## 3 Results and Discussion  
The ZrO\({}_{2}\) NPs required in this study were prepared by a solvothermal method as reported [23]. In this case, solvent benzyl alcohol was also acted as a stabilizing agent by physically adsorbing on the surfaces of the NPs. XRD diffractogram confirmed the preparation of ZrO\({}_{2}\) NPs. For the preparation of Au-ZrO\({}_{2}\), freshly prepared ZrO\({}_{2}\) NPs together with gold precursor was dispersed in ethanol under slow stirring. Then, the resulting mixture was subsequently treated in a probe sonicator for a short time period (i.e., 5 min), which led to the change in color of dispersion milky white to light purple, indicating the formation of Au NPs on the surface of ZrO\({}_{2}\) NPs. Initially, UV analysis confirmed the preparation of Au-ZrO\({}_{2}\), as shown in Figure 1a. To compare the influence of Au in the absorption properties of Au-ZrO\({}_{2}\) nanoparticles, we also measured the UV-Vis spectroscopy of pristine ZrO\({}_{2}\) and Au nanoparticles respectively. Interestingly, it was observed that ZrO\({}_{2}\) NPs also acted as a catalyst in the formation of Au NPs, since under similar conditions in the absence of ZrO\({}_{2}\), Au precursor did not reduce to produce Au NPs. While, in the presence of ZrO\({}_{2}\) nanoparticles, Au was deposited within 5 min, which was reflected by the color change of the solution (Figure 1b) and confirmed by UV-analysis. To compare the surface plasmon band, Au NPs are synthesized using the same concentration of Au precursor (HAuCl\({}_{4}\)) but using citric acid as a reducing agent. The UV spectrum of Au-ZrO\({}_{2}\) exhibited a broad absorption peak centered at -560 nm, which indicated the formation of smaller size Au NPs [24]. The citrate reduced Au nanoparticles showed surface plasmon band centered at \(\sim\)523 nm. As expected, there was a redshift of about 27 nm in the plasmon bands of Au-ZrO\({}_{2}\) nanoparticles as compared to pristine Au nanoparticles. The red-shift in the plasmon band can be attributed to the close contact of the Au and ZrO\({}_{2}\) interface that results in the effective local dielectric function around the gold [10], which was found to be in line with the classical Mie theory [25]. Besides, the shift in surface plasmon band Au, the absorption band of ZrO\({}_{2}\) also red-shifted from 280 nm to 320 nm. This could be due to surface defects created by the binding of Au NPs on the surface of the ZrO\({}_{2}\) NPs [26]. These results are consistent with the evidence obtained from FT-IR analysis. The FT-IR spectrum of Au-ZrO\({}_{2}\) is almost similar to the IR spectrum of pristine ZrO\({}_{2}\) NPs containing benzyl alcohol as stabilizing ligands. The IR spectrum of Au-ZrO\({}_{2}\) contains various characteristic peaks of benzyl alcohol including the peaks between 3600 to 2900 cm\({}^{-1}\) corresponding to hydroxyl groups, C-H stretching of the aromatic ring, and C-H stretching of CH\({}_{2}\) (methylene) groups. The vibrations of phenyl rings appeared in the regions of 1900 to 1600 cm\({}^{-1}\). Whereas, the characteristic peaks of O-H, and C-O stretching occurred in the range of 1420 to 1330 cm\({}^{-1}\) and 1080-1022 cm\({}^{-1}\) respectively. The existence of benzyl alcohol on ZrO\({}_{2}\) can be confirmed by comparing the IR spectra of ZrO\({}_{2}\) and Au-ZrO  
Figure 1: (**a**) Comparison of the UV-Vis spectra of Au-ZrO\({}_{2}\) with pristine ZrO\({}_{2}\) nanoparticles (NPs) stabilized with benzyl alcohol (**b**) digital photos of the dispersion of ZrO\({}_{2}\) nanoparticles, HAuCl\({}_{4}\) and Au-ZrO\({}_{2}\) in ethanol. (cf. Figure 2) indicate the presence of benzyl alcohol attached ZrO\({}_{2}\) and Au-ZrO\({}_{2}\) NPs. However, the concentration of benzyl alcohol is much reduced in the case of Au-ZrO\({}_{2}\) NPs. X-ray diffraction measurements are performed to establish the nature of the crystallographic phase of ZrO\({}_{2}\) support and to confirm the occurrence of Au NPs in the Au-ZrO\({}_{2}\) composite.