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Ce-Containing MgAl-Layered Double Hydroxide-Graphene Oxide Hybrid Materials as Multifunctional Catalysts for Organic Transformations.

ABSTRACT: The combination of layered double hydroxides (LDH) with graphene oxide (GO) enables the formation of nanohybrids with improved properties. This work focuses on the structural and catalytic properties of Ce-containing MgAl LDH-GO composites bearing different concentrations of GO in the range of 5-25 wt.%. The synthesis of the composites was performed by co-precipitating the LDH phase in the presence of GO, while their characterization was performed using XRF, XRD, DRIFT, Raman, SEM, nitrogen adsorption-desorption, and acidity-basicity measurements. The LDH-GO composites, showing redox, basic, and acid catalytic functions, were tested in two different types of organic transformations: (i) Knoevenagel condensation and (ii) one-pot cascade oxidation-Knoevenagel condensation. (i) The cinnamic acid was synthesized by the Knoevenagel condensation of benzaldehyde with diethylmalonate. The composites showed catalytic performances in strong contrast to neat LDH or GO, suggesting a synergistic interaction between the two components. During Knoevenagel condensation, the catalytic activity increased with the GO content in the hybrids up to 15 wt.% and decreased afterwards. (ii) 2-Benzoyl-3-phenylacrylonitrile was synthesized by the aerobic oxidation of benzyl alcohol followed by the Knoevenagel condensation with benzoyl acetonitrile using three different non-polar solvents, i.e., toluene, benzene, and mesitylene. The conversion of benzyl alcohol was higher for the hybrid materials compared to the individual components but decreased with the increase of the graphene oxide concentration.

SUBMITTER: Stamate AE

PROVIDER: S-EPMC8659285 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:In this work, organic-inorganic hybrid nanoarchitectures were prepared in a single coprecipitation step by assembling magnesium-aluminum layered double hydroxides (MgAl-LDH) and a sepiolite fibrous clay, with the simultaneous encapsulation of the herbicide 2-methyl-4-chlorophenoxyacetic acid (MCPA) as the MgAl-LDH retains its ion exchange properties. The synthetic procedure was advantageous in comparison to the incorporation of MCPA by ion exchange after the formation of the LDH/sepiolite nanoarchitecture in a previous step, as it was less time consuming and gave rise to a higher loading of MCPA. The resulting MCPA-LDH/sepiolite nanoarchitectures were characterized by various physicochemical techniques (XRD, FTIR and 29Si NMR spectroscopies, CHN analysis and SEM) that revealed interactions of LDH with the sepiolite fibers through the silanol groups present on the outer surface of sepiolite, together with the intercalation of MCPA in the LDH confirmed by the increase in the basal spacing from 0.77 nm for the pristine LDH to 2.32 nm for the prepared materials. The amount of herbicide incorporated in the hybrid nanoarchitectures prepared by the single-step coprecipitation method surpassed the CEC of LDH (ca. 330 mEq/100 g), with values reaching 445 mEq/100 g LDH for certain compositions. This suggests a synergy between the inorganic solids that allows the nanoarchitecture to exhibit better adsorption properties than the separate components. Additionally, in the release assays, the herbicide incorporated in the hybrid nanoarchitectures could be completely released, which confirms its suitability for agricultural applications. In order to achieve a more controlled release of the herbicide and to act for several days on the surface of the soil, the hybrid nanoarchitectures were encapsulated in a biopolymer matrix of alginate/zein and shaped into spheres. In in vitro tests carried out in bidistilled water, a continuous release of MCPA from the bionanocomposite beads was achieved for more than a week, while the non-encapsulated materials released the 100% of MCPA in 48 h. Besides, the encapsulation may allow for better handling and transport of the herbicide.

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Ce-Containing MgAl-Layered Double Hydroxide-Graphene Oxide Hybrid Materials as Multifunctional Catalysts for Organic Transformations.

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