Synthesis of AgInS₂-ZnS quantum dot/TiO₂ nanocomposites as efficient photocatalysts for methylene blue degradation

Photocatalytic degradation has been demonstrated to be an efficient and eco-friendly method for the removal of dye pollutants. Herein, we report the synergetic effect of glutathione (GSH)-capped AgInS₂-ZnS (AIS-ZnS) core-shell quantum dots (QDs) and titanium dioxide (TiO₂) as a novel nanocomposite for the efficient photocatalytic treatment of methylene blue (MB). The AIS-ZnS core-shell QDs and the corresponding QD/TiO₂ nanocomposites were synthesized directly in an aqueous medium followed by annealing. The optical properties of the AIS-ZnS core-shell QDs showed strong yellow photoluminescence, which decreased gradually with the addition of TiO₂. Fourier transform infrared (FTIR) spectroscopy confirmed the GSH capping on the QDs and nanocomposites. X-ray diffraction and transmission electron microscopy revealed the nanocrystalline nature and shape of the as-synthesized materials and showed the integration of the QDs (3.9 nm) on the TiO₂ particles after annealing. These materials were then investigated as a photocatalyst for MB degradation using visible light irradiation. The effect of TiO₂ content in the catalyst, calcination, photoirradiation period, catalyst dose, and initial MB concentration on photodegradation of MB was studied. The results indicated that the AIS-ZnS QD/TiO₂ nanocomposite exhibited better photodegradation performance compared to AIS-ZnS QDs and TiO₂. The increasing TiO₂ concentration in the nanocomposite also enhanced MB degradation efficiency (up to 99%). The kinetics of MB degradation follows a pseudo-first-order process. The prepared AIS-ZnS QD/TiO₂ nanocomposite would serve as an effective and eco-friendly photocatalyst for MB degradation.