Oxygen vacancy-driven heterojunction OV-Bi12GeO20/Nb2O5 combined with chitosan (CTS) synergistically enhances the photocatalytic reduction of Cr(VI)

Photocatalytic reduction technology enables the transformation of highly toxic Cr(VI) into the less hazardous Cr(III), offering an environmentally friendly and sustainable approach to water treatment. This study innovatively proposes a synergistic strategy of "oxygen vacancy engineering–heterostructure construction–biomass loading" to fabricate a three-dimensional OV-Bi 12 GeO 20 /Nb 2 O 5 /CTS composite photocatalyst. The incorporation of oxygen vacancies (OVs) into Bi 12 GeO 20 via a straightforward hydrothermal approach reduces its bandgap from 3.16 eV to 1.50 eV, thereby improving visible light absorption and extending the lifespan of photo-generated charge carriers. Under identical reaction conditions, the photocatalytic reduction efficiency of Bi 12 GeO 20 is only 24.376 %, while that of OV-Bi 12 GeO 20 reaches 67.255 %. Further construction of I-type heterojunction with Nb 2 O 5 further enhances the carrier separation efficiency, and the photocatalytic efficiency of OV-Bi 12 GeO 20 /Nb 2 O 5 is increased to 94.525 %. OV-Bi 12 GeO 20 /Nb 2 O 5 is immobilized onto chitosan (CTS) via a glutaraldehyde cross-linking strategy. Owing to its abundant hydroxyl and amino functional groups, CTS demonstrates strong adsorption capacity for Cr(VI). After 5 cycles of use, its photocatalytic performance remained at approximately 98.35 % of the initial level. Experimental and mechanistic analyses reveal that OVs function as e − traps, promoting the separation of photo-generated charge carriers, while the I-type heterojunction facilitates the efficient reduction of Cr(VI) by enabling directed charge migration.