Anisotropic a-Fe2O3/Chitosan nanocomposites by electrophoretic deposition

Electrophoretic deposition (EPD) has been developed for the fabrication of composite coatings based on anisotropic hematite particles (a-Fe2O3) and chitosan (CHT) on stainless steel substrates for different technological applications ranging from coatings to sensors. The particles have been synthesized under refluxing conditions starting from a solution of FeCl2 4H2O and Poly-N-vinyl-pyrrolidone (PVP) in N, N-Dimethyl-formamide (DMF). A residual polymer content of around 10 percent by weight was found as part of the structure after the synthesis. Voltage 25 and deposition time of 5 min were selected as best deposition conditions which imply high homogeneous surface, non-delamination and good distribution of a-Fe2O3 particles. X-ray diffraction (XRD) measurements show the presence of hematite phase (a-Fe2O3). Thermogravimetric analysis (TGA) measurements were carried out to find the content of a-Fe2O3 and chitosan in the final coatings. According to this measurement, 60 and 35 percent were the final content. Scanning Electron Microscopy (SEM) images revealed the microstructure of the composite where it is possible to observe the deposition of anisotropic particles across the coating and cracks around them

Directional enhancement of refractive index and tunable wettability of polymeric coatings due to preferential dispersion of colloidal TiO2 nanorods towards their surface

Abstract We demonstrate the fabrication of nanocomposite coatings, of organic-capped colloidal TiO 2 nanorods dispersed into a poly(methyl methacrylate) matrix, with rising value of refractive index from the bottom to the top layers, and UV-induced surface wettability alteration, in a reversible manner. This behaviour is attributable to preferential dispersion of the TiO 2 nanoparticles towards the superficial layers of the coatings. Above a critical TiO 2 loading, the nanorods at the surface form aggregates deteriorating the optical and the surface properties of the nanocomposites. The optimal conditions for nanocomposite films preparation in terms of optimized nanorods dispersion, optical clarity, and surface smoothness are determined

Versatile strategy for homogeneous drying patterns of dispersed particles

After spilling coffee, a tell-tale stain is left by the drying droplet. This universal phenomenon, known as the coffee ring effect, is observed independent of the dispersed material. However, for many technological processes such as coating techniques and ink-jet printing a uniform particle deposition is required and the coffee ring effect is a major drawback. Here, we present a simple and versatile strategy to achieve homogeneous drying patterns using surface-modified particle dispersions. High-molecular weight surface-active polymers that physisorb onto the particle surfaces provide enhanced steric stabilization and prevent accumulation and pinning at the droplet edge. In addition, in the absence of free polymer in the dispersion, the surface modification strongly enhances the particle adsorption to the air/liquid interface, where they experience a thermal Marangoni backflow towards the apex of the drop, leading to uniform particle deposition after drying. The method is independent of particle shape and applicable to a variety of commercial pigment particles and different dispersion media, demonstrating the practicality of this work for everyday processes

Catalysis over zinc-incorporated berlinite (ZnAlPO4) of the methoxycarbonylation of 1,6-hexanediamine with dimethyl carbonate to form dimethylhexane-1,6-dicarbamate

<p>Abstract</p> <p>Background</p> <p>The alkoxycarbonylation of diamines with dialkyl carbonates presents promising route for the synthesis of dicarbamates, one that is potentially 'greener' owing to the lack of a reliance on phosgene. While a few homogeneous catalysts have been reported, no heterogeneous catalyst could be found in the literature for use in the synthesis of dicarbamates from diamines and dialkyl carbonates. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO₄) and zinc-incorporated berlinite (ZnAlPO₄) as heterogeneous catalysts in the production of dimethylhexane-1,6-dicarbamate from 1,6-hexanediamine (HDA) and dimethyl carbonate (DMC). The catalysts were characterized by means of XRD, FT-IR and XPS. Various influencing factors, such as the HDA/DMC molar ratio, reaction temperature, reaction time, and ZnAlPO₄/HDA ratio, were investigated systematically.</p> <p>Results</p> <p>The XRD characterization identified a berlinite structure associated with both the AlPO₄and ZnAlPO₄catalysts. The FT-IR result confirmed the incorporation of zinc into the berlinite framework for ZnAlPO₄. The XPS measurement revealed that the zinc ions in the ZnAlPO₄structure possessed a higher binding energy than those in ZnO, and as a result, a greater electron-attracting ability. It was found that ZnAlPO₄catalyzed the formation of dimethylhexane-1,6-dicarbamate from the methoxycarbonylation of HDA with DMC, while no activity was detected on using AlPO₄. Under optimum reaction conditions (i.e. a DMC/HDA molar ratio of 8:1, reaction temperature of 349 K, reaction time of 8 h, and ZnAlPO₄/HDA ratio of 5 (mg/mmol)), a yield of up to 92.5% of dimethylhexane-1,6-dicarbamate (with almost 100% conversion of HDA) was obtained. Based on these results, a possible mechanism for the methoxycarbonylation over ZnAlPO₄was also proposed.</p> <p>Conclusion</p> <p>As a heterogeneous catalyst ZnAlPO₄berlinite is highly active and selective for the methoxycarbonylation of HDA with DMC. We propose that dimethylhexane-1,6-dicarbamate is formed <it>via </it>a catalytic cycle, which involves activation of the DMC by a key active intermediate species, formed from the coordination of the carbonyl oxygen with Zn(II), as well as a reaction intermediate formed from the nucleophilic attack of the amino group on the carbonyl carbon.</p

