**2. Experiment**

#### *2.1. Synthesis of Sn1*−*<sup>x</sup>ZnxS2 Nanoflakes*

SnS2 and Sn1−*<sup>x</sup>*Zn*x*S2 nanoflakes were prepared via low cost hydrothermal route reported previously [35]. In brief, 0.1753 g SnCl4·5H2O (Tin (IV) chloride pentahydrate) and 0.15 g thioacetamide (TAA) were dissolved in 80 mL distilled water, stirred for 1 h to result in homogeneous solution. The prepared solution was transferred to 100 mL Teflon-line autoclave, sealed and heated up to 160 ◦C for 12 h and finally cooled to room temperature. The prepared SnS2 nanoflakes were then washed with ethanol and deionized water repeatedly and finally dried at 60 ◦C for 12 h in electric oven. For the synthesis of Sn1−*<sup>x</sup>*Zn*x*S2 nanoflakes, 1 and 3 mmol% of Zinc chloride was added to the precursor solution.
