# Photocatalytic Activity of Monosized AuZnO Composite Nanoparticles
## 3 Results and Discussion  
### Transmission Electron Microscope Morphology and Nanostructures of AuZnO Composite Nanoparticles  
The morphology and particle size distribution of AuZnO composite nanoparticles(S1) were analyzed by TEM. As showed in the Figure 1a, the composite nanoparticles are highly crystalline, uniform, and nearly spherical. The histogram was obtained by counting a series of TEM images of the composite nanoparticles using Nano measurer software, as shown in the illustration, revealing that the composite nanoparticles have a narrow particle size distribution and are consistent with the Gaussian distribution with a particle size of \(\sim\)14.5 (\(\pm\)0.9) nm. The TEM analysis gives the particle size of \(\sim\)13.8 (\(\pm\)1.4) nm and \(\sim\)15.3 (\(\pm\)1.5) nm in diameter for S2 and S3, respectively (shown in supplementary materials, Figures S1 and S2). Figure 1b shows the HRTEM image of a single AuZnO composite nanoparticle(S1). Obviously, highly regular lattices are uniformly distributed on the composite nanoparticle, as labeled, with the spacing of 2.35 A indicating the projection of the Au (111) plane, whereas the spacing of 2.60 A corresponds to the ZnO (002) plane. The result shows that Au and Zn are present in the same composite nanoparticle. Figure 1c shows a typical TEM-EDX point-detection for AuZnO composite nanoparticles(S1), which clearly shows that the composite nanoparticles contain zinc and gold elements. As shown in Figure 1d, the typical SAED pattern with bright circular rings corresponding to the (100), (101), (200), (110), (103) and (220) planes show that the nanoparticles obtained are highly crystalline. The sharpness and multi-diffraction spots observed in the pattern confirm the high crystallinity of AuZnO composite nanoparticles. As shown in Figure S6, further TEM element mapping provides more solid information for AuZnO(S1) composite nanoparticles; the positions of the composite nanoparticles as recorded by the elemental mapping in Figure S6b for Au and Figure S6c for Zn, which are consistent with those in the bright-field image of Figure S6a (Figure S6, shown in supplementary materials). The results confirmed the synthesis of AuZnO composite nanoparticles. The formation of the AuZnO composite nanoparticles(S1-S3) was further confirmed by X-ray crystal structure analysis. As shown in Figure 2a-c, the diffraction peaks of the AuZnO composite nanoparticles may be indexed to two sets, one in the inverted triangles, corresponding to the Au  
Figure 1: Transmission electron microscope (TEM) image of AuZnO composite nanoparticles(S1). (**a**) Bright-field TEM particle size distribution (histogram) with Gaussian function fit (in curve) of the composite nanoparticles; (**b**) HRTEM of a single nanoparticle; (**c**) point-detection energy dispersive X-ray analysis (EDX) analysis chart; (**d**) selected-area electron diffraction pattern of the nanoparticles. positions of the (111), (200), (220), (311), and (222) planes (JCPDS NO. 65-8601), and the other in the squares corresponding to the ZnO positions of the (100), (002), (101), (110), (103), (200), (112), (201), and (004) planes (JCPDS NO. 05-0664), indicating the presence of Au and ZnO. The intensity of the diffraction peaks of Au become weakened from S3 (Figure 2a) to S2 (Figure 2b) to S1 (Figure 2c), because Au amount decreases from S3 (Au\({}_{0.15}\)(ZnO)\({}_{1.35}\)) to S2 (Au\({}_{0.075}\)(ZnO)\({}_{1.425}\)) to S1 (Au\({}_{0.03}\)(ZnO)\({}_{1.47}\)). In contrast, the diffraction of the reflective ZnO material is greatly enhanced. The average particle size of the composite nanoparticles is ~14.1 nm, ~13.4 nm, and ~15.1 nm for S1, S2, and S3, respectively, by the Scherrer equation (Equation (1)), based on the full width at half maximum (FWHM); this is slightly smaller than the statistical count of the above TEM analysis, probably due to the small size effect of the nanoparticles, leading to the broadening of the XRD diffraction peaks [28].