Search Results (24)

In this work, the effect of the palladium precursor on the Oxygen Reduction Reaction (ORR) performance of lignin-based electrospun carbon fibers was studied. The fibers were spun from a lignin-ethanol solution free of any binder, where different Pd salts were added at two concentration levels. The system implemented to perform the spinning was a coaxial setup in which the internal flow contains the precursor dispersion with the metallic precursor, and ethanol was used as external flow to help fiber formation and prevent drying before generating the Taylor cone. The obtained cloths were thermostabilized in air at 200 °C and carbonized in nitrogen at 900 °C. The resulting carbon fibers were characterized by physicochemical and electrochemical techniques. The palladium precursor significantly affects nanoparticle distribution and size, fiber diameter, pore distribution, surface area and electrochemical behavior. The fibers prepared with palladium acetylacetonate at high Pd loading and carbonized at 900 °C under a CO₂ atmosphere showed high mechanical stability and the best ORR activity, showing near total selectivity towards the 4-electron path. These features are comparable to those of the commercial Pt/C catalyst but much lower metal loading (10.6 wt.% vs. 20 wt.%). The most promising fibers have been evaluated as cathodes in a zinc–air battery, delivering astonishing stability results that surpassed the performance of commercial Pt/C materials in both charging and discharging processes. Full article

An analysis of the influence of common modifiers on the kinetics of the curing process of epoxy-anhydride vitrimers was carried out. As common modifiers to enhance the “vitrimeric” nature of the material, zinc acetylacetonate as a transesterification catalyst and glycerol as a modifier of hydroxyl group content were chosen. The curing process of all obtained compositions was studied by differential scanning calorimetry (DSC) followed by the application of the isoconversional approach. It was shown that additives significantly affect the curing process. The resulting cured polymers were shown to be chemically recyclable by dissolution in the mixture of ethylene glycol and N-methylpirrolidone in a volume ratio of nine to one. The introduction of both zinc acethylacetonate and glycerol to the neat formulation led to a decrease in the dissolution time by 85.7% (from 35 h for the neat epoxy-anhydride formulation to 5 h for the modified formulation). In order to show the opportunity of the secondary use of recyclates, the mixtures based on the basic composition containing 10 wt. % of secondary polymers were also studied. The introduction of a recycled material to neat composition led to the same curing behavior as glycerol-containing systems. Full article

Sol compositions for transparent TiO₂ and ZnO photocatalytic thin film deposition are of interest for the wet-chemical fabrication of self-cleaning coatings. The choice of stabilizing agent is crucial for the sol film-forming properties, with acetylacetone and monoethanolamine conventionally employed for TiO₂ and ZnO deposition sols, respectively. Salicylic acid (SA), capable of chelating both Ti(IV) and Zn(II) precursors, remains underexplored. This study presents novel SA-based sol formulations for the deposition of both TiO₂ and ZnO films, based on titanium tetraisopropoxide (TTIP) and zinc acetate dihydrate (ZAD) precursors, in a fixed 1:3 (TTIP:SA) and 1:2 (ZAD:SA) ratio, and isopropanol solvent, varied across the 1:10 to 1:20 precursor-to-solvent ratio range. Fourier-Transform Infrared Spectroscopy analysis and Density Functional Theory computations confirmed the formation of H₂Ti[SA]₃ and Zn[SA]₂·2H₂O complexes. Scanning Electron Microscopy, X-ray diffraction, and Ultraviolet-Visible spectroscopy were employed to study the structural and optical properties of the dip-coated films, revealing dense TiO₂ (86–205 nm) and ZnO (35–90 nm) layers of thickness proportional to the salicylate concentration and transmittance in the 70–90% range. Liquid-phase Methylene blue (MB) photooxidation experiments revealed that all films exhibit photocatalytic activity, with ZnO films being superior to TiO₂, with 2.288 vs. 0.366 nm h⁻¹ cm⁻² MB removal rates. Full article

APCs (aliphatic polycarbonates) are one of the most important types of biodegradable polymers and widely used in the fields of solid electrolyte, biological medicine and biodegradable plastics. Zinc-based catalysts have the advantages of being low cost, being non-toxic, having high activity, and having excellent environmental and biological compatibility. Zinc (II) acetylacetonate (Zn(Acac)₂) was first reported as a highly effective catalyst for the melt transesterification of biphenyl carbonate with 1,4-butanediol to synthesize poly(1,4-butylene carbonate)(PBC). It was found that the weight-average molecular weight of PBC derived from Zn(Acac)₂ could achieve 143,500 g/mol with a yield of 85.6% under suitable reaction conditions. The Lewis acidity and steric hindrance of Zn²⁺ could obviously affect the catalytic performance of Zn-based catalysts for this reaction. The main reasons for the Zn(Acac)₂ catalyst displaying a higher yield and M_w than other zinc-based catalysts should be ascribed to the presence of the interaction between acetylacetone ligand and Zn²⁺, which can provide this melt transesterification reaction with the appropriate Lewis acidity as well as the steric hindrance. Full article

