sub-Angstrom Level Research Articles

Precise Control of Ultramicropores of Novel Carbons Molecule Sieves Derived from Coffee Bean for Efficient Sieving Propylene from Propane.

The development of granular carbon materials with outstanding selectivity for the separation of alkenes and alkanes is highly desirable in the petrochemical industry but remains a significant challenge due to closely similar molecular sizes and physical properties of adsorbates. Herein, we report a facile approach of using natural biomass to prepare novel granular carbon molecule sieves with a molecular recognition accuracy of 0.44 Å and propose a new three-region model for the pore size distribution of amorphous porous carbons. Coffee bean-based granule carbon molecular sieves (CFGCs) were prepared with precise micropore regulation with subangstrom accuracy and characterized using molecular probes to reveal the evolution of carbon structure during preparation. The CFGC-0.09-750 demonstrates exceptional selectivity adsorption toward C3H6 while excluding C3H8, with an uptake ratio of 106.75 and a C3H6 uptake of 1.88 mmol/g at 298 K and 100 kPa, showcasing its immense potential in industrial applications for separating C3H6 and C3H8. The novel three-region model established in this work can clearly and reasonably elucidate why the samples CFGCs can screen propylene from propane at the subangstrom level. This study provides important guidance for the development of new carbon molecular sieves with subangstrom accuracy in molecular recognition and separation capacity.

Synthesis of a novel spherical granular microporous carbon with exceptional propylene sieving performance over propane

The development of new spherical granular carbon materials with excellent selectivity for the separation of propylene (C3H6) and propane (C3H8) is of great importance in the petrochemical industry, but remains a significant challenge due to the closely similar molecular sizes and physical property of propylene and propane. Herein, we present a novel approach to fabricate binder-free granular carbon materials exhibiting outstanding selectivity towards C3H6, while also elucidating the evolution of pore structure during the preparation process of these carbon materials. A mixture of starch and molasses was selected as carbon source, and subsequently, novel spherical granular carbon materials (SGCs) were successfully fabricated through the processes of rolling forming, pyrolysis activation and carbonization. The resulting samples were characterized and tested for separation of C3H6 and C3H8. These samples exhibit exceptional selectivity toward C3H6. Its C3H6/C3H8 selectivity reaches as high as 33.6 with C3H6 uptake of 2.21 mmol/g at 298 K and 100 kPa. Breakthrough experiments confirmed its excellent dynamical separation performance, achieving complete separation of C3H6/C3H8 binary mixtures. In addition, the evolutionary mechanism of the pore structure in the samples SGCs is elucidated, revealing that the microstructure of starch-based carbon materials gradually evolves towards graphitization at elevated temperature, causing shrinkage of pores at sub-angstrom level. This work presents a distinctive and promising approach for fabricating spherical granular carbon materials, and the resulting samples SGCs demonstrate great potential for industrial applications in separation of C3H6 and C3H8.

Optimizing gas transport for C3H6/C3H8 size sieving separation via fine pore engineering of carbon microspheres

For the adsorptive separation of propylene/propane (C3H6/C3H8) with high similarities in physiochemical properties, size-exclusive effect is highly attractive that can realize the superior selectivity. Nevertheless, the required narrow pores would unavoidably resist mass transfer of C3H6 molecules. To minimize the hindered diffusion, we report a systematic pore-engineering study in a family of carbon microspheres with fine-tuning pore sizes by exceptional activation-free method. The manipulation of pores was realized by varied temperature during glucose hydrothermal synthesis with acid additive as catalysis. Among as-obtained carbon analogs, GC-190 with optimal pore size closing to the kinetic diameter of C3H8 (5.11 Å), exhibited outstanding C3H6/C3H8 size-sieving property as well as fast C3H6 kinetics plausibly. However, GC-230 with smaller pores closing to the size of C3H6 (4.68 Å) showed sluggish C3H6 diffusion despite retaining size-sieving effect. The C3H6 diffusion constant rate (D’) of 1.21 × 10−2 min−1 on GC-190 is about two orders of magnitude higher than GC-230 of 2.29 × 10−4 min−1. DFT simulation further supports the remarkably reduced diffusion energy barrier of C3H6 by sub-angstrom level increased pore size. This study may deepen the understanding of gas diffusion in confined narrow pores and provides a general design concept.

Molecular Sieving of Propylene from Propane in Metal-Organic Framework-Derived Ultramicroporous Carbon Adsorbents.

