# ZnO@MoS2 Core-Shell Heterostructures Enabling Improved Photocatalytic Performance
## 3 Results and Discussion
In this work, the ZnO materials are single microrods or nanorods, while the MoS\({}_{2}\) materials are nanosheets. The quality and thickness of the ZnO micro/nanorods are much better than those of the MoS\({}_{2}\) nanosheets. As a result, the Raman peak's intensity of the ZnO micro/nanorods is much higher than that of the MoS\({}_{2}\) nanosheets. Moreover, the peak at \(\sim\)437 cm\({}^{-1}\) for the ZnO@MoS\({}_{2}\) heterostructures should be from the ZnO micro/nanorods, thanks to its super-strong intensity. Much recent research has suggested that ZnO micro/nanorods produced by hydrothermal method exhibit smooth surfaces. In contrast, the MoS\({}_{2}\) fabricated by the hydrothermal method usually endows rough surfaces or nanosheet-like structures. This means the surface diversification can be taken as an indirect method to just the hydrothermal growth of the MoS\({}_{2}\) on the ZnO micro/nanorods. Figure 4a represents the SEM image of ZnO micro/nanorods. The SEM image shows that the as-grown ZnO samples consist of micro-rods with a typical diameter of \(\sim\)2 um and many small white particles. The SEM images recorded at high magnification clearly show the smooth surfaces of the ZnO micro/nanorods and the presence of the ZnO nanorods (Figure 4b). Figure 4: SEM images of (**a**) the as-received ZnO micro/nanorods and (**b**) the as-received ZnO@MoS\({}_{2}\) core–shell heterostructures grown for 1 h, (**b**,**d**) are the corresponding high-resolution SEM images of (**a**,**c**), respectively, and (**e**,**f**) are ZnO microrods and (**b**) ZnO@MoS\({}_{2}\) core–shell heterostructures of (**a**,**c**) respectively. The insert picture of Figure 2b is the ZnO nanorods in Figure 2a marked by a red circle. Furthermore, the insert SEM image in Figure 4b steads for the area in Figure 4a marked by a red circle at high magnification, which exhibits the ZnO nanorods, too. The ZnO samples grown hydrothermally in this work are the ZnO micro/nanorods. As illustrated in Figure 4c, after hydrothermal growth of MoS\({}_{2}\), the micro/nanorods become grayish and rough. Figure 4d, a high magnification SEM image, displays the rough surface of micro/nanorods modified with small particles. A single microrod of the ZnO and the ZnO@MoS\({}_{2}\) grown for 1 h are applied for comparison, as shown in Figure 4e,f, respectively. By comparing these two figures, the surface of the ZnO@MoS\({}_{2}\) microrod is much rougher than that of the ZnO microrod, suggesting the growth of MoS\({}_{2}\) again. Based on the discussion above, after the hydrothermal growth of the MoS\({}_{2}\), the ZnO@MoS\({}_{2}\) heterostructures have been obtained successfully. According to our experiment, when the growth time is less than 6 h, the MoS\({}_{2}\) shell layer is composed of nanoparticles. When the MoS\({}_{2}\) growth time is 6 h, the surface morphology of the ZnO@MoS\({}_{2}\) core-shell heterostructures is very distinct from that grown for 1 h, as shown in Figure 5a,b as well as Figure 4d. As shown in Figure 5a, the bottom turns rough with the feature of MoS\({}_{2}\) nanosheets. Additionally, clearly, MoS\({}_{2}\) shell layers are well-decorated on the ZnO micro/nanorods (in Figure 5b). The MoS\({}_{2}\) nanosheets at the bottom grow significantly and more densely as the growth time is increased to 8 h, as shown in Figure 5c. However, it can be observed in Figure 5d that the growth rate of the MoS\({}_{2}\) nanosheets is slower than those of the bottom. Unfortunately, the MoS\({}_{2}\) nanosheets grown for 10 h have turned poor at the bottom, as illustrated in Figure 5e. Maybe due to the slow growth rate, the MoS\({}_{2}\) nanosheets on the ZnO micro/nanorods still keep the shape of the nanosheets well (Figure 5f). [PERSON] et al. [9]. However, the MoS\({}_{2}\) nanosheets shell layer increases the contact angle and shows inactive catalytic sites in Ref. [9], which reduces the photocatalytic efficiency of the ZnO@MoS\({}_{2}\) heterostructures. It is well-known that photocatalytic efficiency is significantly affected by light absorption.