Low-temperature synthesis of CdS/TiO ₂ composite photocatalysts: Influence of synthetic procedure on photocatalytic activity under visible light

CdS/TiO ₂ composites were successfully prepared by hydrothermal treatment at a considerably low temperature (180°C). The effects of four different synthetic procedures on the microstructures of CdS/TiO ₂ composites, such as morphology, crystal structure, porous property and optical response, were investigated in detail. It was found that CdS/TiO ₂ composites consisted of anatase TiO ₂ and cubic phase CdS. The hydrothermal treatment of mixed reactant-containing solution improved the crystallinity of both CdS and TiO ₂. The abundant pores in catalyst particles formed by CO ₂ gas bubbles due to hydrothermal decomposition of the urea molecules increased the specific surface area and pore volume of the catalysts. Meanwhile, the absorption edges of CdS/TiO ₂ samples were drastically extended to around 550 nm. The photocatalytic activities of these prepared samples were evaluated by the photocatalytic decoloration of rhodamine B and methyl orange under visible light irradiation (λ > 420 nm), respectively. The sample prepared by hydrothermal reaction with CdS and TiO ₂ in the molar ratio of 0.25:1 showed the highest photocatalytic activity under visible light irradiation among all samples in this work, which could be attributed to the synergic effects of some factors, such as the excellent crystallinity, high specific surface area, large pore volume and strong absorption in the visible light region. Based on the results of the present study, a reasonable mechanism of photocatalysis on CdS/TiO ₂ composite under visible light was proposed.