Nanomembranes-Affiliated Water Remediation: Chronology, Properties, Classification, Challenges and Future Prospects

Water contamination has become a global crisis, affecting millions of people worldwide and causing diseases and illnesses, including cholera, typhoid, and hepatitis A. Conventional water remediation methods have several challenges, including their inability to remove emerging contaminants and their high cost and environmental impact. Nanomembranes offer a promising solution to these challenges. Nanomembranes are thin, selectively permeable membranes that can remove contaminants from water based on size, charge, and other properties. They offer several advantages over conventional methods, including their ability to remove evolving pollutants, low functioning price, and reduced ecological influence. However, there are numerous limitations linked with the applications of nanomembranes in water remediation, including fouling and scaling, cost-effectiveness, and potential environmental impact. Researchers are working to reduce the cost of nanomembranes through the development of more cost-effective manufacturing methods and the use of alternative materials such as graphene. Additionally, there are concerns about the release of nanomaterials into the environment during the manufacturing and disposal of the membranes, and further research is needed to understand their potential impact. Despite these challenges, nanomembranes offer a promising solution for the global water crisis and could have a significant impact on public health and the environment. The current article delivers an overview on the exploitation of various engineered nanoscale substances, encompassing the carbonaceous nanomaterials, metallic, metal oxide and metal-organic frameworks, polymeric nano-adsorbents and nanomembranes, for water remediation. The article emphasizes the mechanisms involved in adsorption and nanomembrane filtration. Additionally, the authors aim to deliver an all-inclusive review on the chronology, technical execution, challenges, restrictions, reusability, and future prospects of these nanomaterials.

Self-Standing Nanomembranes of Super-Tough Plastics

Nanomembranes are effective coating materials for protecting substrates from external stimuli; however, they are generally not self-standing owing to their low mechanical toughness. Self-standing nanomembranes would be an innovative development in the field of nanotechnology including miniaturized devices. In this study, self-standing nanomembranes were developed by spin-casting supertough polyamides over dimethylformamide solution. The polyamides were synthesized by the polycondensation of two derivatives of 4,4'-diamino-α-truxillic acid (4ATA) with slightly bent diphenylcyclobutane in the core. Mechanical evaluation of the 4ATA polyamides having an appropriate composition of aliphatic diacids revealed a high strain-energy density of 231 MJ m^-3 at its maximum, which is significantly tougher than spider silk. The nanocoats with a thickness of several hundred nanometers showing interference fringes were able to be peeled off the glass substrate without breaking, owing to its ultrahigh toughness. The self-standing nanomembrane would be applied to flexible devices in the future.

Metal-Insulator Transition of Ultrathin Sputtered Metals on Phenolic Resin Thin Films: Growth Morphology and Relations to Surface Free Energy and Reactivity

Nanostructured metal assemblies on thin and ultrathin polymeric films enable state of the art technologies and have further potential in diverse fields. Rational design of the structure–function relationship is of critical importance but aggravated by the scarcity of systematic studies. Here, we studied the influence of the interplay between metal and polymer surface free energy and reactivity on the evolution of electric conductivity and the resulting morphologies. In situ resistance measurements during sputter deposition of Ag, Au, Cu and Ni films on ultrathin reticulated polymer films collectively reveal metal–insulator transitions characteristic for Volmer–Weber growth. The different onsets of percolation correlate with interfacial energy and energy of adhesion weakly but as expected from ordinary wetting theory. A more pronounced trend of lower percolation thickness for more reactive metals falls in line with reported correlations. Ex situ grazing incidence small angle X-ray scattering experiments were performed at various thicknesses to gain an insight into cluster and film morphology evolution. A novel approach to interpret the scattering data is used where simulated pair distance distributions of arbitrary shapes and arrangements can be fitted to experiments. Detailed approximations of cluster structures could be inferred and are discussed in view of the established parameters describing film growth behavior.

