Water/oil nanoemulsion-based synthesis of Bi x Sn 6-2x S y (0.33 ≤ × ≤ 2.95) semiconductor QDs for efficient photocatalytic degradation of MB dye

The development of efficient photocatalysts for the photodegradation of organic dyes in wastewater is highly worthwhile. Herein, the nanoemulsion tactic was utilized to synthesize Bi x Sn 6 −2x S y (0.33 ≤ x ≤ 2.95) photocatalysts with morphological structures that changed from nanowhiskers to quantum dots (QDs). The optical properties of these materials were examined by UV-visible absorbance spectroscopy and photoluminescence, while Mott-Schottky analysis was utilized to study their electronic properties. Bi x Sn 6−2 x S y materials exhibit appreciable absorption in the UV-visible light range with a direct band gap that increases from 1.23 to 1.46 eV. Both crystal structure and composition greatly affect the photocatalytic activity of Bi x Sn 6−2 x S y semiconductors. Among the various synthesized photocatalysts, BiSn 4 S 4.5 can efficiently photodegrade methylene blue dye (MB) in the shortest time under UV-visible light. The photocatalytic activity is positively affected by the change of crystal structure from orthorhombic to cubic symmetry. Based on the Mott-Schottky plots, the flat band potential ( E fb ) and the semiconductor behavior of the fabricated Bi x Sn 6−2 x S y nanomaterials were determined. The obtained E fb values for SnS, Bi 0.33 Sn 5.34 S 5.8 , BiSn 4 S 5.5 , and Bi 2.14 Sn 1.71 S 4.7 are −0.18 V, −0.42 V, −0.53 V, and −0.51 V (vs. Ag/AgCl), respectively. The E fb value is clearly shifted towards more negative potential values with increasing the Bi molar ratio ( x ). However, Bi 2.95 Sn 0.1 S 4.5 semiconductor was found to be of n-type character, having a positive E fb value of +0.66 V (vs. Ag/AgCl). Photocurrent and EIS responses confirm the high stability and photocatalytic activity of BiSn 4 S 5.5 , which also achieves the lowest charge transfer resistance. The modified electronic properties of the Bi x Sn 6−2 x S y semiconductors significantly improve their photocatalytic activity, rendering them to be promising absorbers for sunlight harvesting applications.