Boosting visible-light-driven hydrogen evolution of covalent organic frameworks through compositing with MoS2: a promising candidate for noble-metal-free photocatalysts

Abstract

Covalent Organic Frameworks (COFs) as an emerging class of crystalline and porous materials have exhibited excellent visible-light-driven H₂ generation activity in more recent years. However, noble metal co-catalysts are inevitable even in all COF-based photocatalysts to realize a high hydrogen evolution rate. In this work, for the first time we present a noble-metal free but more efficient COF-based photocatalytic H₂ evolution system. We chose a typical ketoenamine-based TpPa-1-COF as a model and integrated it with MoS₂ to construct MoS₂/TpPa-1-COF composites by in situ growth of the TpPa-1-COF in an exfoliated MoS₂ dispersion solution of N,N-dimethylformamide (DMF). The results of photocatalytic H₂ evolution under visible light irradiation show that the MoS₂/TpPa-1-COF composite with an optimized amount of 3 wt% MoS₂ loading exhibits a H₂ evolution rate of 55.85 μmol h⁻¹ (10 mg photocatalyst) without any noble metal in the catalytic system, and the apparent quantum efficiency is 0.76% at 420 nm. In comparison, this H₂ evolution rate of the MoS₂-3%/TpPa-1-COF composite is 32 times as high as that of the pure TpPa-1-COF (1.72 μmol h⁻¹) and even a little better than that of the Pt/TpPa-1-COF (54.79 μmol h⁻¹) with the same Pt loading (3 wt%). Further investigation demonstrates that MoS₂ in the composite, acting as an effective non-noble-metal co-catalyst, can enormously facilitate the transfer of photogenerated electrons from the COF to MoS₂ and improve the separation of photogenerated charges, leading to the excellent H₂ evolution activity of the resulting composite. Considering the promising future of COF-based photocatalysts and the first report of noble-metal-free photocatalysts of COFs, this work may provide an avenue for the further design and synthesis of low-cost COF-based photocatalysts for efficient H₂ evolution.