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Subsurface injection of carbon dioxide (CO₂) into mafic-ultramafic rocks for permanent storage via mineralization is being studied to reduce emissions. Here, we investigated the carbonation products of enstatite (MgSiO₃) to assess its efficiency in sequestering CO₂ for safe and permanent storage as carbonate minerals. This was accomplished by conducting variable temperature carbonation reactions with samples of differing crystallinities and surface chemistries. Reaction progress was monitored utilizing in situ X-ray diffraction, and the presence of carbonate products was confirmed using additional techniques, such as thermogravimetric analysis coupled with mass spectrometry and scanning electron microscopy with energy dispersive spectrometry. Our results showmore » that crystalline enstatite produces small amounts of the anhydrous form of MgCO₃ (magnesite), while amorphous MgSiO₃, which was used to simulate mafic glass, more readily converts to the hydrated/hydroxylated hydromagnesite [Mg₅(CO₃)₄(OH)₂·4H₂O]. These results, supplemented with dynamic vapor sorption experiments, suggest that surface properties play a significant role in the pathway and degree of carbonation. These developments concerning the reactivity of CO₂ with reactive mafic phases will help further our understanding of the reactivity of these mafic-ultramafic minerals with implications for permanent carbon storage and other subsurface engineering scenarios involving reactive reservoirs.« less

The ongoing use of fossil fuels to supply modern energy demands has necessitated research on combating carbon dioxide (CO₂) emissions and climate change. Carbon storage via mineral trapping in basalt and related rocks is a promising strategy. However, mineralization rates depend on the variable minerology that makes up these rock formations. Diopside (CaMgSi₂O₆) is a common pyroxene mineral in ultramafic and mafic rocks including basalt, but relatively little work has been done to understand its carbon mineralization kinetics using hydrated supercritical CO₂, which induces the formation of reactive nanoscale interfacial water films. Here, in situ XRD experiments at 50–110 °Cmore » and 90 bar indicate that diopside transforms into a myriad of Mg/Ca carbonates, including huntite [Mg₃Ca(CO₃)₄] and very high magnesium calcite (VHMC, i.e., protodolomite). Through ex situ characterization, we were able to constrain reaction pathways for the dissolution–precipitation transformation process including metastable intermediate precipitates. Experiments performed at variable temperatures enabled Avrami-derived rate constants and an apparent activation energy of 97 ± 16 kJ mol^–1, implying the dissolution of diopside is the rate-limiting step. Density functional theory (DFT) calculations, used to gain molecular insight into the surface stability of the diopside during dissolution, suggest that exposed calcium cations are susceptible to dissolution when put in contact with water given their coordination environment. The collective results point to the high CO₂ mineralization potential of diopside in basalts, which could help guide parameterization of reactive transport models needed to design and permit commercial-scale subsurface carbon storage operations.« less

Selective adsorption of trace amounts of C₂H₆ from bulk C₂H₄ is a significantly important and extremely challenging task in industry, which requires an adsorbent with specific pore properties. In this work, we describe a strategy for adjusting the pore environment of metal–organic frameworks (MOFs) by introducing different amounts of methyl groups in the channel to enhance the guest–host interaction between C₂H₆ and the framework. To prove this concept, 2,3,5,6-tetramethylterephthalic acid (TMBDC) was deliberately added to a microporous MOF, Ni(BDC)(DABCO)_0.5, affording a series of mixed-ligand materials, Ni(BDC)_1–x(TMBDC)_x(DABCO)_0.5 (x = 0, 0.2, 0.45, 0.71, 1), having different pore environments. Significantly, these mixed-ligandmore » materials demonstrated improved performance in terms of the adsorption capacity of C₂H₆ and C₂H₄ with an unprecedented C₂H₆ uptake of 2.21 mmol g^–1 for Ni(TMBDC)(DABCO)_0.5 at 0.0625 bar and 298 K. With the best theoretical C₂H₆/C₂H₄ selectivity predicted by IAST, Ni(TMBDC)(DABCO)_0.5 exhibited effective separation of C₂H₆/C₂H₄ (1/15, v/v) and great recyclability in five consecutive adsorption/desorption cycles throughout the breakthrough experiment.« less

The elimination of specific contaminants from high concentrations of competitors poses a significant challenge. Rather than relying on a single direct interaction, the cooperation of multiple functionalities is an emerging strategy for adsorptive materials design to achieve this requisite affinity. Here, we describe that the interaction with the analyte of interest can be altered by modifying the local environment of the direct contact site, as demonstrated by manipulating the affinity of pyridinium-based anion nanotraps toward pertechnetate. Systematic control of the substituent effect allows the resulting anion nanotraps to combine multiple features as ideal pertechnetate scavengers with exceptional performances, substantially overcomingmore » the long-term challenge of TcO_4- segregation under extreme conditions of super acidity and basicity, strong irradiation field, and high ionic strength. The top material exhibits the highest sorption capacity together with unprecedented extraction efficiencies after a single treatment from conditions relevant to the used nuclear fuel (Hanford tank wastes, 95%) and legacy nuclear wastes (Savannah River Sites, 80%) among materials reported thus far.« less

Over millennia, nature has evolved an ability to selectively recognize and sequester specific metal ions by employing a wide variety of supramolecular chelators. Iron-specific molecular carriers—siderophores—are noteworthy for their structural elegance, while exhibiting some of the strongest and most selective binding towards a specific metal ion. Development of simple uranyl (UO₂²⁺) recognition motifs possessing siderophore-like selectivity, however, presents a challenge. Herein we report a comprehensive theoretical, crystallographic and spectroscopic studies on the UO₂²⁺ binding with a non-toxic siderophore-inspired chelator, 2,6-bis[hydroxy(methyl)amino]-4-morpholino-1,3,5-triazine (H₂BHT). The optimal pK_a values and structural preorganization endow H₂BHT with one of the highest uranyl binding affinity and selectivitymore » among molecular chelators. The results of small-molecule standards are validated by a proof-of-principle development of the H₂BHT-functionalized polymeric adsorbent material that affords high uranium uptake capacity even in the presence of competing vanadium (V) ions in aqueous medium.« less