New Paper in ACS catalysis

Abstract

Covalent triazine-based frameworks (CTFs), a group of semi-conductive polymers, have been identified for photocatalytic water splitting recently. Their adjustable band gap and facile processing offer great potential for new discovery and development. Here, we present a series of CTF-0 materials fabricated by two different approaches, a microwave-assisted synthesis and an ionothermal method, for water splitting driven by visible light irradiation. The material (CTF-0-M2) synthesized by microwave technology shows a high photocatalytic activity for hydrogen evolution (up to 7010 µmol h-1 g-1), which is 7 times higher than another (CTF-0-I) prepared by conventional ionothermal trimerization under identical photocatalytic conditions. This leads to a high turnover number (TON) of 726 with respect to the platinum co-catalyst after seven cycles. We attribute this to the narrowed band gap, the most negative conduction band and the rapid photogenerated charge separation and transfer. On the other hand, the material prepared by the ionothermal method is the most efficient for oxygen evolution. CTF-0-I initially produces ca. 6 times greater volumes of oxygen gas than CTF-0-M2 under identical experimental conditions. CTF-0-I presents an apparent quantum efficiency (AQY) of 5.2% at 420 nm for oxygen production without any co-catalyst. The activity for water oxidation exceeds that of most reported CTFs due to a large driving force for oxidation and a large number of active sites. Our findings indicate that the band positions and the interlayer structures of CTF-0 were modulated by varying synthesis conditions. These modulations impact the optical and redox properties, resulting in an enhanced performance for photocatalytic hydrogen and oxygen evolution, confirmed by first principles calculations.