Porphyrin-based metal-organic frameworks for solar fuel synthesis photocatalysis: band gap tuning via iron substitutions

Abstract

Photocatalysts based on metal-organic frameworks (MOFs) are very promising due to a combination of high tuneability and convenient porous structure. Introducing porphyrin units within MOFs is a potential route to engineer these natural photosynthesis molecular catalysts into artificial photosynthesis heterogeneous catalysts. Using computer simulations based on density functional theory, we explore how to modify the electronic structure of porphyrin-based MOFs to make them suitable for the photocatalysis of solar fuel synthesis via water splitting or carbon dioxide reduction. In particular, we have investigated the effect that Fe substitutions have on the electronic properties of porphyrin-based metal organic frameworks. By aligning the electron levels with a vacuum reference, we show that Fe at the porphyrin metal centre has the effect of slightly raising the position of the valence band edge, whereas Fe at the octahedral metal node has the ability to significantly lower the position of the conduction band edge on the absolute scale. Iron is therefore a very useful dopant to engineer the band structure and alignment of these MOFs. We find that the porphyrin-based structure with Al in the octahedral sites and Zn in the porphyrin centres has a band gap that is slightly too wide to take advantage of visible-light solar radiation, while the structure with Fe in the octahedral sites has bandgaps that are too narrow for water splitting photocatalysis. We then show that the optimal composition is achieved by partial substitution of Al by Fe at the octahedral sites, while keeping Zn at the porphyrin centres. Our study demonstrates that porphyrinbased MOFs can be engineered to display intrinsic photocatalytic activity in solar fuel synthesis reactions.

Metal–Organic‐Framework‐Based Catalysts for Photoreduction of CO2

“…Furthermore, the functionalizations of organic linkers [94,95,97,98] and the modifications of the structures of metal clusters [99,100] in MOFs can both reduce their HOMO-LUMO gap width, leading to their expanded light-absorption capacity. Hence, most MOF photocatalysts can exhibit photocatalytic activities in a visible range, which is favorable to the improved light-utilization efficiency.…”

Non-thermal plasma-assisted catalytic CO2 conversion over Zn-TCPP 2D catalyst

“…These semiconductor materials have been extensively investigated and applied in photocatalytic processes, including water splitting and CO 2 reduction as a heterogeneous photocatalyst under visible light (Amayuelas et al 2017). For example, some porphyrin-containing MOFs structures have been applied in photocatalysis (Amayuelas et al 2017), photovoltaic systems (Spoerke et al 2017;Aziz et al 2017) and for photoelectron transfer (Ishihara and Tian 2018). Moreover, their photocytotoxic activity have found application in photodynamic therapy (Buzek et al 2017;Kan et al 2018).…”

Structure, Properties, and Reactivity of Porphyrins on Surfaces and Nanostructures with Periodic DFT Calculations

“…Furthermore, it was shown that the MOFs' band edges align with the redox potentials ( Figure 4b) for water splitting and carbon dioxide reduction with reactions that can occur at neutral pH. This study was followed up with another PDFT study by Aziz et al [4] by modifying the octahedral Aluminum metal center of the lattice structure with Fe +3 metal to determine the changes in the band structure and electronic properties of PMOFs. It was reported that adding Fe at the porphyrin core slightly raises the valence band edge, while Fe at the octahedral node significantly lowers the conduction band edge.…”

“…Porphyrins also have numerous biomedical applications including photoimmunotherapy, photo diagnosis [1], biosensors [2], cancer therapy, etc. Porphyrins also play an important role in organic synthesis of dendrimers [3], metal-organic frameworks (MOFs) [4], biomimetic reactions [5], and as photo-catalysts [6] in numerous oxidation/reduction reactions. Finally, porphyrins act as important components in various technological applications like solar cells [7], chemical sensors [8], optoelectronics [9], spintronics [10], field effect transistors (FETs) [11][12][13][14], and in nanotechnology like single molecule junctions [15], nanowires, nanomotors [10], etc.…”