Molecular insights on NaCl crystal formation approaching PVDF membranes functionalized with graphene.

Membrane-assisted crystallization is an emerging technology where microporous hydrophobic membranes are used not as selective barriers but to promote the water vapor transfer between phases inducing supersaturation in solution. This has been successfully tested in the crystallization of ionic salts, low molecular weight organic acids and proteins. In this work, molecular dynamics simulations were used to study the crystal nucleation and growth of sodium chloride in contact with hydrophobic polymer surfaces at a supersaturated concentration of salt. A pristine polyvinylidene fluoride (PVDF) surface and PVDF containing different concentrations of graphene platelets were studied. Membrane crystallization tests were performed in parallel, in order to compare the experimental results with the computational ones. Here, with an integrated experimental-computational approach, we demonstrate that graphene-containing membranes assisted the crystal growth of NaCl, speeding up crystal nucleation in comparison with the pristine PVDF membranes. The computational results agreed with the experimental data, allowing the possibility of exploring the behavior of nanomaterials in membrane processes at a microscopic level.

Coupling Ultrafiltration-Based Processes to Concentrate Phenolic Compounds from Aqueous Goji Berry Extracts.

In this work, a membrane-based process for the purification and concentration of antioxidant compounds from aqueous Goji (Lycium barbarum L.) berry extracts was investigated. The aqueous extract was previously clarified with hollow fiber ultrafiltration (UF) membranes in order to remove suspended solids and ß-carotene and to produce a clarified extract enriched in phenolic compounds. Then, three UF flat sheet polyamide membranes with a molecular weight cut-off (MWCO) in the range 1000-3500 Da were tested to purify and concentrate phenolic compounds from the clarified extract. The effect of MWCO and transmembrane pressure (TMP) on the performance of selected membranes in terms of productivity and selectivity towards total dissolved solids (TDS), total phenolic compounds (TPC), total carbohydrates (TC) and total antioxidant activity (TAA) was evaluated. Experimental results indicated that the 2500 Da membrane exhibited a lower fouling index, higher cleaning efficiency, lower rejection towards carbohydrates (lower than 30%) and higher rejection towards phenolic compounds (higher than 50%) in comparison to the other investigated membranes. The inclusion of a diafiltration process in the treatment of the clarified extract with this membrane in a spiral-wound configuration improved the concentration of sugar compounds in the permeate stream and increased the purification of phenolic compounds in the retentate fraction.

A Membrane-Based Process for the Recovery of Glycyrrhizin and Phenolic Compounds from Licorice Wastewaters.

In this work, the use of polymeric ultrafiltration and nanofiltration membranes was investigated in order to recover glycyrrhizin and phenolic compounds from licorice wastewaters. Filtration experiments were performed on a laboratory scale using four polyamide thin-film composite membranes (GK, GH, GE, and DK, from GE Osmonics) with different molecular weight cut-offs (from 150 to 3500 Da). The permeate flux and retention values of glycyrrhizin, the total polyphenols, the caffeic acid, the total carbohydrate, and the total antioxidant activity as a function of the transmembrane pressure (TMP) and weight reduction factor (WRF) were evaluated. In selected operating conditions, the membrane productivity decreased in the order of GK > DK > GH > GE, with a similar trend to that of water permeability. Glycyrrhizin was totally rejected by selected membranes, independently of TMP and WRF. For the other antioxidant compounds, the retention values increased by increasing both of the parameters. According to the experimental results, a combination of membranes in a sequential design was proposed as a viable approach to produce concentrated fractions enriched in bioactive compounds and purified water from licorice wastewater.

Experimental Evaluation of the Thermal Polarization in Direct Contact Membrane Distillation Using Electrospun Nanofiber Membranes Doped With Molecular Probes.

