The surface characterisation of coated titanium dioxide by FTIR spectroscopy of adsorbed nitrogen

Infrared (IR) absorption, at 2335 cm−1, of nitrogen adsorbed on high area titanium dioxide samples has been measured for both untreated TiO2 and for two series of samples prepared by precipitating an inorganic coating on the same parent rutile. The intensity of the absorption, at 2335 cm−1 progressively decreases as the amount of inorganic coating increases, i.e. as the probability of ‘bare’, uncoated, titanium dioxide surface decreases. For both oxides the nitrogen band is eliminated, i.e. the rutile surface is completely covered, by ∼30% w/w oxide coating. This corresponds to ∼0.2% of oxide per square metre of rutile. However, at lower coating levels, silica coating reduces adsorption of IR-active nitrogen more effectively than the same weight of alumina. Rates of propan-2-ol photo-oxidation to acetone have also been measured on the uncoated and coated rutiles used for the nitrogen studies. The pattern of decreased activity as a function of the amount of coating broadly follows the decrease in the nitrogen band intensity. Therefore, we conclude that the surface sites associated with the adsorption of IR-active nitrogen are closely associated with the sites responsible for photo-oxidation.