# MoSe\({}_{2}\) with Ultra-Fine Pt Decoration for Efficient Photodegradation
## 3 Results and Discussion  
### MoSe\({}_{2}\)-Pt Morphologies and Crystal Structures  
After synthesis, a drop of the solution containing MoSe\({}_{2}\)-Pt was placed onto a holey carbon grid and dried in air. Then the samples were observed under TEM. The morphologies of MoSe\({}_{2}\) flakes among the three samples were similar in shape and size. Therefore, we chose sample M1 Pt as an example whose morphologies are shown in Figure 1. In Figure 1a, MoSe\({}_{2}\) nanoflakes are of a round shape with a typical size of 40 nm. There are tiny Pt dots on the edge of the MoSe\({}_{2}\). The Pt dots are clearer in the zoomed-in image in Figure 1b. Due to the mild synthetic conditions and low concentration of K\({}_{2}\)PtCl\({}_{4}\) in solution 1, PtCl\({}_{4}\)\({}^{2-}\) was reduced to ultrafine particles. There are more Pt nanoparticles formed on the edge sites compared to the surfaces of the MoSe\({}_{2}\) because the edge sites are more reactive than the basal planes [28]. Although very small in size, the Pt particles were well crystallized in (111) phase with a lattice spacing of 2.29 A, as shown in Figure 1c. Such crystalline structure is compatible with the MoSe\({}_{2}\) (100) facet. It suggests the Pt particles are well grown on MoSe\({}_{2}\). Figure 1d-f show the distribution of Pt nanoparticles for the samples of M1 Pt, M2 Pt, and M3 Pt, respectively. It can be seen that the samples of M1 Pt and M2 Pt have the same dominant Pt size of 1.8 nm, while M3 Pt has a slightly larger Pt size of 1.9 nm.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Samples** & **MoSe\({}_{2}\)** & **K\({}_{2}\)PtCl\({}_{4}\)** & **Conditions** \\ \hline M1 Pt & 0.1 mg/mL \(\times\) 10 mL & 41.5 mg & 50 \({}^{\circ}\)C, 150 min \\ \hline M2 Pt & 0.2 mg/mL \(\times\) 10 mL & 41.5 mg & 50 \({}^{\circ}\)C, 150 min \\ \hline M3 Pt & 0.3 mg/mL \(\times\) 10 mL & 41.5 mg & 50 \({}^{\circ}\)C, 200 min \\ \hline \hline \end{tabular}
\end{table}
Table 1: The synthetic details of the samples.  
In Figure 2, the XRD spectra show the crystal structure of the three samples of MoSe\({}_{2}\)-Pt nanocomposites and pristine MoSe\({}_{2}\) nanopowder. The crystal planes of MoSe\({}_{2}\) and Pt were marked with diamonds and stars, respectively. The MoSe\({}_{2}\) (100), (103), (105), (110) and (200) planes were identified from both samples, which was in good agreement with previous reports [29]. Compared to the pristine MoSe\({}_{2}\), Figure 2 shows that MoSe\({}_{2}\) is stable and keeps its crystal structure after synthesis.  
Figure 1: Morphologies of MoSe\({}_{2}\)-Pt samples. (**a**) TEM image of MoSe\({}_{2}\)-Pt; (**b**) zoomed-in image of the squared region in (**a**); (**c**) HR-TEM image shows the crystal structure of Pt; (**d**–**f**) Pt size distributions of the samples of M1 Pt, M2 Pt, and M3 Pt, respectively.  
Figure 2: XRD spectra of the synthesized MoSe\({}_{2}\)-Pt nanocomposite and MoSe\({}_{2}\) nanopowder.  
Pt (111) and (200) planes were identified in the synthesized MoSe\({}_{2}\)-Pt samples. The Pt (111) lattice spacings are shown in Table 2. We can see that Pt (111) peak positions were slightly varied among the three samples. The lattice spacings are calculated as 0.2285, 0.2291, and 0.2274 nm, respectively. Moreover, the mean crystal sizes (\(D\) (111) in Table 2) were also calculated through Scherrer's equation [30]. They are very close for the M1 Pt and M2 Pt samples, while slightly larger for the M2 Pt sample. It should be noted that the calculated mean crystal sizes are not the particle sizes which could be directly measured under TEM; however, the \(D\) (111) values show the same trends with the particle sizes shown in Figure 1d-f.