Comparison of the photocatalytic efficacy and environmental impact of CdS, ZnFeO, and NiFeO under visible light irradiation.

Three photocatalysts (CdS, ZnFeO, and NiFeO) were synthesized and their ability to photodegrade methylene blue (MB) was evaluated. MB was degraded by both spinel photocatalysts under visible light at room temperature, although their efficacy was less than that for CdS. The photocatalytic efficacies of NiFeO were observed to be much greater than that for ZnFeO. All the synthesized nanoparticles absorbed visible light, while CdS had a larger absorption range within the visible light spectra and the most porous surface. Photo-deactivation was observed during the study, which could be due to the chemical adsorption of the degraded products on the catalyst surface. The factors that affected MB removal efficacy include the absorption range of photocatalysts, initial MB concentrations, amount of photocatalysts added, and photoreactor conditions. Life cycle analysis was used to compare the preparation methods of the photocatalysts in terms of energy consumption and environmental impact. The results showed that the hydrothermal method for NiFeO preparation was less energy-intensive than the sol-gel method for CdS and ZnFeO as the hydrothermal method is effective over a wider range of temperatures in aqueous media. Also, as ZnFeO, and NiFeO have lower environmental impacts than CdS both show promise as photocatalysts.