Nanoporosity of an organo-clay shown by hyperpolarized xenon and 2D NMR spectroscopy

Designing nanoarchitecture for environmental remediation based on the clay minerals as building block

Nanoarchitecture of hybrids materials based on clay minerals as nano building blocks for the environmental remediation is summarized with the emphasis on the utilization of layered clay minerals, especially smectite group of clay minerals, as nano building blocks for designing functional nanostructures for the adsorption of molecular contaminants from the environments. Smectites are well-known adsorbents of cationic contaminants, while surface modification of smectites with organoammonium ions has given hydrophobic and microporous characters to uptake nonionic organic contaminants from environments. Not only on the designed interactions between adsorbent-adsorbate for efficient and higher capacity adsorption, the states of the adsorbed nonionic organic compounds have been altered and varied by the modification of smectites as shown by the controlled release and specific catalytic reactions. The organically modified clays are classified from the nanoarchitecture, and the functions derived from the nanoarchitectures are discussed based on the structure-property relationship.

Mapping the dynamics of methanol and xenon co-adsorption in SWNTs by in situ continuous-flow hyperpolarized 129Xe NMR

A comparative study of the dynamics of methanol in SWNTs and MCM-41 was performed by in situ continuous-flow laser-hyperpolarized ¹²⁹Xe NMR.

Fluorinated porous organic frameworks for improved CO2 and CH4 capture

Hyperpolarized ¹²⁹Xe NMR highlights open porosity of fluorinated organic frameworks which show CO₂ and CH₄ capture with high selectivity towards N₂.

NMR Hyperpolarization Techniques of Gases

Nuclear spin polarization can be significantly increased through the process of hyperpolarization, leading to an increase in the sensitivity of nuclear magnetic resonance (NMR) experiments by 4-8 orders of magnitude. Hyperpolarized gases, unlike liquids and solids, can often be readily separated and purified from the compounds used to mediate the hyperpolarization processes. These pure hyperpolarized gases enabled many novel MRI applications including the visualization of void spaces, imaging of lung function, and remote detection. Additionally, hyperpolarized gases can be dissolved in liquids and can be used as sensitive molecular probes and reporters. This Minireview covers the fundamentals of the preparation of hyperpolarized gases and focuses on selected applications of interest to biomedicine and materials science.

129Xe NMR studies of morphology and accessibility in porous biochar from almond shells

¹²⁹Xe NMR EXSY plot demonstrating pore connectivity in sustainable almond shell biochar generated from anaerobic thermal activation and rainwater washing.

Programming A Molecular Relay for Ultrasensitive Biodetection through (129)Xe NMR

A supramolecular strategy for detecting specific proteins in complex media by using hyperpolarized (129) Xe NMR is reported. A cucurbit[6]uril (CB[6])-based molecular relay was programmed for three sequential equilibrium conditions by designing a two-faced guest (TFG) that initially binds CB[6] and blocks the CB[6]-Xe interaction. The protein analyte recruits the TFG and frees CB[6] for Xe binding. TFGs containing CB[6]- and carbonic anhydrase II (CAII)-binding domains were synthesized in one or two steps. X-ray crystallography confirmed TFG binding to Zn(2+) in the deep CAII active-site cleft, which precludes simultaneous CB[6] binding. The molecular relay was reprogrammed to detect avidin by using a different TFG. Finally, Xe binding by CB[6] was detected in buffer and in E. coli cultures expressing CAII through ultrasensitive (129) Xe NMR spectroscopy.

Confined Polymerization in Highly Ordered Mesoporous Organosilicas

Hybrid mesoporous organosilica exhibiting crystal-like order in the walls provided an ideal channel reaction vessel for the confined polymerization of acrylonitrile (PAN). The resulting high-molecular-mass PAN fills the channels at high yield and forms an ordered nanostructure of polymer nanobundles enclosed into the hybrid matrix. The in situ thermal transformation of PAN into rigid polyconjugated and, eventually, into condensed polyaromatic carbon nanofibers, retains the periodic architecture. Simultaneously, the matrix evolves showing the fusion of the p-phenylene rings and the cleavage of carbonsilicon bonds: this gives rise to graphitic-carbon/silica nanocomposites containing hyper-oxydrylated silica nanophases. Interestingly, the 3D hexagonal mesostructure survives in the carbonaceous material. The exploitation of porous materials of high capacity and a hybrid nature, for polymerization in the confined state, followed by high temperature treatments, allowed us to achieve unique and precisely fabricated nanostructures, thus paving the way for the construction of fine-tuned electronic and light-harvesting materials.

Intercalation and retention of carbon dioxide in a smectite clay promoted by interlayer cations

A good material for CO₂ capture should possess some specific properties: (i) a large effective surface area with good adsorption capacity, (ii) selectivity for CO₂, (iii) regeneration capacity with minimum energy input, allowing reutilization of the material for CO₂ adsorption, and (iv) low cost and high environmental friendliness. Smectite clays are layered nanoporous materials that may be good candidates in this context. Here we report experiments which show that gaseous CO₂ intercalates into the interlayer nano-space of smectite clay (synthetic fluorohectorite) at conditions close to ambient. The rate of intercalation, as well as the retention ability of CO₂ was found to be strongly dependent on the type of the interlayer cation, which in the present case is Li⁺, Na⁺ or Ni²⁺. Interestingly, we observe that the smectite Li-fluorohectorite is able to retain CO₂ up to a temperature of 35°C at ambient pressure, and that the captured CO₂ can be released by heating above this temperature. Our estimates indicate that smectite clays, even with the standard cations analyzed here, can capture an amount of CO₂ comparable to other materials studied in this context.

Hyperpolarized Xenon Nuclear Magnetic Resonance (NMR) of Building Stone Materials

We have investigated several building stone materials, including minerals and rocks, using continuous flow hyperpolarized xenon (CF-HP) NMR spectroscopy to probe the surface composition and porosity. Chemical shift and line width values are consistent with petrographic information. Rare upfield shifts were measured and attributed to the presence of transition metal cations on the surface. The evolution of freshly cleaved rocks exposed to the atmosphere was also characterized. The CF-HP ¹²⁹Xe NMR technique is non-destructive and it could complement currently used techniques, like porosimetry and microscopy, providing additional information on the chemical nature of the rock surface and its evolution.

X-ray studies of carbon dioxide intercalation in Na-fluorohectorite clay at near-ambient conditions

We show experimentally that gaseous CO(2) intercalates into the interlayer space of the synthetic smectite clay Na-fluorohectorite at conditions not too far from ambient. The mean interlayer repetition distance of the clay when CO(2) is intercalated is found to be 12.5 Å for the conditions -20 °C and 15 bar. The magnitude of the expansion of the interlayer upon intercalation is indistinguishable from that observed in the dehydrated-monohydrated transition for H(2)O, but the possibility of water intercalation is ruled out by a careful analysis of the experimental conditions and repeating the measurements exposing the clay to nitrogen gas. The dynamics of the process is observed to be dependent on the pressure, with a higher intercalation rate at increased pressure. The rate of CO(2) intercalation at the studied conditions is found to be several orders of magnitude slower than the intercalation rate of water or humidity at ambient pressure and temperature.