Applications of Functionalized Chitosan in Catalysis†

Study on the effect of graphene and glycerol plasticizer on the properties of chitosan-graphene nanocomposites via in situ green chemical reduction of graphene oxide

Unplasticized and glycerol plasticized chitosan/graphene (CS/GS) nanocomposites were synthesized via in situ chemical reduction of graphene oxide sheets (GO) with l-ascorbic acid (L-AA) as reductant by solution casting. The reduction of GO with L-AA was investigated to establish the optimal amount of reductant required to produce chemically reduced graphene sheets (GS). The combine effect of both nanofiller and glycerol on the structure, thermal, mechanical, and electrical properties of CS/GS nanocomposite films was evaluated. Materials were characterized by FT-IR, NMR, UV-Vis, XPS, XRD, Raman, SEM, TEM, and TGA. The results showed that GS sheets were homogeneously dispersed throughout the CS matrix, and that interactions between CS and the surface of GS took place. When compared with neat CS, nanocomposites showed a decrease in the crystallinity, better thermal stability under oxidative atmosphere, and improved mechanical properties, while maintained the thermal properties of CS under inert conditions. Combined use of glycerol and GS led to substantially enhanced mechanical properties. The electrical conductivity was increased with increasing GS loading in nanocomposite. This study demonstrates how CS/GS nanocomposites performance properties can be tailored by controlling GsS and plasticizer content.

Synthesis and application of chitosan supported vanadium oxo in the synthesis of 1,4-dihydropyridines and 2,4,6-triarylpyridines via anomeric based oxidation

1,4-Dihydropyridines and 2,4,6-triarylpyridines were synthesized via anomeric based oxidation using chitosan supported vanadium oxo.

Preparation and Chemical/Microstructural Characterization of Azacrown Ether-Crosslinked Chitosan Films

Chemically stable porous azacrown ether-crosslinked chitosan films were prepared by reacting varying molar amounts of N,N-diallyl-7,16-diaza-1,4,10,13-tetraoxa-dibenzo-18-crown-6 (molar equivalents ranging from 0, 0.125, 0.167, 0.25 and 0.5) with chitosan. Their chemical and structural properties were characterized by solid state-nuclear magnetic resonance (NMR), elemental, Fourier transform infrared (FTIR), microscopy, and X-ray analyses, as well as gel content. NMR and FTIR analyses of the reaction products suggested that new –CH₂– crosslink bridges were produced between the amine groups of chitosan (Ch) and the allyl groups of the azacrown (DAC). The crosslinking chemistry between allyl and amine groups of the reactants was further evidenced with solution NMR studies on model compound of glucosamine with the azacrown. X-ray diffraction analysis of the Ch/azacrown films using wide angle X-ray scattering (WAXS), including synchrotron-WAXS, revealed that the crystalline arrangement of chitosan (Ch) was partially destroyed with increasing grafting of azacrown ether proportion on the Ch polymer chain. Solubility and gel content determination confirmed network formation with a gel content as high as 84–95 wt %. Microstructural analysis revealed microporous morphology with high surface area. The morphology and structure of the azacrown ether-crosslinked chitosan films could be tailored by stoichiometry of the reacting species.

Novel triazole-modified chitosan@nickel nanoparticles: efficient and recoverable catalysts for Suzuki reaction

The synthesis of triazole-modified chitosan@nickel catalyst through the click reaction of azide-functionalized chitosan with an alkynated imino-thiophene ligand for Suzuki–Miyaura coupling reactions.

