Synthesis and characterization of Z-scheme silver carbonate with cadmium sulfide for enhancement of photocatalytic degradation of methyl orange under visible light

Methyl orange (MO) is an anionic azo dye commonly used in food, textile, leather, and paper industries. However, its discharge into the environment causes serious concerns due to its toxicity, mutagenicity, carcinogenicity, and high stability, which make it difficult to degrade by conventional methods. Among various alternatives, photocatalytic degradation has emerged as an effective approach for removing MO. Silver carbonate (Ag₂CO₃) has demonstrated excellent photocatalytic activity due to its abundant active sites, but the rapid recombination of photogenerated electron–hole pairs limit its efficiency. To overcome this, the construction of Z-scheme heterojunction systems has been proposed, offering improved charge separation and strong redox potential. Cadmium sulfide (CdS), with its suitable band gap energy, is a promising candidate for coupling with Ag₂CO₃ to form such heterostructures. Therefore, this study focuses on synthesizing CdS-loaded Ag₂CO₃ photocatalysts via a facile precipitation method and evaluating their photocatalytic performance in the degradation of methyl orange.In addition, the modified photocatalyst were characterized by using X-ray diffraction (XRD), Field Emission Scanning Electron microscopy (FESEM), Transmission-electron Microscopy (TEM), X-ray Photoelectron spectroscopy (XPS), Photoluminescence (PL), Fourier Transform Infrared (FTIR), and Ultraviolet-visible Diffuse Reflectance Spectroscopy (UV-Vis DRS). The mass ratio of CdS was varied from 5 to 15 wt% and denoted as x-ACD, namely 5 ACD, 10 ACD and 15 ACD. XRD and FTIR analyses the confirmation of the successful preparation of the Ag₂CO₃/CdS composite, where CdS incorporation alters peak intensities due to good dispersion and strong interaction between components, especially evident in the 10ACD sample. In addition, the FESEM mapping and TEM image reveals the same pattern which the Ag₂CO₃/CdS composite exhibits well-dispersed Cd and S elements on Ag₂CO₃ with modified morphology, where the 10ACD sample shows optimal distribution leading to higher active sites and improved surface accessibility. With the good dispersion of both photocatalyst, 10ACD exhibits the lowest PL intensity that illustrates the effective electron hole recombination. Hence, the photocatalytic performance of MO over different ratio loaded on silver carbonates were in following order: 10ACD (94.38%) > 15ACD (83.28%) > 5ACD (80.56%) while Ag2CO3 and CdS obtained 75.22% and 81.61% respectively. The optimum performance was ascribed to the 10 ACD with the higher photocatalytic activity and appropriate band gap energy at 2.05 eV as reported with UV-Vis DRS. As the proposed mechanism for the MO, it successfully illustrated that hydroxyl radical on the surface was the main active species in the reaction which align that CdS has lower negative valence band (VB) and endow more hole with high oxidizing ability. Moreover, XPS analysis revealed that the binding energies of 10ACD were blue shifted compared Ag₂CO₃ highlights the function of electron donor while CdS acts as electron acceptor simultaneously due to the 10ACD showed the reduced binding energy than the pure CdS. As a conclusion, this study elucidates the synergistic interfacial interaction between Ag₂CO₃ and CdS in constructing an efficient Z-scheme heterojunction photocatalyst, leading to enhanced photocatalytic degradation of organic pollutants in wastewater, in alignment with the Sustainable Development Goal of clean water and sanitation (SDG 6).