Abstract
To aid the design of a hierarchically porous unconventional metal-phosphonate framework (HP-UMPF) for practical radioanalytical separation, a systematic investigation of the hydrolytic stability of bulk phase against acidic corrosion has been carried out for an archetypical HP-UMPF. Bulk dissolution results suggest that aqueous acidity has a more paramount effect on incongruent leaching than the temperature, and the kinetic stability reaches equilibrium by way of an accumulation of a partial leached species on the corrosion conduits. A variation of particle morphology, hierarchical porosity and backbone composition upon corrosion reveals that they are hydrolytically resilient without suffering any great degradation of porous texture, although large aggregates crack into sporadic fractures while the nucleophilic attack of inorganic layers cause the leaching of tin and phosphorus. The remaining selectivity of these HP-UMPFs is dictated by a balance between the elimination of free phosphonate and the exposure of confined phosphonates, thus allowing a real-time tailor of radionuclide sequestration. Moreover, a plausible degradation mechanism has been proposed for the triple progressive dissolution of three-level hierarchical porous structures to elucidate resultant reactivity. These HP-UMPFs are compared with benchmark metal-organic frameworks (MOFs) to obtain a rough grading of hydrolytic stability and two feasible approaches are suggested for enhancing their hydrolytic stability that are intended for real-life separation protocols.
Highlights
The insufficient chemical, thermal or mechanical stability of metal-organic frameworks (MOFs) under humid vapor, acidic/basic liquor, toxic chemicals or other critical environments remains a bottleneck for their large-scale application in storage, delivery, separation, transformation and detection of target species, despite ever-increasing reports of “stable” MOFs since the last decade [1,2,3]
Prior to the revelation of structure transformation, self-assembly of archetypical hierarchically porous unconventional metal-phosphonate framework (HP-unconventional metal-phosphonate frameworks (UMPFs)) can be proposed based on previous structural models [23,24]: (i) two anionic P–O groups or one neutral P=O group of each type of alkylphosphonate acids would strongly coordinate with tin(IV) in various bridging modes
This plausible degradation mechanism will afford a paradigm for the design of HP-UMPFs that enables the two crucial aspects together
Summary
The insufficient chemical, thermal or mechanical stability of metal-organic frameworks (MOFs) under humid vapor, acidic/basic liquor, toxic chemicals or other critical environments remains a bottleneck for their large-scale application in storage, delivery, separation, transformation and detection of target species, despite ever-increasing reports of “stable” MOFs since the last decade [1,2,3]. It becomes arguable that these benchmark MOFs are hydrolytically stable in an acidic digestion solution since taking polycrystallinity or surface area as proof of stability lacks quantitative insight into degradation mechanisms An equivalent to these carboxylate MOFs—metal-phosphonate frameworks (MPFs)—has emerged as promising radionuclide separation materials, based on their tunable porosity and miscellaneous linker functionality [8,9,10]. The presumable high level of hydrolytic stability of MPFs stems from their strong tetravalent metal-oxygen-phosphorus bonds and interconnected framework architecture These MPFs remain less explored due to a lack of crystallinity and are designated as unconventional MOFs or unconventional metal-phosphonate frameworks (UMPFs) [11]. Exploring the driving forces behind the instability/stability of UMPFs and MPFs is in its infant stages, and is underexplored in harsh acidic media
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
