Exfoliated Bi2Te3-enabled membranes for new concept water desalination: Freshwater production meets new routes.

Water scarcity forces the science to find the most environmentally friendly propulsion technology for supplying plentiful freshwater at low energy costs. Membrane Distillation well meets criteria of eco-friendly management of natural resources, but it is not yet competitive on scale. Herein, we use a dichalchogenide compound (Bi2Te3) as a conceivable source to accelerate the redesign of advanced membranes technologies such as thermally driven membrane distillation. A procedure based on assisted dispersant liquid phase exfoliation is used to fill PVDF membranes. Key insights are gained in the crucial role of this topological material confined in hydrophobic membranes dedicated to recovery of freshwater from synthetic seawater. Intensified water flux together with reduced energy consumption is obtained into one pot, thereby gathering ultrafast production and thermal efficiency in a single device. Bi2Te3-enabled membranes show ability to reduce the resistance to mass transfer while high resistance to heat loss is opposite. Permeate flux is kept stable and salt rejection is higher than 99.99% during 23 h-MD test. Our results confirm the effectiveness of chalcogenides as frontier materials for new-concept water desalination through breakthrough thermally-driven membrane distillation, which is regarded as a new low-energy and sustainable solution to address the growing demand for access to freshwater.

A few-layer graphene for advanced composite PVDF membranes dedicated to water desalination: a comparative study.

Membrane distillation is envisaged to be a promising best practice to recover freshwater from seawater with the prospect of building low energy-consuming devices powered by natural and renewable energy sources in remote and less accessible areas. Moreover, there is an additional benefit of integrating this green technology with other well-established operations dedicated to desalination. Today, the development of membrane distillation depends on the productivity-efficiency ratio on a large scale. Despite hydrophobic commercial membranes being widely used, no membrane with suitable morphological and chemical feature is readily available in the market. Thus, there is a real need to identify best practices for developing new efficient membranes for more productive and eco-sustainable membrane distillation devices. Here, we propose engineered few-layer graphene membranes, showing enhanced trans-membrane fluxes and total barrier action against NaCl ions. The obtained performances are linked with filling polymeric membranes with few-layer graphene of 490 nm in lateral size, produced by the wet-jet milling technology. The experimental evidence, together with comparative analyses, confirmed that the use of more largely sized few-layer graphene leads to superior productivity related efficiency trade-off for the membrane distillation process. Herein, it was demonstrated that the quality of exfoliation is a crucial factor for addressing the few-layer graphene supporting the separation capability of the host membranes designed for water desalination.

Adsorption-assisted transport of water vapour in super-hydrophobic membranes filled with multilayer graphene platelets.

The effects of confinement of multilayer graphene platelets in hydrophobic microporous polymeric membranes are here examined. Intermolecular interactions between water vapour molecules and nanocomposite membranes are envisaged to originate assisted transport of water vapour in membrane distillation processes when a suitable filler-polymer ratio is reached. Mass transport coefficients are estimated under different working conditions, suggesting a strong dependence of the transport on molecular interactions. Remarkably, no thermal polarization is observed, although the filler exhibits ultrahigh thermal conductivity. In contrast, enhanced resistance to wetting as well as outstanding mechanical and chemical stability meets the basic requirements of water purification via membrane distillation. As a result, a significant improvement of the productivity-efficiency trade-off is achieved with respect to the pristine polymeric membrane when low amounts of platelets are confined in spherulitic-like PVDF networks.

Integrated carboxylic carbon nanotube pathways with membranes for voltage-activated humidity detection and microclimate regulation.

This work describes some single walled carboxylic carbon nanotubes with outstanding transport properties when assembled in a 3D microarray working like a humidity membrane-sensor and an adjustable moisture regulator. Combined nano-assembly approaches are used to build up a better quality pathway through which assisted-charge and mass transport synchronically takes place. The structure-electrical response relationship is found, while controllable and tunable donor-acceptor interactions established at material interfaces are regarded as key factors for the accomplishment of charge transportation, enhanced electrical responses and adjustable moisture exchange. Raman and infrared spectroscopy provides indications about the fine structural and chemical features of the hybrid-composite membranes, resulting in perfect agreement with related morphology and electrical properties. Enhanced and modular electrical response to changes in the surrounding atmosphere is concerned with doping events, while assisted moisture regulation is discussed in relation to swelling and hopping actions. The electro-activated hybrid-composite membrane proposed in this work can be regarded as an attractive 'sense-to-act' precursor for smart long-distance monitoring systems with capability to adapt itself and provide local comfortable microenvironments.

Competitive hydrogen-bonding interactions in modified polymer membranes: a density functional theory investigation.

