•Chitosan has been shown to have antimicrobial properties against microorganisms.•Chitosan can be used as antimicrobial polymer in packaging material.•Methods to produce chitosan films are solution ...casting and blending.•Reactive extrusion seems the most promising blending technique.
An increased interest for hygiene in everyday life as well as in food, feed and medical issues lead to a strong interest in films and blends to prevent the growth and accumulation of harmful bacteria. A growing trend is to use synthetic and natural antimicrobial polymers, to provide non-migratory and non-depleting protection agents for application in films, coatings and packaging. In food packaging, antimicrobial effects add up to the barrier properties of the materials, to increase the shelf life and product quality. Chitosan is a natural bioactive polysaccharide with intrinsic antimicrobial activity and, due to its exceptional physicochemical properties imparted by the polysaccharide backbone, has been recognized as a natural alternative to chemically synthesized antimicrobial polymers. This, associated with the increasing preference for biofunctional materials from renewable resources, resulted in a significant interest on the potential for application of chitosan in packaging materials. In this review we describe the latest developments of chitosan films and blends as packaging material.
This microreview summarizes the use of deep eutectic solvents (DESs) and related melts in organic synthesis. Solvents of this type combine the great advantages of other proposed environmentally ...benign alternative solvents, such as low toxicity, high availability, low inflammability, high recyclability, low volatility, and low price, avoiding many disadvantages of the more modern media. The fact that many of the components of these mixtures come directly from nature assures their biodegradability and renewability. The classification and distribution of the reactions into different sections in this microreview, as well as the emphasis paid to their scope, easily allow a general reader to understand the actual state of the art and the great opportunities opened, not only for academic purposes but also for industry.
21st Century DESs: Worries about the sustainability of our civilization on Earth are forcing changes on all aspects of industrial production. In organic synthesis, solvents (including their production and degradation) are the main waste component in reactions. Deep eutectic solvents (and related mixtures) offer an irresistible opportunity to improve the sustainability of processes in this century.
Gold is a valuable metal that can be dissolved with common household chemicals as reported by Timo Repo et al. in their Research Article (e202117587). By applying catalytic iodine, aqueous hydrogen ...peroxide and 2‐mercaptobenzimidazole, gold promptly dissolves in ethanol. Catalytic reactions and environmentally benign solvents and reagents are the basis for sustainable development and a gateway to a greener future of precious metals recycling.
Amino-triphenolate derived Al(III) complexes combined with suitable nucleophiles have been investigated as binary catalysts for the coupling of limonene oxide and carbon dioxide to afford alternating ...polycarbonates. These catalysts are able to produce stereoregular, perfectly alternating trans-polymers from cis-limonene oxide, whereas the pure trans isomer and cis/trans mixture give rise to lower degrees of stereoregularity. The best Al(III) catalyst shows the potential to mediate the conversion of both stereoisomers of limonene oxide with high conversion levels of up to 71 % under neat conditions, indicating the high degree of robustness and atom-efficiency of this catalytic process. Computational studies have revealed unique features of the binary catalyst system, among which is the preferred nucleophilic attack on the quaternary carbon centre in the limonene oxide substrate.
Frustrated Lewis pairs (FLPs) consist of sterically hindered Lewis acids and Lewis bases, which provide high catalytic activity towards non-metal-mediated activation of "inert" small molecules, ...including CO
among others. One critical issue of homogeneous FLPs, however, is their instability upon recycling, leading to catalytic deactivation. Herein, we provide a solution to this issue by incorporating a bulky Lewis acid-functionalized ligand into a water-tolerant metal-organic framework (MOF), named SION-105, and employing Lewis basic diamine substrates for the in situ formation of FLPs within the MOF. Using CO
as a C1-feedstock, this combination allows for the efficient transformation of a variety of diamine substrates into benzimidazoles. SION-105 can be easily recycled by washing with MeOH and reused multiple times without losing its identity and catalytic activity, highlighting the advantage of the MOF approach in FLP chemistry.
