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

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

Materials science at Swiss universities of applied sciences

Copyright ©Swiss Chemical Society: CHIMIA, Volume 73, Numbers 7-8, August 2019, pp. 645-655(11)In the Swiss Universities of Applied Sciences, several research institutes are involved in Materials Science, with different approaches and applications fields. A few examples of recent projects from different groups of the University of Applied Sciences and Arts Western Switzerland (HES-SO), the Zurich University of Applied Sciences (ZHAW) and the University of Applied Sciences and Arts Northwestern Switzerland (FHNW) are given

Prediction of steam burns severity using raman spectroscopy on ex vivo porcine skin

Skin burns due to accidental exposure to hot steam have often been reported to be more severe than the ones occurring from dry heat. While skin burns due to flames or radiant heat have been thoroughly characterized, the mechanisms leading to steam burns are not well understood and a conundrum still exists: can second degree burns occur without destruction of the epidermis, i.e. even before first degree burns are detected? Skin permeability is dependent both on temperature and on the kinetic energy of incoming water molecules. To investigate the mechanism underlying the injuries related to steam exposure, we used porcine skin as an ex vivo model. This model was exposed to either steam or dry heat before measuring the skin hydration via confocal Raman microspectroscopy. The results show that during the first minute of exposure to steam, the water content in both the epidermis and dermis increases. By analyzing different mechanisms of steam diffusion through the multiple skin layers, as well as the moisture-assisted bio-heat transfer, we provide a novel model explaining why steam burns can be more severe, and why steam can penetrate deeper and much faster than an equivalent dry heat

Towards Biocompatible Cellulose Nanofiber Sponges with Tailored Pore Geometries

Cellulose nanofiber (CNF) sponges or CNF aerogels are promising biocompatible materials with applications ranging from biomedicine to environmental remediation. The highly porous architecture of these sponges – which is crucial for their functionality – is significantly influenced by the freezing step during fabrication. This review explores the critical role of freezing techniques in tailoring pore geometry and, consequently, the macroscopic properties of CNF sponges. We discuss conventional directional freezing methods and their limitations, highlighting the advantages of dynamic freezing for achieving isotropic pore structures. Furthermore, we examine various crosslinking strategies to enhance the stability and mechanical properties of CNF sponges. Finally, we present recent findings from our laboratory demonstrating the successful fabrication of biocompatible and crosslinked CNF sponges with tailored pore geometries using a dynamic freezing approach

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

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

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