Interparticle Forces of a Native and Encapsulated Metal-Organic Framework and Their Effects on Colloidal Dispersion

The colloidal properties of suspended metal-organic frameworks (MOFs) are critical for device fabrication and application. Herein, van der Waals attractive, electric double layer repulsive, and steric repulsive forces of a native and encapsulated MOF are quantified for the first time. The van der Waals attractive forces were investigated by conducting environmental ellipsometric porosimetry (EEP) and spectroscopic ellipsometry (SE) on submicron, optical-quality nanoparticle films. The repulsive forces were determined from colloid and material characterization measurements. These data were used to predict suspension properties via extended Derjaguin, Landau, Verwey, and Overbeek theory. The state of dispersion was quantified for comparison with theoretical predictions for nine solvents. The MOF encapsulated with a surface-selective modification showed superior suspension in hydrophobic solvents. These findings should expedite the formulation of MOF colloidal suspensions for future works

Liquid-phase synthesis of 2′-methyl-RNA on a homostar support through organic-solvent nanofiltration

Due to the discovery of RNAi, oligonucleotides (oligos) have re-emerged as a major pharmaceutical target that may soon be required in ton quantities. However, it is questionable whether solid-phase oligo synthesis (SPOS) methods can provide a scalable synthesis. Liquid-phase oligo synthesis (LPOS) is intrinsically scalable and amenable to standard industrial batch synthesis techniques. However, most reported LPOS strategies rely upon at least one precipitation per chain extension cycle to separate the growing oligonucleotide from reaction debris. Precipitation can be difficult to develop and control on an industrial scale and, because many precipitations would be required to prepare a therapeutic oligonucleotide, we contend that this approach is not viable for large-scale industrial preparation. We are developing an LPOS synthetic strategy for 2′-methyl RNA phosphorothioate that is more amenable to standard batch production techniques, using organic solvent nanofiltration (OSN) as the critical scalable separation technology. We report the first LPOS-OSN preparation of a 2′-Me RNA phosphorothioate 9-mer, using commercial phosphoramidite monomers, and monitoring all reactions by HPLC, (31)P NMR spectroscopy and MS

Low energy intensity production of fuel-grade bio-butanol enabled by membrane-based extraction

Widespread use of biofuels is inhibited by the significant energy burden of recovering fuel products from aqueous fermentation systems. Here, we describe a membrane-based extraction (perstraction) system for the recovery of fuel-grade biobutanol from fermentation broths which can extract n-butanol with high purity (>99.5%) while using less than 25% of the energy of current technology options. This is achieved by combining a spray-coated thin-film composite membrane with 2-ethyl-1-hexanol as an extractant. The membrane successfully protects the micro-organisms from the extractant, which, although ideal in other respects, is a metabolic inhibitor. In contrast to water, the extractant does not form a heterogeneous azeotrope with n-butanol, and the overall energy consumption of for n-butanol production is 3.9 MJ kg−1, substantially less than other recovery processes (17.0–29.4 MJ kg−1). By (a) extracting n-butanol from the fermentation broth without a phase change, (b) breaking the heterogeneous azeotrope relationship (less energy consumption for distillation), and (c) utilizing a small volume ratio of extractant : fermentation broth (1 : 100, v/v), the need for high energy intensity processes such as pervaporation, gas stripping or liquid–liquid extraction is avoided. The application of this perstraction system to continuous production of a range of higher alcohols is explored and shown to be highly favourable

On the influence of salt concentration on the transport properties of reverse osmosis membranes in high pressure and high recovery desalination

In this work, we investigate the effect of varying the concentration of sodium chloride up to 70 g L−1 - equivalent to a recovery of approximately 50% in seawater desalination-on the transport properties of different reverse osmosis membranes. The study was performed using five commercial thin film composite (TFC) membranes and an analogue TFC membrane fabricated via the interfacial reaction of m-phenylenediamine and trimesoyl chloride. The surface properties of the membranes as measured by atomic force microscopy (AFM), zeta potential, and X-ray photoelectron spectroscopy (XPS) are presented. The solution diffusion model coupled with film theory was used to calculate the permeance of water and salt through the membranes, to account for the effect of concentration polarisation. The mass transfer coefficient in the test cells was estimated independently using the dissolution rate of benzoic acid; and was found to be approximately . A linear reduction in salt permeance was observed in some of the RO membranes, while it remained constant for other membranes, including the analogue membrane. All the tested membranes maintained constant water permeance below 45 g L−1 NaCl. However, when the salt concentration at the membrane surface exceeded 45 g L−1, water permeance either increased, remained constant or decreased. The results demonstrate the dependence of water and salt transport on the concentration of sodium chloride at the membrane surface

A smart and responsive crystalline porous organic cage membrane with switchable pore apertures for graded molecular sieving

Membranes with high selectivity offer an attractive route to molecular separations, where technologies such as distillation and chromatography are energy intensive. However, it remains challenging to fine tune the structure and porosity in membranes, particularly to separate molecules of similar size. Here, we report a process for producing composite membranes that comprise crystalline porous organic cage films fabricated by interfacial synthesis on a polyacrylonitrile support. These membranes exhibit ultrafast solvent permeance and high rejection of organic dyes with molecular weights over 600 g mol-1. The crystalline cage film is dynamic, and its pore aperture can be switched in methanol to generate larger pores that provide increased methanol permeance and higher molecular weight cut-offs (1,400 g mol-1). By varying the water/methanol ratio, the film can be switched between two phases that have different selectivities, such that a single, 'smart' crystalline membrane can perform graded molecular sieving. We exemplify this by separating three organic dyes in a single-stage, single-membrane process

Nanoscale chemical heterogeneity in aromatic polyamide membranes for reverse osmosis applications

Reverse osmosis membranes are used within the oil and gas industry for sea water desalination on off-shore oilrigs. The membranes consist of three layers of material – a polyester backing layer, a polysulfone support and a polyamide (PA) thin film separating layer. It is generally thought that the PA layer controls ion selectivity within the membrane, but little is understood about its structure or chemistry at the molecular scale. This active polyamide layer is synthesized by interfacial polymerisation at an organic/aqueous interface between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), producing a highly cross-linked polyamide (PA) polymer. It has been speculated that the distribution of functional chemistry within this layer could play a role in solute filtration. The only technique potentially capable of probing the distribution of functional chemistry within the active PA layer with sufficient spatial and energy resolution is scanning transmission electron microscopy combined with electron energy-loss spectroscopy (STEM-EELS). Its use is a challenge because organic materials suffer beam-induced damage at relatively modest electron doses. Here we show that it is possible to use the N K-edge to map the active layer of a PA film using monochromated EELS spectrum imaging. The active PA layer is 12 nm thick, which supports previous neutron reflectivity data. Clear changes in the fine structure of the C K-edge across the PA films are measured and we use machine learning to assign fine structure at this edge. Using this method, we map highly heterogeneous intensity variations in functional chemistry attributed to N-C=C bonds within the PA. Similarities are found with previous molecular dynamics simulations of PA showing regions with a higher density of amide bonding as a result of the aggregation process at similar length scales. The chemical pathways that can be deduced may offer a clearer understanding of the transport mechanisms through the membrane