Benzothiadiazole functionalized D–A type covalent organic frameworks for effective photocatalytic reduction of aqueous chromium( vi )

Covalent organic frameworks (COFs) have received increasing research interest as an emerging class of crystalline and porous polymers. Herein, we prepared two new benzothiadiazole (BT) functionalized COFs ( i.e. TPB-BT-COF and TAPT-BT-COF), which exhibit good crystallinity, high porosity, and excellent stability in harsh conditions. Their applications for photoreduction of Cr( vi ) species under visible light irradiation were investigated. Over 99% Cr( vi ) was reduced by utilizing TPB-BT-COF as catalyst without any sacrificial agents or additional pH adjustment. The photocatalytic rate of TPB-BT-COF is faster than that of TAPT-BT-COF, which can be attributed to more negative conduction band and narrower bandgap. Our results indicate that co-condensation of electron deficient units into the COF skeleton is conducive to efficient separation of photoexcited electrons and holes, which in turn leads to superior photocatalytic activities.