Kinetic studies of Congo Red Photodegradation on the hetero-system CoAl2O4/ZnO with a stirred reactor under solar light

The hetero-system CoAl2O4/ZnO was successfully used for the photo-degradation of Congo Red (CR), a hazardous and recalcitrant dye. The spinel was prepared by nitrate route and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermal analysis (TG). The electrical conductivity augments exponentially with the inverse of absolute temperature and activation energy of 0.19 eV was computed. n-type conduction is evidenced from the anodic photocurrent at the semiconductor/electrolyte junction, thus improving the separation of electron /hole (e(-)/h(+)) pairs by the interfacial electric field. The quenching experiments were carried and the results demonstrate that the radical O-2(center dot-) is the responsible active specie for the CR photooxidation. The solar photocatalysis over the hetero-system CoAl2O4/ZnO exhibits an increased performance in the CR degradation due to ZnO activation by the UVA part of the solar light. An elimination conversion of 97% was obtained after 4 h at room temperature for a CR concentration of 20 mg/L. The TOC analysis (66.9%) indicates that the dye CR is effectively mineralized on the hetero-system upon solar light. The kinetic indicates that the Langmuir-Hinshelwood (L-H) model is well adapted to the experimental data. A first order kinetic was found from the photo oxidation with a photocatalytic half-life of 29 min.

Automated summary

The CoAl2O4/ZnO hetero-system was successfully used for the photodegradation of CR, with O-2(center dot-) identified as the active species responsible for CR photooxidation, and ZnO activated by solar light contributing to enhanced degradation. A high removal rate of 97% was achieved after 4 hours of solar photocatalysis, indicating effective mineralization of CR on the hetero-system.