includes polyoxometalates and other nanocomplexes. Investigation of the Al3+ based polycation system is of particular importance given the environmental relevance within acid mine drainage and application in wastewater treatment. Within streams impacted with acid mine drainage, different toxic metal species, including chromium, can incorporate into these soluble polycations and impact the transport of contaminants. Currently, there is a limited understanding about chemical interaction of chromium with Keggin-type aluminum polycations; therefore, the work herein describes the synthesis and characterization Cr3+ substitution within Keggin-based polyaluminum species. The polyaluminum cations crystallized as [Al25.7Cr6.3O8(OH)60(H2O)28(SO4)2](SO4)8 (H2O)29 from a partially hydrolyzed Al3+ solution and structural elucidation obtained by single crystal X-ray diffraction revealed the presence of Cr3+ within the octahedral sites of the Keggin species. Inductively coupled plasma mass spectroscopy confirmed the presence of Cr3+ in the structure with Al3+/Cr3+ similar to refined crystal structure. Additional physicochemical characterization, including vibrational spectroscopy, thermogravimetry and powder X-ray diffraction were performed on the isolated crystals and confirm the structural model of the solid phase.

» Author: Mohammad Shohel, Jack A. Smith, Tori Z. Forbes

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This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement Nº 768737


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