Freely suspended perforated polymer nanomembranes for protein separations

Selective removal of nanometer-sized compounds such as proteins from fluids is an often challenging task in many scientific and industrial areas. Addressing such tasks with highly efficient and selective membranes is desirable since commonly used chromatographic approaches are expensive and difficult to scale up. Nanomembranes, molecularly thin separation layers, have been predicted and shown to possess outstanding properties but in spite ultra-fast diffusion times and high-resolution separation, to date they generally lack either of two crucial characteristics: compatibility with biological fluids and low-cost production. Here we report the fast and easy fabrication of highly crosslinked polymer membranes based on a thermoset resin (poly[(o-cresyl glycidyl ether)-co-formaldehyde (PCGF) cured with branched polyethyleneimine (PEI)) with nanoscale perforations of 25 nm diameter. During spin casting, microphase separation of a polylactide-co-glycolide induces the formation of nanometer sized domains that serve as templates for perforations which penetrate the 80 nm thick membranes. Ultrathin perforated nanomembranes can be freely suspended on the cm scale, exhibit high mechanical strength, low surface energies and a sharp permeability cutoff at a hydrodynamic diameter of 10 nm suitable for protein separations.

Membrane thinning for efficient CO2 capture

Enhancing the fluxes in gas separation membranes is required for utilizing the membranes on a mass scale for CO2 capture. Membrane thinning is one of the most promising approaches to achieve high fluxes. In addition, sophisticated molecular transport across membranes can boost gas separation performance. In this review, we attempt to summarize the current state of CO2 separation membranes, especially from the viewpoint of thinning the selective layers and the membrane itself. The gas permeation behavior of membranes with ultimate thicknesses and their future directions are discussed.

Flexible thermoresponsive nanomembranes at the aqueous–air interface

Thermoresponsive freestanding nanomembranes were grown by surface-initiated polymerization at the aqueous–air interface of a pendant drop. We demonstrate formation of liquid-like interfaces supporting anisotropic stress and mechanical flexibility.

Insulating and semiconducting polymeric free-standing nanomembranes with biomedical applications

Free-standing nanomembranes, which are emerging as versatile elements in biomedical applications, are evolving from being composed of insulating (bio)polymers to electroactive conducting polymers.

Surface functionalization by decal-like transfer of thermally cross-linked urushiol thin films

We have demonstrated surface functionalization through the decal-like transfer of thermally cross-linked urushiol thin films onto various substrates. Tensile adhesive strength measurements showed that the film adheres strongly to the surface of various substrates including chemically inert materials, such as polyolefins and thermosetting resins, because of the properties of urushiol. Furthermore, the highly cross-linked structure of urushiol made the films mechanically robust. These two properties allowed the fabrication of practicable thin films for indirect surface modification. Actually, the robust thin film served as a scaffold for an Au thin film, which was then bound to various substrates. Surface-texturing of nanodecal was also demonstrated as an application aspects.

Thermoplastic polyurethane:polythiophene nanomembranes for biomedical and biotechnological applications

Nanomembranes have been prepared by spin-coating mixtures of a polythiophene (P3TMA) derivative and thermoplastic polyurethane (TPU) using 20:80, 40:60, and 60:40 TPU:P3TMA weight ratios. After structural, topographical, electrochemical, and thermal characterization, properties typically related with biomedical applications have been investigated: swelling, resistance to both hydrolytic and enzymatic degradation, biocompatibility, and adsorption of type I collagen, which is an extra cellular matrix protein that binds fibronectin favoring cell adhesion processes. The swelling ability and the hydrolytic and enzymatic degradability of TPU:P3TMA membranes increases with the concentration of P3TMA. Moreover, the degradation of the blends is considerably promoted by the presence of enzymes in the hydrolytic medium, TPU:P3TMA blends behaving as biodegradable materials. On the other hand, TPU:P3TMA nanomembranes behave as bioactive platforms stimulating cell adhesion and, especially, cell viability. Type I collagen adsorption largely depends on the substrate employed to support the nanomembrane, whereas it is practically independent of the chemical nature of the polymeric material used to fabricate the nanomembrane. However, detailed microscopy study of the morphology and topography of adsorbed collagen evidence the formation of different organizations, which range from fibrils to pseudoregular honeycomb networks depending on the composition of the nanomembrane that is in contact with the protein. Scaffolds made of electroactive TPU:P3TMA nanomembranes are potential candidates for tissue engineering biomedical applications.

