Unexpected Size Effect Observed in ZnO-Au Composite Photocatalysts

Abstract

Semiconductor-metal nanocomposites prepared with well-defined gold nanoclusters, such as Au25, Au144, and Au807, showed size-dependent photocatalytic activities for the reduction of nile blue and azobenzene. Whereas the photoreduction of nile blue was directly related with the charge separation and transfer rate from the photoexcited ZnO to gold nanoclusters, the photoreaction of azobenzene showed unexpected size effect with a clear threshold. Mechanistic investigations revealed that the photoreduction of azobenzene proceeded via a proton-coupled electron transfer process. The photocatalytic activity of the ZnO-Au nanocomposites was also dependent on the excitation intensity, demonstrating that the multielectron/multiproton process was controlled by the charge separation and transfer in the nanocomposites.

Power‐dependent Photocatalytic Activity of ZnO

“…As the irradiation time increased, the fluorescence of Rh101 decreased (inset of Figure (a)), suggesting a decrease in the concentration of Rh101 because of the photoreaction. On the other hand, the photoluminescence intensity of ZnO remained unchanged, as was expected for a stable catalyst. Consequently, the time evolution of spectra indicated photocatalytic activity of ZnO in the degradation of Rh101 (Figure (b)), which implied a single‐electron reduction process of Rh101 by electrons supplied from the conduction band of ZnO …”

“…The details of the preparation and measurement system have been reported elsewhere . Zinc oxide nanoparticles, rhodamine 101, aniline, and methanol were purchased from Sigma‐Aldrich (St. Louis, MO, USA).…”

“…Remarkably, the photoreduction‐efficiency‐dependence was similar to the photoluminescence‐intensity‐dependence of ZnO on the excitation intensity (Figure ), indicating that the saturation of defect states played a role in the photoreaction efficiency. Finally, it is noted that the efficiency dependence of AN was not as drastic as that of azobenzene, which implied that the single‐electron reduction process linearly reflected the available electrons in ZnO to some extent, in contrast to the nonlinear amplification of the multielectron processes.…”

Comparison of photocatalytic reaction-induced selective corrosion with photocorrosion: Impact on morphology and stability of Ag-ZnO

“…For another thing, significant efforts have been devoted to enhancing the photocatalytic performance and suppressing the photocorrosion by surface modification, such as combination with another semiconductor, deposition of noble metals, and coupling with versatile carbon materials [20][21][22][23][24][25][26][27].…”

Isolation and Total Structure Determination of an All‐Alkynyl‐Protected Gold Nanocluster Au144

“…[22,23] Formore than two decades, investigations were performed in the absence of precise structural information. It was reported that thiolate-protected Au 144 clusters show promising catalytic activities [24][25][26][27][28] and electrochemiluminescence, [29,30] and can be employed as precursors in the synthesis of Au 99 [31] and Au 133 [12,13,32] nanoclusters.M oreover,A u 144 has applications in organic solar cell [33] and floating memory devices, [34] etc.More importantly, it was also found that thiolate-protected Au 144 exhibits both molecular and bulklike behaviors,w ith its size in the critical transition range.F or example,A u 144 (SR) 60 exhibits ah ighly structured UV-vis-NIR spectrum with absorption bands over the entire region. [35,36] This spectrum indicates the molecular nature of Au 144 ,and was also supported by density functional theory (DFT) calculations.…”