Multifunctional Cu/Ag quantum dots on TiO 2 nanotubes as highly efficient photocatalysts for enhanced solar hydrogen evolution

Metallic Cu/Ag quantum dots on TiO2 nanotubes (Cu/[email protected]) 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 (H2) generation performance of Cu/[email protected] catalyst was carried out in aqueous glycerol suspension under natural solar light. Optimized Cu/[email protected] (CAT-2.0) showed enhanced photocatalytic H2 evolution rate compared with monometallic [email protected] (CT-2.0), [email protected] (AT-2.0), and TNT. Furthermore, the role of Cu and Ag quantum dots present in Cu/[email protected] photocatalysts was elucidated by illuminating the reaction system under visible and UV–visible light. The superior photocatalytic H2 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 H2 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 H2 generation. A plausible reaction mechanism of the Cu/[email protected] photocatalyst was suggested by explaining the beneficial effects, namely the LSPR effect of Ag and the co-catalytic role of Cu for enhanced H2 evolution.