Electrospinning Nonspinnable Sols to Ceramic Fibers and Springs

Electrospinning has been applied to produce ceramic fibers using sol gel-based spinning solutions consisting of ceramic precursors, a solvent, and a polymer to control the viscosity of the solution. However, the addition of polymers to the spinning solution makes the process more complex, increases the processing time, and results in porous mechanically weak ceramic fibers. Herein, we develop a coelectrospinning technique, where a nonspinnable sol (<10 mPa s) consisting of only the ceramic precursor(s) and solvent(s) is encapsulated inside a polymeric shell, forming core-shell precursor fibers that are further calcined into ceramic fibers with reduced porosity, decreased surface defects, uniform crystal packing, and controlled diameters. We demonstrate the versatility of this method by applying it to a series of nonspinnable sols and creating high-quality ceramic fibers containing TiO2, ZrO2, SiO2, and Al2O3. The polycrystalline TiO2 fibers possess excellent flexibility and a high Young's modulus reaching 54.3 MPa, solving the extreme brittleness problem of the previously reported TiO2 fibers. The single-component ZrO2 fibers exhibit a Young's modulus and toughness of 130.5 MPa and 11.9 KJ/m3, respectively, significantly superior to the counterparts prepared by conventional sol-gel electrospinning. We also report the creation of ceramic fibers in micro- and nanospring morphologies and examine the formation mechanisms using thermomechanical simulations. The fiber assemblies constructed by the helical fibers exhibit a density-normalized toughness of 3.5-5 times that of the straight fibers due to improved fracture strain. This work expands the selection of the electrospinning solution and enables the development of ceramic fibers with more attractive properties.

Functional Fiber Membranes with Antibacterial Properties for Face Masks

Reusable face masks are an important alternative for minimizing costs of disposable and surgical face masks during pandemics. Often complementary to washing, a prolonged lifetime of face masks relies on the incorporation of self-cleaning materials. The development of self-cleaning face mask materials requires the presence of a durable catalyst to deactivate contaminants and microbes after long-term use without reducing filtration efficiency. Herein, we generate self-cleaning fibers by functionalizing silicone-based (polydimethylsiloxane, PDMS) fibrous membranes with a photocatalyst. Coaxial electrospinning is performed to fabricate fibers with a non-crosslinked silicone core within a supporting shell scaffold, followed by thermal crosslinking and removal of the water-soluble shell. Photocatalytic zinc oxide nanoparticles (ZnO NPs) are immobilized on the PDMS fibers by colloid-electrospinning or post-functionalization procedures. The fibers functionalized with ZnO NPs can degrade a photo-sensitive dye and display antibacterial properties against Gram-positive and Gram-negative bacteria (Escherichia coli and Staphylococcus aureus) due to the generation of reactive oxygen species upon irradiation with UV light. Furthermore, a single layer of functionalized fibrous membrane shows an air permeability in the range of 80-180 L/m2s and 65% filtration efficiency against fine particulate matter with a diameter less than 1.0 µm (PM1.0).

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s42765-023-00291-7.

A novel SPR based Fe@Ag core-shell nanosphere entrapped on starch matrix an optical probe for sensing of mercury(II) ion: A nanomolar detection, wide pH range and real water sample application

Recent trends in nanotechnology paved a way for the development of detection systems for heavy metals, toxins and environmental pollutants. The present study focused on Hg²⁺ detection by a core shell Fe@Ag-starch nanosphere phenylalanine conjugate. The characterization of core shell Fe@Ag-starch nanosphere was performed by using TEM, zetasizer, particlesize analyzer, UV-visible absorption spectrophotometer, EDAX, FTIR and TGA. The NPs showed λmax at 408 nm. The effective diameter of synthesized nanosphere was 37 ± 2 nm and it possessed the surfaces charge of -36.12 ± 2.5 mV. The Fe@Ag-starch-phenylalanine conjugate reacted with Hg²⁺, the yellow colour of the nanosphere phenylalanine conjugate became colourless. The real water sample was collected and the amount of Hg²⁺ was calculated by using the prepared nanosphere. The detection of Hg²⁺ at different conditions including various saline concentrations, temperature and pH were also studied and the detection was found to be effective at 40 °C, pH 5 and 0.1% of saline concentration. The LOD of Hg²⁺ ions by Fe@Ag-starch nanosphere were calculated to be 1.84 nM. The influence of other metal ions present in the analyte did not show any interference on Hg²⁺ detection. In addition, the photocatalytic and antibacterial activities of Fe@Ag-starch nanosphere were also studied. The study confirmed that the core shell nanosphere can also be used for environmental cleanup and disinfection.

