Nanotechnology and nanomaterials

Synthesis and sorption properties of nanosized supported ammonium molybdophosphate
Zakutevskyy O.I., Khalameida S.V., Sydorchuk V.V ., Kovtun M.F 
Institute for Sorption and Problems of Endoecology of the NAS of Ukraine, 13 Gen. Naumova Str, Kyiv-03164, Ukraine. 
E-mail: svkhal@ukr.net

Ammonium phosphomolybdate (AMP) is classical effective sorbent for removal and uptake of cesium as well as strontium and other cations of heavy metals from aqueous media. However, the microcrystalline state of AMP and low specific surface area has not been applied as a sorbent on a large scale owing to fine powder morphology, which is unsuitable for efficient separation such as column operations. Among the ways to overcoming of the listed shortcomings are deposition of AMP onto surface of granulated support. Mechanochemical treatment (milling) is also used for deposited of active phase onto different supports. It is also known that milling of solids results in to surface activation, creation of new active sites and increase of adsorption capacity. 
We prepared sorbents using three procedures: 1) mechanochemical deposition of AMP onto fumed SiO2 and TiO2; 2) introduction of AMP in reaction mixture during TEOS hydrolysis-condensation; 3) hydrolysis-co-condensation of TEOS–APTEOS mixture with adding to the reaction mixture  phosphorous-molybdenum HPA. Deposited, even milled, samples are crystalline, and that there is a very important, retain the Keggin structure. This was confirmed by XRD and FTIR spectroscopy data. Just Keggin structure provides excellent sorption properties of heteropolyacid. The bulk AMP samples (initial and milled) are non-porous and have low specific surface area (4 and 11 m2/g, correspondingly). At the same time, supported AMP samples prepared via sol-gel process are micro-mesoporous with mesopores size about 3.0-3.7 nm and have high values of specific surface area (535-816 m2/g) and total pore volume (0.27-0.60 cm3/g). In addition, sorbent synthesized from APTEOS-TEOS mixture contains macropores (0.14 cm3/g). Finally, the samples obtained by mechanochemical deposition of AMP onto fumed oxides are mesoporous (dme= 30-32 nm) and possess average values of specific surface area (226 m2/g).
The synthesis of AMP/support compositions allows to increase their specific sorption capacity with respect to Cs +, Sr 2+ and U (VI) ions by more than 10 times and prepare in granular form, which favorably compares them with the initial fine - grained ammonium molybdophosphate.