Size-controllable synthesis of functional heterostructured TiO2–WO3 core–shell nanoparticles

Mono and bicomponent TiO2 and WO3 nanoparticles were synthesized inside Vycor® glass pores, by cycles of impregnation of the glass with the respective oxide precursor followed by its thermal decomposition. The impregnation-decomposition cycle (IDC) methodology promoted a linear mass increase of the glass matrix, and allowed tuning the nanoparticle size. X-ray diffraction and Raman spectroscopy data allowed identifying the formation of TiO2 as anatase phase, while WO3 is a mixture of the γ-WO3 (monoclinic) and δ-WO3 (triclinic) phases. High resolution transmission electron microscopy images revealed that for 3, 5, and 7 IDC, the TiO2 nanoparticles obtained presented average diameters of 3.4, 4.3, and 5.1 nm, and the WO3 nanoparticles have 2.9, 4.6, and 5.7 nm sizes. These TiO2 and WO3 monocomponent nanoparticles were submitted to IDC with the other oxide precursor, resulting in bicomponent nanoparticles. The broadening and shift of the Raman bands related to titanium and tungsten oxides suggest the formation of hetero-structure core–shell nanoparticles with tunable core sizes and shell thicknesses.