Briefly, 0.3 g of polyvinylpyrrolidone (PVP) K30 was dissolved in the mixture of2.54 ml of ethanol and 3.82 ml of acetic acid under continuous magnetron stirring. About 10 min later, 7.0 ml of tetrabutyl titanate (Ti(oBu)4) was added, and the mixed solution was kept stirring for ca. 1 h to get a uniform PVP@TBT sol.