Experimental Demonstration of Dynamic Temperature-Dependent Behavior of UiO-66 Metal–Organic Framework: Compaction of Hydroxylated and Dehydroxylated Forms of UiO-66 for High-Pressure Hydrogen Storage

Abstract

High-pressure (700 MPa or~100 000 psi) compaction of dehydroxylated and hydroxylated UiO-66 for H2 storage applications is reported. The dehydroxylation reaction was found to occur between 150 -300 o C. The H2 uptake capacity of powdered hydroxylated UiO-66 reaches 4.6 wt% at 77 K and 100 bar, which is 21% higher than that of dehydroxylated . On compaction the H2 uptake capacity of dehydroxylated UiO-66 pellets reduces by 66% from 3.8 wt% to 1.3 wt%, while for hydroxylated UiO-66 the pellets show only a 9% reduction in capacity from 4.6 wt% to 4.2 wt%. This implies the H2 uptake capacity of compacted hydroxylated UiO-66 is at least three times higher than that of dehydroxylated UiO-66, and therefore hydroxylated UiO-66 is more promising for hydrogen storage applications. The H2 uptake capacity is closely related to compaction induced changes in the porosity of UiO-66. The effect of compaction is greatest in partially dehydroxylated UiO-66 samples that are thermally treated at 200 and 290 o C. These compacted samples exhibit XRD patterns indicative of an amorphous material, low porosity (surface area reduces from between 700 and 1300 m 2 /g to ca. 200 m 2 /g and pore volume from between 0.4 and 0.6 cm 3 /g to 0.1 and 0.15 cm 3 /g) and very low hydrogen uptake (0.7 -0.9 wt% at 77 K and 100 bar). The observed activation temperature-induced dynamic behaviour of UiO-66 is unusual for MOFs and has previously only been reported in computational studies. After compaction at 700 MPa, the structural properties and H2 uptake of hydroxylated UiO-66 remain relatively unchanged, but are extremely compromised upon compaction of dehydroxylated UiO-66. Therefore, UiO-66 responds in a dynamic manner to changes in activation temperature within the range in which it has hitherto been considered stable.

Mechanochemical Synthesis of Nickel-Modified Metal–Organic Frameworks for Reduction Reactions

“…Such results confirmed both the successful synthesis of UiO-66 MOFs and the suitability of the mechanochemical approach for the modification of MOFs with metal entities. Even if the presence of both peaks related to the main crystallographic planes of UiO-66 indicated the retention of the crystal structure, certain amorphization occurred after the incorporation of higher Ni amounts in the sample [25,26]. Magnified XRD diffractograms (Figure 2B-E) revealed the typical characteristic pattern UiO-66 but with a clear decrease in crystallinity in the samples with 3 and 5% Ni.…”

Defect Engineering in Metal–Organic Frameworks Towards Advanced Mixed Matrix Membranes for Efficient Propylene/Propane Separation

“…[13a] This is attributed to the collapse of the crystalline structure caused by the harsh activation condition, which in turn drastically diminishes the porosity of UiO-TF36 despite the most increased concentration of open metal sites. [16] In this regard, we chose an intermediate activation temperature of 200 8 8Cf or defectengineered UiO-66 throughout the following studies,e nsuring the presence of open metal sites formed by the partial removal of modulators as well as the maintained original porous structure.…”

Recent advancement in consolidation of MOFs as absorbents for hydrogen storage

“…82 Recently, attempt was made to study the effect of compaction on dehydroxylated and hydroxylated UiO-66 for hydrogen storage applications. 141 The gravimetric H 2 capacity of 4.6 wt% was and 3.8 wt% were obtained on powder hydroxylated and dehydroxylated UiO-66 respectively at 77K and 100 bar. However, a significant reduction was observed in the gravimetric hydrogen capacity of compacted dehydroxylated Zr-MOF compared to the hydroxylated compacts.…”

“…However, high compression pressure of MOFs resulted in pellet with narrow pore apertures which yielded low volumetric and gravimetric H 2 useable capacities. 141,142 Recently, Chen et al 143 reported BET surface area of 7310 m 2 g −1 and volumetric BET surface area of 2060 m 2 cm −3 for NU-1501-Al. High gravimetric and volumetric storage capacities of 14.0 wt% and 46.2 g/L respectively were obtained under temperature and pressure swing of 77K/100 bar to 160K/5 bar.…”