Membrane distillation (MD) has recently gained considerable attention as a valid process for the production of fresh-water due to its ability to exploit low grade waste heat for operation and to ensure a nearly feed concentration-independent production of high-purity distillate. Limitations have been related to polarization phenomena negatively affecting the thermal efficiency of the process and, as a consequence, its productivity. Several theoretical models have been developed to predict the impact of the operating conditions of the process on the thermal polarization, but there is a lack of experimental validation. In this study, electrospun nanofiber membranes (ENMs) made of Poly(vinylidene fluoride) (PVDF) and doped with (1, 10-phenanthroline) ruthenium (II) Ru(phen)3 were tested at different operating conditions (i.e., temperature and velocity of the feed) in direct contact membrane distillation (DCMD). The temperature sensitive luminophore, Ru(phen)3, allowed the on-line and non-invasive mapping of the temperature at the membrane surface during the process and the experimental evaluation of the effect of the temperature and velocity of the feed on the thermal polarization.

Neuronal Differentiation Modulated by Polymeric Membrane Properties.

In this study, different collagen-blend membranes were successfully constructed by blending collagen with chitosan (CHT) or poly(lactic-co-glycolic acid) (PLGA) to enhance their properties and thus create new biofunctional materials with great potential use for neuronal tissue engineering and regeneration. Collagen blending strongly affected membrane properties in the following ways: (i) it improved the surface hydrophilicity of both pure CHT and PLGA membranes, (ii) it reduced the stiffness of CHT membranes, but (iii) it did not modify the good mechanical properties of PLGA membranes. Then, we investigated the effect of the different collagen concentrations on the neuronal behavior of the membranes developed. Morphological observations, immunocytochemistry, and morphometric measures demonstrated that the membranes developed, especially CHT/Col30, PLGA, and PLGA/Col1, provided suitable microenvironments for neuronal growth owing to their enhanced properties. The most consistent neuronal differentiation was obtained in neurons cultured on PLGA-based membranes, where a well-developed neuronal network was achieved due to their improved mechanical properties. Our findings suggest that tensile strength and elongation at break are key material parameters that have potential influence on both axonal elongation and neuronal structure and organization, which are of fundamental importance for the maintenance of efficient neuronal growth. Hence, our study has provided new insights regarding the effects of membrane mechanical properties on neuronal behavior, and thus it may help to design and improve novel instructive biomaterials for neuronal tissue engineering.

Immobilized biocatalytic process development and potential application in membrane separation: a review.

Biocatalytic membrane reactors have been widely used in different industries including food, fine chemicals, biological, biomedical, pharmaceuticals, environmental treatment and so on. This article gives an overview of the different immobilized enzymatic processes and their advantages over the conventional chemical catalysts. The application of a membrane bioreactor (MBR) reduces the energy consumption, and system size, in line with process intensification. The performances of MBR are considerably influenced by substrate concentration, immobilized matrix material, types of immobilization and the type of reactor. Advantages of a membrane associated bioreactor over a free-enzyme biochemical reaction, and a packed bed reactor are, large surface area of immobilization matrix, reuse of enzymes, better product recovery along with heterogeneous reactions, and continuous operation of the reactor. The present research work highlights immobilization techniques, reactor setup, enzyme stability under immobilized conditions, the hydrodynamics of MBR, and its application, particularly, in the field of sugar, starch, drinks, milk, pharmaceutical industries and energy generation.

Preparation of Pd-Loaded Hierarchical FAU Membranes and Testing in Acetophenone Hydrogenation.

Pd-loaded hierarchical FAU (Pd-FAU) membranes, containing an intrinsic secondary non-zeolitic (meso)porosity, were prepared and tested in the catalytic transfer hydrogenation of acetophenone (AP) to produce phenylethanol (PE), an industrially relevant product. The best operating conditions were preliminarily identified by testing different solvents and organic hydrogen donors in a batch hydrogenation process where micron-sized FAU seeds were employed as catalyst support. Water as solvent and formic acid as hydrogen source resulted to be the best choice in terms of conversion for the catalytic hydrogenation of AP, providing the basis for the design of a green and sustainable process. The best experimental conditions were selected and applied to the Pd-loaded FAU membrane finding enhanced catalytic performance such as a five-fold higher productivity than with the unsupported Pd-FAU crystals (11.0 vs. 2.2 mgproduct gcat(-1)·h(-1)). The catalytic performance of the membrane on the alumina support was also tested in a tangential flow system obtaining a productivity higher than that of the batch system (22.0 vs. 11.0 mgproduct gcat(-1)·h(-1)).

