Application of ultrasound-aided method for the synthesis of CdS-incorporated three-dimensional TiO2 photocatalysts with enhanced performance.

In this study, an ultrasound-aided hydrothermal-impregnation method was used to synthesize three-dimensional (3D) urchin-like CdS-TiO2 nanostructures (UCTs) with variable CdS content. The photocatalytic efficiencies (for degrading limonene and toluene vapor) of UCTs synthesized using the ultrasound-aided process were greater than those of UCTs fabricated without ultrasound treatment. In addition, the photocatalytic efficiencies of ultrasound-treated UCTs were greater than those of zero-dimensional ultrasound-treated CdS-TiO2 particles, which, in turn, were greater than those of untreated 3D TiO2. These results indicate that ultrasonication is an amicable process for the synthesis of UCTs with high photocatalytic activity. The enhanced activity of ultrasound-treated photocatalysts is ascribed to the greater charge carrier efficiency, adsorption capacity, and light absorption efficiency of these materials. The photocatalytic efficiencies of ultrasound-treated UCTs increased as the CdS loading was increased from 0.1% to 0.3%, gradually dropping as the loading was further increased to 3.0%, which indicated the existence of an optimum CdS loading. UCT photocatalytic efficiencies depended on the input concentration of target pollutants, relative humidity, and air flow rate. The photocatalytic efficiency for the decomposition of limonene mixed with 2-propanol was lower than that for limonene alone, likely due to the radical scavenging properties of 2-propanol. However, the photocatalytic degradation efficiency of the latter alcohol was not changed upon admixture. Toluene exhibited the same behavior. The mineralization ratios of both target compounds were lower than their decomposition ratios, indicating formation of byproducts due to incomplete oxidation. In addition to CO, three organic compounds were observed as photocatalytic decomposition byproducts of limonene (acetic acid, limonene oxide, and methacrolein) and toluene (benzene, benzaldehyde, and p-xylene). UCTs synthesized by the ultrasound-aided hydrothermal-impregnation method could be used to decompose organic vapors with an efficiency of up to 98%, depending on operating conditions.