A thiazolo[5,4-d]thiazole functionalized covalent triazine framework showing superior photocatalytic activity for hydrogen production and dye degradation

Abstract

Covalent triazine frameworks (CTFs) which contain triazine ring structures similar to that of graphitic carbon nitride (g-C₃N₄) have a strong conjugation system, excellent visible light absorption capacity, and high chemical stability. The flexibility to design synthetic monomers endows CTFs with diverse structural modes and preparation methods. Therefore, these fantastic materials have presented unique advantages as photocatalysts applied in the fields of photocatalytic hydrogen production and photodegradation of pollutants. The photocatalytic activity of CTFs benefits from the triazine moiety, but its photocatalytic performance still needs to be improved. The introduction of photoactive functional moieties is an effective way to improve the photocatalytic performance of CTFs. Here, we report a microstructural modulation strategy to improve the photocatalytic performance of CTFs. The representative material named CTF-NWU-1 was synthesized through a condensation reaction between terephthalimidamide and 4,4′-(thiazolo[5,4-d]thiazole-2,5-diyl)dibenzaldehyde. To verify the role of thiazolo[5,4-d]thiazole heterocycles in photocatalysis, a reference polymer, CTF-NWU-2, was synthesized by replacing the aldehyde monomer with 1,4-di(4-formylphenyl)benzene. Optical and electrical tests show that CTF-NWU-1 has a narrower energy band and a more efficient electron–hole separation and transfer capability compared to CTF-NWU-2. Impressively, the photocatalytic hydrogen production reaction rate of CTF-NWU-1 was as high as 17 600 μmol h⁻¹ g⁻¹, while the hydrogen production rate of CTF-NWU-2 was only 4100 μmol h⁻¹ g⁻¹. The CTF-NWU-1 also demonstrates photocatalytic activity for the degradation of dyes without Pt loading. The photocatalytic degradation of both rhodamine B (20 mg L⁻¹) and tetracycline hydrochloride (20 mg L⁻¹) with CTF-NWU-1 (0.2 mg mL⁻¹) can be accomplished within 30 minutes. Furthermore, its photocatalytic degradation activity remained almost constant during the five cycles of testing. This study shows that the introduction of n-type semiconductors into CTFs can significantly improve photocatalytic activity.