Ultraflexible, freestanding nanomembranes based on poly(ethylene glycol)

Extremely elastic and highly stable nanomembranes of variable thickness (5-350 nm) made completely of poly(ethylene glycol) are prepared by a simple procedure. The membranes exhibit distinct biorepulsive and hydrogel properties. They offer new possibilities for applications such as supports in transmission electron microscopy, matrices for inorganic nanoparticles, and pressure-sensitive elements for sensors.

Scaffold for growing dense polymer brushes from a versatile substrate

We have demonstrated a universal approach to growing polymer brushes from various substrates. Urushiol was mixed with initiator-containing catechol, and it was spin-coated or cast on various substrates. Because urushiol is strongly adhered to various substrates, the thin film can serve as a general scaffold for grafting polymer brushes from various substrates. Note that the film was formed even onto the surface of polyolefins and thermosetting resins that are known as chemically inert materials to functionalize the surface. Moreover, the initiator-immobilized scaffold showed mechanical robustness and chemical inertness because of the flexible long unsaturated hydrocarbon side chain of urushiol. After the grafting of polyelectrolyte PMTAC polymer brushes, the material obtained exhibited hydrophilicity, typical of PMTAC. The concept shown here could provide a general approach for grafting practical polymer brushes from various substrates.

Concealing surface topography by attachment of nanometer-thick film

Concealing of surface topology of substrates by decal-like attachment of nanomembrane is demonstrated. The nanomembrane attachment provides a flat surface on various substrates, including porous substrates, and the surface property such as wettability was changed to that of the nanomembrane. The monitoring of drying process revealed that a nanomembrane with certain thickness tolerates their flexural deflection during the procedure. Moreover, the supporting position of nanomembranes as well as the physical properties of nanomembranes strongly affected the degree of deflection. The decal-like attachment of nanomembranes shown here is potentially a powerful method for creating a new functional surface that is independent of the topological and chemical properties of the original substrate.

Thinning and shaping solid films into functional and integrative nanomembranes

Conventional solid films on certain substrates play a crucial role in various applications, for example in flat panel displays, silicon technology, and protective coatings. Recently, tremendous attention has been directed toward the thinning and shaping of solids into so-called nanomembranes, offering a unique and fantastic platform for research in nanoscience and nanotechnology. In this Review, a conceptual description of nanomembranes is introduced and a series of examples demonstrate their great potential for future applications. The thinning of nanomembranes indeed offers another strategy to fabricate nanomaterials, which can be integrated onto a chip and exhibit valuable properties (e.g. giant persistent photoconductivity and thermoelectric property). Furthermore, the stretching of nanomembranes enables a macroscale route for tuning the physical properties of the membranes at the nanoscale. The process by which nanomembranes release from a substrate presents several approaches to shaping nanomembranes into three-dimensional architectures, such as rolled-up tubes, wrinkles, and the resulting channels, which can provide fascinating applications in electronics, mechanics, fluidics, and photonics. Nanomembranes as a new type of nanomaterial promise to be an attractive direction for nanoresearch.

Surface wrinkling: a versatile platform for measuring thin-film properties

Surface instabilities in soft matter have been the subject of increasingly innovative research aimed at better understanding the physics of their formation and their utility in patterning, organizing, and measuring materials properties on the micro and nanoscale. The focus of this Review is on a type of instability pattern known as surface wrinkling, covering the general concepts of this phenomenon and several recent applications involving the measurement of thin-film properties. The ability of surface wrinkling to yield new insights into particularly challenging materials systems such as ultrathin films, polymer brushes, polyelectrolyte multilayer assemblies, ultrasoft materials, and nanoscale structured materials is highlighted. A perspective on the future directions of this maturing field, including the prospects for advanced thin-film metrology methods, facile surface patterning, and the control of topology-sensitive phenomena, such as wetting and adhesion, is also presented.