Evaluation of the Photocatalytic Activity and Anticorrosion Performance of Electrospun Fibers Doped with Metallic Oxides

Antifungal Activity of Chitosan/Poly(Ethylene Oxide) Blend Electrospun Polymeric Fiber Mat Doped with Metallic Silver Nanoparticles

In this work, the implementation of advanced functional coatings based on the combination of two compatible nanofabrication techniques such as electrospinning and dip-coating technology have been successfully obtained for the design of antifungal surfaces. In a first step, uniform and beadless electrospun nanofibers of both polyethylene oxide (PEO) and polyethylene (PEO)/chitosan (CS) blend samples have been obtained. In a second step, the dip-coating process has been gradually performed in order to ensure an adequate distribution of silver nanoparticles (AgNPs) within the electrospun polymeric matrix (PEO/CS/AgNPs) by using a chemical reduction synthetic process, denoted as in situ synthesis (ISS). Scanning electron microscopy (SEM) has been used to evaluate the surface morphology of the samples, showing an evolution in average fiber diameter from 157 ± 43 nm (PEO), 124 ± 36 nm (PEO/CS) and 330 ± 106 nm (PEO/CS/AgNPs). Atomic force microscopy (AFM) has been used to evaluate the roughness profile of the samples, indicating that the ISS process induced a smooth roughness surface because a change in the average roughness Ra from 84.5 nm (PEO/CS) up to 38.9 nm (PEO/CS/AgNPs) was observed. The presence of AgNPs within the electrospun fiber mat has been corroborated by UV-Vis spectroscopy thanks to their characteristic optical properties (orange film coloration) associated to the Localized Surface Plasmon Resonance (LSPR) phenomenon by showing an intense absorption band in the visible region at 436 nm. Energy dispersive X-ray (EDX) profile also indicates the existence of a peak located at 3 keV associated to silver. In addition, after doping the electrospun nanofibers with AgNPs, an important change in the wettability with an intrinsic hydrophobic behavior was observed by showing an evolution in the water contact angle value from 23.4° ± 1.3 (PEO/CS) up to 97.7° ± 5.3 (PEO/CS/AgNPs). The evaluation of the antifungal activity of the nanofibrous mats against Pleurotus ostreatus clearly indicates that the presence of AgNPs in the outer surface of the nanofibers produced an important enhancement in the inhibition zone during mycelium growth as well as a better antifungal efficacy after a longer exposure time. Finally, these fabricated electrospun nanofibrous membranes can offer a wide range of potential uses in fields as diverse as biomedicine (antimicrobial against human or plant pathogen fungi) or even in the design of innovative packaging materials for food preservation.

A Comparative Study in the Design of TiO2 Assisted Photocatalytic Coatings Monitored by Controlling Hydrophilic Behavior and Rhodamine B Degradation

This work presents a comparative study related to the photocatalytic efficiency associated with wettability measurements and organic dye degradation, as well as other relevant properties (i.e., corrosion resistance, roughness, wettability, and adhesion to a substrate). The photocatalytic precursors are titanium dioxide nanoparticles (TiO₂ NPs) which are dispersed onto a polymeric electrospun fiber matrix by using three different deposition techniques such as electrospraying, spraying, and dip-coating, respectively. In this work, the host electrospun matrix is composed of poly(acrylic acid) fibers crosslinked with cyclodextrin (β-CD), which shows a good chemical affinity and stability with the other deposition techniques which are responsible for incorporating the TiO₂ NPs. In order to evaluate the efficacy of each coating, the resultant photocatalytic activity has been monitored by two different tests. Firstly, the reduction in the water contact angle is appreciated, and secondly, the degradation of an organic dye (Rhodamine B) is observed under UV irradiation. In addition, the final roughness, adherence, and pitting corrosion potential have also been controlled in order to determine which solution provides the best combination of properties. Finally, the experimental results clearly indicate that the presence of TiO₂ NPs deposited by the three techniques is enough to induce a super hydrophilic behavior after UV irradiation. However, there are notable differences in photocatalytic efficiency on the Rhodamine B as a function of the selected deposition technique.

Novel Design of Superhydrophobic and Anticorrosive PTFE and PAA + β - CD Composite Coating Deposited by Electrospinning, Spin Coating and Electrospraying Techniques

A superhydrophobic composite coating consisting of polytetrafluoroethylene (PTFE) and poly(acrylic acid)+ β-cyclodextrin (PAA + β-CD) was prepared on an aluminum alloy AA 6061T6 substrate by a three-step process of electrospinnig, spin coating, and electrospraying. The electrospinning technique is used for the fabrication of a polymeric binder layer synthesized from PAA + β-CD. The superhydrophilic characteristic of the electrospun PAA + β-CD layer makes it suitable for the absorption of an aqueous suspension with PTFE particles in a spin-coating process, obtaining a hydrophobic behavior. Then, the electrospraying of a modified PTFE dispersion forms a layer of distributed PTFE particles, in which a strong bonding of the particles with each other and with the PTFE particles fixed in the PAA + β-CD fiber matrix results in a remarkable improvement of the particles adhesion to the substrate by different heat treatments. The experimental results corroborate the important role of obtaining hierarchical micro/nano multilevel structures for the optimization of superhydrophobic surfaces, leading to water contact angles above 170°, very low contact angle of hysteresis (CAH = 2°) and roll-off angle (αroll−off < 5°). In addition, a superior corrosion resistance is obtained, generating a barrier to retain the electrolyte infiltration. This study may provide useful insights for a wide range of applications.