Functional carbon nanotubes for high-quality charge transfer and moisture regulation through membranes: structural and functional insights.

Functional single walled carbon nanotubes (SWCNTs) are assembled onto porous supports by using layer-by-layer (LBL) approaches. Directed nano-assembly of nanotubes is identified as a crucial factor for controlling the combined functions of hybrid-composite membranes, including charge and moisture transport. In both the cases, donor-acceptor interactions are indicated to be responsible for the rearrangement of nanotubes inside the LBL multilayer and their related properties. Aggregation and stratification of the carbon nanotubes along with the availability of selective-site interactions are complementarily investigated by using SEM, Raman and infrared spectroscopy, while high electrical charge and water vapor transfer are achievable, provided that a large number of connections and competitive interactions are allowed. Ohmic behavior is observed for all types of carbon nanotubes, even if better-quality charge transfer pathways are obtained with carboxylated conductive filaments. Likewise, assisted moisture regulation is succeeded when using functional filaments with the capability to establish competitive H-donor-acceptor interactions with water.

Remediation of textile effluents by membrane based treatment techniques: a state of the art review.

The textile industries hold an important position in the global industrial arena because of their undeniable contributions to basic human needs satisfaction and to the world economy. These industries are however major consumers of water, dyes and other toxic chemicals. The effluents generated from each processing step comprise substantial quantities of unutilized resources. The effluents if discharged without prior treatment become potential sources of pollution due to their several deleterious effects on the environment. The treatment of heterogeneous textile effluents therefore demands the application of environmentally benign technology with appreciable quality water reclamation potential. These features can be observed in various innovative membrane based techniques. The present review paper thus elucidates the contributions of membrane technology towards textile effluent treatment and unexhausted raw materials recovery. The reuse possibilities of water recovered through membrane based techniques, such as ultrafiltration and nanofiltration in primary dye houses or auxiliary rinse vats have also been explored. Advantages and bottlenecks, such as membrane fouling associated with each of these techniques have also been highlighted. Additionally, several pragmatic models simulating transport mechanism across membranes have been documented. Finally, various accounts dealing with techno-economic evaluation of these membrane based textile wastewater treatment processes have been provided.

Neuroprotective effect of didymin on hydrogen peroxide-induced injury in the neuronal membrane system.

In this study, the flavonoid didymin was administered in vitro in neuronal cells after hydrogen peroxide (H2O2)-induced injury (neurorescue) in order to investigate the effects of this natural molecule on cell damage in a neuronal membrane system. The results showed the effects of didymin in neuronal cells by using a polycaprolactone biodegradable membrane system as an in vitro model. Two major findings are presented in this study: first is the antioxidant property of didymin and, second, for the first time we provide evidence concerning its ability to rescue neuronal cells from oxidative damage. Didymin showed radical scavenging activities and it protected the neuronal cells against H2O2-induced neurotoxicity. Didymin increased cell viability, decreased intracellular reactive oxygen species generation, stimulated superoxide dismutase, catalase and glutathione peroxidase activity in neuronal cells which were previously insulted with H2O2. In addition, didymin strikingly inhibited H2O2-induced mitochondrial dysfunctions in terms of reduction of mitochondria membrane potential and the activation of cleaved caspase-3, and also decreased dramatically the H2O2-induced phosphorylation of c-Jun N-terminal kinase. Therefore, this molecule is capable of inducing recovery from oxidative damage, and promoting and/or restoring normal cellular conditions. Moreover, the mechanism underlying the protective effects of didymin in H2O2-injured neuronal cells might be related to the activation of antioxidant defense enzymes as well as to the inhibition of apoptotic features, such as p-JNK and caspase-3 activation. These data suggest that didymin may be a potential therapeutic molecule for the treatment of neurodegenerative disorders associated with oxidative stress.

