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.