New photocatalysts stimulated by visible light for organic-waste remediation: (La/Ce) and (La/Gd) codoped BiFeO3

Bi0.96La0.02Gd0.02FeO3 catalyst revealed a fast photodegradation efficiency for Congo red (CR), acid green 25 (AG25) and Reactive yellow 145 (RY) dyes under sunlight irradiation. Nanocrystalline BiFeO3, Bi0.96La0.02Ce0.02FeO3 and Bi0.96La0.02Gd0.02FeO3 compositions were synthesized by autocombustion route. The X-ray diffraction peaks of all samples were indexed to single phase of BiFeO3 with rhombohedral structure without detection of any impurities. The SEM micrographs showed that the incorporation of (La, Gd) ions changes the morphology of BiFeO3 powder. BiFeO3, Bi0.96La0.02Ce0.02FeO3 and Bi0.96La0.02Gd0.02FeO3 samples have a broad response to visible light spectrum with measured bandgap energy of 2.23, 2.05 and 2 eV, respectively. The photocatalytic measurements illustrated that the incorporation of (La/Ce) and (La/Gd) ions strongly improved the degradation efficiency of BiFeO3 towards CR, AG25 and RY pollutants. Bi0.96La0.02Gd0.02FeO3 catalyst has shown a significant efficiency within 94-97% for degradation of 20 ppm CR, AG25 and RY (100 mL solution, catalyst dose 40 mg) after 35-40 min of sunlight irradiation. Under Xenon lamp, the photocatalytic activity of Bi0.96La0.02Gd0.02FeO3 catalyst was found to be 97, 98 and 99% for 20 ppm CR, AG25 and RY dyes, respectively. The reusability test for CR dye for six cycles showed that Bi0.92La0.02Gd0.02FeO3 catalyst has a high stability with initial and final efficiency of 94% and 82%, respectively. The results of the total organic carbon analysis shown a high level of mineralization of RY (94%) and AG25 (95%) dyes after 60 min. The dual separation of the photoexcited charge carriers by (La3+ + e -> La2+)/(Gd3+ + e -> Gd2+) into BiFeO3 leads to remarkable depollution properties towards many organic dyes.