Mixed-dimensional membranes: chemistry and structure-property relationships

Tremendous progress in two-dimensional (2D) nanomaterial chemistry affords abundant opportunities for the sustainable development of membranes and membrane processes. In this review, we propose the concept of mixed dimensional membranes (MDMs), which are fabricated through the integration of 2D materials with nanomaterials of different dimensionality and chemistry. Complementing mixed matrix membranes or hybrid membranes, MDMs stimulate different conceptual thinking about designing advanced membranes from the angle of the dimensions of the building blocks as well as the final structures, including the nanochannels and the bulk structures. In this review, we survey MDMs (denoted nD/2D, where n is 0, 1 or 3) in terms of the dimensions of membrane-forming nanomaterials, as well as their fabrication methods. Subsequently, we highlight three kinds of nanochannels, which are 1D nanochannels within 1D/2D membranes, 2D nanochannels within 0D/2D membranes, and 3D nanochannels within 3D/2D membranes. Strategies to tune the physical and chemical microenvironments of the nanochannels as well as the bulk structures based on the size, type, structure and chemical character of nanomaterials are discussed. Some representative applications of MDMs are illustrated for gas molecular separations, liquid molecular separations, ionic separations and oil/water separation. Finally, current challenges and a future perspective on MDMs are presented

Increased E. coli bio-adsorption resistance of microfiltration membranes, using a bio-inspired approach

Cells have inherent anti-fouling properties. The mechanisms underpinning these natural properties inform the design of an anti-biosorption coating for a polyethersulfone microfiltration membrane, which includes polydopamine and chitosan layers. This tri-layered membrane is created using quick and easy synthesis method. Its ability to resist bio-adsorption and membrane extracellular polymeric substances (EPS) formation is investigated using the bacterium E. coli (ATCC 11775, 1.5 × 10^{7} CFU/mL). In addition, the proliferative bio-adsorption process is explored on the microfiltration membrane surface, using natural water under static and shaken conditions, while monitoring the bio-adsorption kinetics and EPS dynamic changes. The characterization results show that the modification by polydopamine and chitosan change the membrane surface morphology and increase its hydrophilicity. After 10 min dipping in 5 g/L chitosan solution, the pure water flux of the modified membrane is 5469 ± 30 L/(m^{2} ·h) (0.2 bar) and the contact angle decreases to 36.7 ± 1.0°, compared with 9889 ± 23 L/(m^{2} ·h) (0.2 bar) and 60.3 ± 1.5° for the unmodified polyethersulfone membrane, respectively. In proliferative bio-adsorption tests, the modified membrane is shown to decrease bio-adsorption by 0.4–2.3 orders of magnitude. However, no antimicrobial function is observed, probably due to the alkaline environment and insufficient functional amino groups. A series of linear and non-linear kinetic models is applied to fit the proliferative bio-adsorption process. The pseudo-second-order model is found to describe the proliferative bio-adsorption process best. Neither total organic carbon (TOC) nor protein is detected on the modified membrane surface. In contrast, on the unmodified PES membrane the ratios of protein/TOC (%), TOC/abundance ((μg/cm^{2}/CFU (log)) and protein/abundance ((μg/cm^{2}/CFU(log)) are 10%–16%, 0.17–0.28 and 0.02–0.04, respectively. No significant difference (p > 0.05) is found between static and shaken conditions. All these results point to improved anti-biosorption properties for water treatment applications, encouraging further studies on this membrane

Bioinspired supramolecular macrocycle hybrid membranes with enhanced proton conductivity

Enhancing the proton conductivity of proton exchange membranes (PEMs) is essential to expand the applications of proton exchange membrane fuel cells (PEMFCs). Inspired by the proton conduction mechanism of bacteriorhodopsin, cucurbit[n]urils (CB[n], where n is the number of glycoluril units, n = 6, 7, or 8) are introduced into sulfonated poly(ether ether ketone) (SPEEK) matrix to fabricate hybrid PEMs, employing a nature-inspired chemical engineering (NICE) methodology. The carbonyl groups of CB[n] act as proton-conducting sites, while the host–guest interaction between CB[n] and water molecules offers extra proton-conducting pathways. Additionally, the molecular size of CB[n] aids in their dispersion within the SPEEK matrix, effectively bridging the unconnected proton-conducting sulfonic group domains within the SPEEK membrane. Consequently, all hybrid membranes exhibit significantly enhanced proton conductivity. Notably, the SPEEK membrane incorporating 1 wt.% CB[8] (CB[8]/SPEEK-1%) demonstrates the highest proton conductivity of 198.0 mS·cm−1 at 60 °C and 100% relative humidity (RH), which is 228% greater than that of the pure SPEEK membrane under the same conditions. Moreover, hybrid membranes exhibit superior fuel cell performance. The CB[8]/SPEEK-1% membrane achieves a maximum power density of 214 mW·cm−2, representing a 140% improvement over the pure SPEEK membrane (89 mW·cm−2) at 50 °C and 100% RH. These findings serve as a foundation for constructing continuous proton-conducting pathways within membranes by utilizing supramolecular macrocycles as fuel cell electrolytes and in other applications. [Figure not available: see fulltext.]

