Samuel A. Morris

Expansion of the ADOR Strategy for the Synthesis of Zeolites: The Synthesis of IPC-12 from Zeolite UOV

Abstract The assembly–disassembly–organization–reassembly (ADOR) process has been used to disassemble a parent zeolite with the UOV structure type and then reassemble the resulting layers into a novel structure, IPC‐12. The structure of the material has previously been predicted computationally and confirmed in our experiments using X‐ray diffraction and atomic resolution STEM‐HAADF electron microscopy. This is the first successful application of the ADOR process to a material with porous layers.

In situ solid-state NMR and XRD studies of the ADOR process and the unusual structure of zeolite IPC-6

The assembly–disassembly–organization–reassembly (ADOR) mechanism is a recent method for preparing inorganic framework materials and, in particular, zeolites. This flexible approach has enabled the synthesis of isoreticular families of zeolites with unprecedented continuous control over porosity, and the design and preparation of materials that would have been difficult—or even impossible—to obtain using traditional hydrothermal techniques. Applying the ADOR process to a parent zeolite with the UTL framework topology, for example, has led to six previously unknown zeolites (named IPC-n, where n = 2, 4, 6, 7, 9 and 10). To realize the full potential of the ADOR method, however, a further understanding of the complex mechanism at play is needed. Here, we probe the disassembly, organization and reassembly steps of the ADOR process through a combination of in situ solid-state NMR spectroscopy and powder X-ray diffraction experiments. We further use the insight gained to explain the formation of the unusual structure of zeolite IPC-6. The assembly–disassembly–organization–reassembly (ADOR) process has recently enabled the synthesis of unusual — and sometimes previously inaccessible — inorganic materials. Further insight into its complex mechanism has now been gained that explains the unexpected formation and structure of such a zeolite.

Hydrolytic stability in hemilabile metal–organic frameworks

Highly porous metal–organic frameworks (MOFs), which have undergone exciting developments over the past few decades, show promise for a wide range of applications. However, many studies indicate that they suffer from significant stability issues, especially with respect to their interactions with water, which severely limits their practical potential. Here we demonstrate how the presence of ‘sacrificial’ bonds in the coordination environment of its metal centres (referred to as hemilability) endows a dehydrated copper-based MOF with good hydrolytic stability. On exposure to water, in contrast to the indiscriminate breaking of coordination bonds that typically results in structure degradation, it is non-structural weak interactions between the MOF’s copper paddlewheel clusters that are broken and the framework recovers its as-synthesized, hydrated structure. This MOF retained its structural integrity even after contact with water for one year, whereas HKUST-1, a compositionally similar material that lacks these sacrificial bonds, loses its crystallinity in less than a day under the same conditions.The promise shown by metal–organic frameworks for various applications is somewhat dampened by their instability towards water. Now, an activated MOF has shown good hydrolytic stability owing to the presence of weak, sacrificial coordination bonds that act as a ‘crumple zone’. On hydration, these weak bonds are cleaved preferentially to stronger coordination bonds that hold the MOF together.

Monitoring the assembly–disassembly–organisation–reassembly process of germanosilicate UTL through in situ pair distribution function analysis

A study into the disassembly and organisation steps of the ADOR process has been undertaken through in situ Pair Distribution Function (PDF) analysis. Three aqueous systems (water, 6 M HCl and 12 M HCl) were introduced to a parent zeolite germanosilicate UTL in a cell. Hydrolysis could be clearly seen when UTL was exposed to water over a period of 8 h, forming the disorder layered material, IPC-1P. In hydrochloric acid, the hydrolysis step is too quick to observe and a Ge–Cl containing species could be seen. In 6 M HCl, the rearrangement of the interlayer region began after an induction period of 8 h, with the process still occurring after 15 h. In 12 M HCl, the rearrangement appears to have come to an end after only 6 h.

Microwave heating and the fast ADOR process for preparing zeolites

The microwave assisted ADOR process was applied to quickly disassemble zeolites IWW and UTL in acidic media and obtain the novel IPC-5 zeolite from IWW and a variant of the IPC-6 structure from UTL. XRD and Cs aberration-corrected STEM were used to characterise the structures. The results show that the speed of the process can be vastly increased using microwave heating.

Physisorption-induced structural change directing carbon monoxide chemisorption and nitric oxide coordination on hemilabile porous metal organic framework NaNi3(OH)(SIP)2(H2O)5·H2O (SIP = 5-sulfoisophthalate)

Structural changes occur during the thermal activation of NaNi3(OH)(SIP)2(H2O)5·H2O and NaCo3(OH)(SIP)2(H2O)5·H2O to form porous framework materials. Activation of NaNi3(OH)(SIP)2(H2O)5·H2O at 400 K gave NaNi3(OH)(SIP)2(H2O)2 and 513 K gave NaNi3(OH)(SIP)2. CO adsorption/desorption on NaNi3(OH)(SIP)2(H2O)2 at 348 K and 20 bar was hysteretic, but all CO was desorbed in vacuum. NaNi3(OH)(SIP)2(H2O)2 was exposed to NO to establish the accessibility of unsaturated metal centers and crystallographic results show that NO binds to Ni with bent coordination geometry. The adsorption characteristics of CO on isostructural NaNi3(OH)(SIP)2 and NaCo3(OH)(SIP)2 were studied over the temperature range 268–348 K and pressures up to 20 bar. CO surface excess isotherms for NaNi3(OH)(SIP)2 at 348 K were reversible and non-hysteretic for pressures below the isotherm point of inflection. However, above this point, isotherms had both reversible and irreversible adsorption components. The irreversible component remaining adsorbed in ultra-high vacuum at 348 K was 4.9 wt%. Subsequent sequential CO adsorption/desorption isotherms were non-hysteretic and fully reversible. The thermal stability and stoichiometry of the product were investigated by in situ temperature programmed desorption combined with thermogravimetric analysis and mass spectrometry. This gave a discrete CO peak at ∼500 K indicating thermally stable bonding of CO to the framework (0.42 × CO per formula desorbed (2.31 wt%)) and a weaker CO2 peak was observed at 615 K. The remaining adsorbed species were desorbed as a mixture of CO and CO2 overlapping with NaNi3(OH)(SIP)2 framework decomposition. CO physisorption induces structural change, which leads to CO chemisorption on NaNi3(OH)(SIP)2 above the point of inflection in the isotherm, with the formation of a new thermally stable porous framework. The porous structure of the framework was confirmed by CO2 adsorption at 273 K. Therefore, CO chemisorption is attributed to breaking of the hemilabile switchable sulfonate group, while the framework structural integrity is retained by the stable carboxylate linkers. In contrast, studies of CO adsorption on NaCo3(OH)(SIP)2 showed hysteretic isotherms, but no evidence for irreversible chemisorption CO was observed. The CO/N2 selectivity for NaNi3(OH)(SIP)2 and NaCo3(OH)(SIP)2 were 2.4–2.85 (1–10 bar) and 1.74–1.81 (1–10 bar). This is the first demonstration of physisorption driving structural change in a hemilabile porous framework material and demonstrates a transition from physisorption to irreversible thermally stable CO chemisorption.