Lu modified ZnO/CNTs composite: A promising photocatalyst for hydrogen evolution under visible light illumination

We report high photocatalytic hydrogen evolution from water-glycerol mixture under visible light illumination using sol-gel method synthesized zinc oxide (ZnO), Lutetium (Lu) modified ZnO and Lu modified ZnO/CNTs composite. X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), Brunauer-Emmett-Teller (BET), UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), photocurrent transient response and electrochemical impedance spectroscopy (EIS) Nyquist studies were used to determine the reason for improved photocatalytic hydrogen evolution. The highest hydrogen evolution rate of 380 µmolh^-1 was obtained for Lu modified ZnO/CNTs composite, 3.11 times the amount generated over Lu modified ZnO and 10.5 times than using pure ZnO sample. This efficient enhancement in the photocatalytic hydrogen evolution was apparently attributed to the red shift in the optical absorption, increased charge separation, high surface area, cleavage of glycerol by Lu and synergistic effect between Lu and CNTs. Moreover, the effect of Lu and CNTs loading on the photocatalytic hydrogen evolution activity of Lu modified ZnO/CNTs was also studied under analogous experimental conditions. A mechanism of photocatalytic hydrogen evolution by Lu modified ZnO/CNTs composite was also proposed. Additionally, synthesized samples showed prolonged photostability with steady hydrogen evolution in successive cycle runs. This report might attract much attention to design highly efficient and inexpensive photocatalyst for hydrogen evolution under visible light illumination.