**2. Results and Discussion**

### *2.1. Annealing*

To distinguish between the different samples of oxide nanowhiskers and the molybdenum disulfide nanotubes studied in this work a labeling system was used (see Table 1). For this work, two different precursors were investigated: MoO3í*x* (2) nanowhiskers and MoS2 (2) nanotubes, which were left one year in the drawer after solar ablation synthesis. The detailed description of their synthesis can be seen in the experimental part. Due to the small quantities of the MoS2 nanotubes and MoO3í*<sup>x</sup>* nanowhiskers that are obtained in the synthesis (~1%–2% yield) only single particle EDS measurement can be suitable for their chemical analysis.


**Table 1.** The samples labeling that were used during the experimental work.

The experimental work which has recently been carried-out indicated that the Pb atoms are not stable in high concentrations in the MoO3í*x* or MoS2 lattice. According to the EDS measurements the initial lead concentration in the molybdenum suboxide nanowhiskers MoO3í*x* (1) was reduced by one order of magnitude after one year in the drawer (Pb:Mo ratio reduced from ~0.28 to 0.03 in MoO3í*x*(2)) (Figure 2). The same analysis showed that in the case of MoS2 (1) nanotubes the Pb concentration decreased from ~0.12 to 0.03 in MoS2; (2). Subsequent annealing of both types of nanostructures, *i.e.*, MoO3í*x* (2) nanowhiskers and MoS2 (2) nanotubes, leads to additional reduction of the Pb concentration. The Pb:Mo ratio before and after annealing calculated from EDS measurements can be seen in Figure 2. It should be emphasized that the accuracy of the EDS is greatly compromised at the lower concentration limit of Pb.

The outdiffusion of the lead from the molybdenum oxide nanowhiskers MoO3í*x* (2) did influence their high-temperature stability and their conversion into MoS2 (3) nanotubes upon annealing in H2S atmosphere at 810 °C. In all cases, MoS2 (3,4) nanotubes were observed after the sulfidization and annealing of the lead-depleted MoO3í*x* (2) nanowhiskers and MoS2 (2) nanotubes. TEM images of the precursors and products can be seen in Figure 3. Detailed description of the annealing conditions can be seen in the experimental section.

**Figure 2.** Pb:Mo ratio of the precursors and products according to the EDS measurements, (**a**) MoO3í*x* (2) nanowhiskers as a precursor material; (**b**) MoS2 (2) nanotubes as a precursor material.

Due to the overlap between the Mo(L) and Pb(M) peaks (2.3 KeV) in the EDS spectra, the calculated atomic concentration of Pb is based on the Pb(L) (10.5 KeV) and Mo(K) (17.4 KeV) peaks, which provide lower accuracy. Therefore, the detection of Pb atoms after a year in the drawer is limited to the detected range (>0.2 at%). On the other hand, it can be seen from the EDS spectra of the samples before and after annealing that in the case of molybdenum suboxide nanowhiskers MoO3í*<sup>x</sup>* (2) as a precursor material, the Pb peak disappears after two hours annealing in H2S atmosphere, while the same peak disappears after 30 min annealing at 810 °C in the case of MoS2 (2) nanotubes (Figure 4).

**Figure 3.** TEM images, (**a**) MoO3í*x* (1) nanowhisker obtained after the synthesis (solar ablation for 30 s); (**b**) MoO3í*x* (2) nanowhisker a year after the synthesis; (**c**–**e**) MoS2 (3) nanotubes after 30 min, 1 and 2 h of H2S annealing, respectively, with MoO3í*x* nanowhiskers as a precursor; (**f**) MoS2 (1) nanotubes after the synthesis (solar ablation for 10 min); (**g**) MoS2 (2) nanotube a year after the synthesis, (**h**–**j**) MoS2 (4) nanotubes after 30 min, 1 and 2 h (H2S) annealing, respectively, with MoS2 (2) nanotubes as a precursor.

**Figure 4.** EDS spectra of the samples before and after annealing at 810 °C, (**a**) MoO3í*<sup>x</sup>* (2) nanowhiskers as a precursor; (**b**) MoS2 (2) nanotubes as a precursor.
