The effect of phosphate anions on surface and acidic properties of TiO2 hydrolyzed from titanium ethoxide

TiO2 obtained from the hydrolysis of titanium ethoxide was impregnated with different amounts of ammonium hydrogen phosphate, and subjected to heat treatment at different temperatures. Textural and acidic properties were determined. It was found that the presence of increasing amounts of phosphate groups within the TiO2 reduces surface area and total pore volume. The development of the bidentate state of ligation of the phosphate, starting at 400 °C is associated with enhanced surface acidity. Although, the bidendate phosphate groups persist till 800 °C, a significant decrease in surface acidity is observed at this temperature, believed to result from the elimination of water from the structure. The presence of the phosphate groups delays the anatase to rutile phase transformation. Moreover, bidentate phosphate groups appear to play a role in stabilizing the pore structure of TiO2.