Bio-mimetic sensors based on molecularly imprinted membranes.

An important challenge for scientific research is the production of artificial systems able to mimic the recognition mechanisms occurring at the molecular level in living systems. A valid contribution in this direction resulted from the development of molecular imprinting. By means of this technology, selective molecular recognition sites are introduced in a polymer, thus conferring it bio-mimetic properties. The potential applications of these systems include affinity separations, medical diagnostics, drug delivery, catalysis, etc. Recently, bio-sensing systems using molecularly imprinted membranes, a special form of imprinted polymers, have received the attention of scientists in various fields. In these systems imprinted membranes are used as bio-mimetic recognition elements which are integrated with a transducer component. The direct and rapid determination of an interaction between the recognition element and the target analyte (template) was an encouraging factor for the development of such systems as alternatives to traditional bio-assay methods. Due to their high stability, sensitivity and specificity, bio-mimetic sensors-based membranes are used for environmental, food, and clinical uses. This review deals with the development of molecularly imprinted polymers and their different preparation methods. Referring to the last decades, the application of these membranes as bio-mimetic sensor devices will be also reported.

Preparation, Modification, and Application of Ethylene-Chlorotrifluoroethylene Copolymer Membranes.

Ethylene-chlorotrifluoroethylene (ECTFE) was first commercialized by DuPont in 1974. Its unique chemical structure gives it high heat resistance, mechanical strength, and corrosion resistance. But also due to these properties, it is difficult to prepare a membrane from it by the nonsolvent-induced phase separation (NIPS) method. However, it can be prepared as a microfiltration membrane using the thermally induced phase separation (TIPS) method at certain temperatures and with the selection of suitable solvents, and the use of green solvents is receiving increasing attention from researchers. The surface wettability of ECTFE membranes usually needs to be modified before use to strengthen its performance to meet the application requirements, usually by graft modification and surface oxidation techniques. This paper provides an overview of the structure of ECTFE and its preparation and modification methods, as well as recent advances in its application areas and prospects for the future methods of preparing high-performance ECTFE membranes.

Optimization of Membrane Condenser Process with PTFE Hollow Fiber Membrane.

A membrane condenser (MC) is a novel membrane separation technology that utilizes the hydrophobic nature of porous membranes to capture water vapor from humid gas. Factors such as temperature, pressure, flow rate, and gas composition entering the membrane condenser play a crucial role in water recovery efficiency. This study utilized hydrophobic polytetrafluoroethylene (PTFE) hollow fiber membranes to create multiple identical membrane modules. This research investigated the impact of temperature, flow rate, pressure on the intake side, gas flow on the cooling side, membrane area, and other variables on the performance of the membrane condenser process. This study compared water extraction efficiency under different conditions, focusing on feed flow temperature and sweeping flow. Results showed that at a temperature of 60 °C, the water recovery rate was 24.7%, while a sweep gas flow rate of 4 L/min resulted in a recovery rate of 22.7%. The efficiency of the membrane condenser decreased with higher feed flow rates but increased with larger membrane areas. A proportional relationship between inlet flow and membrane area was observed, suggesting an optimal range of 0.51-0.67 cm/s for both parameters. These findings offer valuable insights for the practical implementation of hydrophobic membrane-based membrane condenser technology.

Insights into the polymorphism of glycine: membrane crystallization in an electric field.

