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.
Highlights
Developing improved strategies for the manufacture of two-dimensional (2D) nanohybrid multifunctional materials has attracted a lot of interest in advanced research and technology
The cationic content of the materials continuously decreased with increasing the GO theoretical content (Figure S1) (Supplementary Materials), confirming the insertion of graphene oxide
The co-precipitation of Ce-containing MgAl-layered double hydroxides (LDH) in the presence of a GO suspension led to HT3Ce-xGO composites with increased crystallinity as indicated by the XRD analysis
Summary
Developing improved strategies for the manufacture of two-dimensional (2D) nanohybrid multifunctional materials has attracted a lot of interest in advanced research and technology. Graphene oxide and layered double hydroxides are among the various compounds that can be combined [2]. Layered double hydroxides (LDH), called hydrotalcite (HT)-like compounds, are anionic clays having the general formula [MII 1-x MIII x (OH)2 ]x+ [An− ]x/n ·zH2 O, where MII is a bivalent metal cation and MIII is a trivalent metal cation, An− is a charge-compensating anion which may be either inorganic or organic, and x has a value between 0.2 and 0.4. The combination of layered double hydroxides (LDH) with components such as graphene oxide (GO), a 2D honeycomb material with oxidizing properties [4,5], can lead to the formation of nanohybrids with improved properties that can be valorized in many applications, including catalysis [1,2]. Despite its advantageous properties such as increased optical, electronic, and thermal stability [4,6], graphene oxide tends to agglomerate and restack [1,4]
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