Improvement of dye degradation by photocatalysis and synergistic effect of sonophotocatalysis processes using CaMoO4/g-C3N4 heterojunction

The development of heterostructures between different semiconductors for environmental decontamination applications requires adequate adjustments of semiconductor concentration and optical band gap to improve its properties. Herein, we report the synthesis of type II CaMoO4/g-C3N4 heterojunction by the microwave-assisted hydrothermal method with different molar percentages of g-C3N4 (between 40% and 70%). The successful formation of pure CaMoO4 and g-C3N4 materials was confirmed by a wide range of experimental techniques, including XRD analysis, Raman, XPS, and EPR spectroscopy. Furthermore, UV-Vis characterization showed that heterojunctions were able to be activated under visible light, and photoluminescence analysis suggested a decrease in the recombination of the photogenerated charges. The CaMoO4/g-C3N4 heterojunction was evaluated by the degradation of methylene blue (MB) and crystal violet (CV) dyes. The photocatalytic experiments showed that the heterojunction with 70% g-C3N4 performed the best photocatalytic properties due to a lower band gap energy and higher surface area, reaching a photodegradation efficiency of 95% for MB and 74% for CV in 210 min. The crystalline structure stability of heterojunction CaMoO4 with 70% g-C3N4, was evaluated by three reuse cycles for both dyes, and its photocatalytic capacity was preserved. The scavenger experiments and EPR results revealed that the key degradation success of MB and CV dyes can be attributed to the active superoxide and hydroxyl species present in the heterojunction with 70% g-C3N4. Under the heterojunction of CaMoO4/g-C3N4 with 70% g-C3N4, the sonophotodegradation efficiencies of MB and CV dyes were up to 97% and 95% after sonification and irradiating for 210 min, respectively.