The effect of type (AgInS 2 , SnS, CuS 2 , Bi 2 S 3 ) and amount (5, 10, 15 wt%) of quantum dots (QDs) on the surface properties and photocatalytic activity of QDs-sensitized TiO 2 composite, was investigated. AgInS 2 , SnS, CuS 2 , Bi 2 S 3 QDs were obtained by hot-injection, sonochemical, microwave, and hot-injection method, respectively. To characterize of as-prepared samples high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), UV-Vis spectroscopy and photoluminescence (PL) emission spectroscopy were applied. The size of AgInS 2 , SnS, CuS 2 , Bi 2 S 3 QDs were 12; 2-6; 2-3, and 1-2 nm, respectively. The QDs and QDs-sensitized TiO 2 composites obtained have been tested in toluene degradation under LEDs light irradiation (λ max = 415 nm and λ max = 375 nm). For pristine QDs the efficiency of toluene degradation increased in the order of AgInS 2 < Bi 2 S 3 < CuS < SnS under 375 nm and AgInS 2 < CuS < Bi 2 S 3 < SnS under 415 nm. In the presence of TiO 2 /SnS QDs_15% composite, 91% of toluene was degraded after 1 h of irradiation, and this efficiency was about 12 higher than that for pristine QDs under 375 nm. Generally, building the TiO 2 /AgInS 2 and TiO 2 /SnS exhibited higher photoactivity under 375 nm than the pristine TiO 2 and QDs which suggests a synergistic effect between QDs and TiO 2 matrix. Catalysts 2020, 10, 403 2 of 18 application of metal sulfides (M x S y ) for wide band semiconductors modification, because of their high charge separation efficiency and narrow band gaps, which possibly enable light harvesting at longer wavelengths [9]. Liu et al. studied the efficiency of AgInS 2 /TiO 2 heterostructures in 1,2-dichlorobenzene (o-DCB) degradation under visible light [10]. They observed that AgInS 2 /TiO 2 composites could expand the visible-light response range and greatly decreased the recombination of photogenerated electron−hole pairs in the composites. The degradation of o-DCB for the most active sample reaches about 50% after 8h of irradiation. Jang et al. prepared Ag-SnS-TiO 2 nanocomposite for methylene blue and rhodamine B degradation under simulated sunlight [11].The photoactivity of the produced photocatalysts was about 2-3 times higher than that of P25. Compared with bare TiO 2 the CuS/TiO 2 [12], CdS/TiO 2 [13-15], SnS/TiO 2 [16], Ag 2 S/TiO 2 [17,18], CuInS 2 /TiO 2 [19-21], Bi 2 S 3 /TiO 2 [22][23][24] nanocomposites present a significant improvement on photocatalytic reactions due to the decreasing recombination of electron-hole pairs and the broadened light absorption spectra. However, the metal sulfides commonly employed for TiO 2 modification have been used in nanoparticle sizes and not in quantum dots sizes. Further, it has been shown that the size of metal sulfides (MS) particles can have an impact on its physicochemical and optical properties. Recently, the literature data demonstrated that the decrease in particle size lowers the recombination of the electron-hole pair within the semiconductor particle. Quantum...