Exploring the Parameter Space of p-Cresyl Sulfate Adsorption in Metal–Organic Frameworks

Abstract

Metal–organic frameworks (MOFs) have high porosity and surface area, making them ideal candidates for adsorption-mediated applications. One high-value application is the removal of uremic toxins from solution for dialysis. Previous studies have reported adsorptive removal of the uremic toxin p-cresyl sulfate from solution via zirconium-based MOFs, but a specific analysis of parameters contributing to adsorptive uptake is needed to clarify differences in uptake performance between MOFs. We synthesized zirconium 1,3,5-benzenetricarboxylate (MOF-808) and an iron-based analog, MIL-100­(Fe), and compared their adsorptive uptake with previously reported values of other zirconium-based MOFs. MIL-100­(Fe) adsorbed three times more p-cresyl sulfate from solution on a per mass basis than MOF-808 and had a greater adsorption efficiency than 75% of previously reported Zr-based MOFs. We compared p-cresyl sulfate uptake by MOFs as a function of BET surface area, number of aromatic carbons in the organic linker, internal cage diameter, and pore window diameter. There is poor correlation between p-cresyl sulfate uptake and each of the variables considered, but the number of aromatic carbons of the MOF linker was a better predictor of uptake than BET surface area (R 2 = 0.7034 and 0.1430, respectively), and pore window aperture was a better predictor of uptake than the pore cage diameter (R 2 = 0.4780 and 0.0383, respectively). We hypothesize that the greater adsorptive capacity of MIL-100­(Fe) compared to MOF-808 results from direct coordination of p-cresyl sulfate to vacant metal sites in the MOF, and the total adsorption may be accounted for by some combination of adsorptive interactions occurring at both metal and organic linker sites near to the exterior particle surface. The adsorptive uptake of p-cresyl sulfate by MIL-100­(Fe) was observed to increase with p-cresyl sulfate content, mass of MIL-100­(Fe), and volume of p-cresyl sulfate solution; the mass of MIL-100­(Fe) had the greatest effect on total adsorption.

Improved Dialysis Removal of Protein-Bound Uraemic Toxins with a Combined Displacement and Adsorption Technique

“…Therefore, to further enhance PBUTs removal, it may be necessary to consider alternative approaches, such as the use of adsorbent technology. Adsorptive devices can be coupled to the bloodstream or can be directly brought into the dialysate to generate a virtual sink, and thus to maintain a diffusive concentration gradient across the dialyser fibre during the HD session [28][29][30][31][41][42][43][44][45]. So far, 2 major types of absorbents for the removal of PBUTs have been developed.…”

Recent trends in therapeutic application of engineered blood purification materials for kidney disease

“…Metal-organic framework (MOF) is one kind of novel hybrid material, which has high thermal and chemical stability, and has been demonstrated to be more effective than AC or mesoporous silica materials, due to its ultrahigh porosity and active sites [ 40 – 42 ]. And BET surface area and internal MOF cage diameter have been previously hypothesized as key parameters in the adsorption capacity of MOFs [ 43 ]. MOF is made of metal ions and organic linkers through coordinatebounds to form a 1D, 2D or 3D structure [ 40 , 44 ].…”

“…These two locations approximately have the same occupancy, where electrostatic interactions with hydroxyl groups on the Zr 6 nodes and π-π interactions with pyrene-based linkers are important factors in adsorption ability. However, Cuchiaro et al pointed out that application of NU-1000 is limited as it is commercially unavailable, and iron is a desirable alternative to zirconium [ 43 ]. Cuchiaro et al synthesized MIL-100(Fe) and MOF-808, both of which have the same organic linker with MOF-808 but MIL-100(Fe) is less toxic due to its iron-based metal nodes [ 43 ].…”

“…However, Cuchiaro et al pointed out that application of NU-1000 is limited as it is commercially unavailable, and iron is a desirable alternative to zirconium [ 43 ]. Cuchiaro et al synthesized MIL-100(Fe) and MOF-808, both of which have the same organic linker with MOF-808 but MIL-100(Fe) is less toxic due to its iron-based metal nodes [ 43 ]. They found p-cresyl sulfate uptake for MIL-100(Fe) was three times greater than that for MOF-808, which was less correlated to BET surface area, pore window size, cage diameter, and number of aromatic carbons in organic linker, indicating that metal-iron interactions maybe occurring more favorably in MIL-100(Fe) than MOF-808.…”

In Search of Effective UiO-66 Metal–Organic Frameworks for Artificial Kidney Application

“…From among the literature reports on the use of materials such as zeolites, carbon nanotubes, ordered mesoporous carbon, and metal–organic frameworks (MOF), − the latter seems to be a relatively unexplored area. Although metal–organic frameworks have been successfully used in various applications including gas adsorption and separation, adsorption of toxins, , environmental protection, , catalysis, − medicine, and drug release, , their use as effective adsorbents of uremic toxins is currently undergoing intensive research. − …”