Efficient dye adsorption by highly porous nanofiber aerogels

Electrospun nanofiber membranes are frequently used in adsorption processes thanks to their high specific surface area, tailored surface functionality, and fiber uniformity. However, they are still facing challenges such as low mechanical stability and unfavorable mass transport properties. In this study, an ultra-light and robust 3D nanofiber aerogel (NFA) or nanofiber sponge with tunable porosity and flexibility was synthesized from short pullulan/polyvinyl alcohol/polyacrylic acid nanofibers using a freeze casting process followed by thermal crosslinking. We demonstrate time the application of such NFAs in batch and continuous adsorption systems and compare their performance with flat nanofiber membranes (NFM). The NFAs proved to be promising adsorbents for cationic dyes due to their high adsorption capacity (383 mg/g) and their reusability. Langmuir isotherm was a suitable model for describing the adsorption process. The endothermic system followed a pseudo second order kinetic model and intra-fiber adsorption is found to be involved in the adsorption process. Dye adsorption by 3D NFAs was four times faster than for the respective flat NFMs and when used in a continuous process as a deep-bed filter, the pressure drop through the NFA was reduced by a factor of 40 while maintaining equal adsorption performance as for the NFM

A chitosan nanofiber sponge for oyster-inspired filtration of microplastics

For the first time, an ultralight chitosan-glutaraldehyde nanofiber sponge (chitosan NF sponge) was prepared. The present work describes its processing from pure electrospun chitosan nanofibers and its use for filtration applications. Chitosan/polyethylene oxide (PEO) nanofibers (NF) were electrospun from acetic acid into 309 ± 56 nm-thick nanofibers using high-throughput free-surface electrospinning. To yield chitosan NF sponges, PEO was extracted from the defect-free nanofiber mats. From these mats, nanofiber suspensions were prepared followed by casting and freeze-drying. Cross-linking of such obtained pristine chitosan NF sponges with glutaraldehyde improved water stability and resulted in chitosan NF sponges with a bulk density of 5.77 mg cm–3 and a porosity of 99.59%. The hierarchical pore architecture of the chitosan NF sponges was perfectly suited for particle adsorption as tested for poly(ethylene terephthalate)-microplastic (PET-MP) and Arizona test dust (ISO 12103-1) suspensions. Hydrostatic filtration with chitosan NF sponges reduced turbidity of particle suspensions by 99.46% nephelometric turbidity units (NTU) (PET-MP) and 99.49% (Arizona test dust). An oyster-inspired adsorption setup with 4000 actuated compression/relaxation cycles reduced the turbidity of PET-MP and Arizona test dust suspensions by 80.1 ± 1.5 and 91.9 ± 0.3% NTU, respectively. The preparation of biocompatible NF sponges from chitosan marine biomass has been demonstrated. These chitosan NF sponges can be used as efficient filters to tackle environmental challenges such as microplastics

Welches Gas steckt im Öl? : Integrierte Diagnostik gibt Antwort

Leistungstransformatoren sind das Rückgrat unserer Stromversorgung. Um deren sicheren Betrieb zu gewährleisten, müssen sie turnusmässig überwacht werden. Zur Diagnose ist unter anderem die Analyse von gelösten Gasen wie Wasserstoff, Methan, oder Acetylen vorgeschrieben (Dissolved Gas Analysis DGA nach IEC 60599). Diese ist sehr aufwändig, da weltweit Ölproben entnommen und zur Analyse verschickt werden müssen. Ein integriertes Messverfahren ist deshalb eine interessante Alternative

From short electrospun nanofibers to ultralight aerogels with tunable pore structure

Nanofiber production by electrospinning has made great progress within the past two decades. Yet, recently the research area was revolutionized by a novel post-processing approach. By cutting the endless and intertwined nanofibers into short pieces, it is now possible to reassemble them into interconnected 3D structures. Such highly porous structures are built from dispersed short nanofibers by freeze-casting. This solid templating process controls the structures’ ultimate properties and architecture in terms of primary and secondary pores below 5 µm and between 10 and 300 µm, respectively. The objective of this review is to provide insight into this young field of research, in particular highlighting the processing steps, materials and current applications, from scaffolds for tissue engineering, acoustics, sensors and catalyst supports to filtration

The separation power of highly porous 3D nanofiber sponges

Sponges formed by the self-assembly of nanofiber building blocks are versatile materials used in various fields such as filtration, thermal insulation, scaffolding or sound absorption. Their potential seems to be constantly expanding given the variety of possible fiber materials, from bio-based to fossil polymers to inorganic nanofibers. In general, nanofiber sponges – also called nanofiber aerogels – are flexible, have low density, and a large specific surface area thanks to their tunable open-porous nanofiber based architecture. The latter property makes nanofiber sponges an interesting material for separation problems, as recently demonstrated for a variety of mixtures such as aerosols, emulsions, dispersions, solutions or two-phase systems. Due to their highly porous structure, they generally exhibit high filtration efficiency, flow rate and capacity. This article reviews the state of the art in the application of 3D nanofiber sponges for the different classes of mixtures. We will discuss on a mechanistic basis why nanofiber sponges are particularly well suited for separation applications. Finally, their performance in terms of efficiency, flow rate, capacity and regeneration will be compared to other fiber-based filter media