Encaging Palladium Nanoparticles in Chitosan Modified Montmorillonite for Efficient, Recyclable Catalysts

Metal nanoparticles, once supported by a suitable scaffolding material, can be used as highly efficient heterogeneous catalysts for numerous organic reactions. The challenge, though, is to mitigate the continuous loss of metals from the supporting materials as reactions proceed, so that the catalysts can be recycled multiple times. Herein, we combine the excellent chelating property of chitosan (CS) and remarkable stability of montmorillonite (MMT) into a composite material to support metal catalysts such as palladium (Pd). The in situ reduction of Pd²⁺ into Pd⁰ in the interstices of MMT/CS composites effectively encages the Pd⁰ nanoparticles in the porous matrices, while still allowing for reactant and product molecules of relatively small sizes to diffuse in and out the matrices. The prepared Pd⁰@MMT/CS catalysts are highly active for the Heck reactions of aromatic halides and alkenes, and can be recycled 30 times without significant loss of activities. Positron annihilation lifetime analysis and other structural characterization methods are implemented to elucidate the unique compartmentalization of metal catalysts in the composite matrices. As both CS and MMT are economical and abundant materials in nature, this approach may facilitate a versatile platform for developing highly recyclable, heterogeneous catalysts containing metal nanoparticles.

Shell Biorefinery: Dream or Reality?

Shell biorefinery, referring to the fractionation of crustacean shells into their major components and the transformation of each component into value-added chemicals and materials, has attracted growing attention in recent years. Since the large quantities of waste shells remain underexploited, their valorization can potentially bring both ecological and economic benefits. This Review provides an overview of the current status of shell biorefinery. It first describes the structural features of crustacean shells, including their composition and their interactions. Then, various fractionation methods for the shells are introduced. The last section is dedicated to the valorization of chitin and its derivatives for chemicals, porous carbon materials and functional polymers.

Metal-Polysaccharide Interplay: Beyond Metal Immobilization, Graphenization-Induced-Anisotropic Growth

Such sweet support: Metal-polysaccharide interplay affords, after pyrolytic transformation, highly active catalysts based on anisotropically oriented nanoparticles supported on graphene sheets.

Sorption of Cu(II) Ions on Chitosan-Zeolite X Composites: Impact of Gelling and Drying Conditions

Chitosan-zeolite Na-X composite beads with open porosity and different zeolite contents were prepared by an encapsulation method. Preparation conditions had to be optimised in order to stabilize the zeolite network during the polysaccharide gelling process. Composites and pure reference components were characterized using X-ray diffraction (XRD); scanning electron microscopy (SEM); N₂ adsorption-desorption; and thermogravimetric analysis (TG). Cu(II) sorption was investigated at pH 6. The choice of drying method used for the storage of the adsorbent severely affects the textural properties of the composite and the copper sorption effectiveness. The copper sorption capacity of chitosan hydrogel is about 190 mg·g(-1). More than 70% of this capacity is retained when the polysaccharide is stored as an aerogel after supercrititcal CO₂ drying, but nearly 90% of the capacity is lost after evaporative drying to a xerogel. Textural data and Cu(II) sorption data indicate that the properties of the zeolite-polysaccharide composites are not just the sum of the properties of the individual components. Whereas a chitosan coating impairs the accessibility of the microporosity of the zeolite; the presence of the zeolite improves the stability of the dispersion of chitosan upon supercritical drying and increases the affinity of the composites for Cu(II) cations. Chitosan-zeolite aerogels present Cu(II) sorption properties.

Copper(ii) supported on magnetic chitosan: a green nanocatalyst for the synthesis of 2,4,6-triaryl pyridines by C–N bond cleavage of benzylamines

In this paper, Cu/magnetic chitosan has been synthesized and used as a new green nanocatalyst for highly efficient synthesis of 2,4,6-triaryl pyridines via C–N bond cleavage of benzylamines under aerobic oxidation at 90 °C.

Eco-friendly synthesis and catalytic application of chitosan/gold/carbon nanotube nanocomposite films

Novel eco-friendly chitosan nanocomposite membranes containing gold nanoparticles and carbon nanotubes (CNTs) have been synthesized to produce reusable catalytic membranes.

