Photocatalytic activity measurement

The photocatalytic activity measurement was carried out at room temperature. In this work, a 250 W Xenon lamp was used as a light source and was placed about 30 cm vertically relative to the organic pollution solution to diminish the heat effect. The organic pollution solution temperature was kept at 27 ^oC by the circulating cool water. The fabricated samples (2 cm × 2 cm) were immersed in 100 ml RhB solution with the initial concentration of 10 ppm under stirring and maintained in the dark for 30 min to allow adsorption-desorption equilibrium before light irradiation. The schematic diagram of photocatalytic activity measurement was shown in Fig. ^S1. During the photocatalytic activity measurement, after each given interval (20 min), 3 mL of solution was withdrawn and analyzed by an UV-vis spectrometer (Jasco, V-670) with RhB peak at a wavelength of 554 nm. For the reusability test of the ZnO NRs/CuO composite film in photocatalytic activity, after each cycle, the composite film was rinsed to remove residual molecules and re-immersed into a fresh RhB solution with the same volume and concentration. The process was repeated for 3 times to confirm the reusability of the ZnO NRs/CuO composite film as a photocatalyst. The degradation efficiency of RhB molecules was calculated from the following equation:

where C_o and C_t are the initial absorbance and the absorbance at a certain time t, respectively.