The electro-Fenton (EF) process is regarded as an efficient and promising sewage disposal technique for sustainable water environment protection. However, current developments in EF are largely restricted by cathode electrocatalysts. Herein, a supramolecular self-assembly strategy is adopted for synthetization, based on melamine–cyanuric acid (MCA) supramolecular aggregates integrated with carbon fixation using 5-aminosalicylic acid and zinc acetylacetonate hydrate. The prepared carbon materials characterize an ordered lamellar microstructure, high specific surface area (595 m² g⁻¹), broad mesoporous distribution (4~33 nm) and high N doping (19.62%). Such features result from the intrinsic superiority of hydrogen-bonded MCA supramolecular aggregates via the specific molecular assembly process. Accordingly, noteworthy activity and selectivity of H₂O₂ production (~190.0 mg L⁻¹ with 2 h) are achieved. Excellent mineralization is declared for optimized carbon material in several organic pollutants, namely, basic fuchsin, chloramphenicol, phenol and several mixed triphenylmethane-type dyestuffs, with total organic carbon removal of 87.5%, 74.8%, 55.7% and 54.2% within 8 h, respectively. This work offers a valuable insight into facilitating the application of supramolecular-derived carbon materials for extensive EF degradation. Full article

Manganese-zinc ferrite (MZF) is known as high-performance magnetic material and has been used in many fields and development. In the biomedical applications, the biocompatible MZF formulation attracted much attention. In this study, water-soluble amphiphilic vitamin E (TPGS, d-alpha-tocopheryl poly(ethylene glycol 1000) succinate) formulated MZF nanoparticles were synthesized to serve as both a magnetic resonance imaging (MRI) contrast agent and a vehicle for creating magnetically induced hyperthermia against cancer. The MZF nanoparticles were synthesized from a metallic acetylacetonate in an organic phase and further modified with TPGS using an emulsion and solvent-evaporation method. The resulting TPGS-modified MZF nanoparticles exhibited a dual-contrast ability, with a longitudinal relaxivity (35.22 s⁻¹ mM Fe⁻¹) and transverse relaxivity (237.94 s⁻¹ mM Fe⁻¹) that were both higher than Resovist^®. Furthermore, the TPGS-assisted MZF formulation can be used for hyperthermia treatment to successfully suppress cell viability and tumor growth after applying an alternating current (AC) electromagnetic field at lower amplitude. Thus, the TPGS-assisted MZF theranostics can not only be applied as a potential contrast agent for MRI but also has potential for use in hyperthermia treatments. Full article

Vitrimers constitute a new class of covalent adaptable networks (CANs), in which thermally stimulated associative exchange reactions allow the topological rearrangement of the dynamic network while keeping the number of bonds and the crosslink density constant. The current study proposed a solvent-free method to synthesize vitrimers by reactive melt mixing using a commercial biobased/biodegradable polyester, poly(butylene succinate), PBS. More specifically, a two-step process was followed; the first step involved reactive mixing of PBS with the crosslinker (diglycidyl ether of bisphenol A, DGEBA) and the transesterification catalyst (Zinc(II) acetylacetonate hydrate, Zn(acac)2) in a twin-screw mini-compounder, in order to incorporate the epoxy groups in the polymer backbone. The second step (vitrimerization) comprised a crosslinking process of the homogenous mixtures in a vacuum oven at 170 °C, resulting in the formation of a dynamic crosslinked network with epoxy moieties serving as the crosslinkers. By tuning the crosslinker content (0–10% mol with respect to PBS repeating unit) and the Zinc(II) catalyst to crosslinker ratio (0 to 1), tailor-made vitrimers were prepared with high insolubility and improved melt strength. Moreover, PBS vitrimers could still be reprocessed by compression molding after the crosslinking, which enables the recycling process. This work was made possible by the “Basic Research Programme, NTUA, PEVE 2020 NTUA” [PEVE0050] of the National Technical University of Athens and is gratefully acknowledged. Full article