Virucidal PVP-Copper Salt Composites against Coronavirus Produced by Electrospinning and Electrospraying

Electrospinning technology was used to produced polyvinylpyrrolidone (PVP)-copper salt composites with structural differences, and their virucidal activity against coronavirus was investigated. The solutions were prepared with 20, 13.3, 10, and 6.6% w/v PVP containing 3, 1.0, 0.6, and 0.2% w/v Cu (II), respectively. The rheological properties and electrical conductivity contributing to the formation of the morphologies of the composite materials were observed by scanning electron microscopy (SEM). SEM images revealed the formation of electrospun PVP-copper salt ultrafine composite fibers (0.80 ± 0.35 µm) and electrosprayed PVP-copper salt composite microparticles (1.50 ± 0.70 µm). Energy-dispersive X-ray spectroscopy (EDS) evidenced the incorporation of copper into the produced composite materials. IR spectra confirmed the chemical composition and showed an interaction of Cu (II) ions with oxygen in the PVP resonant ring. Virucidal composite fibers inactivated 99.999% of coronavirus within 5 min of contact time, with moderate cytotoxicity to L929 cells, whereas the virucidal composite microparticles presented with a virucidal efficiency of 99.999% within 1440 min of exposure, with low cytotoxicity to L929 cells (mouse fibroblast). This produced virucidal composite materials have the potential to be applied in respirators, personal protective equipment, self-cleaning surfaces, and to fabric coat personal protective equipment against SARS-CoV-2, viral outbreaks, or pandemics.

Design of Photocatalytic Functional Coatings Based on the Immobilization of Metal Oxide Particles by the Combination of Electrospinning and Layer-by-Layer Deposition Techniques

This work reports the design and characterization of functional photocatalytic coatings based on the combination of two different deposition techniques. In a first step, a poly(acrylic acid) + β-Cyclodextrin (denoted as PAA+ β-CD) electrospun fiber mat was deposited by using the electrospinning technique followed by a thermal treatment in order to provide an enhancement in the resultant adhesion and mechanical resistance. In a second step, a layer-by-layer (LbL) assembly process was performed in order to immobilize the metal oxide particles onto the previously electrospun fiber mat. In this context, titanium dioxide (TiO2) was used as the main photocatalytic element, acting as the cationic element in the multilayer LbL structure. In addition, two different metal oxides, such as tungsten oxide (WO3) and iron oxide (Fe2O3), were added into PAA anionic polyelectrolyte solution with the objective of optimizing the photocatalytic efficiency of the coating. All of the coatings were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM) images, showing an increase in the original fiber diameter and a decrease in roughness of the mats because of the LbL second step. The variation in the wettability properties from a superhydrophilic surface to a less wettable surface as a function of the incorporation of the metal oxides was also observed by means of water contact angle (WCA) measurements. With the aim of analyzing the photocatalytic efficiency of the samples, degradation of methyl blue (MB) azo-dye was studied, showing an almost complete discoloration of the dye in the irradiated area. This study reports a novel combination method of two deposition techniques in order to obtain a functional, homogeneous and efficient photocatalytic coating.

Modeling Experimental Parameters for the Fabrication of Multifunctional Surfaces Composed of Electrospun PCL/ZnO-NPs Nanofibers

In this work, a one-step electrospinning technique has been implemented for the design and development of functional surfaces with a desired morphology in terms of wettability and corrosion resistance by using polycaprolactone (PCL) and zinc oxide nanoparticles (ZnO NPs). The surface morphology has been characterized by confocal microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and water contact angle (WCA), whereas the corrosion resistance has been evaluated by Tafel polarization curves. Strict control over the input operational parameters (applied voltage, feeding rate, distance tip to collector), PCL solution concentration and amount of ZnO NPs have been analyzed in depth by showing their key role in the final surface properties. With this goal in mind, a design of experiment (DoE) has been performed in order to evaluate the optimal coating morphology in terms of fiber diameter, surface roughness (Ra), water contact angle (WCA) and corrosion rate. It has been demonstrated that the solution concentration has a significant effect on the resultant electrospun structure obtained on the collector with the formation of beaded fibers with a higher WCA value in comparison with uniform bead-free fibers (dry polymer deposition or fiber-merging aspect). In addition, the presence of ZnO NPs distributed within the electrospun fibers also plays a key role in corrosion resistance, although it also leads to a decrease in the WCA. Finally, this is the first time that an exhaustive analysis by using DoE has been evaluated for PCL/ZnO electrospun fibers with the aim to optimize the surface morphology with the better performance in terms of corrosion resistance and wettability.