Surface Engineering of 2D Metal-Porphyrin Metal-Organic Frameworks Z-Scheme Heterostructure for Boosting and Stable Photocatalytic Hydrogen Evolution

How to improve the stability and activity of metal-organic frameworks is an attractive but challenging task in energy conversion and pollutant degradation of metal-organic framework materials. In this paper, a facile method is developed by fabricating titanium dioxide nanoparticles (TiO2 NPs) layer on 2D copper tetracarboxylphenyl-metalloporphyrin metal-organic frameworks with zinc ions as the linkers (ZnTCuMT-X, "Zn" represented zinc ions as the linkers, the first "T" represented tetracarboxylphenyl-metalloporphyrin (TCPP), "Cu" represented the Cu2+ coordinated into the porphyrin macrocycle, "M" represented metal-organic frameworks, the second "T" represented TiO2 NPs layer, and "X" represented the added volume of n-tetrabutyl titanate (X = 100, 200, 300 or 400)). It is found that the optimized ZnTCuMT-200 showed greatly and stably enhanced H2 generation, which is approximate to 28.2 times and 47.0 times as high as those of the original ZnTCuM and TiO2, respectively. Combined with the results of free radical capture, X-ray photoelectron spectra (XPS), electron spin resonance (ESR), and theoretical calculation, a direct Z-scheme electron transfer mechanism is achieved to fully explain the enhanced photocatalytic performance. It demonstrates that facilely designing Z-scheme heterostructures based on porphyrin MOFs modified with an inorganic semiconductor layer can be an advantageous strategy for enhancing the stability and activity of photocatalytic hydrogen evolution.