Catalytic Reduction of Graphene Oxide Membranes and Water Selective Channel Formation in Water–Alcohol Separations

Graphene oxide (GO) is a promising membrane system for chemical separation applications due to its 2-D nanofluidics properties and an ability to control interplanar spacing for selectivity. The permeance of water, methanol (MeOH) and isopropyl alcohol (IPA) through 5 µm thick membranes was found to be 0.38 ± 0.15, 0.33 ± 0.16 and 0.42 ± 0.31 LMH/bar (liter/m2·h·bar), respectively. Interestingly, the permeance of a water–alcohol mixture was found to be dramatically lower (~0.01 LMH/bar) than any of its components. Upon removing the solvent mixture, the transmembrane flux of the pure solvent was recovered to near the original permeance. The interlayer space of a dried GO membrane was found to be 8.52 Å, which increased to 12.19 Å. 13.26 Å and 16.20 Å upon addition of water, MeOH and IPA. A decrease in d-space, about 2 Å, was consistently observed when adding alcohol to water wetted GO membrane and an optical color change and reduction in permeance. A newly proposed mechanism of a partial reduction of GO through a catalytic reaction with the water–alcohol mixture is consistent with experimental observations.

THE ROLE OF SORPTION PROCESSES IN THE TRANSMEMBRANE TRANSFER OF ALKALINE METAL SALTS THROUGH A NANOFILTRATION MEMBRANE

The article provides data on the effect of the concentration of I-I electrolyte salt on the transfer through the Vontron VNF 1812 nanofiltration membrane. Data for NaNO3, NaCl, NaHCO3, NaH2PO4 and alkali metal nitrates are presented. The experimental data obtained suggest that the flux of water and salt are determined by the interaction of anions with protonated amino groups, which are part of the material of the selective membrane layer. An increase in the transmembrane flux of alkali metal nitrates is observed in the series CsNO3>KNO3>NaNO3>LiNO3. This series is opposite to the series of selectivity in the sorption of metals on carboxyl cation exchangers, but this series coincides with the series of increasing diffusant mass. It is noted that for all the solutions under study, water transfer can occur at an operating pressure significantly lower than the osmotic pressure calculated by the Van't Hoff equation, which indicates the essential role of filtration in the traditional understanding of this term

Optimizing the Axial Resistance Profile of Submerged Hollow Fiber Membranes

Submerged hollow fiber membranes (SHFMs) are used for a wide variety of applications. Their applicability and their advantages, however, depend crucially on the prevailing hydrodynamics within single fibers. In this respect, the non-uniform distribution of transmembrane flux is a known problem related to inhomogeneous membrane fouling and disadvantages for cleaning. To address this problem, we propose an approach to homogenize transmembrane flux by varying the local membrane resistance using optimal control methods for the first time in SHFM research. Based on an established model, different scenarios are optimized, namely with different fiber lengths and inner radii. In addition, a double-end setup is explored. It is shown that the optimization goal is reached very well in all tested cases, which underlines the general validity of our strategy. Further uses and extensions of the optimization method are provided, as well as hints for the practical implementation of the suggested measures.

Low-Temperature Direct Contact Membrane Distillation for the Treatment of Aqueous Solutions Containing Urea

Research activities on the application of direct contact membrane distillation (DCMD) for processing at low temperature (up to 50 °C) solutions containing urea were presented and discussed. Feeds were urine (also in mixture) and human plasma ultrafiltrate. Moreover, as a case study, the performance of membrane modules of different sizes and features was investigated for reaching the productivities needed in the treatment of the human plasma ultrafiltrate. In particular, two modules were equipped with the same type of capillaries, but differed in terms of membrane area, while the third module contained a different type of membranes and presented a membrane area in between those of the two previous modules. The three modules were compared, at a parity of operating temperatures and streams velocity, in terms of transmembrane flux, permeate production and size, underlining the directions to follow for a real implementation of the technique.

