## 3 Results and Discussion  
### Structure, Morphology, Surface and Spectroscopic Studies  
X-ray diffraction (XRD) patterns were collected to study the crystal phase and the crystallinity of the prepared nanomaterials. Figure 1 displays a comparison of the XRD results for the pure CdS nanoparticles, Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers, and P25/Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanocomposite. The refraction peaks of pure CdS and Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers samples are well-indexed to the hexagonal CdS phase (JCPDS No.41-1049), while for Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers, there is no peak for Zn, indicating that it is not a mixture of Zn and CdS phases. It can be observed that P25/Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanocomposite consists of two kinds of crystal phases, indicating that it is a mixture of CdS and TiO\({}_{2}\) phases (P25). Diffraction peaks at 20 of 25.3\({}^{\circ}\), 37.8\({}^{\circ}\), 48.05\({}^{\circ}\), 55.0\({}^{\circ}\), and 62.7\({}^{\circ}\) are attributed to anatase TiO\({}_{2}\) (JCPDS card No. 21-1272). However, when the molar ratio of P25 increases, two additional peaks appear at 27.4\({}^{\circ}\) and 36.1\({}^{\circ}\), which can be attributed to the rutile phase of TiO\({}_{2}\) (JCPDS card No. 65-0191), as shown in P25/Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanocomposite 1-5 and 1-3 with P25:Cd = 1:5 and 1:3, respectively. Doping CdS with Zn causes a slight shift in the peaks from (110) and (112) crystals planes for Zn\({}_{0.15}\)Cd\({}_{0.85}\)S toward lower diffraction angles, as shown in Figure 1b,c. Obviously, Zn\({}^{2+}\) ions are incorporated into the CdS crystal lattice or entered its interstitial sites as the ionic radius of the substitute Zn\({}^{2+}\) (\(r_{\rm Zn}\)\({}^{2+}\) = 0.74 A) is smaller than that of Cd\({}^{2+}\) (\(r_{\rm Cd}\)\({}^{2+}\) = 0.97 A) [27]. The morphological features of CdS nanoparticles, Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers, and P25/Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanocomposite were studied using FESEM and HRTEM micrographs. Figure 2a depicts the SEM image of one particle of pure CdS with agglomeration in different sizes, the diameter was about 1 \(\upmu\)m. In the case of Zn\({}_{0.15}\)Cd\({}_{0.85}\)S, the particle of CdS changes to flower-like morphology with around 1.5 \(\upmu\)m diameter of an entire flower, which composes of some petals, each petal contains many small particles existing outside of the main petal after doping by Zn ions to form the Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers shown in Figure 2b, this morphology may enhance the absorption properties on the surface [28]. Figure 2c-e show SEM images of P25/Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanocomposite with different P25:Cd ratios of 1:10, 1:5 and 1:3, respectively. It reveals that the petals of flower-like structure will disappear when molar ratio of P25 increases. This is due to the fact that the P25 will deposit inside the petals and the excess particles of P25 will be deposited on the surface of Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers, leading to the complete coverage of the petals and the disappearance of the flower-like structure. The flower-like surfaces could provide nucleating sites for P25 nanoparticles resulting in the formation of P25/Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanocomposite. P25 has higher BET surface area than pure CdS and Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers, thus it might cover the surface of Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers. The surface area of CdS nanoparticles was originally 0.26 m\({}^{2}\) g\({}^{-1}\) and it increases slightly to 0.63 m\({}^{2}\) g\({}^{-1}\) after the doping with zinc ions, then increases to 7.50, 21.4, and 37.8 m\({}^{2}\)g\({}^{-1}\) respectively, after decorating with P25, as shown in Table 1. One can observe that the Zn\({}_{0.15}\)Cd\({}_{0.85}\)S nanoflowers with an approximate diameter around 1.5 \(\upmu\)m have flower-like structure, which is consistent with the TEM image shown in Figure 2f.