Nanocomposites and nanomaterials

Formation of lithium-selective sorbents in nanoreactors of the support based on titanium-manganese double oxide
Chaban M.O.1, Rozhdestvenska L.M.1, Dzyazko Yu.S.1, Palchik O.V.1, Dzyazko O.G.2
1 V.I. Vernadskii Institute of General and Inorganic Chemistry of the NAS of Ukraine, 32/34 Palladin ave., 03142, Kyiv, Ukraine
E-mail: kolomiyetsy@gmail.com
2 Taras Shevchenko National University of Kyiv, Volodymyrska str. 60, 01601, Kyiv, Ukraine

Lithium-containing spinel-like compounds, which are based on titanium-manganese double oxide, were synthesized in nanoreactors, namely in mesopores  of hydrated titanium-manganese double oxide (HTMDO). Xerogels contained different amount of Ti and Mn: their molar ratio was 2:1, 1:1 and 1:2. The sorbents were trasformed into Li-substituted form, calcined an washed with nitric acid. After calcination, the compounds of complex composition were formed, it was difficult to recognize them. After washing with nitric acid followed by conversion in Li-form, two phases were found for all sorbents: rutile (bonding component) and spinel (selective component). Depending on the synthesis conditions, such spinel as LiMn1.6Ti0.4O4, Li0.75Mn0.25Ti2O4, LiMn1.9Ti0.1O4, Li0.75Mn0.25Ti2O4 was formed. These compounds were identified using a XRD analysis, the particle size of nanocrystallites was estimated as 15-30 nm. These data were confirmed with a method of transmission electron microscopy.
After conversion into H-form, the materials are able to sorb Li+ ions, Sorption involves intercalation, which provides selectivity, as well as adsorption on the nanocrystallite surface. In a neutral media, sorption capacity towards Li+ ions reaches 0.36-0.62 mmol g-1.The sorption isotherms are approximated with Temkin equation indicating linear energy distributions of sorption centers. In the presence of the excess of Na+ ions, sorption capacity reaches more than 2 mmol g-1. It means, Na+ form dissociated ion pairs of O-Na+ facilitating Li+ sorption due to Li+Na+ exchange. This direction is more preferable than the dissociation of OH groups followed by Li+H+ exchange. The Freundlich model is applied to sorption in this case reflecting exponential energy distributions of sorption centers. This is caused by a number of ionic pairs: O-Na+, ONa,  O- Li++ and OLi. The largest exponent value has been found for the sorbents containing large amount of manganese, since they sorb Li+ preferably.