Enzymolysis of chitosan by papain and its kinetics

Low molecular weight chitosan (LMWC) was obtained by the enzymolysis of chitosan by papain. Enzymolysis conditions (initial chitosan concentration, temperature, pH and ratio of papain to chitosan) were optimized by conducting experiments at three different levels using the response surface methodology (RSM) to obtain high soluble reducing sugars (SRSs) concentrations. Meanwhile, the influence of chitosan substrate concentration on the activity of papain was assessed in the experiments. The enzymolysis process was analyzed using pseudo-first-order and pseudo-second-order kinetic models and the experiment data were found to be more consistent with the pseudo-second-order kinetic model. In addition, the kinetic behavior of the enzymolysis was also investigated by using Haldane model, and chitosan exhibited substrate inhibition. It was clear that the Haldane kinetic model adequately described the dynamic behavior of the chitosan enzymolysis by papain. When the initial chitosan concentration was above 8.0g/L, the papain was overloaded and exhibited significant inhibition.

Changes in spectrochemical and catalytic properties of biopolymer anchored Cu(II) and Ni(II) catalysts by electron beam irradiation

Chitosan (a biopolymer) anchored Cu(II) and Ni(II) Schiff base complexes, [M(OIAC)Cl2] (M: Cu/Ni and OIAC: ([2-oxo-1H-indol-3-ylidene]amino)chitosan) were electron beam irradiated by different doses (100 Gy, 1 kGy and 10 kGy). The electron beam has shown potential impact on biopolymer's support, in detail chain linking and chain scissoring, as evidenced by viscosity studies, FT-IR and X-ray diffraction spectroscopic techniques. Due to these structural changes, thermal properties of the complexes were found to be changed. The surface of these heterogeneous complexes was also effectually altered by electron beam. As a consequence, pores and holes were created as probed by SEM technique. The catalytic activity of both non-irradiated and irradiated complexes was investigated in the aerobic oxidation of cyclohexane using hydrogen peroxide oxidant. The catalytic ability of the complexes was enhanced significantly after irradiation as the result of surface changes. The reusability of the complexes was also greatly affected because of the structural variations in polymeric support. In terms of both better catalytic activity along with the reusability, 1 kGy is suggested as the best dose to attain adequate increase in catalytic activity and good reusability.

A magnetic porous chitosan-based palladium catalyst: a green, highly efficient and reusable catalyst for Mizoroki–Heck reaction in aqueous media

We have prepared a highly active and recyclable heterogeneous catalyst for the Heck reaction in aqueous media in high yields.

Novel chitosan-based/montmorillonite/palladium hybrid microspheres as heterogeneous catalyst for Sonogashira reactions

The objective of this study was to develop novel chitosan-based/montmorillonite/palladium (CS/MMT/Pd) hybrid microsphere catalysts with improved properties for use in Sonogashira reactions.

Alginic acid aerogel: a heterogeneous Brønsted acid promoter for the direct Mannich reaction

Alginic acid, a biopolymer from brown algae, promotes a Brønsted acid catalyzed Mannich reaction in its aerogel formulation.

Proline-functionalized chitosan–palladium(ii) complex, a novel nanocatalyst for C–C bond formation in water

An environmentally friendly palladium-based catalyst supported on proline-functionalized chitosan was successfully prepared and evaluated as a heterogeneous nanocatalyst in the Suzuki cross-coupling reaction of various aryl halides with phenylboronic acid.

Hydration of nitriles to amides by a chitin-supported ruthenium catalyst

Chitin-supported ruthenium (Ru/chitin) promotes the hydration of nitriles to carboxamides under aqueous conditions.

Dual catalysis with magnetic chitosan: direct synthesis of cyclic carbonates from olefins with carbon dioxide using isobutyraldehyde as the sacrificial reductant

Magnetic chitosan was further functionalized with (ii) acetylacetonate complex [Co(acac)₂] and quaternary triphenylphosphonium bromide by targeting the –NH₂ and –OH moieties located on the surface of chitosan.