CeO₂/g-C₃N₄/V₂O₅ ternary nano hetero-structures decorated with CQDs for enhanced photo-reduction capabilities under different light sources: Dual Z-scheme mechanism

In this work, a carbon quantum dots (CQDs) decorated dual Z-scheme CeO₂/g-C₃N₄/V₂O₅ heterojunction (CCGV) was rationally synthesized by simple hydrothermal method. The crystal structure, morphology, and optical properties of the photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-Vis diffuse reflectance spectroscopy. CCGV catalyst shows high visible absorption, including near infra-red region and solar light via two-channel charge transfer (dual Z-scheme), reduced recombination, and up-conversion effect of CQDs. The heterojunction was used for visible assisted photo-reduction of carcinogenic hexavalent chromium ions (Cr(VI)) with a 99% reduction in 100 min without any sacrificial agent or hole scavenger. The reaction becomes more rapid with tartaric acid as a scavenger with a complete reduction in just 30 min under visible light. Photogenerated electrons are the dominant active species, followed by ^●O₂⁻, as revealed by the scavenging experiments. The use of sacrificial agents and scavengers suggests that photogenerated electrons were the dominant active species followed by ^●O₂⁻ radicals. The electrochemical impedance spectroscopy and photoluminescence results confirm highly reduced recombination, high charge separation, and charge transfer capacity in the dual Z-scheme heterojunction. The conduction band edges of CeO₂ and V₂O₅ (which are protected by the dual charge transfer) have an appropriate potential for the rapid reduction of hexavalent chromium. The XPS scan of the catalyst after separation shows the presence of Cr in the +3 oxidation state, suggesting complete photo-reduction. This study is promising for developing wide spectrum active simple heterojunction photocatalysts for pollutant removal with high efficiency.