Mechanochemical synthesis, characterization, and photocatalytic activity of CdS/TiO2 composites in air purification

Two samples of CdS/TiO2 composites have been prepared by single-step solid-state mechanochemical route. Sample 1 was prepared in a ball mill by mixing commercial TiO2 Degussa P25 with CdS mechanochemically synthesized in advance (cubic hawleyite phase). Sample 2 has been obtained by the mechanochemical synthesis from cadmium acetate and sodium sulphide in the presence of TiO2 Degussa P25. Characterization of the synthesized composite materials by means of XRD, DRS, PL, SEM, and EDX showed that the CdS particles were attached to titania. XRD analysis proved that the rutile TiO2 phase is prevailing in Sample 1, unlike the case of Sample 2, which contained mainly anatase TiO2 phase. UV-vis diffuse reflectance spectroscopy was applied in order to evaluate the band gaps of the synthesized samples. Obtained values of the band gap for the composite CdS/TiO2 samples are lying below the band gap value interval of pure anatase TiO2 phase (3.2 eV) and that of pure CdS (2.42 eV) enabling visible light illumination. The photocatalytic oxidation of ethylene (model air contaminant) was studied both under the effect of UV-and under visible light irradiation. It was established that the mechanochemically synthesized CdS/TiO2 shows a higher photocatalytic activity in the oxidation of ethylene under visible light irradiation in comparison with pure titania due to the effect of the CdS component.