Preparation and characterization of quantum-size titanium dioxide

Abstract

The syntheses of transparent colloidal solutions of extremely small titanium dioxide particles (d < 3 nm) in water, ethanol, 2-propanol, and acetonitrile are presented. Quantum-size effects are observed during particle growth and at the final stages of synthesis. They are quantitatively interpreted by using a quantum mechanical model developed by Brus. The particles prepared in aqueous solution possess the anatase structure and consist of about 200 Ti02 molecules at their final growth stage. The colloidal particles can be isolated from solution as white powders that are soluble in water and ethanol with no apparent change in their properties. In organic solvents the quantum-size Ti02 particles appear to form with rutile structure. Excess negative charge on the particles resulting either from deprotonated surface hydroxyl groups or from photogenerated or externally injected charge carriers causes a blue shift in the electronic absorption spectrum, which is explained by an electrostatic model. Electrons can be trapped in the solid as a Ti3+ species, which has a characteristic visible absorption spectrum. As much as 10% of the available Ti4+ ions can be reduced photochemically in the solid with a quantum yield of 3%. Molecular oxygen reoxidizes the Ti3+ centers, leading to detectable amounts of surface-bound peroxides. The pH of zero point of charge (pHzpc) of the aqueous colloidal suspension has been determined to be 5.1 ± 0.2. The acid-catalyzed dissolution of the aqueous colloid yielding Ti(IV) oligomers has been studied, and an activation energy £a = 58 ± 4 kJ/mol has been measured for this reaction. The photocatalytic activity of the small Ti02 particles is demonstrated.

Tunable optical properties of hybrid inorganic–organic [(TiO2)m(Ti–O–C6H4–O–)k]n superlattice thin films

“…32 The present threshold TiO2 domain size (< 2 nm) for onset for confinement effects is in line with the reported threshold for TiO2 nanoparticles (< 3 nm). 33 The 0.5 eV increase in the band gap between the pure TiO2 and hybrid films is in line with the results of Abdulagatov et al 28 and Yoon et al 34 The absorbance of pure hydroquinone peaks slightly below 300 nm, 35 and hence can not explain the broad feature. The fact that the intensity of the feature appeared to depend rather on the amount k×n of the (Ti-O-C6H4-O-) layers than on the superlattice period indicated that the 14 absorption was not inherent to the superlattice structure; instead it appeared to stem from the local (Ti-O-C6H4-O-) environment.…”

Sub-10 nm rutile titanium dioxide nanoparticles for efficient visible-light-driven photocatalytic hydrogen production

“…1f). Band-gap broadening due to quantum size effect, expressed as equation (2), could be neglected with TiO 2 particle size of 43 nm 59,60 .…”

Effect of titanium dioxide crystalline structure on the photocatalytic production of hydrogen

“…By contrast, the absorption edge of R1-C is blue-shifted with respect to that of the other rutile samples. This can reasonably be attributed to the so-called "size quantisation effect" observed with ultra-small semiconductor particles, 30 which is known to lead to a widening of the band gap. In fact, R1-C possesses a surface area much larger than those of the R and R2-C rutile samples (139 vs. 25 and 2.2 m 2 g -1 , respectively) and consequently it is expectedly constituted of smaller size particles, as confirmed by the average crystallite diameter D XRD (Table 1) and also by the SEM micrographs reported in Fig.…”