Improved Photocatalytic Activity of Polysiloxane TiO2 Composites by Thermally Induced Nanoparticle Bulk Clustering and Dye Adsorption

Fine control of nanoparticle clustering within polymeric matrices can be tuned to enhance the physicochemical properties of the resulting composites, which are governed by the interplay of nanoparticle surface segregation and bulk clustering. To this aim, out-of-equilibrium strategies can be leveraged to program the multiscale organization of such systems. Here, we present experimental results indicating that bulk assembly of highly photoactive clusters of titanium dioxide nanoparticles within an in situ synthesized polysiloxane matrix can be thermally tuned. Remarkably, the controlled nanoparticle clustering results in improved degradation photocatalytic performances of the material under 1 sun toward methylene blue. The resulting coatings, in particular the 35 wt % TiO2-loaded composites, show a photocatalytic degradation of about 80%, which was comparable to the equivalent amount of bare TiO2 and two-fold higher with respect to the corresponding composites not subjected to thermal treatment. These findings highlight the role of thermally induced bulk clustering in enhancing photoactive nanoparticle/polymer composite properties.

A potent multifunctional MnS/Ag-polyvinylpyrrolidone nanocomposite for enhanced detection of Hg2+ from aqueous samples and its photocatalytic and antibacterial applications

The development of nanotechnology for hazardous heavy metal detection with nanoparticles (NPs) created an interest for the preparation of MnS/Ag nanocomposite. Here, MnS/Ag-polyvinylpyrrolidone (PVP) nanocomposite was developed for the detection of mercury. The prepared composite was analyzed using particle size analyzer, X-ray powder diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), Ultraviolet-visible (UV-vis) spectroscopy, zetasizer, high resolution transmission electron microscope (HRTEM) and Fourier-transform infrared spectroscopy (FTIR). The λ_max of MnS/Ag-PVP nanocomposite was observed at 404 nm. The particle size was determined to be 21 ± 1.7 nm and the surface charge was -31.19 ± 3 mV. The brownish yellow colour of the nanocomposite changed into colourless when Hg²⁺ was added. The different metal ions present with the analyte did not show any interference on detection of Hg²⁺. The MnS/Ag-PVP nanocomposite incorporated paper and gel exhibited visual detection of Hg²⁺ from aqueous sample. There was an excellent linearity (y = -0.0015x + 0.8744) found in plot of 20 to 100 nM Hg²⁺ concentrations versus absorbance at 404 nm and the LOD was calculated to be 16 nM. The probe was applied to quantify Hg²⁺ from spiked environmental sample and the results were further confirmed with atomic absorption spectrophotometric analysis. Hence, the investigation suggests that the present probe could efficiently detect and quantify Hg²⁺ at nano molar level. In addition, the study suggests that MnS/Ag-PVP nanocomposite exhibit multifunctional property including efficient photocatalytic and antimicrobial activity. The antibacterial activity was evaluated against both gram positive and gram negative bacteria.

A potent multifunctional Ag/Co-polyvinylpyrrolidone nanocomposite for enhanced detection of Cr(III) from environmental samples and its photocatalytic and antibacterial applications

Trivalent chromium (Cr(III)) is considered to exhibit hormesis (bi-phasic dose-response) property, where low dose be beneficial and high dose shows toxic effect. The present work describe the development of a bimetallic Ag/Co-polyvinylpyrrolidone nanocomposite (Ag/Co-PVP NPs) probe to detect and quantify Cr(III) ions from aqueous samples. The hydrodynamic size and zeta potential of the particle was determined to be 29 ± 1.3 nm and -37.19 ± 2.4 mV respectively. The interaction of Cr(III) with Ag/Co-PVP probe showed drastic change in colour of NPs from dark brown to pale yellow, with corresponding blue shift, tapering width and increased peak intensity. The probe showed high specificity towards Cr(III) among the tested metal ions. A linearity was observed between various dilutions of Cr(III) ions (10 to 50 nM) and the absorbance of Ag/Co-PVP NPs at 428 nm with R² value of 0.998. The minimum detectable limit of Cr(III) was calculated to be 0.6 nM. The influence of salinity, temperature and pH on detection was studied. The probe was found to detect Cr(III) at acidic pH effectively. Competitive metal ions did not interfere the detection of Cr(III). The water sample collected from Noyyal river was taken to estimate Cr(III) by using the prepared probe to ensure practical applicability. The sample contains 9.3 nM of Cr(III) that was cross verified with AAS analysis. Hence, it is understood that the reported probe can be used to detect Cr(III) selectively with high accuracy from aqueous samples. In addition, the particles also exhibited excellent photocatalytic activity under visible light. Ag/Co-PVP nanocomposites exhibited excellent antibacterial activity against both gram +ve (B. subtilis) and gram -ve (E. coli) bacteria.