3D PCL/gelatin/genipin nanofiber sponge as scaffold for regenerative medicine

Special Issue "Organic Nanofibers : Fabrication, Properties and Applications"Recent advancements in tissue engineering and material science have radically improved in vitro culturing platforms to more accurately replicate human tissue. However, the transition to clinical relevance has been slow in part due to the lack of biologically compatible/relevant materials. In the present study, we marry the commonly used two-dimensional (2D) technique of electrospinning and a self-assembly process to construct easily reproducible, highly porous, three-dimensional (3D) nanofiber scaffolds for various tissue engineering applications. Specimens from biologically relevant polymers polycaprolactone (PCL) and gelatin were chemically cross-linked using the naturally occurring cross-linker genipin. Potential cytotoxic effects of the scaffolds were analyzed by culturing human dermal fibroblasts (HDF) up to 23 days. The 3D PCL/gelatin/genipin scaffolds produced here resemble the complex nanofibrous architecture found in naturally occurring extracellular matrix (ECM) and exhibit physiologically relevant mechanical properties as well as excellent cell cytocompatibility. Samples cross-linked with 0.5% genipin demonstrated the highest metabolic activity and proliferation rates for HDF. Scanning electron microscopy (SEM) images indicated excellent cell adhesion and the characteristic morphological features of fibroblasts in all tested samples. The three-dimensional (3D) PCL/gelatin/genipin scaffolds produced here show great potential for various 3D tissue-engineering applications such as ex vivo cell culturing platforms, wound healing, or tissue replacement

Membranes for specific adsorption : immobilizing molecularly imprinted polymer microspheres using electrospun nanofibers

Molecularly imprinted polymer microspheres were immobilized within a polymer nanofiber membrane by electrospinning. Such membranes simplify the handling of functional microspheres and provide specific recognition capabilities for solid-phase extraction and filtration applications. In this study, microspheres were prepared by precipitation polymerization of methacrylic acid and divinylbenzene as a cross-linker with the target molecule (-)-cinchonidine and then, they were electrospun into a non-woven polyacrylonitrile nanofiber membrane. The composite membrane showed specific affinity for (-)-cinchonidine which was attributed to the functional microspheres as confirmed by Raman microscopy. The target molecule capturing capacity of the composite membrane was 5 mg/g or 25 mg/g immobilized functional microsphere. No difference in target affinity was observed between the immobilized microspheres and the free microspheres. These results reveal that electrospun composite membranes are a feasible approach to immobilizing functional microspheres

Label free non-invasive imaging of topically applied actives in reconstructed human epidermis by confocal Raman spectroscopy

Raman spectroscopy has become a versatile tool for the in vivo charaterisation of skin. Here we describe use of Raman spectroscopy for high resolution optical cross sectioning to resolve skin constituents and administered drugs at the cellular level. Percutaneous penetration is typically studied using permeation cells with biopsies of animals or human skin. Although this technique provides valuable clinical data, little insight is gained in the microstructure of drug penetration (intercellular or transcellular) or in the mode of action of applied vehicles or penetration enhancers. Therefore, a Raman microspectroscopic method was combined with a confocal scanning setup to image the microstructure of commercially available skin models (SkinEthic®) and the spatial distribution of penetrated actives. The models’ microstructure was scanned without any special treatment or environment such as cutting, staining, freezing, or application of vacuum. The non-invasive Raman images reveal the layered structure of stratum corneum. This in particular for lipids while water tends to be more evenly distributed. When penetration of the hydrophilic active glycerol and the lipophilic octyl methoxycinnamate, OMC, was studied, a strong correlation between the local distribution of skin constituents and the hydrophilic/lipophilic character of the active was observed

Surface enriched nanofiber mats for efficient adsorption of Cr(VI) inspired by nature

Adsorption is a surface process. By evolution, nature has created design principles such as scaffolds that allow to carrying surface bound agents at high density. We used a nanofibrous pullulan/poly(vinyl alcohol)/poly(acrylic acid) (Pul/PVA/PAA) support to carry surface active PAMAM dendrimer similar to spores attached to mushroom gills. A monolayer of ceria (CeO2) nanoparticles served as the linker between PAMAM and the nanofiber. The nanocomposite was a highly effective Cr(VI) adsorbent and the maximum adsorption capacity qmax = 847 mg g-1 is the highest reported value for the same kind of materials so far. The materials was characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform-infrared spectroscopy (FTIR), zeta potential and multipoint BET method to measure the specific surface area. Removal of Cr(VI) from aqueous media was tested under different batch and fixed bed column operation conditions such as pH, temperature and competing ions. Thermodynamic properties were determined based on a modified Langmuir adsorption isotherm and the adsorption kinetic was investigated. Positive entropy of adsorption and an endothermic adsorption process was found, while the rate-limiting step was pseudo second order which is associated with a chemisorption process. The nanocomposite was reusable and up to 95% of the adsorbed Cr(IV) ions were recovered by alkyne washing