In this work we studied glycine crystallization with two main objectives: (i) to get improved control of crystal growth and polymorphic selectivity of organic molecules; (ii) to achieve additional insights into the nucleation mechanisms of glycine polymorphs. To reach these goals, membrane crystallization technology, a tool which allows improved control of supersaturation in solution crystallization, was used under different operating conditions: the variable solvent removal rate, acidic and almost neutral pH, the presence of a pulsed electric field. The traditional explanation for the crystallization of α and γ glycine polymorphs from aqueous solution is based on the general cyclic dimer hypothesis and the self-poisoning mechanism. In contrast with both the conventional theories, experimental results suggest that the relative nucleation rates with respect to the relative growth kinetics of the two forms under the different conditions play a dominant role in determining the polymorphic outcome. Our results instead support a molecular nucleation route where open chain dimers can behave as building units for both γ- and α-glycines in the rate determining structuring step of the two-step nucleation mechanism.

Production of total reducing sugar (TRS) from acid hydrolysed potato peels by sonication and its optimization.

Potato peel is a waste biomass which can be a source of raw material for biofuel production. This biomass contains a sufficient amount of total reducing sugar (TRS), which can be extracted and further treated with microbial pathways to produce bioethanol. The extraction of TRS from potato peels by hydrolysis in dilute sulphuric acid was investigated at different acid concentrations (0.50%, 0.75% and 1% w/v) and sonication was carried out to improve the extent of sugar extraction after hydrolysis. Response surface methodology based on central composite design was used to verify the experimental data and later applied for the optimization of the main important reaction variables including amplitude (60%, 80% and 100%), cycle (0.6, 0.8 and 1.0) and treatment time (5, 10 and 15 min) for the responses of TRS extraction by acid hydrolysis and later compared with the experimental data.

Plasmonic Phenomena in Membrane Distillation.

Water scarcity raises important concerns with respect to human sustainability and the preservation of important ecosystem functions. To satisfy water requirements, seawater desalination represents one of the most sustainable solutions. In recent decades, membrane distillation has emerged as a promising thermal desalination process that may help to overcome the drawbacks of traditional desalination processes. Nevertheless, in membrane distillation, the temperature at the feed membrane interface is significantly lower than that of the bulk feed water, due to the latent heat flux associated with water evaporation. This phenomenon, known as temperature polarization, in membrane distillation is a crucial issue that could be responsible for a decay of about 50% in the initial transmembrane water flux. The use of plasmonic nanostructures, acting as thermal hotspots in the conventional membranes, may improve the performance of membrane distillation units by reducing or eliminating the temperature polarization problem. Furthermore, an efficient conversion of light into heat offers new opportunities for the use of solar energy in membrane distillation. This work summarizes recent developments in the field of plasmonic-enhanced solar evaporation with a particular focus on solar-driven membrane distillation applications and its potential prospects.

Preparation of Hyflon AD/Polypropylene Blend Membrane for Artificial Lung.

A high-performance polypropylene hollow fiber membrane (PP-HFM) was prepared by using a binary environmentally friendly solvent of polypropylene as the raw material, adopting the thermally induced phase separation (TIPS) method, and adjusting the raw material ratio. The binary diluents were soybean oil (SO) and acetyl tributyl citrate (ATBC). The suitable SO/ATBC ratio of 7/3 was based on the size change of the L-L phase separation region in PP-SO/ATBC thermodynamic phase diagram. Through the characterization and comparison of the basic performance of PP-HFMs, it was found that with the increase of the diluent content in the raw materials, the micropores of outer surface of the PP-HFM became larger, and the cross section showed a sponge-like pore structure. The fluoropolymer, Hyflon ADx, was deposited on the outer surface of the hollow fiber membrane using a physical modification method of solution dipping. After modification, the surface pore size of the Hyflon AD40L modified membranes decreased; the contact angle increased to around 107°; the surface energy decreased to 17 mN·m-1; and the surface roughness decreased to 17 nm. Hyflon AD40L/PP-HFMs also had more water resistance properties from the variation of wetting curve. For biocompatibility of the membrane, the adsorption capacity of the modified PP membrane for albumin decreased from approximately 1.2 mg·cm-2 to 1.0 mg·cm-2, and the adsorption of platelets decreased under fluorescence microscopy. The decrease in blood cells and protein adsorption in the blood prolonged the clotting time. In addition, the hemolysis rate of modified PP membrane was reduced to within the standard of 5%, and the cell survival rate of its precipitate was above 100%, which also indicated the excellent biocompatibility of fluoropolymer modified membrane. The improvement of hydrophobicity and blood compatibility makes Hyflon AD/PP-HFMs have the potential for application in membrane oxygenators.

