Mesostructure Au/TiO2 nanocomposites for highly efficient catalytic reduction of p-nitrophenol

Mesoporous Au/TiO2 nanocomposites have been synthesized using two methods. (1) In situ preparation; (2) photochemical deposition of Au onto either highly ordered mesoporous TiO2 or disordered TiO2. Following the photodeposition process, the Au nanoparticles are dispersed and uniform exhibiting diameters of similar to 10 nm; however, following the in situ preparation, the Au particles are ranging diameters of approx. 25-300 nm based on the Au content (0.3-5 wt%). The prepared catalysts have been tested for catalytic reduction of p-nitrophenol (p-NPh) in presence of sodium borohydride. Using the Au/TiO2 prepared by in situ method, the reaction rate of the catalytic reduction of p-NPh was found to be 6 times higher when the amount of Au decreases from 5 wt% to 0.3 wt%. However, Au photodeposited onto TiO2 is much better 2 times higher than that in situ Au/TiO2 prepared. The larger catalytic activity of the Au/TiO2 nanocomposites prepared by photodeposition process is attributed to the higher dispersity and the small size of the Au particles (10 nm). The results indicated that a highly ordered mesoporous system is not a prerequisite for high catalytic activity. However, the sample clacined at 350 degrees C must be considered as economically more viable catalysts as compared to that clacined at 500 degrees C since the preparation energy can be saved in the calcination step. The recycling tests indicated that Au/TiO2 nanocomposites was quite stable no significant decrease in catalytic reduction of p-NPh was observed even after being used repetitively for 5 times, showing a good potential in practical application. (C) 2012 Elsevier B.V. All rights reserved.