The development of adsorption-based separation processes alternative to the energy-intensive cryogenic distillation for a mixture of propylene and propane remains essential but challenging in gas industries. Molecular sieving separation of C3H6/C3H8 on stable carbon adsorbents appeals to be promising, while it is quite challenging to realize due to the random distributions and arrangements of the internal pores in common carbons. Herein, a series of polysaccharide-based CD-MOF-derived ultramicroporous carbon adsorbents with their pore size tuned at a subangstrom level were prepared. Molecular sieving separation of C3H6/C3H8 was realized on the optimal C-CDMOF-2-700 owing to the delicate structure with an appropriate pore size (5.0 Å). Besides, C-CDMOF-2-700 exhibited a high C3H6 uptake of 1.97 mmol g-1 under ambient conditions. An ultrahigh uptake ratio of C3H6/C3H8 at 1.0 kPa (403) was also achieved, outperforming all reported adsorbents. Kinetic adsorption tests and breakthrough experiments further demonstrate this well-designed carbon adsorbent to be promising in industrial C3H6/C3H8 separation.

Subsurface structural change of silica upon nanoscale physical contact: Chemical plasticity beyond topographic elasticity

Surface defects or flaws on materials made by physical contacts with foreign objects can deteriorate their mechanical properties and limit technical applications. Thus, understanding the contact-induced subsurface damage is of great importance. Using nanoscale infrared spectroscopy and reactive molecular dynamics simulations, the subsurface structural changes of silica upon nanoindentation and nanoscratch are investigated. The results reveal an elongation of the SiO bond length distribution even after the topographically-elastic contact, indicating a “chemical plasticity” at the sub-Angstrom level. In the plastic region with subsurface densification, the SiO bond is found to be slightly longer than the pristine region, indicating the decrease in molar volume is accompanied with the elongation, not shortening, of the SiO bond. These results elucidate the structural damage of a material upon physical contact cannot be delineated based on the topographic deformation of the surface.

A novel mechanism of controlling ultramicropore size in carbons at sub-angstrom level for molecular sieving of propylene/propane mixtures

We developed a novel mechanism to control the ultramicropore size in carbons at sub-angstrom level that enables complete size-sieving of C3H6/C3H8.

Sub-Angstrom Characterization of the Structural Origin for High In-Plane Anisotropy in 2D GeS2.

Materials with layered crystal structures and high in-plane anisotropy, such as black phosphorus, present unique properties and thus promise for applications in electronic and photonic devices. Recently, the layered structures of GeS2 and GeSe2 were utilized for high-performance polarization-sensitive photodetection in the short wavelength region due to their high in-plane optical anisotropy and wide band gap. The highly complex, low-symmetric (monoclinic) crystal structures are at the origin of the high in-plane optical anisotropy, but the structural nature of the corresponding nanostructures remains to be fully understood. Here, we present an atomic-scale characterization of monoclinic GeS2 nanostructures and quantify the in-plane structural anisotropy at the sub-angstrom level in real space by Cs-corrected scanning transmission electron microscopy. We elucidate the origin of this high in-plane anisotropy in terms of ordered and disordered arrangement of [GeS4] tetrahedra in GeS2 monolayers, through density functional theory (DFT) calculations and orbital-based bonding analyses. We also demonstrate high in-plane mechanical, electronic, and optical anisotropies in monolayer GeS2 and envision phase transitions under uniaxial strain that could potentially be exploited for nonvolatile memory applications.

Revisiting the Interaction Force Measurement between Lipid Bilayers Using a Surface Forces Apparatus (SFA).

In this review, previous researches that measured intermembrane forces using the Surface Forces Apparatus are recapitulated. Different types of interaction forces are reported between two lipid bilayers including non-specific interactions (e.g., van der Waals, electrostatic, steric hydration, thermal undulation, and hydrophobic) and specific interactions (e.g., ligand-receptor). By measuring absolute distance and interaction forces at the sub-angstrom level and at a few nano-Newtons resolution, respectively, magnitudes, working ranges, and decay lengths of interaction between lipid bilayers are investigated. Utilizing recently developed fluorescence microscopy attachments, simultaneous fluorescence imaging of membrane proteins and lipid phases can be performed during approach/separation cycles of two lipid bilayer deposited surfaces, which can reveal cooperative effects between lipid phases and various types of membrane proteins.