Performance of High Molecular Weight Osmotic Solution for Opuntia Betacyanin Concentration by Forward Osmosis

Background: Forward osmosis is a sustainable membrane process employed for concentrating thermo-sensitive compounds to minimize storage and transportation costs with improved shelf life. Objective: In this study, the intervention of high molecular weight osmotic agents in the concentration of Opuntia betacyanin using forward osmosis was studied. Furthermore, the statistical model was used to estimate the probabilistic behavior of the forward osmosis process during concentration. Method: By using 2k-full factor analysis, the hydrodynamic variables, such as flow rate (50 and 150 mL/min) and temperature (20 and 50ºC) of the feed solution and osmotic agent solution (OAS) were selected. The study focused on inquiring and developing a statistically significant mathematical model using four independent variables on transmembrane flux, concentration factor and concentrate recovery. Results: Betacyanin feed flow rate of 50 mL/min at 28ºC, and OAS flow rate of 150 mL/min at 50ºC were determined as optimal conditions with a 2.5-fold increase in total soluble solids for a processing time of 4 h. Furthermore, forward osmosis enhanced the betacyanin concentration from 898 to 1004 mg/L and 98.7% recovery with 0.40 L/m2h transmembrane flux with comparable improvement in its physicochemical characteristics. The lower p-value of the main effects on the responses validated the significance of the process parameters on betacyanin concentration. Conclusion: The study suggested that a high molecular weight sucrose could be used as an osmotic agent for the concentration of Opuntia betacyanin during forward osmosis.

Molecular and Functional Characterization of Grapevine NIPs through Heterologous Expression in aqy-Null Saccharomyces cerevisiae

Plant Nodulin 26-like Intrinsic Proteins (NIPs) are multifunctional membrane channels of the Major Intrinsic Protein (MIP) family. Unlike other homologs, they have low intrinsic water permeability. NIPs possess diverse substrate selectivity, ranging from water to glycerol and to other small solutes, depending on the group-specific amino acid composition at aromatic/Arg (ar/R) constriction. We cloned three NIPs (NIP1;1, NIP5;1, and NIP6;1) from grapevine (cv. Touriga Nacional). Their expression in the membrane of aqy-null Saccharomyces cerevisiae enabled their functional characterization for water and glycerol transport through stopped-flow spectroscopy. VvTnNIP1;1 demonstrated high water as well as glycerol permeability, whereas VvTnNIP6;1 was impermeable to water but presented high glycerol permeability. Their transport activities were declined by cytosolic acidification, implying that internal-pH can regulate NIPs gating. Furthermore, an extension of C-terminal in VvTnNIP6;1M homolog, led to improved channel activity, suggesting that NIPs gating is putatively regulated by C-terminal. Yeast growth assays in the presence of diverse substrates suggest that the transmembrane flux of metalloids (As, B, and Se) and the heavy metal (Cd) are facilitated through grapevine NIPs. This is the first molecular and functional characterization of grapevine NIPs, providing crucial insights into understanding their role for uptake and translocation of small solutes, and extrusion of toxic compounds in grapevine.

Direct Observation of Deformation in Microgel Filtration

Colloidal filtration processes using porous membranes suffer from productivity loss due to colloidal matter retention and continuous build-up by the retained matter. Especially during filtration of soft matter, the deformation of the individual colloids that make up the filter cake may be significant; however, this deformation and its impact remain unresolved so far. Yet, understanding the deformation on the single colloid level as well as on the ensemble level is important to be able to deconvolute filter cake properties from resistance increase of the membrane either by simultaneous internal adsorption or blocking of pores. Here, we report on the compression of a filter cake by filtrating soft microgels in a microfluidic channel in front of a model membrane. To study the single colloid deformation amorphous and crystalline domains were built up in front of the membrane and visualized on-line using confocal fluorescence microscopy while adjusting the degree of permeation, i.e., the transmembrane flux. Results show locally pronounced asymmetric deformation in amorphous domains, while the microgels in colloidal crystals approached regular polyeder shape. Increasing the flux beyond the maximum colloid deformation results in non-isochoric microgel behavior. The presented methodology enables a realistic description of complex colloidal matter deposits during filtration.

Rapid zero-trans kinetics of Cs+ exchange in human erythrocytes quantified by dissolution hyperpolarized 133Cs+ NMR spectroscopy

Transmembrane flux of Cs+ (a K+ congener) was measured in human red blood cells (RBCs; erythrocytes) on the 10-s time scale. This is the first report on dissolution dynamic nuclear polarization (dDNP) nuclear magnetic resonance (NMR) spectroscopy with this nuclide in mammalian cells. Four technical developments regularized sample delivery and led to high quality NMR spectra. Cation-free media with the Piezo1 (mechanosensitive cation channel) activator yoda1 maximized the extent of membrane transport. First-order rate constants describing the fluxes were estimated using a combination of statistical methods in Mathematica, including the Markov chain Monte Carlo (MCMC) algorithm. Fluxes were in the range 4–70 μmol Cs+ (L RBC)−1 s−1; these are smaller than for urea, but comparable to glucose. Methodology and analytical procedures developed will be applicable to transmembrane cation transport studies in the presence of additional Piezo1 effectors, to other cellular systems, and potentially in vivo.