Hybrid colloids consisting of noble metal cores and metal oxide shells have been under intense investigation for over two decades and have driven progress in diverse research lines including sensing, ...medicine, catalysis, and photovoltaics. Consequently, plasmonic core–shell particles have come to play a vital role in a plethora of applications. Here, an overview is provided of recent developments in the design and utilization of the most successful class of such hybrid materials, silica‐coated plasmonic metal nanoparticles. Besides summarizing common simple approaches to silica shell growth, special emphasis is put on advanced synthesis routes that either overcome typical limitations of classical methods, such as stability issues and undefined silica porosity, or grant access to particularly sophisticated nanostructures. Hereby, a description is given, how different types of silica can be used to provide noble metal particles with specific functionalities. Finally, applications of such nanocomposites in ultrasensitive analyte detection, theranostics, catalysts, and thin‐film solar cells are reviewed.
Metal/silica nanocomposites have been under intensive investigation for over 20 years. Besides the development of a wide array of synthesis strategies for the preparation of highly regular hybrid plasmonic nanoparticles, a considerable number of practical applications are presented in sensing, theranostics, catalysis, and photovoltaics. An overview of the recent advances in the design and utilization of such materials is provided.
In the present study, property-enhanced polylactide (PLA) nanocomposites containing bacterial cellulose nanowhiskers (BCNW) were prepared by melt compounding. With the aim of improving the ...nanocrystals' dispersion in the final melt processed nanocomposites, these were preincorporated either into PLA nanostructured fibers by electrospinning or into an ethylene vinyl-alcohol copolymer (EVOH) by solution precipitation. An optimized dispersion of the nanofiller in the nanocomposites produced by applying these preincorporation methods, when compared to the direct melt mixing of the freeze-dried nanowhiskers with the polymeric matrix, was confirmed by morphological studies. Enhanced dispersion of BCNW was critical for enhancing the barrier and mechanical properties of the nanocomposites. Thus, for concentrations around the percolation threshold, that is, 2-3 wt % BCNW, nanocomposites produced by the electrospinning preincorporation method showed increased elastic modulus and tensile strength, preserving the ductility of the pure PLA. Moreover, in the optimized nanocomposites the water permeability of PLA was reduced by 43% and the oxygen barrier also decreased to a significant extent. This paper provides a successful route to solve the long-standing issue related to the dispersion of highly polar unmodified cellulose nanowhiskers into PLA via the industrially meaningful melt compounding processing.
In this study, curcumin was encapsulated within electrospun protein (i.e. gelatin and zein) fibers to generate bioactive coatings for food packaging. Additionally, a green tea extract (GTE) was also ...incorporated within the formulations to evaluate its impact on the stability, protective ability, and release properties of the curcumin-loaded fibers.
Due to the poor solubility of curcumin in aqueous media, a strategy based on its incorporation through liposomes was developed, allowing to successfully incorporating curcumin into gelatin fibers. Very high encapsulation efficiencies were attained for both zein and gelatin, with the former showing an enhanced protection effect and a more limited and slower release of the curcumin in hydrophobic food simulants. The addition of GTE resulted in strong interactions being established with the proteins and, in the particular case of gelatin, it improved the protective effect and slowed down the curcumin release from the fibers, although it did not prevent their collapse in water.
The results showed that while the developed gelatin coatings showed a promising release behavior in contact with fatty food simulants, zein-based coatings would be more adequate for packaging of high water content food products.
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•Curcumin-containing protein-based coatings were developed through electrospinning.•The effect of addition of an antioxidant extract to the formulations was evaluated.•High encapsulation efficiencies and enhanced curcumin protection were attained.•The antioxidant extract improved protection and modified the release.•Selection of the protein matrix needs to be done depending on final application.
Simple synthetic routes, high active layer thickness tolerance as well as stable organic solar cells are relentlessly pursued as key enabling traits for the upscaling of organic photovoltaics. Here, ...the potential to address these issues by tuning donor polymer molecular weight is investigated. Specifically, the focus is on PTQ10, a polymer with low synthetic complexity, with number average molecular weights of 2.4, 6.2, 16.8, 52.9, and 54.4 kDa, in combination with three different non‐fullerene acceptors, namely Y6, Y12, and IDIC. Molecular weight, indeed, unlocks a threefold increase in power conversion efficiency for these blends. Importantly, efficiencies above 10% for blade coated devices with thicknesses between 200 and 350 nm for blends incorporating high molecular weight donor are shown. Spectroscopic, GIWAXS and charge carrier mobility data suggest that the strong photocurrent improvement with molecular weight is related to both, improved electronic transport and polymer contribution to exciton generation. Moreover, it is demonstrated that solar cells based on high molecular weight PTQ10 are more thermally stable due to a higher glass transition temperature, thus also improving device stability.
This work shows how increasing the molecular weight of a low synthetic complexity polymer, PTQ10, when paired with different acceptors yielded a notable threefold enhancement in power conversion efficiency. These high‐efficiency blends show good thickness tolerance, and exhibited both improved stability and efficiency, underscoring the potential of cost‐effective organic solar cells.