Computational Molecular Modeling of Transport Processes in Nanoporous Membranes

In this report we have discussed the important role of molecular modeling, especially the use of the molecular dynamics method, in investigating transport processes in nanoporous materials such as membranes. With the availability of high performance computers, molecular modeling can now be used to study rather complex systems at a fraction of the cost or time requirements of experimental studies. Molecular modeling techniques have the advantage of being able to access spatial and temporal resolution which are difficult to reach in experimental studies. For example, sub-Angstrom level spatial resolution is very accessible as is sub-femtosecond temporal resolution. Due to these advantages, simulation can play two important roles: Firstly because of the increased spatial and temporal resolution, it can help understand phenomena not well understood. As an example, we discuss the study of reverse osmosis processes. Before simulations were used it was thought the separation of water from salt was purely a coulombic phenomenon. However, by applying molecular simulation techniques, it was clearly demonstrated that the solvation of ions made the separation in effect a steric separation and it was the flux which was strongly affected by the coulombic interactions between water and the membrane surface. Additionally, because of their relatively low cost and quick turnaround (by using multiple processor systems now increasingly available) simulations can be a useful screening tool to identify membranes for a potential application. To this end, we have described our studies in determining the most suitable zeolite membrane for redox flow battery applications. As computing facilities become more widely available and new computational methods are developed, we believe molecular modeling will become a key tool in the study of transport processes in nanoporous materials.

Sub-Angstrom Gold Nanoparticle/Liposome Interfaces Controlled by Halides.

A hallmark of nanoscience is size-dependent and distance-dependent physical properties. Although most previous studies focused on optical properties, which are often tuned at nanometer scale, we herein report on the interaction between halide-capped gold nanoparticles (AuNPs) and phosphocholine (PC) liposomes at the sub-Angstrom level. Halide-capped AuNPs are adsorbed by PC liposomes attributable to van der Waals force. Iodide-capped AuNPs interact much more weakly with the liposomes compared with bromide- and chloride-capped AuNPs, as indicated by a liposome leakage assay and differential scanning calorimetry. This is explained by the slightly larger size of iodide separating the AuNP core more from the liposome surface. Cryo-transmission electron microscopy indicates that the liposomes remain intact when mixed with these halide-capped AuNPs of 13 or 70 nm in diameter. Other even larger ligands, including small thiol compounds, DNA oligonucleotides, proteins, and polymers, fully blocked the interaction, whereas AuNPs dispersed in noninteracting ions, including fluoride, phosphate, perchlorate, nitrate, sulfate, and bicarbonate, are still adsorbed strongly by 1,2-dioleoyl- sn-glycero-3-phosphocholine liposomes. Taken together, halides can be used to control interparticle distances at an extremely small scale with remarkable effects on materials properties, allowing surface probing, biosensor development, and fundamental surface science studies.

Accurate measurement of thickness of large-area graphene layers by neutron reflectometry

Neutron reflectometry was used to determine the thickness of large-area graphene layers on SiO2/Si substrates. Preliminary simulations showed that the optimum thickness of the SiO2 layer for neutron reflection is about a few hundred angstroms. The thicknesses of the graphene and the SiO2 layers were obtained by fitting the experimental reflectivity spectra. Transmission electron microscopy and Raman experiments were performed on the same samples, and verified that the neutron reflection results are reliable and accurate at the subangstrom level. This neutron reflectometry is nondestructive and applicable to wafer-size layers to yield the mean thickness. This accurate determination of the thickness will be helpful for managing quality of large-area graphene films.

Double-aberration corrected TEM/STEM of solid acid nanocatalysts in the development of pharmaceutical NSAIDS

We report nanostructural and physico-chemical studies in the development of an efficient low temperature heterogeneous catalytic process for nonsteroidal anti-inflammatory drugs (NSAIDS) such as N-acetyl-p-aminophenol (paracetamol or acetaminophen) on tungstated zirconia nanocatalysts. Using a double-aberration corrected TEM/STEM, modified in-house for in-situ studies at the sub-Angstrom level, we directly observed in real-time, the dynamic precursor transformation to the active catalyst. We quantified the observations with catalytic activity studies for the NSAIDS. The studies have provided the direct evidence for single tungsten promoter atoms and surface WOx species of ≤ 0.35 nm, with nanoclusters of WOx (0.6 to 1nm), located at grain boundaries on the surface of the zirconia nanoparticles. The correlation between the nanostructure and catalytic activity indicates that the species create Brønsted acid sites highly active for the low temperature process. The results open up opportunities for developing green heterogeneous methods for pharmaceuticals.

