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 ∼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 °C must be considered as economically more viable catalysts as compared to that clacined at 500 °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.

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► Mesoporous Au/TiO2 nanocomposites have been synthesized.
► The catalysts have been tested for catalytic reduction of p-nitrophenol (NP).
► Catalytic reduction of NP with Au (25 nm) was fastest about 6 times than that of Au (300 nm).
► Highly ordered mesoporous system is not a prerequisite for high catalytic activity.