Co3O4 spinel has been widely investigated as a promising catalyst for the oxidation of volatile organic compounds (VOCs). However, the roles of tetrahedrally coordinated Co2+ sites (Co2+ Td ) and ...octahedrally coordinated Co3+ sites (Co3+ Oh ) still remain elusive, because their oxidation states are strongly influenced by the local geometric and electronic structures of the cobalt ion. In this work, we separately studied the geometrical-site-dependent catalytic activity of Co2+ and Co3+ in VOC oxidation on the basis of a metal ion substitution strategy, by substituting Co2+ and Co3+ with inactive or low-active Zn2+(d0), Al3+(d0), and Fe3+(d5), respectively. Raman spectroscopy, X-ray absorption fine structure (XAFS), and in situ DRIFTS spectra were thoroughly applied to elucidate the active sites of a Co-based spinel catalyst. The results demonstrate that octahedrally coordinated Co2+ sites (Co2+ Oh ) are more easily oxidized to Co3+ species in comparison to Co2+ Td , and Co3+ are responsible for the oxidative breakage of the benzene rings to generate the carboxylate intermediate species. CoO with Co2+ Oh and ZnCo2O4 with Co3+ Oh species have demonstrated good catalytic activity and high TOFCo values at low temperature. Benzene conversions for CoO and ZnCo2O4 are greater than 50% at 196 and 212 °C, respectively. However, CoAl2O4 with Co2+ Td sites shows poor catalytic activity and a low TOFCo value. In addition, ZnCo2O4 exhibits good durability at 500 °C and strong H2O resistance ability.
Dicarboxylic acids (DCAs) are highly value-added chemicals and intermediates extensively applied in various fields of the chemical industry. Transformation of the renewable and abundant biomass and ...its derivatives is viewed as a promising and sustainable process for DCA production, thus being paid considerable attention. The present Review provides a summary of recent achievements in the development of catalytic systems for synthesis of DCAs, including oxalic acid, malonic acid, tartronic acid, maleic acid, fumaric acid, succinic acid, adipic acid, glucaric acid, 2,5-furandicarboxylic acid, and terephthalic acid from biomass derivatives in thermocatalytic routes. The performances of catalytic systems are assessed in aspects of reactivity, selectivity toward each DCA, reusability, and operating conditions. The involved reaction pathways and mechanisms are discussed to offer deep insights into DCA formations from biomass derivatives.
Polymers are used in simple consumer items like carpets, furniture, glues, and clothing but are also used in advanced engineering, including materials used in the aerospace industry. Therefore, ...polymers and consequently their monomers play an important role in our everyday life. Currently, most of the monomers are produced from fossil resources, the supply of which is diminishing. In this paper we review strategies and catalytic processes to obtain currently used and potentially new monomers from renewable bio-based feedstocks and platform chemicals. This Review is divided by type of monomer and includes diacids and esters, diols, hydroxy acids and esters, lactones, carbonates, cyclic ethers, diamines, amino acids and lactams, alkenes, acrylics, and conjugated dienes. Only routes based on the use of homogeneous catalysis, heterogeneous catalysis, or bio-catalysis are described. Fermentative processes are not discussed.
Two-stage leaching of delaminated waste printed circuit boards followed by individual solvent extraction steps delivers copper and gold solutions from electronic waste.
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•New ...hydrometallurgical route to copper and gold recycling from e-waste.•Two-stage leaching process provides bulk separation of base from precious metals.•Individual metals refined using highly selective copper and gold extractants.•Proof of concept for the recycling of valuable metals from end-of-life electronics.
The recycling of metals such as gold and copper from discarded end-of-life electronic waste (e-waste or WEEE) is an important aspect to the development of environmentally benign manufacturing processes that exhibit circularity in materials flow. Global e-waste production is increasing at a 3–5% rate, so it is concerning that only 30% is recycled using regulated processes. We present here a new hydrometallurgical route for the technically feasible recycling of copper and gold from waste printed circuit boards (WPCBs) of mobile phones. This process comprises the liberation of the metallic fractions from downsized WPCBs, a two-stage acid leaching process to provide a bulk separation of copper and gold from the other metals present, and subsequent purification of the copper and gold-containing solutions by solvent extraction using highly selective phenolic oxime and amide extractants, respectively. Complete dissolution of the base metals was seen using 3 M nitric acid at 30 °C and the selective separation of copper from this leach liquor was achieved by solvent extraction using ACORGA M5640 dissolved in kerosene. The residues from base-metal leaching were treated with a mixture of 3 M sulfuric acid and 3 M sodium bromide at 70 °C, resulting in greater than 95% gold dissolution. The selective separation of gold from this precious metal leachate was achieved by solvent extraction using 0.1 M tertiary amide extractant dissolved in toluene. This process delivers complete copper and gold recycling from WPCBs under relatively benign laboratory conditions and represents a proof of concept for liberating valuable and critical metals back into active service from end-of-life electronic devices.
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