A hybrid Z-scheme heterojunction using GQD, g-C₃N₅, and NiCo LDH for Rhodamine B degradation under visible light...

Degradation of organic pollutants in aquatic environments is crucial because of the importance of environmental preservation and maintenance of cleanliness. Despite the existence of numerous methods for degrading organic pollutants, photocatalysts have garnered significant attention from researchers in the fields of chemistry and environmental science owing to their numerous advantages. In this study, a highly attractive ternary nanocomposite composed of GQD (graphene quantum dot)/g-C₃N₅/NiCo LDH (layered double hydroxide), synthesized by combining hydrothermal and ultrasonic techniques, was employed as a light-active catalyst for the degradation of Rhodamine B (RhB), a highly harmful pollutant to water and the environment. Several techniques, including FESEM, TEM, FTIR, XRD, EDS, XPS, and UV-Vis DRS, were used to characterize the produced materials. The RhB degradation efficiency of the optimized g-C₃N₅/NiCo-LDH/GQDs composite was 98.9%, which was much higher than that of GQDs (34%) and GQD/g-C₃N₅ (46.6%). The apparent pseudo-first-order rate constant (k) for the ternary system was found to be 0.0344 min⁻¹ by kinetic analysis. This is 10.75 and 6.14 times higher than the rates for GQDs (0.0032 min⁻¹) and GQD/g-C₃N₅ (0.0056 min⁻¹), respectively. The synergistic Z-scheme charge transfer mechanism, in which GQDs function as an effective electron mediator to accelerate interfacial charge migration and suppress charge recombination. At the same time, NiCo-LDH provides an abundance of redox-active sites and enhanced electrical conductivity and is responsible for the notable increase in photocatalytic activity. Improved charge separation efficiency was confirmed by photoluminescence, and radical trapping experiments. The main reactive species that degrade RhB were found to be ^•OH and O₂•⁻. The strategic advancement in carbon nitride-based heterojunction engineering is represented by the logical combination of nitrogen-rich g-C₃N₅ with conductive GQDs and dual-metal NiCo-LDH. This work offers new insights into the design of multi-component Z-scheme photocatalysts for sustainable wastewater treatment applications, as well as a demonstration of a highly effective and metal-efficient photocatalytic system.