“…After 12 h, the resultant suspension was transferred to a petri-dish and dried at room temperature to allow solvent evaporation. After complete evaporation of ethanol, the obtained solid sample (1.0 g) was finely milled with urea, and then the mixture was calcined in air at 500 • C for 10 h with a heating rate of 2 • C/min [39]. By changing the volume (1, 3, 6, 12, and 30 mL) of Ti(O-i-Pr) 4 and the mass (0.25, 1.0, 2.0, and 3.0 g) of urea, a series of samples with different loading amounts of TiO 2 and contents of doped N were obtained.…”