Au 25 Nanoclusters Incorporating Three-Dimensionally Ordered Macroporous In 2 O 3 for Highly Sensitive and Selective Formaldehyde Sensing.

Detection of formaldehyde ( FA ) in the atmosphere is of significant importance because exposure to FA may cause serious health problems such as sick-house syndrome, leukemia, and cancer. Modifying metal oxide semiconductors (MOSs) with noble metal nanoparticles (NPs) is an efficient method to enhance FA -sensing properties. Herein, a series of Au 25 nanocluster (NC)-decorated three-dimensionally ordered macroporous In 2 O 3 materials (Au 25 /3DOM In 2 O 3 ) is created, and the loading amount of Au 25 NCs was optimized based on FA responses. To reveal the effect of gold size on FA responses, we constructed Au 144 NC-loaded 3DOM In 2 O 3 and Au NP (2.9 nm)-modified 3DOM In 2 O 3 and compared their gas-sensing properties with the optimal Au 25 /3DOM In 2 O 3 . The results show that in comparison with its counterparts, the optimal Au 25 /3DOM In 2 O 3 presents higher sensitivity, shorter response/recovery times, better selectivity, and excellent reproducibility. More attractively, the responses to FA are dependent on the size of Au particles loaded on In 2 O 3 . We suggest that the enhanced FA responses for the optimal material are mainly attributed to the electronic and chemical-sensitization effects of Au 25 NCs, and the size-dependent effect of FA responses is ascribed to the size of Au NPs affecting the formation of oxygen-adsorbing species. This work provides an efficient way for fabricating noble metal NP-loaded MOSs with tunable gas-sensing properties.