Epoxy/silica thermosets with tunable matrix (vitrimers) were prepared by thermal curing of diglycidyl ether of bisphenol A (DGEBA) in the presence of a hardener—4-methylhexahydrophthalic anhydride (MHHPA), a transesterification catalyst—zinc acetylacetonate (ZAA), and 10–15 nm spherical silica nanoparticles. The properties of the resulting material were studied by tensile testing, thermomechanical and dynamic mechanical analysis. It is shown that at room temperature the introduction of 5–10 wt% of silica nanoparticles in the vitrimer matrix strengthens the material leading to the increase of the elastic modulus by 44% and the tensile stress by 25%. Simultaneously, nanoparticles enhance the dimensional stability of the material since they reduce the coefficient of thermal expansion. At the same time, the transesterification catalyst provides the thermoset with the welding ability at heating, when the chain exchange reactions are accelerated. For the first time, it was shown that the silica nanoparticles strengthen welding joints in vitrimers, which is extremely important, since it allows to repeatedly use products made of thermosets and heal defects in them. Such materials hold great promise for use in durable protective coatings, adhesives, sealants and many other applications. Full article

The paper presents a synthesis of poly(l-lactide) with bacteriostatic properties. This polymer was obtained by ring-opening polymerization of the lactide initiated by selected low-toxic zinc complexes, Zn[(acac)(L)H₂O], where L represents N-(pyridin-4-ylmethylene) tryptophan or N-(2-pyridin-4-ylethylidene) phenylalanine. These complexes were obtained by reaction of Zn[(acac)₂ H₂O] and Schiff bases, the products of the condensation of amino acids and 4-pyridinecarboxaldehyde. The composition, structure, and geometry of the synthesized complexes were determined by NMR and FTIR spectroscopy, elemental analysis, and molecular modeling. Both complexes showed the geometry of a distorted trigonal bipyramid. The antibacterial and antifungal activities of both complexes were found to be much stronger than those of the primary Schiff bases. The present study showed a higher efficiency of polymerization when initiated by the obtained zinc complexes than when initiated by the zinc(II) acetylacetonate complex. The synthesized polylactide showed antibacterial properties, especially the product obtained by polymerization initiated by a zinc(II) complex with a ligand based on l-phenylalanine. The polylactide showed a particularly strong antimicrobial effect against Pseudomonas aeruginosa, Staphylococcus aureus, and Aspergillus brasiliensis. At the same time, this polymer does not exhibit fibroblast cytotoxicity. Full article

Epoxy vitrimers with reprocessability, recyclability, and a self-healing performance have attracted increasingly attention, but are usually fabricated through static curing procedures with a low production efficiency. Herein, we report a new approach to fabricate an epoxy vitrimer by dynamic crosslinking in a torque rheometer, using diglycidyl ether of bisphenol A and sebacic acid as the epoxy resin and curing agent, respectively, in the presence of zinc acetylacetonate as the transesterification catalyst. The optimal condition for fabricating the epoxy vitrimer (EVD) was dynamic crosslinking at 180 °C for ~11 min. A control epoxy vitrimer (EVS) was prepared by static curing at 180 °C for ~11 min. The structure, properties, and stress relaxation of the EVD and EVS were comparatively investigated in detail. The EVS did not cure completely during static curing, as evidenced by the continuously increasing gel fraction when subjected to compression molding. The gel fraction of the EVD did not change with compression molding at the same condition. The physical, mechanical, and stress relaxation properties of the EVD prepared by dynamic crosslinking were comparable to those of the EVS fabricated by static curing, despite small differences in the specific property parameters. This study demonstrated that dynamic crosslinking provides a new technique to efficiently fabricate an epoxy vitrimer. Full article

The commonly used curing system for chloroprene rubber (CR) is a combination of two metal oxides, such as magnesium oxide (MgO) and zinc oxide (ZnO). Application of MgO and ZnO enables to obtain a good balance between processability of rubber compounds and mechanical properties of the vulcanizates. Despite high activity in crosslinking reactions, ZnO is classified as ecotoxic to aquatic organisms, thus environmental legislation requires its quantity in technology to be limited. In our studies more environmentally friendly curing systems were applied, which enabled eliminating ZnO from CR compounds. These curing systems consisted of manganese acetylacetonate (Mn(acac)) or nickel acetylacetonate (Ni(acac)) and triethanolamine (TEOA) used as a base necessary to perform Heck’s reaction. Both metal acetylacetonates exhibited high activity in crosslinking reactions, which was confirmed by a great torque increment during rheometric measurements and high degree of elastomer crosslinking. The type of metal acetylacetonate and the amount of TEOA seemed to have less influence on the efficiency of the curing system than the filler used. Rubber compounds filled with carbon black (CB) were characterized by definitely shorter optimal vulcanization times and higher degree of crosslinking compared to CR composites filled with nanosized SiO₂. Moreover, application of the proposed curing systems allowed to obtain CR vulcanizates with mechanical properties comparable with the benchmarks cured with metal oxides. Full article

