Abstract
A simple, robust and versatile hydrothermal synthesis route to in situ functionalized TiO2 nanoparticles was developed using titanium(IV) isopropoxide as Ti-precursor and selected silane coupling agents (3-aminopropyltriethoxysilane (APTES), 3-(2-aminoethylamino)propyldimethoxymethylsilane (AEAPS), and n-decyltriethoxysilane (DTES)). Spherical nanoparticles (ca. 9 nm) with narrow size distribution were obtained by using DTES or by synthesis performed without silane coupling agents. Rod-like nanoparticles along with 9 nm spherical nanoparticles were formed using aminosilane coupling agents because of a combination of oriented attachment of nanoparticles and specific adsorption of the aminosilane on crystallographic faces of anatase nanoparticles. The nanoparticles were functionalized in situ and became hydrophobic as silanes reacted to form covalent bonds on the surface of TiO2. The versatility of the aqueous synthesis route was demonstrated, and by selecting the type of silane coupling agent the surface properties of the TiO2 nanoparticles could be tailored. This synthesis route has been further developed into a two-step synthesis to TiO2–SiO2 core–shell nanoparticles. Combustion of the silane coupling agents up to 700 °C leads to the formation of a nanometric amorphous SiO2 layer, preventing growth and phase transition of the in situ functionalized nanoparticles.
Highlights
Because of the high surface-to-volume ratio, the intrinsic properties of titanium dioxide (TiO2) nanoparticles have led to exploitation in many fields such as in photocatalysis [1], solar cells [2], and in biomedical applications [3]
The broad diffraction lines demonstrate small crystallite sizes, which were determined by refinement to be between 4.7 and 9.1 nm (Table 1)
Samples were degassed for 12 h at 180 °C in vacuum prior to analysis
Summary
Because of the high surface-to-volume ratio, the intrinsic properties of titanium dioxide (TiO2) nanoparticles have led to exploitation in many fields such as in photocatalysis [1], solar cells [2], and in biomedical applications [3]. We report on a novel and versatile in situ aqueous hydrothermal synthesis route to surface-functionalized TiO2 nanoparticles using selected silane coupling agents. XRD patterns of TiO2 and in situ surface-functionalized TiO2 nanoparticles, presented, show anatase as main phase with around 25 wt % of brookite in the case of pure TiO2 and Ti-DTES samples (for Rietveld refinements see Figure S1 of Supporting Information File 1).
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