Effects of ethanol content on the properties of silicone rubber foam

In this study, silicone rubber foam (SF) was prepared through cross-linking and foaming. The effects of ethanol content on the SF were investigated in terms of the physical properties, static cushioning properties, dynamic thermomechanical properties, and dynamic fatigue properties. The cell structure was characterized using scanning electron microscopy and its relationship with the SF properties was analyzed. With increasing ethanol content, the cell diameter increases gradually and its uniformity deteriorates. Moreover, the density, tensile strength, and elongation at breaking of the SF samples gradually decrease. In addition, with the increase of strain and stress, the cushioning coefficient of SF decreases initially and then increases, and the fatigue times worsens with increasing ethanol content. However, fatigue process has little effect on the cushioning performance of SF, which means the SF can be used as reusable packaging materials and thereby reduce environmental pollution.

Stable Hydrophobic Metal-Oxide Photocatalysts via Grafting Polydimethylsiloxane Brush

Polydimethylsiloxane (PDMS) can be grafted to metal-oxide photocatalysts such as titanium oxide by simple UV irradiation in solution or melt. The PDMS graft metal oxides are still photocatalytically active. They are hydrophobic, liquid repellent, self-cleaning, prevent biofouling and are long-term stable even in UV light.

Nanocomposite Electrospun Nanofiber Membranes for Environmental Remediation

Rapid worldwide industrialization and population growth is going to lead to an extensive environmental pollution. Therefore, so many people are currently suffering from the water shortage induced by the respective pollution, as well as poor air quality and a huge fund is wasted in the world each year due to the relevant problems. Environmental remediation necessitates implementation of novel materials and technologies, which are cost and energy efficient. Nanomaterials, with their unique chemical and physical properties, are an optimum solution. Accordingly, there is a strong motivation in seeking nano-based approaches for alleviation of environmental problems in an energy efficient, thereby, inexpensive manner. Thanks to a high porosity and surface area presenting an extraordinary permeability (thereby an energy efficiency) and selectivity, respectively, nanofibrous membranes are a desirable candidate. Their functionality and applicability is even promoted when adopting a nanocomposite strategy. In this case, specific nanofillers, such as metal oxides, carbon nanotubes, precious metals, and smart biological agents, are incorporated either during electrospinning or in the post-processing. Moreover, to meet operational requirements, e.g., to enhance mechanical stability, decrease of pressure drop, etc., nanofibrous membranes are backed by a microfibrous non-woven forming a hybrid membrane. The novel generation of nanocomposite/hybrid nanofibrous membranes can perform extraordinarily well in environmental remediation and control. This reality justifies authoring of this review paper.

Solution parameters for the fabrication of thinner silicone fibers by electrospinning

Silicone fibers were synthesized by electrospinning, where 17 solvents with different chemical properties (boiling point, conductivity, viscosity, dielectric constant, and solubility parameter) were used to dissolve the silicone polymer for the formation of fibers through electrospinning. Previous reports on the miniaturization of fibers of polymers dissolved in a solvent suggested that the low viscosity and the high conductivity of the polymer solution were the key parameters to form thinner fibers when using a single solvent. Here we have found a powerful way to search for good solvents to reduce the fiber diameters as well as to dissolve the polymers. By considering different types of solvents, it was found that the solubility parameters conclusively determined the smallest fiber diameters of the silicone polymers. The solubility parameter of the silicone polymer should be lower than those of the solvents to make thinner fibers. The results have revealed the strong relationship between the diameters of the fibers and the solubility parameters of the solvents, and they indicate that the solubility parameter could be a good indicative parameter in selecting solvents during the fabrication of thinner fibers by electrospinning, especially for siloxane polymers.