# MoSe\({}_{2}\) with Ultra-Fine Pt Decoration for Efficient Photodegradation
## 3 Results and Discussion
### Photodegradation  
The aforementioned characterizations provide chemical and optical insights into the synthesized materials. Their photocatalytic performance is evaluated by MB degradation, as shown in Figure 5. The time-course photodegradation results are shown in Figure 5a. Here, C/C\({}_{0}\) is used to represent the decrease of MB concentration, where C\({}_{0}\) and C are the original MB concentration and the MB concentration at a certain time, respectively. The dark process suggests that the synthesized materials show obvious adsorption of MB, while the pristine MoSe\({}_{2}\) can hardly adsorb MB. Such adsorption abilities are usually related to the photocatalytic process. We can see that pristine MoSe\({}_{2}\) can hardly degrade MB and the samples are all reactive with MB. Within around 60 min, MB is nearly removed by the samples of M1 Pt and M2 Pt. However, the M3 Pt sample performs slightly less efficiently, but it can still degrade more than 90% of MB after 120 min. Such photocatalytic results are in accordance with the optical absorption properties shown in Figure 4. Considering the catalyst amount used in the degradation process, the above photocatalytic performance is comparable to other popular photocatalysts, such as Bi\({}_{2}\)WO\({}_{6}\)/BiOCI [35]. As a comparison, pristine MoSe\({}_{2}\) removes only 5.4% of the MB in 120 min with the same irradiation condition. It suggests that the introduction of Pt to MoSe\({}_{2}\) edges greatly improves the photocatalytic property.  
The photodegradation kinetics was evaluated by the pseudo-first-order model. With this model, the pseudo-first-order constant \(k\) could be expressed as  
\[k=\frac{\ln(C_{0}/C)}{t} \tag{1}\]  
The results of \(\ln(C_{0}/C)\) are shown in Figure 5b. The constants were calculated as 0.0361 min\({}^{-1}\), 0.0379 min\({}^{-1}\), and 0.0185 min\({}^{-1}\) for the three samples, respectively. It is obvious that the M2 Pt sample has the best photocatalytic kinetics. The constant values have the same trends as the Pt-Se contents. This indicates the correlation between Se-Pt bonding and photocatalytic performance. On the other hand, \(k\) values are not lineally affected by either the Pt amount used in the synthesis nor the relative contents of Pt-Se bonding. This may indicate that the surface segregation occurred during synthesis [36].  
The possible photocatalytic mechanism can therefore be discussed. During the degradation process, photo-generated electrons from valence bands of MoSe\({}_{2}\) reach the conduction bands, and finally migrate to the active sites provided by Pt nanoparticles. The electron-hole pairs participate in redox reactions, where the holes oxidize water to H\({}^{+}\) and -OH. The hydroxyl radicals then react with MB [9]. Meanwhile, the electrons reduce H  
Figure 5: The time-course photocatalytic MB degradation under visible light irradiation. (**a**) Photodegradation of the synthesized samples and pristine MoSe\({}_{2}\). (**b**) Photodegradation kinetics of In(C\({}_{0}\)/C).  
to \(\cdot\)H. The Pt-Se bonding offers stable and efficient routes for charge transfer during the whole process.