In this paper, we report a comprehensive investigation of Pt nanoparticles (NPs) deposition on nitrogen- and sulfur-doped or codoped mesoporous carbons (N-MC, S-MC, and N,S-MC) to develop active and ...durable oxygen reduction catalysts for fuel cells. N-MC, S-MC, and N,S-MC were prepared by employing mesoporous silica as hard template and suitable organic precursors. Pt NPs were deposited by solid-state reduction of platinum acetylacetonate under N2/H2 flow on the three different supports. Pt NPs resulted to be well-dispersed over the doped MC supports with size distributions (from 1.8 nm to 3.5 nm) that are dependent on the type of doping heteroatom (N, S, or N and S). The influence of nitrogen and/or sulfur incorporated into the carbon matrix on the nucleation and growth of Pt NPs was also rationalized based on density functional theory (DFT) simulations. They highlighted that both nitrogen and sulfur increase the interactions between Pt and carbon support, but the interaction decreases as the nitrogen and sulfur functional groups become closer. The effect of sulfur content on the size and activity of Pt NPs was also evaluated. Electrochemical measurements in 0.5 M H2SO4 electrolyte allowed us to investigate the behavior of Pt NPs and to assess the relationship with electrochemical activity and stability. The Pt/S-MC showed mass activity and specific activity comparable with the state-of-the-art commercial standard Pt/C Tanaka (Pt 46% on Vulcan XC72), and the highest catalytic activity, with respect to Pt/N-MC and Pt/N,S-MC, was associated with a stronger interaction between Pt NPs and a thiophenic-like group, as proven by DFT calculations and X-ray photoelectron spectroscopy (XPS) analysis. Pt/S-MC was incorporated in a membrane electrode assembly and tested as cathode material in a PEM fuel cell, while accelerated degradation tests up to 10 000 voltammetric cycles were carried out in 0.5 M H2SO4: the influence of the doped support on the durability of the catalyst under harsh operational conditions has been highlighted.
Cyclic poly‐2‐ethyl‐2‐oxazoline (PEOXA) ligands for superparamagnetic Fe3O4 nanoparticles (NPs) generate ultra‐dense and highly compact shells, providing enhanced colloidal stability and ...bio‐inertness in physiological media. When linear brush shells fail in providing colloidal stabilization to NPs, the cyclic ones assure long lasting dispersions. While the thermally induced dehydration of linear PEOXA shells cause irreversible aggregation of the NPs, the collapse and subsequent rehydration of similarly grafted cyclic brushes allow the full recovery of individually dispersed NPs. Although linear ligands are densely grafted onto Fe3O4 cores, a small plasma protein such as bovine serum albumin (BSA) still physisorbs within their shells. In contrast, the impenetrable entropic shield provided by cyclic brushes efficiently prevents nonspecific interaction with proteins.
Shields designed to last: When cyclic polymer ligands are grafted onto inorganic nanoparticles (NPs), ultra‐dense and highly compact brush shells are generated. Core‐cyclic shell NPs are significantly more stable than their linear brush‐functionalized counterparts and show full bio‐inertness towards serum proteins.
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Thermosetting urea–formaldehyde (UF) resins as the most common adhesives for wood-based composites emit formaldehyde, which forces producers to lower formaldehyde/urea (F/U) molar ...ratio for the UF resins synthesis. However, low-molar-ratio (below 1.0) UF resins have low formaldehyde emission at the expense of poor adhesion, which is responsible for the formation of crystalline domains as a result of hydrogen bonds between linear molecules. For the first time, this study reports the conversion of crystalline UF resins to amorphous polymers by blocking the hydrogen bonds, using transition metal ion-modified bentonite (TMI-BNT) nanoclay through in situ intercalation. The modified UF resins with 5% TMI-BNT showed an almost amorphous structure, faster curing and higher cross-linking density compared with those of neat resins, and resulted in 56.4% increase in the adhesion strength and 48.3% reduction in the formaldehyde emission. Thus, blocking hydrogen bonds in low F/U molar ratio UF resins with TMI-BNT converted crystalline UF resins to almost amorphous ones, resulting in a significant improvement in their adhesion with a low crystallinity.