This work reports on the valorization of residues from Posidonia oceanica leaves for the purpose of obtaining lignocellulosic fractions of interest for the development of bio-based materials for food ...packaging. The lignocellulosic fractions were characterized, thereby confirming the purification of cellulose and showing increases in crystallinity and thermal stability after the consecutive extraction steps. Subsequently, pure lignocellulosic films were obtained and characterized and the pure cellulose film showed the best properties in terms of mechanical performance and water vapor permeability. Finally, composite starch films containing lignocellulosic fractions were developed by melt compounding and characterized. Although the film containing the pure cellulose additive showed the optimum improvement in terms of mechanical properties (with an increase of 85% in the elastic modulus and 38% in the tensile strength), similar water vapor permeability reduction (~40%) was achieved with the least purified fractions, explained by their effect on starch gelatinization, as evidenced by SAXS/WAXS.
Noble metal nanoparticles are widely used as probes or substrates for surface enhanced Raman scattering (SERS), due to their characteristic plasmon resonances in the visible and near-IR spectral ...ranges. Aiming at obtaining a versatile system with high SERS performance, we developed the synthesis of quasi-monodisperse, nonaggregated gold nanoparticles protected by radial mesoporous silica shells. The radial mesoporous channels were used as templates for the growth of gold tips branching out from the cores, thereby improving the plasmonic performance of the particles while favoring the localization of analyte molecules at high electric field regions: close to the tips, inside the pores. The method, which additionally provides control over tip length, was successfully applied to gold nanoparticles with various shapes, leading to materials with highly efficient SERS performance. The obtained nanoparticles are stable in ethanol and water upon thermal consolidation and can be safely stored as a powder.
This study reports on the effect of pH and polysaccharide concentration (protein:polysaccharide ratios of 95:5, 85:15 and 75:25) on the interactions established between xanthan gum (XG) and micellar ...casein (MC), investigating the impact on the type of structures formed at the micro- and nanoscale. At pH ≥ 6, the micellar casein formed stable suspensions where micelles with diameters of ca. 130–150 nm showed a compact inner structure stabilised by colloidal calcium phosphate (CCP) nanoclusters, while at pH ≤ 3, a more loosely packed interconnected network structure, stabilised by protein-protein interactions, was noted. The addition of XG, even at low MC:XG ratios (95:5), resulted in increased stability of the system, preventing the formation of micelle aggregates at the microscale, and reducing the pH range at which casein precipitated close to the isoelectric point. For all the XG loadings, coacervates were formed at pH = 2–3 due to polysaccharide-protein electrostatic interactions, leading to separation into a solid gel-like phase composed of polysaccharide-protein fibrillar structures and a liquid phase rich in protein. At the nanoscale, XG was mostly coating the micelles and filling in the inner water channels when added at MC:XG ratios ≤85:15, while the higher polysaccharide content at the ratio 75:25 allowed to form an interconnected structure. Therefore, by adjusting pH and XG concentration, it is possible to improve casein stability, reduce agglomeration and manipulate the size of protein-polysaccharide complexes formed. This will be of great relevance for the development of novel food formulations with improved stability and modulated sensory and nutritional properties.
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•System stability and coacervate formation depend on pH and xanthan gum concentration.•Xanthan gum increases stability of casein micelles even at low loadings.•At pH ≥ 6, xanthan gum prevents micelle aggregation, forming a stable network.•Xanthan gum-casein coacervates with fibrillar structures are formed at pH = 2–3.•Xanthan gum can affect the casein inner micelle nanostructure.
This work aims at examining the various factors that affect cellulose nanowhiskers (CNWs) extraction from bacterial cellulose (BC). Specifically, the effect of sulfuric acid hydrolysis time and ...further treatments such as neutralization and dialysis on the properties of the obtained nanoparticles was studied. The morphology of BCNWs was examined by TEM, showing a decrease in the nanowhiskers’ length when increasing hydrolysis time as expected. The XRD patterns of the different samples showed a crystalline structure characteristic of the cellulose I allomorph. From the calculated crystallinity indexes it was deduced that long hydrolysis times, such as 48
h, are required when intending to digest a significant fraction of amorphous material and thus, obtaining a significant increase in crystallinity by comparison with the native BC. Nevertheless, as a consequence of this extensive acid hydrolysis treatment, the thermal stability of the material is significantly decreased, making it unsuitable for most melt-compoundable polymer-based nanocomposites applications. On the other hand, neutralization produced a slight increase in the crystallinity index, and, most importantly, it led to a remarkable increase on the BCNWs thermal stability, as determined by TGA. Furthermore, it was found out that dialysis applied after neutralization did not present any additional improvement on the BCNWs’ properties.
This work reports on the development of electrosprayed chitosan/gelatin microparticles for encapsulation purposes. Initially, the effects of the chitosan molecular weight (Mw), biopolymers and ...solvent composition on solution properties and capsule formation were investigated. Results demonstrated that the sprayability of the blend solutions was mainly determined by a critical range of solids content, which was needed for chain entanglement and subsequent capsule formation, and by their rheological properties. SAXS experiments from selected electrospraying solutions showed that clustered networks between both biopolymers were formed due to the electrostatic interactions between the positively charged amino groups in chitosan and negatively charged amino acid residues in gelatin. As a model bioactive extract, an anthocyanin-rich black carrot extract (BCE) was loaded into selected chitosan/gelatin electrosprayed structures and the encapsulation efficiency and release into two food simulants (ethanol 10% and acetic acid 3%) was evaluated. Faster and greater release was observed in the acetic acid medium as expected and the results showed that the main factor affecting the bioactive release was the blend composition, i.e. increasing the chitosan content of the formulations limited BCE release.
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•Gelatin/chitosan microcapsules were developed by electrospraying.•Rheological properties and total solids content were key for capsule formation.•An anthocyanin-rich extract was loaded into the microcapsules.•Bioactive extract release was mainly affected by matrix composition.
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