TiO2-promoted electron-tunneling of COF-based MIS nanostructures for efficient photocatalytic hydrogen production

Abstract

Crystalline and porous covalent organic frameworks (COFs) have attracted extensive attention due to their excellent performance in visible-light-driven hydrogen production. However, further enhancing the separation of photogenerated electron-hole pairs in COFs remains a considerable challenge. Here, we aim to tune semiconductor structures in metal-insulator-semiconductor systems to enhance the separation of the photogenerated carriers in the whole system. The visible-light-driven photocatalytic hydrogen production rate over triformylphloroglucinol (TP)-COF/TiO2 heterojunction which in the case of using polyvinyl pyrrolidone-capped Pt nanoparticles as the cocatalyst is up to 25.9 mmol g-1 h-1, this is three times higher than that of pure TP-COF and ten times higher than TP-COF/TiO2 with Pt as the cocatalyst, respectively. The enhanced photocatalytic performance can not only attribute to the existence of TiO2 acting as the electron collector and transporter but also benefit from the photogenerated electrons that can smoothly tunnel into the Pt nanoparticles by the electrostatic field between the semiconductor and the insulating layer in the metal-insulator-semiconductor system. Both result in more efficient charge separation and greater photoexcitation rates.