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► Electrospun PVDF fibers with different amounts of montmorillonite were produced. ► Clay acted as a processing aid agent, improving the quality of the fibers. ► Clay and ...electrospinning acted synergically on chain mobility favoring PVDF β phase. ► Control of chain mobility allows to shape the structure and properties of PVDF. ► Electrospinning does not aid the dispersion of clay within the matrix.
Electrospun poly(vinylidene fluoride) (PVDF) fibers, containing different amounts of montmorillonite clay were produced, in order to study the effect of clay and of the electrospinning process on the polymorphism, structure and morphology of the PVDF matrix. Clay acted as a processing aid agent, avoiding the formation of beads and improving the quality of the fibers. Clay and the electrospinning process acted synergically on the chain mobility, favoring the formation of β phase of PVDF, the most valuable for its piezoelectric properties, and shaping its semicrystalline morphology. Electrospinning did not significantly aid the dispersion of clay within the matrix. The interplay of formulation and processing in these composites allowed to obtain PVDF-based materials with varying polymorphism, structure and morphology, offering the possibility to ultimately control their functional properties.
A family of homodinuclear Ln3+ (Ln3+ = Gd3+, Eu3+) luminescent complexes with the general formula Ln2(β-diketonato)6(N-oxide) y has been developed to study the effect of the β-diketonato and N-oxide ...ligands on their thermometric properties. The investigated complexes are Ln2(tta)6(pyrzMO)2 (Ln = Eu (1·C7H8), Gd (5)), Ln2(dbm)6(pyrzMO)2 (Ln = Eu (2), Gd (6)), Ln2(bta)6(pyrzMO)2 (Ln = Eu (3), Gd (7)), Ln2(hfac)6(pyrzMO)3 (Ln = Eu (4), Gd (8)) (pyrzMO = pyrazine N-oxide, Htta = thenoyltrifluoroacetone, Hdbm = dibenzoylmethane, Hbta = benzoyltrifluoroacetone, Hhfac = hexafluoroacetylacetone, C7H8 = toluene), and their 4,4′-bipyridine N-oxide (bipyMO) analogues. Europium complexes emit a bright red light under UV radiation at room temperature, whose intensity displays a strong temperature (T) dependence between 223 and 373 K. This remarkable variation is exploited to develop a series of luminescent thermometers by using the integrated intensity of the 5D0 → 7F2 europium transition as the thermometric parameter (Δ). The effect of different β-diketonato and N-oxide ligands is investigated with particular regard to the shape of thermometer calibration (Δ vs T) and relative thermal sensitivity curves: i.e.. the change in Δ per degree of temperature variation usually indicated as S r (% K–1). The thermometric properties are determined by the presence of two nonradiative deactivation channels, back energy transfer (BEnT) from Eu3+ to the ligand triplet levels and ligand to metal charge transfer (LMCT). In the complexes bearing tta and dbm ligands, whose triplet energy is ca. 20000 cm–1, both deactivation channels are active in the same temperature range, and both contribute to determine the thermometric properties. Conversely, with bta and hfac ligands the response of the europium luminescence to temperature variation is ruled by LMCT channels since the high triplet energy (>21400 cm–1) makes BEnT ineffective in the investigated temperature range.
This study investigated impacts of the synthesis method and melamine content of UMF resins on their characteristics in the cohesive features, interphase features, and adhesion performance in plywood ...and medium density fiberboard. The results showed that the cohesive features of UMF resins controlled by the synthesis method and melamine content mainly regulated the adhesion performance, while the interphase features have a partial contribution to the adhesion. Please let me know if you need further information on the manuscript.
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This study investigated impacts of the synthesis method and melamine content of urea-melamine-formaldehyde (UMF) resins to their cohesive and interphase features, and adhesion in bonding wood products. Melamine at three addition levels was simultaneously reacted with urea and formaldehyde to obtain melamine-urea-formaldehyde (MUF) resins, while melamine at the same levels was initially reacted with formaldehyde and then with urea to prepare melamine-formaldehyde-urea (MFU) resins. As the melamine content increased, molecular weights, curing peak temperature, activation energy, bond-line thickness, E′max, and adhesion strength of wood products increased. These results indicated that the cohesive features of these resins mainly affected the adhesion strength in wood products while the interphase features had a partial contribution to the adhesion.
