Halide-Alloying-Induced Electric Field Modulation in BiOI-Cl-Br Solid Solutions for Enhanced Piezo-Photocatalytic Degradation of Organic Contaminants.

Halide alloying provides an effective strategy for engineering the electronic structure, internal electric field, and piezoelectric polarization of BiOX (X = Cl, Br, I) photocatalysts to enhance piezo-photocatalytic performance. Herein, Cl-rich ternary BiOI-Cl-Br solid solutions were synthesized to elucidate the role of halide alloying in regulating charge-carrier dynamics and the built-in electric field. Comprehensive structural, optical, piezoelectric, electrochemical, and catalytic investigations revealed that the optimized BiOI0.15Cl0.70Br0.15 exhibits a remarkably enhanced piezoelectric response with a d33 value of 86.9 ± 4.2 pm V-1, exceeding those of pristine BiOX materials. Rhodamine B (RhB) was employed as a model organic pollutant to evaluate the piezo-photocatalytic performance. Under simultaneous visible-light irradiation and ultrasonic excitation, the optimized catalyst achieved 99.9% RhB degradation within 20 min with 89% total organic carbon removal, demonstrating rapid degradation and efficient mineralization. Electrochemical analyses revealed enhanced charge separation, accelerated interfacial charge transfer, reduced electron-hole recombination, and favorable band energetics arising from halide-alloying-induced lattice distortion and strengthened internal electric fields. Liquid chromatography-mass spectrometry (LC-MS) identified the degradation intermediates, enabling the proposal of a piezo-photocatalytic degradation pathway involving sequential N-deethylation, chromophore cleavage, aromatic ring opening, and progressive mineralization of RhB into CO2 and H2O. The synergistic coupling of the built-in electric field with piezoelectric polarization promotes efficient migration of photoinduced and piezo-induced charge carriers, thereby enhancing reactive oxygen species generation and interfacial redox kinetics. This work establishes ternary halide alloying as a powerful strategy for designing high-performance BiOX-based piezo-photocatalysts for sustainable wastewater remediation and provides mechanistic insights into their degradation pathways.