All-Solid-State Z-Scheme Photocatalyst with Carbon Nanotubes as an Electron Mediator for Hydrogen Evolution under Simulated Solar Light

In this contribution, the effectiveness of tailor-made multi-walled carbon nanotubes (MWCNTs) as a solid-state electron mediator for facilitating Z-schematic water splitting is demonstrated. An anisotropic Zn0.5Cd0.5S-MWCNT-TiO2 ternary core-shell nanocomposites fabricated by a facile coating and hydrothermal route renders a much higher photocatalytic activity than the corresponding single- and two-component systems, revealing MWCNTs can shuttle photogenerated electrons from PS II (TiO2) to PS I (Zn0.5Cd0.5S). This unique type of vectorial electron transfer between the two photosystems imparts an efficient spatial charge isolation and endows suitable relative band positions with strong redox ability to the Z-scheme system. Consequently, the simulated solar-light-driven (AM 1.5) photocatalytic H2 evolution rate of the as-prepared Zn0.5Cd0.5S-MWCNT-TiO2 photocatalyst (21.9 μmol h−1) is ca. 4.5- and 2.8-fold enhancement over pristine Zn0.5Cd0.5S and MWCNT-Zn0.5Cd0.5S samples, respectively. The structural and chemical properties of the typical photocatalysts were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and ultraviolet–visible diffuse spectroscopy (UV–Vis). Besides, electrochemical characterizations (transient photocurrent, Nyquist and Mott-Schottky measurements) were performed to depict the ascendency of the Z-scheme system. Based on the outcomes of the experiment, a plausible charge transfer mechanism for the Z-schematic Zn0.5Cd0.5S-MWCNT-TiO2 system was postulated.