High affinity lanthanum doped iron oxide nanosheets for phosphate removal

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Abstract

Phosphorus induced eutrophication of freshwaters is one of the great global challenges. As the critical threshold concentration for eutrophication is very low, there is a strong need for development of phosphate sorbents with high affinity and selectivity. Single sheet iron oxide (SSI), a nanomaterial prepared from oxidation and exfoliation of layered iron(II)-iron(III) hydroxide (green rust), is a fast reacting and promising sorbent. Phosphate sorption affinity and selectivity may be improved by incorporation of lanthanum (La) in the structure. Lanthanum was added during SSI synthesis resulting in La-SSIs with 0 to 22.5 wt% of La content. XPS and EXAFS showed all La was present as La(OH)3 nanoclusters between iron hydroxide layers and on the surface of SSI. The sorbent showed fast phosphate sorption with 90% completion within 30 min and high stability with minimal La leaching. All La-SSI nanomaterials showed better sorption affinity than non-doped SSI, and the La-SSI with the highest La content showed an extreme affinity with Kd of 105 L/kg at solution concentration of 0.1 mg P/L. The sorption affinity was not seriously affected by pH. The La-SSIs showed high selectivity for phosphate with<10% reduction in phosphate sorption in presence of co-existing solutes (Cl, NO3, SO42-, HCO3 and humic acid). Similar high affinity and selectivity was seen for phosphate sorption in real natural waters. The main phosphate sorption mechanism is attributed to inner sphere Fe-O-P and La-O-P surface complexation. In conclusion La doping turns SSI into a high-affinity and selectivity sorbent that has potential for polishing low-phosphate yet eutrophying natural waters such as drainage and lake waters.

Details

Authors
Organisations
External organisations
  • University of Copenhagen
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Chemistry

Keywords

  • Lanthanum coordination, Phosphate bonding, Selectivity, Sorption isotherms, Sorption kinetics
Original languageEnglish
Article number130009
JournalChemical Engineering Journal
Volume422
Publication statusPublished - 2021 Oct 15
Publication categoryResearch
Peer-reviewedYes