The limits of ultrahigh-resolution x-ray mapping: estimating uncertainties in thin-film and interface structures determined by phase retrieval methods

Capturing subtle details at the sub-Angstrom level is key to understanding the structural basis of many intriguing interfacial phenomena in epitaxial thin films and nanostructures. X-ray phase retrieval methods are ideally suited to this task but the usual approaches for determination of uncertainties, based on refining a parametrized model, are not applicable in this case. Here we describe a method to estimate the uncertainties of the system electron density, obtained by phase retrieval, and of parameters of interest obtained from it. The method is based on the bootstrap approach and it can be generally applied to surface x-ray scattering data. Several examples are given which illustrate the method's utility in determining uncertainties arising from random and systematic errors. The approach also provides a quantitative measure of the validity of structural solutions obtained by phase retrieval methods.

Diffraction phase microscopy with white light

We present white light diffraction phase microscopy (wDPM) as a quantitative phase imaging method that combines the single shot measurement benefit associated with off-axis methods, high temporal phase stability associated with common path geometries, and high spatial phase sensitivity due to the white light illumination. We propose a spatiotemporal filtering method that pushes the limit of the pathlength sensitivity to the subangstrom level at practical spatial and temporal bandwidths. We illustrate the utility of wDPM with measurements on red blood cell morphology and HeLa cell growth over 18 hours.

Hindered Rotation of a Cofactor Methyl Group as a Probe for Protein−Cofactor Interaction

Exploring protein-cofactor interactions on a molecular level is one of the major challenges in modern biophysics. Based on structural data alone it is rarely possible to identify how subtle interactions between a protein and its cofactor modulate the protein's reactivity. In the case of enzymatic processes in which paramagnetic molecules play a certain role, EPR and related methods such as ENDOR are suitable techniques to unravel such important details. In this contribution, we describe how cryogenic-temperature ENDOR spectroscopy can be applied to various LOV domains, the blue-light sensing domains of phototropin photoreceptors, to gain information on the direct vicinity of the flavin mononucleotide (FMN) cofactor by analyzing the temperature dependence of methyl-group rotation attached to C(8) of the FMN's isoalloxazine ring. More specifically, mutational studies of three amino acids surrounding the methyl group led to the identification of Asn425 as an important amino acid that critically influences the dark-state recovery of Avena sativa LOV2 domains. Consequently, it is possible to probe protein-cofactor interactions on a sub-angstrom level by following the temperature dependencies of hyperfine couplings.

Alteration of citrine structure by hydrostatic pressure explains the accompanying spectral shift.

A protein molecule is an intricate system whose function is highly sensitive to small external perturbations. However, no examples that correlate protein function with progressive subangstrom structural perturbations have thus far been presented. To elucidate this relationship, we have investigated a fluorescent protein, citrine, as a model system under high-pressure perturbation. The protein has been compressed to produce deformations of its chromophore by applying a high-pressure cryocooling technique. A closely spaced series of x-ray crystallographic structures reveals that the chromophore undergoes a progressive deformation of up to 0.8 A at an applied pressure of 500 MPa. It is experimentally demonstrated that the structural motion is directly correlated with the progressive fluorescence shift of citrine from yellow to green under these conditions. This protein is therefore highly sensitive to subangstrom deformations and its function must be understood at the subangstrom level. These results have significant implications for protein function prediction and biomolecule design and engineering, because they suggest methods to tune protein function by modification of the protein scaffold.

Micromachining of semiconductor by femtosecond laser for integrated circuit defect analysis

The latest International Technology Roadmap for Semiconductors (ITRS) has highlighted the detection and analysis of defects in Integrated Circuits (IC) as a major challenge faced by the semiconductor industry. Advanced tools used today for defect cross sectioning include dual beams (focused ion- and electron-beam technologies) with resolution down to the sub-Angstrom level. However ion milling an IC with a FIB is time consuming because of the need to open wide cavities in front of the cross-sections that need to be analyzed. Therefore the use of a femtosecond laser as a tool for direct material removal is discussed in this paper. Experiments were performed on IC structures to reveal the different layers of fabrication: selective or total ablation can occur depending on the laser energy density, without delamination of the layers. Different laser irradiation conditions like pressure (air, vacuum), polarization, beam shaping, and scanning parameters have been used to produce different types of cavities. The femtosecond laser engraving of silicon-based structures could be useful for cross-sectioning devices but also for other applications like direct-write lithography, photomask repair, maskless implantation or reverse engineering/restructuring.

Do not adjust your set

Researchers are for ever looking for ways to increase the resolution achieved by electron microscopes. Tricks used in imaging a silicon crystal by transmission electron microscopy avoid the worst effects of lens aberrations, a limiting factor in achieving better results, and take resolution to the subangstrom level.