The subject of this work is the density functional theory (DFT) investigation of competitive hydrogen-bonding interactions that occur in modified block poly(ether/amide) (PEBAX) membranes. Previously, an evaluation of hydrogen-bonding interactions occurring between N-ethyl-o,p-toluensulfonamide (KET) modifiers was performed to establish the role of these interactions in affinity processes when the modifier is dissolved in PEBAX matrixes. However, some issues related to polymer-polymer (host-host) and modifier-polymer (host-guest) interactions were not analyzed from a theoretical point of view in the previous analysis. Here, a comparative computational analysis of these intermolecular interactions is discussed. New insights into the role of hydrogen bonding in domino processes are provided. Calculations in solvent and in vacuum have been done, yielding indications about the change in the availability of the polar groups of the polymer, which is considered to be partially responsible for the enhanced hydrophilicity of the membranes. This study can open the way to the construction of new predictive quantum modeling approaches for designing improved modifiers, enabling the optimization of polymer membrane performance.

Supercritical gel drying: a powerful tool for tailoring symmetric porous PVDF-HFP membranes.

In this work, poly(vinylidene fluoride) copolymer with hexafluoropropylene (PVDF-HFP) membrane-like aerogels have been generated for the first time. PVDF-HFP gels have been prepared from polymer-acetone solutions by adding various amounts of ethanol. A series of supercritical drying experiments have been performed at different pressures (from 100 to 200 bar) and temperatures (from 35 to 45 degrees C) and at various polymer concentrations (from 5 to 12 wt %). The effects of the process conditions on the membrane morphology have been evaluated, and structure-property relationships have been found. In all cases, the membranes exhibit interconnected structures with nanosized pores and high porosity, leading to reduced resistance to the gas mass transfer and high hydrophobic character of the surfaces. These membrane-like aerogels promise to form a new class of highly hydrophobic porous interfaces, potentially suitable to be used in membrane operations based, for example, on the contactor technology.

Intermolecular interactions as controlling factor for water sorption into polymer membranes.

A multidisciplinary approach was used for delineating the mechanisms controlling water sorption into modified block co-poly-(ether/amide) (PEBAX) membranes. In particular, incorporation of aromatic sulfonamide (KET) into the polymer matrix led to a nonlinear increase of water sorption in the membrane. The modification in sorption was accompanied by a nonlinear behavior in membrane surface energies. Infrared analysis revealed a different availability and accessibility of free polar groups supporting the formation of hydrogen bonding as a function of modifier concentration. A combination of both experimental and theoretical procedures was used to analyze the molecular processes of water sorption on PEBAX membranes. Molecular dynamics (MD) and quantum chemical (QC) calculations demonstrated that the formation of KET-KET dimers in the polymeric matrix led to a decrease in the interaction energy between water and modifiers. In addition, no variations in the dipole moments of water-dimer structures were found in comparison to a single KET and water-KET molecule. The formation of water-dimer complexes at higher concentration of modifier decreases the number of the dipole moment, thus preventing the polarization of polymer chains.

Study of the surface character as responsible for controlling interfacial forces at membrane-feed interface.

The role of the interfacial forces was emphasized in interactive processes, involving membrane surface and penetrating molecules. The surface character controlling the dissolution process of some species (CO2, H2O, C3H6O2, C4H8O2, C5H10O2) was evaluated in relation to the supra-molecular chemistry of membranes based on 80PTMO/PA12. Infrared analyses combined with the estimation of the hydrophilic and hydrophobic domains of the membrane surface yielded useful information about the distribution, availability and accessibility of the polar moieties responsible for the penetrant sorption. At the interface, attractive Lewis acid/base interactions such as H-bonding directed the sorption of vapor species into the membranes, whereas quadrupolar CO2 participated in specific Lifshitz-van der Waals interactions with the modified polymers. In both the cases, the presence of additional polar moieties such as carbonyl, sulfonamide, and hydroxyl groups enhanced the affinity of the Pebax-based membranes for the penetrating species considered in this work. As a result, the quantification of the reactivity of a membrane surface for specific molecules may allow predictive models to be constructed and selective membranes to be designed.

Novel PEEK-WC membranes with low plasma protein affinity related to surface free energy parameters.

There has been growing interest in innovative materials with specific physico-chemical properties that provide an improved blood/cell compatibility. In this paper we evaluated the performance of new membranes prepared from a modified polyetheretherketone (PEEK-WC) contacting human plasma proteins. These membranes were prepared by using the phase inversion technique. Membrane wettability and affinity to proteins were evaluated by means of contact angle experiments, roughness measurements, and quantitative UV analysis. The energy parameters of membrane surfaces were determined according to Good, van Oss and Chaudhury's theory. The extent of human albumin, fibrinogen and immunoglobulin G adsorption was related to quantitative expressions of the membrane surface hydrophilicity: the base parameter of surface free energy and the free energy of interfacial interaction. The performance of PEEK-WC membranes was compared to that of commercial membranes, which conventionally are used in biomedical applications. The experimental results showed a reduction of protein adsorption on PEEK-WC membranes with respect to other commercial membranes. The low protein affinity of PEEK-WC membranes is due to the intrinsic physico-chemical characteristics of the polymeric material which makes these membranes interesting for potential use in biomedical applications.