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Multi-heterojunctions are more promising than single heterojunctions in photocatalysis due to the availability of more interfaces between each component. However, photocatalytic activity is highly dependent on the contact mode of individual components. In this work, we assembled gold nanoparticles/oxygen-deficient (anatase/B-phase) TiO₂ multi-heterojunction microspheres using spray pyrolysis and focused on their contact mode-governed photocatalytic activity. The results reveal that using oxygen-deficient (anatase/B-phase) TiO₂ microspheres as building blocks could significantly enhance the absorption of visible light and the photocatalytic activity of a gold–TiO₂ system toward the photocatalytic carbon monoxide oxidation. Furthermore, loading gold nanoparticles onto B-phase TiO₂ could facilitate a more prominent enhancement of activity than that of pure B-phase TiO₂, benefiting from the two-electron reduction of oxygen at the interface of TiO₂/Au. Meanwhile, the high crystallinity of B-phase TiO₂ microspheres allows for a gold loading amount of 1 wt% in the gold/(anatase/B-phase) TiO₂ system, which is 1.67 times more active than pure B-phase TiO₂ microspheres, in the photocatalytic oxidation of carbon monoxide to generate carbon dioxide.