Potential contribution of nanotechnology to the circular economy of plastic materials

The problem of plastic accumulation in the environment requires the development of effective strategies to shift the paradigm of used plastics from wastes to resources. In the present contribution, after an overview of the current plastic management strategies, the possible role of nanotechnology to this emerging field is considered. In particular, the challenges related to the use of nano-additives to improve the properties of recycled plastics is discussed based on the fundamental aspects of colloid stabilisation. Finally, the contribution of nanotechnology to the fabrication of effective catalysts for the depolymerisation of plastics into the constituent monomers is outlined

Synthesis of goethite α-FeOOH particles by air oxidation of ferrous hydroxide Fe(OH)2 suspensions: Insight on the formation mechanism

Iron oxide and iron oxyhydroxide particles, particularly, the goethite α-FeOOH phase, are environmentally friendly materials and are used in various technological applications as adsorbents, precursors of Fe powders for magnetic recording media, and pigments. In this work, the formation process of α-FeOOH by air oxidation of Fe(OH)2 suspensions has been studied. The effects of the air flow rate, as well as of the reactant concentration ratio, R (=[(OH)-]/[Fe(II)]), on the reaction product were analyzed. It has been found that the morphology and the size of the α-FeOOH particles can be modified by means of the air flow rate. Furthermore, by performing a detailed microscopic analysis of the morphology of the initial, intermediate, and final reaction products, we have obtained evidence of epitaxial growth of α-FeOOH on the Fe(OH)2 substrate. It is suggested that the similarity between the anion arrangements in both phases facilitates this process. Based on these results, a pathway for the formation of α-FeOOH in highly alkaline medium is proposed in which the size and shape of the initial Fe(OH)2 particles plays a significant role in the formation the α-FeOOH particles obtained upon completion of the oxidation process.Fil: Encina, Ezequiel Roberto. Universitat Erlangen-Nuremberg; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Distaso, Monica. Universitat Erlangen-Nuremberg; AlemaniaFil: Klupp Taylor, Robin N.. Universitat Erlangen-Nuremberg; AlemaniaFil: Peukert, Wolfgang. Universitat Erlangen-Nuremberg; Alemani

ZnO superstructures via oriented aggregation initiated in a block copolymer melt

A fast and simple one pot synthesis of ZnO nano- and microparticles initiated and driven by an amino block copolymer O,O′-bis(2-aminopropyl)polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol (Jeffamine®) is reported. The specific building mechanism of ZnO mesocrystals is investigated in detail using electron microscopy and diffraction methods. Mesocrystals with a complex superstructure are formed as a result of a consecutive and oriented multiple stage aggregation process: first a 0D → 1D aggregation process is observed, then a 1D → 3D aggregation process occurs in which secondary particles form cones and multiple cone symmetries. Dots, rods, cones, and multiple cones have been isolated within a time resolved study which clearly supports the growth model. To control the morphology of the product particles, the influence of relevant synthesis parameters including stirring and sonication of the intermediate were investigated. Extensive surface characterization of the resulting mesocrystals is presented using infrared and photoluminescence spectroscopies as well as thermogravimetric analysis. Even after multiple washing steps, the particles exhibit a Jeffamine® coated surface that allows for easy dispersion in both polar and nonpolar solvents. The obtained mesocrystals efficiently scatter in the whole range of visible light