Controlled Morphological Transformation, Photocatalytic Properties, and Electrocatalytic OER Performance of Fe-MOF Nanopolyhedra

In this work, we prepared a series of Fe-MOF polyhedra [metal organic framework (MOF)-1 similar to -13] by introducing beta-cyclodextrin (CD) as a morphology modifier using an interaction between ferric chloride and terephthalic acid in dimethylformamide. A novel structural evolution from a hexagonal bipyramid to a bipyramidal hexagonal prism was clearly observed. This evolution was gradual and could be well reflected by the height ratio of the prism and pyramid in these polyhedral structures. It is the relative concentration of beta-CD that drives this structural evolution. Although the reaction temperature and time can also affect the height ratio to some extent, their influence can only be realized in the presence of beta-CD. In the absence of beta-CD, only hexagonal bipyramid structures were obtained. It is worth noting that Fe-MOF-1 with a bipyramidal hexagonal prism structure (prism height, similar to 130 nm) showed typical paramagnetic characteristics, and its saturation magnetization was determined to be 23.1 emu.g(-1). Furthermore, we found that Fe-MOF-1 exhibited good photocatalytic performance for different types of dyes (crystal violet with positives and methyl orange with negative charges). At the same time, a possible photocatalytic mechanism was proposed to explain the difference of degradation efficiency between the two dyes. Also, we use the combination of specific surface area and zeta potential to explain the differences in the catalytic properties of a series of Fe-MOF materials. In addition, MOF-1 shows the same electrocatalytic oxygen evolution reaction performance as some bimetallic MOFs such as Fe-Co-MOF. For example, the overpotential of MOF-1 is 398 mV at 10 mA.cm(-2) current density, while that of Fe-Co-MOF is 410 mV. We believe that the current work can contribute to the adjustment, modification, and application of MOF nanostructures.

Automated summary

In this work, Fe-MOF polyhedra were successfully prepared by introducing beta-cyclodextrin as a morphology modifier. A novel structural evolution was observed from a hexagonal bipyramid to a bipyramidal hexagonal prism. The presence of beta-CD drives this evolution, with different structures exhibiting different magnetic and catalytic properties, as well as good photocatalytic performance for various dyes.