B and Zr co-doping can effectively improve the visible-light photocatalytic activity of TiO₂ by more than twice.

XRD, Raman, and XPS measurements demonstrated that all the samples are anatase phase of TiO₂ and Zr⁴⁺ ions replace the Ti⁴⁺ ions while the B³⁺ ions occupy the interstitial sites.

The incorporation of interstitial boron dopants creates oxygen vacancies (Ov) and reduce Ti⁴⁺ to Ti³⁺ to form [Ov-Ti³⁺]⁺, which traps the carriers and prolongs carrier lifetime.

Zr⁴⁺ ions replace Ti⁴⁺ ions and form impurity levels, which could improve visible light response.

The co-doped samples are benefited from both B interstitials and Zr substitutes.