Bandgap Modulation in Zr-Based Metal–Organic Frameworks by Mixed-Linker Approach

Abstract

Metal–organic frameworks (MOFs) have been a promising material for many applications, e.g., photocatalysis, luminescence-based sensing, optoelectronics, and electrochemical devices, due to their tunable electronic properties through linker functionalization. In this work, we investigate the effect of mixed organic linkers on the bandgap modulation of polymorphic zirconium-based MOFs, UiO-66 and MIL-140A using density functional theory (DFT) calculations. We show that the electronic properties of both MOFs are in contrast to Vegard’s law for semiconductors, that is, mixed-linker systems exhibit bandgaps not intermediate within the range of single-linker systems. Calculations of the total and partial density of states revealed the formation of mid-gap states in mixed-linker MOFs, causing the bandgap reduction. Interestingly, although both MOFs have similar composition, the effect is more significant in MIL-140A than in UiO-66. This is due to the presence of π–π stacking interactions in MIL-140A, which does not occur in UiO-66. The simulation results reveal a direct relationship between the strength of π–π interactions and the bandgap. This illustrates that distinct structural features, particularly the orientation of organic linkers can give rise to different consequences in bandgap modulation. Moreover, this computational work highlights the possibility to engineer the electronic properties of MOFs through a mixed-linker approach.

Tailoring defect-type and ligand-vacancies in Zr(iv) frameworks for CO2 photoreduction

“…5a). 26,48,49 Mott–Schottky plots with positive slopes in Fig. S16† indicate the n-type characteristic of the samples.…”

Effect of the Defect Modulator and Ligand Length of Metal–Organic Frameworks on Carbon Dioxide Photoreduction

“…The orbital composition DOS of the above samples demonstrates that in the first step of photocatalysis, E abs is controlled by the HOMO and LUMO on the linker as their pristine ones, which almost equals their band gap (vide post, Figure S26). , Diffuse reflectance ultraviolet–visible–near-infrared (UV–vis–NIR) spectroscopy was employed to investigate the optoelectronic properties of these samples. As shown in Figure b, all the samples have optical absorption in the UV–vis region, and the defects formed by the amino-modified modulators influence the absorption feature throughout the visible-light range as UiO-68-NH 2 -2ABA, UiO-67-NH 2 -2ABA, and UiO-66-NH 2 -2ABA all represent a broad absorption in the visible range of 400–800 nm due to the catoptric light reflected by the nut-brown color of the powder.…”

“…The orbital composition DOS of the above samples demonstrates that in the first step of photocatalysis, E abs is controlled by the HOMO and LUMO on the linker as their pristine ones, which almost equals their band gap (vide post, Figure S26). 26,37 Diffuse reflectance ultraviolet−visible−near- In order to survey the separation and transformation behaviors of photoinduced electrons, photoelectrochemical measurements were conducted by means of time-resolved fluorescence decay spectroscopy, photoluminescence (PL) emission spectroscopy, transient photocurrent response measurement, and electrochemical impedance spectroscopy (EIS). Time-resolved fluorescence decay spectroscopy, whose results are shown in Figure 4a, is employed to examine the photoexcited carrier transfer dynamics of the six samples.…”

Directing the Morphology, Packing, and Properties of Chiral Metal–Organic Frameworks by Cation Exchange**

“…Such proposed dynamic behavior is more likely to occur with pyridine linkers that have a moderate ligand field strength than with hard ligands such as carboxylic acids. [36] Engineering of the optical properties of MOFs can be achieved by anion exchange, [88] ligand modifications, [89][90][91][92] doping MOFs with metal ions, and metal ion inclusions. [88,[93][94][95] In our MOFs, the different metal cations strongly affect the electronic and vibronic properties reflected in ligand-to-metal and metal-to-ligand charge transfer contributions and notable changes in the fluorescence properties.…”