Effects of zeolite particle size and internal grain boundaries on Pt/Beta catalyzed isomerization of n-pentane

The impact of particle size and internal grain boundaries of Beta zeolites was investigated in n-pentane isomerization over bifunctional Pt/Beta catalysts, by comparing the catalytic performance of four as-synthesized Pt/Beta samples that possess an identical Pt loading (0.5 wt%), but use four distinct Beta zeolites. Three of them contain polycrystalline zeolites, consisting of nano-sized crystals with a similar size of 9–13 nm, but having different average particle sizes (i.e., 1340, 830, and 250 nm) and numerous internal grain boundaries, as found via high-resolution transmission electron microscopy. The last catalyst contains single-crystalline zeolite, with an average particle size of 225 nm, and no observed internal grain boundaries. At low reaction temperature ( 614 K), a large particle size and the presence of internal grain boundaries significantly reduce the apparent activity, because of the extended diffusion path and additional diffusion barriers, which are probably caused by a mismatch in micropore alignment and gas-zeolite interfaces at these grain boundaries. Due to the small particle size and absence of internal grain boundaries, the observed activity for single-crystalline Beta can be 60–212% higher than for polycrystalline counterparts, even though it possesses a much weaker intrinsic acidity. This shows, remarkably, that single-crystalline zeolites with less internal grain boundaries can achieve a much higher catalytic activity

Fractal self-organization of bacteria-inspired agents

We develop an agent-based model as a preliminary theoretical basis to guide the synthesis of a new class of materials with dynamic properties similar to bacterial colonies. Each agent in the model is representative of an individual bacterium capable of: the uptake of chemicals (nutrients), which are metabolized; active movement (part viscous, part diffusive), consuming metabolic energy; and cellular division, when agents have doubled in size. The agents grow in number and self-organize into fractal structures, depending on the rules that define the actions of the agents and the parameter values. The environment of the agents includes chemicals responsible for their growth and is described by a diffusion-reaction equation with Michaelis-Menten kinetics. These rules are modeled mathematically by a set of equations with five dimensionless groups that are functions of physical parameters. Simulations are performed for different parameter values. The resulting structures are characterized by their fractal scaling regime, box-counting and mass-radius dimensions, and lacunarity. Each parameter influences the overall structure in a unique way, generating a wide spectrum of structures. For certain combinations of parameter values, the model converges to a steady state, with a finite population of agents that no longer divide. © 2012 World Scientific Publishing Company

Time-resolved single-crystal X-ray crystallography

In this chapter the development of time-resolved crystallography is traced from its beginnings more than 30 years ago. The importance of being able to “watch” chemical processes as they occur rather than just being limited to three-dimensional pictures of the reactant and final product is emphasised, and time-resolved crystallography provides the opportunity to bring the dimension of time into the crystallographic experiment. The technique has evolved in time with developments in technology: synchrotron radiation, cryoscopic techniques, tuneable lasers, increased computing power and vastly improved X-ray detectors. The shorter the lifetime of the species being studied, the more complex is the experiment. The chapter focusses on the results of solid-state reactions that are activated by light, since this process does not require the addition of a reagent to the crystalline material and the single-crystalline nature of the solid may be preserved. Because of this photoactivation, time-resolved crystallography is often described as “photocrystallography”. The initial photocrystallographic studies were carried out on molecular complexes that either underwent irreversible photoactivated processes where the conversion took hours or days. Structural snapshots were taken during the process. Materials that achieved a metastable state under photoactivation and the excited (metastable) state had a long enough lifetime for the data from the crystal to be collected and the structure solved. For systems with shorter lifetimes, the first time-resolved results were obtained for macromolecular structures, where pulsed lasers were used to pump up the short lifetime excited state species and their structures were probed by using synchronised X-ray pulses from a high-intensity source. Developments in molecular crystallography soon followed, initially with monochromatic X-ray radiation, and pump-probe techniques were used to establish the structures of photoactivated molecules with lifetimes in the micro- to millisecond range. For molecules with even shorter lifetimes in the sub-microsecond range, Laue diffraction methods (rather than using monochromatic radiation) were employed to speed up the data collections and reduce crystal damage. Future developments in time-resolved crystallography are likely to involve the use of XFELs to complete “single-shot” time-resolved diffraction studies that are already proving successful in the macromolecular crystallographic field.</p

