RESUMO
The increase in the atmospheric carbon dioxide level is a significant threat to our planet, and therefore the selective removal of CO2 from the air is a global concern. Metal-organic frameworks (MOFs) are a class of porous materials that have shown exciting potential as adsorbents for CO2 capture due to their high surface area and tunable properties. Among several implemented technologies, direct air capture (DAC) using MOFs is a promising strategy for achieving climate targets as it has the potential to actively reduce the atmospheric CO2 concentration to a safer levels. In this study, we investigate the stability and regeneration conditions of N,N'-dimethylethylenediamine (mmen) appended Mg2(dobpdc), a MOF with exceptional CO2 adsorption capacity from atmospheric air. We employed a series of systematic experiments including thermogravimetric analysis (TGA) coupled with Fourier transformed infrared (FTIR) and gas chromatography mass spectrometer (GCMS) (known as TGA-FTIR-GCMS), regeneration cycles at different conditions, control and accelerated aging experiments. We also quantified CO2 and H2O adsorption under humid CO2 using a combination of data from TGA-GCMS and coulometric Karl-Fischer titration techniques. The quantification of CO2 and H2O adsorption under humid conditions provides vital information for the design of real-world DAC systems. Our results demonstrate the stability and regeneration conditions of mmen appended Mg2(dobpdc). It is stable up to 50% relative humidity when the adsorption temperature varies from 25-40 °C and the best regeneration condition can be achieved at 120 °C under dynamic vacuum and at 150 °C under N2.
RESUMO
Solvent plays a vital role in the recrystallization process and resulting crystallinity of materials. This role is of such importance that it can control the stability and utility of materials. In this work, the inclusion of a solvent in the crystalline lattice, specifically water, drastically affects the overall stability of two platinum polymorphs. [Pt(tpy)Cl]BF4 (tpy = 2,2';6'2â³-terpyridine) crystallizes in three forms, red (1R) and blue (1B) polymorphs and a yellow nonsolvated form (2). 1R is the more stable of the two polymorphs, whereas 1B loses crystallinity upon dehydration at ambient conditions resulting in the formation of 2. Close examination of the solid-state extended structures of the two polymorphs reveals that 1R has a lattice arrangement that is more conducive to stronger intermolecular interactions compared to 1B, thereby promoting greater stability. In addition, these two polymorphs exhibit unique vapochromic responses when exposed to various solvents.
RESUMO
PtI2(5,5'-bis(HCF2CH2OCH2)-2,2'-bpy)], 55-2FH-PtI2, is the first example of a substituted fluorinated diiodoplatinum diimine complex that exhibits polymorphism. The complex, upon recrystallization, forms two different polymorphs, denoted as α and ß forms. The luminescence of the α and ß forms are the same in glassy solution at 77 K; however, in the solid state, they differ significantly. The major difference between them lies in the solid-state packing of the crystalline structure. The α form is a square planar polyfluorinated PtI2-containing complex. Its extended herringbone structure consists of two neighboring stacked bipyridyl planes that do not overlap. The α form emits stronger than its parent molecule, [PtI2bpy], and much stronger than the ß polymorph. The ß form has a slight tetrahedral distortion about the metal center that ultimately changes the geometry of the complex and decreases the d-orbital splitting from square planar. Furthermore, overlapping bipyridine rings in the extended structure of the ß form quench the emission thus resulting in a lower energy emission. Additionally, the ß form shows only one type of C-H···O intermolecular stacking interaction that can cause the moderate distortion of the metal core.