Exergetic analysis of direct contact membrane distillation (DCMD) using PVDF hollow fiber membranes for the desalination brine treatment.

The brines from desalination plants need to be disposed of due to their strong impact on the environment. Membrane operations, like direct contact membrane distillation (DCMD), provide a possible solution to reduce the amount of brine while producing further desalinated water. In this study, an exergy analysis of a laboratory membrane distillation unit working with brines from reverse osmosis (RO) is analyzed. Exergy analysis enables us to assess the energy lost in entropy generation; therefore, it commits us to identify the less efficient configuration of the DCMD module. Unlike other exergy analyses for distillation, in this study, only module inputs and outputs were incorporated. The exergy is calculated at different infeed temperatures, for both in-out and out-in feed configurations of hollow fiber membrane modules. Also, exergy difference, flux, and exergetic efficiency for both configurations are calculated. At high feed temperatures, there is an increase in both flux and exergy change, which increases water recovery and feed side exergetic efficiency. The highest flux that is obtained in the out-in configuration is 13.3 kg/h.m2 while it is only 6.23 kg/h.m2 for the in-out system of the module. Also, these exergy changes and feed efficiencies are higher in the out-in module configuration than in the in-out module configuration. Conversely, the exergetic efficiency of the permeate is higher at lower feed temperatures, due to the lower accumulation of concentration polarization along the membrane wall.

Topographical cues of PLGA membranes modulate the behavior of hMSCs, myoblasts and neuronal cells.

Biomaterial surface modification through the introduction of defined and repeated patterns of topography helps study cell behavior in response to defined geometrical cues. The lithographic molding technique is widely used for conferring biomaterial surface microscale cues and enhancing the performance of biomedical devices. In this work, different master molds made by UV mask lithography were used to prepare poly (D,L-lactide-co-glycolide) - PLGA micropatterned membranes to present different features of topography at the cellular interface: channels, circular pillars, rectangular pillars, and pits. The effects of geometrical cues were investigated on different cell sources, such as neuronal cells, myoblasts, and stem cells. Morphological evaluation revealed a peculiar cell arrangement in response to a specific topographical stimulus sensed over the membrane surface. Cells seeded on linear-grooved membranes showed that this cue promoted elongated cell morphology. Rectangular and circular pillars act instead as discontinuous cues at the cell-membrane interface, inducing cell growth in multiple directions. The array of pits over the surface also highlighted the precise spatiotemporal organization of the cell; they grew between the interconnected membrane space within the pits, avoiding the microscale hole. The overall approach allowed the evaluation of the responses of different cell types adhered to various surface patterns, build-up on the same polymeric membrane, and disclosing the effect of specific topographical features. We explored how various microtopographic signals play distinct roles in different cells, thus affecting cell adhesion, migration, differentiation, cell-cell interactions, and other metabolic activities.

Treatment of Aniline Wastewater by Membrane Distillation and Crystallization.

Aniline is a highly toxic organic pollutant with "carcinogenic, teratogenic and mutagenesis" characteristics. In the present paper, a membrane distillation and crystallization (MDCr) process was proposed to achieve zero liquid discharge (ZLD) of aniline wastewater. Hydrophobic polyvinylidene fluoride (PVDF) membranes were used in the membrane distillation (MD) process. The effects of the feed solution temperature and flow rate on the MD performance were investigated. The results showed that the flux of the MD process was up to 20 L·m-2·h-1 and the salt rejection was above 99% under the feeding condition of 60 °C and 500 mL/min. The effect of Fenton oxidation pretreatment on the removal rate of aniline in aniline wastewater was also investigated, and the possibility of realizing the ZLD of aniline wastewater in the MDCr process was verified.