ABSTRACT
Metal-organic frameworks (MOFs) can be constructed using conventional molecular linkers or polymeric linkers (polyMOFs), but the relationship and relative properties of these related materials remain understudied. As an intermediate between these two extremes, a library of oligomeric ligand precursors (dimers, trimers) was used to prepare a series of oligomeric-linker MOFs (oligoMOFs) based on the prototypical IRMOF-1 system. IRMOF-1 was found to be remarkably tolerant to a wide variety of oligomeric linkers, the use of which greatly enhanced the MOF yield and prevented framework interpenetration. Tether length-dependent ordering of ligand and metal cluster orientations was also observed in these oligoMOFs. Improved low-humidity stability was found in oligoIRMOF-1 samples, with surface area preservation varying as a function of tether length and a complete suppression of crystalline hydrolysis products for all oligoIRMOF-1 materials. These findings pave the way toward a better understanding of the structure-function relationships between monomeric, oligomeric, and polymeric MOFs and highlight an underutilized strategy for tuning MOF properties.
ABSTRACT
Linker exchange is a widely applied, robust technique for elaboration of metal-organic frameworks (MOFs) post-synthesis. The observation of core-shell microstructures under certain conditions was hypothesized to arise from diffusion rates into the MOF that are slower than linker exchange. Here the relative contributions of these processes are manipulated through solvent choice in order to modulate shell thickness and exchange extent. The findings allow tailoring MOF microstructure to application.
ABSTRACT
Metal-organic frameworks (MOFs) are generally synthesized in toxic formamide solvents. Greener solvents would lower production barriers and facilitate applications such as drug delivery. N,N-Diethyl-3-methylbenzamide (DEET), the most widely used insect repellent, is shown to serve this role. Furthermore, DEET-loaded MOFs can be leveraged in controlled-release insect repellent formulations.
ABSTRACT
Measuring the acidity of atmospheric aerosols is critical, as many key multiphase chemical reactions involving aerosols are highly pH-dependent. These reactions impact processes, such as secondary organic aerosol (SOA) formation, that impact climate and health. However, determining the pH of atmospheric particles, which have minute volumes (10-23-10-18 L), is an analytical challenge due to the nonconservative nature of the hydronium ion, particularly as most chemical aerosol measurements are made offline or under vacuum, where water can be lost and acid-base equilibria shifted. Because of these challenges, there have been no direct methods to probe atmospheric aerosol acidity, and pH has typically been determined by proxy/indirect methods, such as ion balance, or thermodynamic models. Herein, we present a novel and facile method for direct measurement of size-resolved aerosol acidity from pH 0 to 4.5 using quantitative colorimetric image processing of cellular phone images of (NH4)2SO4-H2SO4 aqueous aerosol particles impacted onto pH-indicator paper. A trend of increasing aerosol acidity with decreasing particle size was observed that is consistent with spectroscopic measurements of individual particle pH. These results indicate the potential for direct measurements of size-resolved atmospheric aerosol acidity, which is needed to improve fundamental understanding of pH-dependent atmospheric processes, such as SOA formation.
