Improving the photocatalytic properties of CdMoO4 under visible light through Ca doping and Ag decoration

Abstract

In this study, doping and decorating techniques were used to improve the photocatalytic properties of CdMoO₄ (CMO) under visible light. According to the XRD results, Ca-doped CMO samples were successfully obtained through a sonochemical method, and the Ag was decorated through photoreduction. The chemical composition and binding energy states on the surface of the pure and 2CMO/Ag (2% Ca-doped CMO decorated with 10% Ag) samples were confirmed by XPS. The EDS, FRX, and ICP‒MS results also confirmed the sample composition. The morphologies observed via FESEM and TEM revealed micrometric spherical types for all the samples, in which the addition of Ca ions decreased part of the agglomeration. Furthermore, metallic silver nanoparticles were observed across the surface, with an average particle size of 29.56 nm. Thus, doping and decorating the CMO sample promoted an increase in the specific surface area from 4.47 to 5.40 m²/g for the 2CMO/Ag sample. For the absorbance results, the Ag samples presented a band in the region between 400 and 600 nm, which indicates their activation under visible light. The optical properties were studied through photoluminescence and photocatalytic tests. While Ca doping weakens the degree of recombination of photogenerated electron‒hole pairs, decorating the surface with Ag also creates surface plasmons to promote the absorption of visible light. The photocatalytic properties of the materials under solar radiation were tested against methylene blue (MB) and crystal violet (CV) separately and mixed, obtaining efficiencies of 92.93 and 93.52%, respectively, after 120 min with the 2CMO/Ag sample against the mixture. After reuse cycles, the results are still satisfactory and show the stability of the material in the XRD pattern. The relative energy band positions were calculated, and a scavenging methodology was used for analysis, after which a possible photocatalytic mechanism was proposed, verifying the role of ·OH, ·O₂^– and h⁺ radicals as the dominant active species in the medium. The results suggest that 2CMO/Ag is a promising material for water treatment and serves as an effective alternative for degrading a mixture of contaminants under solar radiation.