Photocatalytic Activity Measurement

The optical system used for photocatalytic reaction consisted of xenon lamp (300 W) and two bandpass filters (with the bandwidth of 400–780 nm and 600–780 nm) that ensure the irradiation in visible range. Four kinds of photocatalysts including Au nanoparticles, CdS counterpart, Au@CdS thick, and Au@CdS-CdS nanoflowers were used to degrade rhodamine 6G (R6G) solution. Typically, 6 mg photocatalyst was added into 20 mL R6G solution (1.0 × 10⁻⁵ M) and stirred for 30 min in the dark to achieve adsorption equilibrium before irradiation. The photocatalytic experiments were conducted under two irradiation range, 400–780 nm and 600–780 nm, respectively. Then, 2.5 mL solution were extracted every 10 min and centrifuged to remove the photocatalyst. The UV-Vis absorption spectra of filtrates were recorded using PerkinElmer Lambda 35 photometer to monitor the catalytic reaction. All the photocatalysis experiments were conducted at room temperature in air. Degradation of R6G was defined as follows:

Degradation (%) = [(C₀-C_t) / C₀] × 100.

where C₀ is the initial concentration of R6G, C_t is the concentration of R6G at a certain time after the photocatalytic reaction.