Effective design and synthesis of donor-acceptor covalent triazine polymers with boosted photocatalytic performance for Cr(VI) reduction

Two new donor-acceptor covalent triazine polymers (CTPs), namely Th-Trz (JOU-6) and Th-Ph-Trz (JOU-7), containing electron-donating thieno[2,3-b]thiophene (Th) units and electron-withdrawing triazine (Trz) units have been successfully constructed (Ph = benzene ring). The unique conjugated structure of the CTPs invokes wide absorption range and high charge transfer efficiency. Because of these advantages, the as-prepared CTPs are highly effective photocatalysts for Cr(VI) reduction. It is found that high acid concentration in the photocatalytic system may assist the protonation of triazine groups in CTPs, which not only can enhance their adsorption ability for Cr2O72-, but also can promote their charge transfer ability. Another important finding is that compared with JOU-6, JOU-7 shows more efficient charge separation owing to the introduction of benzene ring between the donor and acceptor units, inducing a spatial separation of photogenerated electrons and holes, and thereby giving a better photocatalytic performance. The spatial charge distribution of the CTPs was also investigated by theoretical calculation based on molecular orbital theory. Fascinatingly, Cr(VI) and organic pollutions can be simultaneously removed by JOU-7 without any sacrificial agents, oxidizer, or acid. This work provides a valuable strategy for the design and construction of effective photocatalysts for the removal of pollutants in wastewater.