ABSTRACT
Metal-organic framework (MOF)-based materials possess numerous attractive characteristics; however, the application of MOF-based photocatalysts in the area of visible-light photocatalytic H2 evolution is still in its infancy. Herein, we develop a series of novel UiO-66-NH2-based composites with embedded NiO nanoparticles via solvothermal treatment and subsequent calcination. Their characterizations demonstrate intimate lattice-level contacts between UiO-66-NH2 photocatalysts and NiO nanoparticles. By optimizing each component, even without noble metal loading, the U6N-NiO-2 sample (the weight ratio of NiO to U6N-NiO-2 is theoretically calculated to be ca. 10 wt%) with 15 mg eosin Y as a sensitizer causes an enhanced H2 generation rate of 2561.32 µmol h-1 g-1 under visible-light irradiation using TEOA as a sacrificial reagent; furthermore, its corresponding quantum efficiency is as high as 6.4% at 420 nm. The H2 evolution activity of U6N-NiO-2 is about 5 times higher than that of the UiO-66-NH2 photocatalyst (denoted as U6N) and 23 times higher than that of U6N-NiO-2 without sensitizer. It is demonstrated that the high efficiency originates from the visible-light generated electrons of eosin Y and UiO-66-NH2, the efficient separation of carriers by the cascaded band structure and more negative CB of NiO as well as the good dispersion of NiO nanoparticles on the octahedral skeleton. This study provides new insights for the design of MOF-based materials without noble metal loading for visible-light photocatalytic H2 evolution.
ABSTRACT
The design and development of highly efficient and long lifetime Pd-based catalysts for hydrogenation reactions have attracted significant research interest over the past few decades. Rational selection of supports for Pd loadings with strong metal-support interaction (SMSI) is beneficial for boosting catalytic activity and stability. In this context, we have developed a facile approach for uniformly immobilizing ultra-small Pd nanoparticles (NPs) with a clean surface on a Pr6O11 support by a hydrogen thermal reduction method. The hydrogenations of p-nitrophenol and styrene are used as model reactions to evaluate the catalytic efficiency. The results show highly efficient styrene hydrogenation performance under 1 atm H2 at room temperature with a TOF value as high as 8957.7 h-1, and the rate constant value of p-nitrophenol reduction is 0.0191 s-1. Strong metal-support interaction and good dispersion of Pd nanoparticles, as demonstrated by XPS and HRTEM results, contribute to the excellent hydrogenation performance. Electron paramagnetic resonance (EPR) results suggest the presence of oxygen vacancies in the support, which serve as electron donors and enhance the adsorption and activation of reactants and subsequent conversion into products. Moreover, the catalyst can be recovered and reused up to 10 consecutive cycles without marked loss of activity. Overall, our results indicate that oxygen-deficient Pr6O11 nanorods (NRs) not only play a role as support but also work as the promoter to substantially boost the catalytic activities for organic transformations, therefore, providing a novel strategy to develop other high-performance nanostructured catalysts for environmental sustainability.
