Figure 3 PEC performance. (a) Current density-potential (J-V) characteristics obtained from CdSe nanotube arrays under dark conditions and visible light illumination (λ > 400 nm, 100 mW/cm2). The scan rate is 10 mV/s. (b) The photocurrent response to on-off cycles of illumination at a constant potential of −0.2 V vs. Ag/AgCl. CYC202 in vivo photocatalytic activities In order to evaluate the photocatalytic performance of CdSe nanotube arrays on ITO, the degradation of MB Proteasome inhibitor was chosen as a probe for photoreaction. The results indicate that CdSe nanotubes were efficient in the photodegradation of MB under visible light irradiation (blue symbols in Figure 4). The degradation

reaction of MB can be described as a pseudo-first-order reaction with the kinetics expressed by the following equation when the MB concentration is low (<1 mM): where C 0 is the initial concentration of MB in the solution; C, the concentration of MB at a given reaction time, t; and k, the reaction

rate constant [42]. From the linear extrapolations, the calculated reaction rate constant of the nanotube arrays is estimated to be 3.3 × 10−3 min−1 after subtracting learn more the direct photolysis of MB. The cycling properties of CdSe nanotube arrays were also studied. The photocatalyst shows a slight decrease in the catalytic activities after being tested for three times (Additional file 1: Figure S1). Figure 4 Photocatalytic degradation performance. Photocatalytic degradation performance of CdSe nanotube arrays on ITO under visible light irradiation Aldol condensation (λ > 400 nm) in the MB aqueous solution (blue symbols) and the solution added with 10 vol.% ethanol (green symbols). C is the concentration of MB at a given reaction time; C 0 is the initial concentration of MB. The photocatalytic degradation mechanism of CdSe nanotube arrays is proposed in Figure 5. The energy diagram shows that the valence band maximum (VBM) of CdSe is more positive than the oxidation potential of MB and the redox potential E(·OH/OH−). The conduction band minimum is more positive than the reduction potential

of MB but negative than the redox potential E(O2/HO2 ·) [43–45]. Upon visible light irradiation, electron-hole pairs are generated (Equation 1) in the CdSe, and their separation is driven by the band bending formed at the interface of CdSe and the solution. The n-type conductivity of unintentionally doped CdSe promotes the charge carrier separation. The photogenerated holes oxidize MB molecules directly (Equation 2) and/or hydroxide ion (OH−) to produce ·OH radicals (Equation 3), which also contribute to MB degradation via other route (Equation 4). At the same time, the photogenerated electrons can reduce the oxygen adsorbed on the catalyst (Equation 5), resulting in free HO2 · radicals, which also contribute to the oxidation of MB. However, such electron injection is not efficient due to the small offset between the VBM of CdSe and E(O2/HO2).