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

Gao, Meng-Yao, Li, Chang-Cheng, Tang, Hong-Liang, Sun, Xiao-Jun, Dong, Hong, Zhang, Feng-Ming
Journal of materials chemistry A 2019 v.7 no.35 pp. 20193-20200
dimethylformamide, electrons, hydrogen, hydrogen production, irradiation, light, models, molybdenum disulfide, photocatalysis, photocatalysts, porous media
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.