The emergence of bifunctional catalytic properties by the introduction of Bi3+ in defect fluorite-structured PrO1.833

Abstract

In the present study, the utility of Pr^3+/Pr⁴⁺ and Bi³⁺/Bi(0) redox couples for oxidation and reduction reactions is demonstrated by synthesizing bismuth-substituted PrO_1.833 samples following a solution combustion method. The samples retained the defect fluorite structure of PrO_1.833 with the inclusion of up to 40 mol% of bismuth, beyond which the rhombohedral structure emerged. The microscopic analysis also reinforced the defect fluorite structure of these samples. The lattice expanded with the inclusion of bismuth. The samples had porous morphology, and the X-ray energy dispersive spectral analysis ensured the presence of Pr and Bi closer to the nominal molar ratio. The intense band at 565 cm⁻¹ in the Raman spectrum shifted to higher values with a progressive increase in bismuth content due to the creation of more oxygen vacancies. In Pr_0.60Bi_0.40O_2−δ, Pr existed in +3 and +4 oxidation states, as revealed by the X-ray photoelectron spectral analysis. The photoluminescence spectra consisted of 4f–4f transitions of Pr³⁺ and emission in the blue region (due to oxygen vacancies). Both Pr_0.60Bi_0.40O_2−δ and PrO_1.833 remained paramagnetic in field-dependent and temperature-dependent measurements down to 2 K. The effective magnetic moment, retentivity, and coercivity decreased on moving from PrO_1.833 to Pr_0.60Bi_0.40O_2−δ. The bismuth-substituted samples catalyzed the oxidative degradation of xylenol orange and methyl orange. The degraded products from these reactions were identified. The bismuth-substituted samples also catalyzed the reduction of nitroaromatics. These transformations followed pseudo-first-order kinetics.