Undoped and nickel-doped zinc oxide thin films were deposited on sodalime glass substrates by utilizing dip coating and ultrasonic spray pyrolysis deposition techniques. In both cases zinc acetate and nickel acetylacetonate were used as zinc precursor and nickel dopant source, respectively. XRD analysis confirms the ZnO wurtzite structure with (002) as the preferential orientation.SEM studies show the formation of two types of morphologies, primarily a porous spherical grains with a grain size distribution from 40 to 150 nm and another, rose-like structures with size distribution from 30 to 200 nm, based on different deposition techniques utilized. The elemental depth profiles across the films were investigated by the secondary-ion mass spectrometry (SIMS). Different gas sensing responses of all ZnO films were obtained for both propane and carbon monoxide gases, at different gas concentrations and operating temperatures. The highest sensing response (~6) for undoped ZnO films was obtained for films deposited by ultrasonic spray pyrolysis (USP). Nevertheless, the highest sensing response (~4 × 10⁴) for doped ZnO films was obtained for films deposited by dip coating method. The behavior of sensing responses is explained in detail based on the morphological properties and the amount of Ni impurities incorporated into the crystal lattice. Full article

The traditional methods for preparing magnesium aluminum layered double hydrotalcite (Mg₂Al-CO₃LDHs) in industry include coprecipitation and hydrothermal methods. Both these methods have the disadvantages of high preparation cost and complicated water washing process. Using Mg(OH)₂, Al(OH)₃, and CO₂ as raw materials in this work, the Mg₂Al-CO₃ LDHs are successfully prepared by mechanochemical method, which solves the shortcomings of traditional preparation method and realizes the conversion and utilization of CO₂ resource. The prepared Mg₂Al-CO₃ LDHs are evaluated as a heat stabilizer in poly(vinyl chloride) (PVC). The result indicates that, when 2.4 phr Mg₂Al-CO₃ LDHs, 0.3 phr ZnSt₂, and 0.3 phr of zinc acetylacetonate are added to the PVC, the thermal stability time of PVC can reach 190 min, which is better than PVC containing commercial Mg₂Al-CO₃ LDHs. Meanwhile, its processing performance is basically the same as the PVC containing commercial Mg₂Al-CO₃ LDHs. Full article

Zinc Oxide nanostructured thin films were grown by a novel plasma assisted vapour deposition method, which aims to combine the versatility of deposition processes that are mediated by plasma with the capability to control particles diffusion and nucleation. For this purpose, the proposed approach spatially separates into two different vacuum chambers the creation of zinc oxide from a metalorganic precursor from the actual film growth, thanks to the extraction of a supersonic jet of plasma seeded by the precursor fragments. The characterization of the reactor in different plasma conditions has been carried out by means of optical emission spectroscopy (OES). ZnO films with different degrees of purity, thickness uniformity, as well as different morphologies can be obtained varying the deposition parameters. The samples profiles have been collected in order to evaluate deposition rates and films uniformity. The as-prepared as well as annealed thin films were characterized by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) to evaluate their chemical composition and purity. According to Raman analyses, the annealed samples are high-purity wurtzite-type crystalline zinc oxide films. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) confirm a surface morphology characterized by columnar structures. Full article

Highly ordered vertically grown zinc oxide nanorods (ZnO NRs) were synthesized on ZnO-coated SiO₂/Si substrate using zinc acetylacetonate hydrate as a precursor via a simple hydrothermal method at 85 °C. We used 0.05 M of ZnO solution to facilitate the growth of ZnO NRs and the immersion time was varied from 0.5 to 4 h. The atomic force microscopy revealed the surface roughness of ZnO seed layer used to grow the ZnO NRs. The morphology of vertically grown ZnO NRs was observed by field emission scanning electron microscopy. X-ray diffraction examination and transmission electron microscopy confirmed that the structure of highly ordered ZnO NRs was crystalline with a strong (002) peak corresponded to ZnO hexagonal wurtzite structure. The growth of highly ordered ZnO NRs was favorable due to the continuous supply of Zn²⁺ ions and chelating agents properties obtained from the acetylacetonate-derived precursor during the synthesis. Two-point probe current–voltage measurement and UV–vis spectroscopy of the ZnO NRs indicated a resistivity and optical bandgap value of 0.44 Ω.cm and 3.35 eV, respectively. The photoluminescence spectrum showed a broad peak centered at 623 nm in the visible region corresponded to the oxygen vacancies from the ZnO NRs. This study demonstrates that acetylacetonate-derived precursors can be used for the production of ZnO NRs-based devices with a potential application in biosensors. Full article