Nanocomposites and nanomaterials

Synthesis of CeO2-ZrO2 solid solution in nano-sized state

Sydorchuk V.1, Khalameida S.1, Skubiszewska-Zięba J.2
1 Institute for Sorption and Problems of Endoecology of NAS of Ukraine. Naumov Str. 13 Kyiv-03164, Ukraine. 
E-mail: bilychi@ur.net
2Faculty of Chemistry, Maria Curie-Skłodowska University. Maria Curie-Skłodowska Sq 3, Lublin, Poland.

    The CeO2-ZrO2 compositions are a key constituent of many catalysts, including photocatalysts, due to their redox properties, oxygen storage, thermal stability. The solid solution and cerium zirconates can be formed in this system during synthesis and next modification. We used some new approaches for preparation of CeO2-ZrO2 samples containing 20 mol.% of cerium dioxide. Initial composition was prepared using two techniques: co-precipitation from aqueous solutions and mechanochemical.	
    We established occurrence of solid solution based on zirconia during co-precipitation of oxides: a value decreases from 0.5411 to 0.5349 nm. Following calcinations of precipitated sample causes formation CeZrO4 phase having a =1.0527 nm. On the contrary, solid solution does not formed during ball milling of oxide mixture, although value of a slightly decreases (to 0.5403 nm). The thermal treatment of milled samples results in only crystallization of stabilized cubic ZrO2 after dry milling or monoclinic and tetragonal phases of zirconia after milling in water. Prepared samples have specific surface area within 125-200 m2/g and nano-sized crystallites. UV-Vis spectra show noticeable red (bathochromic) shift of absorption edge: from 403 to 415-425 nm for precipitated sample after calcinations. This means narrowing the band gap from 3.08 to 2.91-2.98 eV. Increase of absorption value for visible light is observed for the same samples. 
    The photocatalytic properties of CeO2-ZrO2 samples were estimated using process of rhodamine B degradation in aqueous medium. The constant rate of degradation Kd for precipitated samples is equaled 3.5-7.0·10-5 and 1.5-2.2·10-5 s-1 under UV- and visible irradiation, respectively. Mechanochemical samples revealed higher activity. Thus, corresponding values of Kd for sample milled in water reach 1.0-2.2·10-4 and 3.0·10-5 s-1.