Melamine-assisted thermal activation enables defect and phase regulation of biobr-based nanosheets for piezo-photocatalytic H2O2 production and tetracycline degradation

Layered BiOBr is promising for environmental catalysis but suffers from limited visible-light utilization and rapid charge-carrier recombination. Here, a nested-crucible melamine-assisted thermal activation strategy was developed to regulate the defect and phase structure of BiOBr-based materials while avoiding direct contact between melamine and BiOBr. The melamine-derived atmosphere introduced defect-related states, including possible oxygen-vacancy-related species, and induced minor bromine-deficient phase evolution. These changes enhanced light absorption, charge-separation behavior, and local piezoelectric response, whereas excessive melamine caused severe debromination and Bi 2 O 3 formation. The optimized M-BOB-5 achieved an H 2 O 2 yield of 1772.6 μmol g −1 within 120 min under piezo-photocatalytic conditions, which was 1.8 and 6.9 times those obtained under piezocatalysis and photocatalysis alone, respectively, together with nearly 99% TCH removal within 60 min. The improved performance may originate from defect- and phase-related electronic modulation combined with ultrasound-induced piezoelectric polarization, which facilitates charge separation, O 2 reduction to H 2 O 2 , and pollutant oxidation. This study provides a practical melamine-assisted thermal strategy for regulating the defect and phase structures of BiOBr-based piezo-photocatalytic materials.