La-Induced Phase Transformation and Band Structure Modulation of Bi2O3 for Enhanced Visible-Light Photocatalytic Degradation of Rhodamine B

Using bismuth oxide (Bi2O3) as the matrix and employing a doping modification strategy to introduce the rare-earth element La, this study prepared La/Bi2O3 visible-light-responsive photocatalysts with different doping ratios. The research systematically investigated the regulation mechanisms of La doping on the material’s phase structure, microstructure, band structure characteristics, and visible-light photocatalytic performance. The results indicate that an appropriate amount of La3+ equivalently substitutes Bi3+ in the lattice, inducing the complete transformation of pure α-Bi2O3 into the tetragonal β-Bi2O3 phase while maintaining the integrity of the crystal framework. Meanwhile, the modulation of the local electronic structure caused by La3+ substitution effectively narrows the bandgap width and broadens the visible-light response range; it also acts as an electron trap to significantly suppress the recombination of photo-generated electron–hole pairs, thereby enhancing charge transport efficiency. Visible-light catalytic degradation experiments confirmed that 4% La/Bi2O3 exhibits the optimal degradation kinetics for RhB, achieving a 72.88% degradation rate of Rhodamine B within 60 min of visible-light irradiation. The first-order reaction rate constant was 23 times that of pure Bi2O3, and the material demonstrated good stability under repeated cycles. Radical trapping experiments indicated that the order of contribution of active species was ·O2− > h+ > ·OH, with the superoxide radical (·O2−) being the dominant active species. This study confirms that appropriate lattice doping with La can synergistically optimize the structure and optoelectronic properties of Bi2O3, providing experimental evidence and theoretical references for the rational design of highly efficient and stable visible-light-responsive Bi2O3-based photocatalytic materials.