Local environment of CdS nanoparticles incorporated into anatase/brookite matrix via sol-gel route: HRTEM, Raman spectroscopy and MD simulation

Abstract

The preferred local environment of CdS nanoparticles within the sol-gel synthesized TiO2/CdS composites with a multiphase titania matrix was unveiled in detail. Evolution of the environment was traced along the full path of the gel aging. HRTEM showed that the CdS particles are typically surrounded by amorphous titania within the composites based on complex amorphous-rich anatase/brookite matrix, while the brookite crystallites are more preferable in the vicinity of CdS within the composites with anatase/brookite matrix. Transformation path from amorphous into crystalline titania phases in the vicinity of CdS nanoparticles is seemingly regulated by the cohesion between titania and CdS, which degree has been estimated on the models of "core-shell" CdS@TiO2 composite nanoparticles as a function of titania polymorphism. MD simulations demonstrate that the thermodynamic stability and the interface interaction decrease in the series of amorphous titania, nanocrystalline brookite, nanocrystalline anatase. The structural analysis reveals that, in contrast to anatase, the enhanced CdS||TiO2 interface interaction in the case of brookite is due to a genuinely more distorted lattice of brookite, hence, due to its better match to a foreign irregular interface. It is suggested that the TiO2/CdS composites with the prevalent brookite surrounding of CdS nanoparticles can exhibit enhanced photocatalytic activity compared to the composites with a random anatase/brookite surrounding of CdS nanoparticles, since brookite has a moderate depth of electron traps.