A novel Z-scheme Ag/AgBr/Bi4O5Br2 heterojunction with rich oxygen vacancy for enhanced photocatalytic degradation of formaldehyde

Fabrication of a plasma-based Z-scheme heterojunction can significantly accelerate the charge separation and broaden the light response range. Herein, a series of Ag/AgBr/Bi₄O₅Br₂-x% (abbr. A/AB/BOB-x%; x = 5, 10, 30 and 50) Z-scheme heterojunctions containing rich oxygen vacancies (Ovs) were successfully synthesized via the alcoholysis method, followed by ion-exchange and photoreduction method to enhance photocatalytic formaldehyde degradation. The formaldehyde degradation efficiency of A/AB/BOB-10 % composite reached 94.3 % at 3 h of light irradiation, which was 1.6, 1.2 and 2.3 times higher than that of BiOBr (60.1 %), BOB (78.3 %) and Ag/AgBr (41.2 %), respectively. The enhanced photodegradation activity was ascribed to the synergistic effects arising from the formation of Z-scheme heterojunction, the surface plasmon resonance (SPR) effect induced by Ag nanoparticles (Ag NPs) and the rich oxygen vacancies. Moreover, the cycle experiments demonstrated that A/AB/BOB-10 % composite had favorable stability and repeatability, achieving a degradation efficiency of 81.2 %. The electron spin resonance (ESR) and radical capturing tests demonstrated that the active species involved in photocatalytic degradation of formaldehyde include h⁺, ·OH and ·O₂⁻, with h⁺ playing a predominant role. Additionally, ion chromatography revealed that formic acid (HCOOH) was an intermediate during the removal process of formaldehyde. Finally, the Z-scheme charge transfer mechanism bridged by Ag NPs for the photocatalytic degradation of formaldehyde was proposed based on the ESR tests and an analysis of energy band structure. The current study presents a promising approach for the fabrication of high-efficiency plasma-based Z-scheme heterojunction photocatalysts for formaldehyde degradation.