Thermochromic dynamic cool materials present a reversible change of their properties wherein by increasing the temperature, the reflectance, conductivity, and transmittance change due to a reversible ...crystalline phase transition. In particular, vanadium (IV) dioxide shows a reversible phase transition, accompanied by a change in optical properties, from monoclinic VO2(M1) to tetragonal VO2(R). In this paper, we report on a systematic exploration of the parameters for the synthesis of vanadium dioxide VO2(M1) via an easy, sustainable, reproducible, fast, scalable, and low-cost hydrothermal route without hazardous chemicals, followed by an annealing treatment. The metastable phase VO2(B), obtained via a hydrothermal route, was converted into the stable VO2(M1), which shows a metal–insulator transition (MIT) at 68 °C that is useful for different applications, from energy-efficient smart windows to dynamic concrete. Within this scenario, a further functionalization of the oxide nanostructures with tetraethyl orthosilicate (TEOS), characterized by an extreme alkaline environment, was carried out to ensure compatibility with the concrete matrix. Structural properties of the synthesized vanadium dioxides were investigated using temperature-dependent X-ray Diffraction analysis (XRD), while compositional and morphological properties were assessed using Scanning Electron Microscopy, Energy Dispersive X-ray Analysis (SEM-EDX), and Transmission Electron Microscopy (TEM). Differential Scanning Calorimetry (DSC) analysis was used to investigate the thermal behavior.
One of the major challenges currently in the field of material science is finding natural alternatives to the high-performing plastics developed in the last century. Consumers trust synthetic ...products for their excellent properties, but they are becoming aware of their impact on the planet. One of the most attractive precursors for natural polymers is tannin extracts and in particular condensed tannins. Quebracho (
) extract is one of the few industrially available flavonoids and can be exploited as a building block for thermoset resins due to its phenol-like reactivity. The aim of this study was to systematically investigate different hardeners and evaluate the water resistance, thermal behavior, and chemical structure of the quebracho tannin-based polymers in order to understand their suitability as adhesives. It was observed that around 80% of the extract is resistant to leaching when 5% of formaldehyde or hexamine or 10% of glyoxal or furfural are added. Additionally, furfuryl alcohol guarantees high leaching resistance, but only at higher proportions (20%). The quebracho-based formulations showed specific thermal behavior during hardening and higher degradation resistance than the extract. Finally, these polymers undergo similar chemistry to those of mimosa, with exclusive reactivity of the A-ring of the flavonoid.
This study investigated effects of sonication treatment on characteristics and drug release behavior of hydrogels prepared by supramolecular cellulose microfibrils (CMFs) isolated by ...2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation which made carboxylate negative charge available on the CMFs’ surface. The hydrogels were fabricated by inducing ionic interactions between negatively charged CMFs and a positive metal ion (Al3+). The sonication time showed no influence on the carboxylate content of CMFs, but it greatly influenced characteristics and drug release behavior of the hydrogels. These results indicate that the sonication time has an impact on hydrogels’ characteristics and drug release behavior.
Fillers based on crosslinked hyaluronic acid (HA) are becoming increasingly important in the field of aesthetic medicine, for example for treating wrinkles or for volumizing purposes. However, ...crosslinking agents are usually associated with toxicity and adverse reactions. The aim of this study is the development of an innovative technology to manufacture high performance HA-based fillers using minimal amounts of crosslinking agent. In this work, new fillers based on HA, functionalized with different amounts of 1,4-butanediol diglycidyl ether (BDDE) (degree of modification ranging between 3.5% and 8.8%) and formulated with a lactose modified chitosan (CTL), were investigated. The relative quantities of these polymeric building blocks in the formulations were 20-25 and 5 mg/mL for HA and CTL, respectively. Due to its cationic nature, CTL could interact with the anionic HA and enhance the elastic properties of the filler. Fillers manufactured with this novel technology (HACL-CTL) were characterized and compared with several fillers available in the market. In particular, resistance against hyaluronidase, swelling, cohesivity and rheological properties were investigated. Cohesivity, resistance to hydrolysis and swelling of HACL-CTL were comparable to commercial products. However, HACL-CTL fillers showed excellent elastic performance that reached 94% of elasticity in response to shear stresses. Surprisingly, these fillers also showed a resistance to compression higher than that of currently marketed products, making them very promising for their lifting effect.
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