Method for generating pore networks in porous particles of arbitrary shape, and its application to catalytic hydrogenation of benzene

A method is established to generate pore networks within domains of arbitrary shape, as long as the domain can be mathematically described by a set of inequalities. In this method, a stochastic network algorithm is adopted to construct pore network skeletons, which are then cut into the desired shapes using a new pore network cutting algorithm. The latter can be embedded into other methods to transplant its ‘pore network cutting’ function. Using this method, pore networks with four archetypical two-dimensional shapes (namely, cross-sections of one-holed rings, trilobes, four-holed rings, and wheels) and four three-dimensional shapes (namely, spheres, cylinders, trilobes, and hollow cylinders) are constructed as examples. Then, some of these pore networks are applied to simulate diffusion and reaction in Pd/γ-alumina catalyst particles for hydrogenation of benzene to cyclohexane. It is shown that the randomness of the pore network and the external particle shape significantly affect the performance of catalysts, because of their impact on effective diffusivity and diffusion length, respectively, indicating that this structural information must be accounted for to achieve a model with high accuracy. The versatile method proposed in this article is ideal to study the effect of particle shape and pore network structure on the performance of porous materials for catalysis and other applications

Oxygen Moment Formation and Canting in Li2CuO2

The possibilities of oxygen moment formation and canting in the quasi-1D cuprate Li2CuO2 are investigated using single crystal neutron diffraction at 2 K. The observed magnetic intensities could not be explained without the inclusion of a large ordered oxygen moment of 0.11(1) Bohr magnetons. Least-squares refinement of the magnetic structure of Li2CuO2 in combination with a spin-density Patterson analysis shows that the magnetization densities of the Cu and O atoms are highly aspherical, forming quasi-1D ribbons of localised Cu and O moments. Magnetic structure refinements and low-field magnetization measurements both suggest that the magnetic structure of Li2CuO2 at 2 K may be canted. A possible model for the canted configuration is proposed.Comment: 10 pages, 8 figures (screen resolution

Changes to cholesterol trafficking in macrophages by Leishmania parasites infection

Leishmania spp. are protozoan parasites that are transmitted by sandfly vectors during blood sucking to vertebrate hosts and cause a spectrum of diseases called leishmaniases. It has been demonstrated that host cholesterol plays an important role during Leishmania infection. Nevertheless, little is known about the intracellular distribution of this lipid early after internalization of the parasite. Here, pulse‐chase experiments with radiolabeled cholesteryl esterified to fatty acids bound to low‐density lipoproteins indicated that retention of this source of cholesterol is increased in parasite‐containing subcellular fractions, while uptake is unaffected. This is correlated with a reduction or absence of detectable NPC1 (Niemann–Pick disease, type C1), a protein responsible for cholesterol efflux from endocytic compartments, in the Leishmania mexicana habitat and infected cells. Filipin staining revealed a halo around parasites within parasitophorous vacuoles (PV) likely representing free cholesterol accumulation. Labeling of host cell membranous cholesterol by fluorescent cholesterol species before infection revealed that this pool is also trafficked to the PV but becomes incorporated into the parasites’ membranes and seems not to contribute to the halo detected by filipin. This cholesterol sequestration happened early after infection and was functionally significant as it correlated with the upregulation of mRNA‐encoding proteins required for cholesterol biosynthesis. Thus, sequestration of cholesterol by Leishmania amastigotes early after infection provides a basis to understand perturbation of cholesterol‐dependent processes in macrophages that were shown previously by others to be necessary for their proper function in innate and adaptive immune responses

Bleeding phenotype and diagnostic characterization of patients with congenital platelet defects

Phenotypic characterization of congenital platelet defects (CPDs) could help physicians recognize CPD subtypes and can inform on prognostic implications. We report the analyses of the bleeding phenotype and diagnostic characteristics of a large cohort of adult patients with a confirmed CPD. A total of 96 patients were analyzed and they were classified as Glanzmann thrombasthenia, Bernard-Soulier syndrome, dense granule deficiency, defects in the ADP or thromboxane A2 (TxA2) pathway, isolated thrombocytopenia or complex abnormalities. The median ISTH-BAT bleeding score was nine (IQR 5-13). Heavy menstrual bleeding (HMB) (80%), post-partum hemorrhage (74%), post-operative bleeds (64%) and post-dental extraction bleeds (57%) occurred most frequently. Rare bleeding symptoms were bleeds from the urinary tract (4%) and central nervous system (CNS) bleeds (2%). Domains with a large proportion of severe bleeds were CNS bleeding, HMB and post-dental extraction bleeding. Glanzmann thrombasthenia and female sex were associated with a more severe bleeding phenotype