Selective adsorption of uranyl and potentially toxic metal ions at the core-shell MFeO-TiO (M=Mn, Fe, Zn, Co, or Ni) nanoparticles.

Potentially toxic metal ions (X: Rb, Sr, Cr, Mn, Ni, Zn, Cd) usually coexist with uranyl (UO), which will have a great influence on the selective adsorption process. Here, the core-shell MFeO-TiO (M = Mn, Fe, Zn, Co, or Ni) nanoparticles were synthesized and assessed as new selective adsorbents. The results reveal that TiO(101) preferentially grows along the MFeO(311)/(111) orientation. The M ions as the mediators transfer the holes from MFeO to TiO, at the conduction bands. On the TiO(101) surfaces and TiO(101)-TiO(101) gaps, the paired active electrons mainly complex with water molecules as hydroxyl radicals to capture X ions, forming an ion layer to block UO from being adsorbed. Simultaneously, it should be noted that an interesting adsorption pathway was UO being horizontally and irreversibly adsorbed in the MFeO(311)/(111)-TiO(101) interface, and therein, the stable adsorption capacity was found to be 66.78 mg g in the MnFeO(311)/(111)-TiO(101) interface. Finally, a mechanism of hybrid orbitals between MnFeO-TiO and UO-X was proposed.