Journal of Catalysis, Vol.350, 226-239, 2017
Multifunctional Cu/Ag quantum dots on TiO2 nanotubes as highly efficient photocatalysts for enhanced solar hydrogen evolution
Metallic Cu/Ag quantum dots on TiO2 nanotubes (Cu/Ag@TNT) have been prepared by a photodeposition method. The structural, optical, and morphological properties of the nanostructured composites have been characterized by a series of techniques, including X-ray diffraction (XRD), Raman spectroscopy, diffuse reflectance ultraviolet-visible light (DRS UV-vis) spectroscopy, high-resolution transmission electron microscopy (HR-TEM), HR-TEM elemental mapping, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The hydrogen (H-2) generation performance of Cu/Ag@TNT catalyst was carried out in aqueous glycerol suspension under natural solar light. Optimized Cu/Ag@TNT (CAT 2.0) showed enhanced photocatalytic H-2 evolution rate compared with monometallic Cu@TNT (CT 2.0), Ag@TNT (AT-2.0), and TNT. Furthermore, the role of Cu and Ag quantum dots present in Cu/Ag@TNT photocatalysts was elucidated by illuminating the reaction system under visible and UV-visible light. The superior photocatalytic H-2 evolution rate of CAT-2.0 was claimed due to the localized surface plasmon resonance (LSPR) effect of Ag-injected visible-light-generated charge carriers into the conduction band (CB) of the TiO2 catalyst, while the Cu co-catalyst acts as an electron acceptor from TiO2 for reduction of H+ ions in solution into H-2 gas. In this way, the synthesized photocatalyst was activated by the UV and visible region of solar light and the charge carriers' lifetime was prolonged, and thus the electron-hole pairs were effectively utilized for H-2 generation. A plausible reaction mechanism of the Cu/Ag@TNT photocatalyst was suggested by explaining the beneficial effects, namely the LSPR effect of Ag and the co-catalytic role of Cu for enhanced H-2 evolution. (C) 2017 Elsevier Inc. All rights reserved.