Room-Temperature Construction of Z-Scheme Bi4O5I2/BiOBr Heterojunction for Highly Efficient Visible-Light Photocatalytic Degradation of Organic Dyes

A novel Bi 4 O 5 I 2 /BiOBr Z-scheme heterojunction is fabricated via a room-temperature co-precipitation method. • The Z-scheme mechanism preserves strong redox potentials, generating abundant ·OH, ·O 2 - , and h + . • Bi 4 O 5 I 2 /BiOBr achieves 85.8% MB degradation in 150 min, with a rate constant 16.06 times that of BiOBr. • The composite exhibits excellent stability and reusability over four consecutive degradation cycles. • This work provides a green, scalable strategy for designing high-performance bismuth-based photocatalysts : Bismuth and bismuth-rich oxyiodides, such as BiOX and Bi 4 O 5 I 2 , are promising visible-light photocatalysts but suffer from rapid photogenerated carrier recombination. Here, we construct a novel Bi 4 O 5 I 2 /BiOBr heterojunction via a facile room-temperature co-precipitation method that creates a tight heterointerface between two layered bismuth-based semiconductors. This yields intimate contact confirmed by HRTEM and XPS. The composite also shows enhanced visible light absorption (UV–Vis DRS) and markedly suppressed photoluminescence, indicating efficient charge separation, further supported by higher photocurrent and smaller EIS arc radius. More importantly, the work proposes a Z-scheme charge transfer mechanism rather than a conventional type-II junction. Based on band-edge calculations (Mott–Schottky) and radical trapping experiments, the composite preserves the strong reduction ability of electrons in Bi 4 O 5 I 2 and the strong oxidation ability of holes in BiOBr, while the less energetic charge carriers recombine. This mechanism is a key conceptual advance because it overcomes the redox-capacity loss typical of type-II systems and generates highly reactive species (h + , ·OH, and ·O 2 - ), as verified by scavenger tests. The k value of Bi 4 O 5 I 2 /BiOBr-3 (0.01333 min -1 ) is 7.98 and 16.06 times higher than those of Bi 4 O 5 I 2 (0.00167 min -1 ) and BiOBr (0.00083 min -1 ), respectively. The composite also demonstrates excellent stability over four consecutive cycles. This work offers a simple, energy-efficient strategy for constructing high-performance bismuth-based Z-scheme heterojunctions, providing a viable route for wastewater remediation and advancing the rational design of photocatalysts with synergistic redox capability.