Photocatalytic Reduction of Cr(VI) by MOF@Azo-COF Under Strongly Acidic Conditions.

Cr(VI) poses a serious threat to the ecosystem and human health; in order to efficiently remove Cr(VI), a stable MOF@COF core-shell photocatalyst (MOF-808@TpAzo) was developed. Through a post-modification strategy, MOF-808 was functionalized with amino groups on its surface. Subsequently, the TpAzo-based covalent organic framework (COF) was grown in-situ on its surface, successfully yielding the core-shell structured MOF-808@TpAzo composite. Under highly acidic conditions, the MOF-808@TpAzo composite shows an excellent photocatalytic reduction of Cr(VI) performance, which is significantly better than that of its single component. Especially, as little as 5 mg of the catalyst, 99.42% of Cr(VI), was removed from the acidic simulated wastewater within 120 min, and the material exhibited excellent cycling stability. The highly effective catalysis is attributed to the heterojunction formed via the covalent connection between the MOF and COF components, promoting charge separation and transport. This work provides a new alternative for developing stable photocatalysts capable of the reduction of Cr(VI) in strongly acidic environments.