Experimental and quantum-chemical studies of the surface interactions between organic molecules and nanocrystals of (a) RE2O3 (RE = Y or Gd); and (b) TiOb2

Sammanfattning: The increasing interest for using nanocrystals in bio-medical and optical applications has highlighted the need of molecular functionalisation of nanocrystals. Knowledge of how to attach molecules to the nanocrystal surface is a key factor. This thesis focuses on the surface interactions between nanocrystals of (a) RE2O3 (RE = Y or Gd); and (b) TiO2 and organic molecules, which have been studied experimentally and by quantum-chemical calculations with the intent to elucidate the chemisorption characteristics such as adsorption geometries and energies.(a) RE2O3 nanocrystal synthesis was performed by a colloidal method based on polyols and by a rapid combustion method. The products were experimentally characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR), Raman, and X-ray photoelectron spectroscopy (XPS). By quantum chemical calculations the chemisorption of formic acid, DEG, water and TMOS at the surface of RE12O18 clusters was studied. From comparison between calculated and experimental vibrational spectra, the binding mode for formic acid on RE2O3 was inferred to be of bridge or bidentate type. XPS and IR showed that DEG chemisorbs on the particle surface and experimental IR spectra of DEG chemisorbed on RE2O3 were consistent with an adsorption mode where the hydroxyl groups are deprotonated according to the quantum-chemical computations.(b) Synthesis of single-phase rutile TiO2 nanocrystals was done by a sol-gel method and the nanocrystals was subsequently functionalized by organic acids and glycine. Quantum-chemical studies indicate that formic- and acetic acid adsorbs in a bridge or monodentate binding mode, while glycine is suggested to adsorb as a zwitterion with bridge bonded carboxylic group and a hydrogen bonded amino group. However, spectroscopic data showed that the amino acid, unlike the other acids did not adsorb on TiO2 under the given experimental conditions.