Copper-coordination polymer-controlled Cu@N-rGO and CuO@C nanoparticle formation: reusable green catalyst for A³-coupling and nitroarene-reduction reactions

Abstract

The intriguing structural properties of coordination polymers (COPs), together with the huge variety of metal ions and organic linkers to choose from, make COPs potential precursors for fabricating carbon-encapsulated metal and metal oxide nanoparticles (NPs). Herein, we have studied the role of the COP structural assembly, prepared through making subtle changes to the ligand structure, on the formation of NPs in a carbon matrix. Cu-COPs (Cu-COP-1-Cu-COP-7), generated using different amino acid-based reduced Schiff base phenolic chelating ligands, exhibited crystalline structures with differing structural organization in the solid state. Interestingly, the calcination of Cu-COP-1 and Cu-COP-5 at 330 °C produced pure CuNPs, whereas Cu-COP-2, Cu-COP-3, Cu-COP-4 and Cu-COP-7 gave CuONPs encapsulated by carbon matrix. The calcination of Cu-COP-6 produced both CuNPs and CuONPs together in the carbon matrix. The formation of CuNPs and CuONPs in the carbon matrices was unambiguously confirmed by PXRD and XPS studies. The sizes and morphologies of the Cu/CuONPs were analyzed using HR-TEM and FE-SEM. BET studies revealed higher surface areas with small pores for the CuNPs encapsulated by carbon and lower surface areas with higher porosity for the CuONP-carbon matrix. Raman spectra revealed the formation of a nitrogen-doped reduced graphene oxide (N-rGO) carbon matrix in CuNPs-1. The N-rGO coverage and high surface area with small pores provided CuNPs-1 with good stability in strong acid (10 M HSO). Importantly, the fabricated N-rGO-encapsulated CuNPs-1 and carbon-covered CuONPs-4 nanocomposites were used as green catalysts in solvent-free neat A-coupling and nitroarene-reduction reactions, respectively. The products were confirmed using H-NMR spectra. The recovered CuNPs-1 and CuONPs-4 catalysts, after the completion of the reactions, also showed similar catalytic activity at up to five cycles, without significant loss of catalytic activity. Thus, the present studies demonstrate the influence of Cu-COP structural assembly on the formation of Cu/CuONPs as well as the carbon matrix, and open the possibility of fabricating functional nanomaterials from the vast number of available COPs with intriguing structural motifs.

Reduction of Nitro Compounds Using 3d-Non-Noble Metal Catalysts

“…S. P. Anthony and co-workers recently demonstrated copper on coordination polymers (COPs) as reusable catalysts for the reduction of nitroarenes . Seven different materials were synthesized by complexation of Cu 2+ with an amino acid-based reduced Schiff base ligand, followed by calcination at 330 °C for 12 h. The structure of the ligands only differed in one moiety from each other (Figure ).…”

“…Synthesis of Cu NPs and CuO NPs from Cu-COPs, as was demonstrated by Anthony and co-workers. Reproduced with permission from ref . Copyright 2017 The Royal Society of Chemistry.…”

Tuning of Surface Wettability and Interfacial Electron Transfer in Cupric Oxide Nanosheets for Highly Efficient Hydrogen Peroxide Production and Electro-Fenton Catalysis

“…On the CuO NSs/ACF, the oxygen element is from both the substrate of ACF and the CuO structure. The composition of adsorbed oxygen on CuO NSs/ACF (23.79%) is much lower than that of pristine ACF (38.30%), resulting from the increased composition of lattice oxygen from CuO nanosheets . The Cu 2p spectra in Figure d exhibit two spin–orbit peaks of Cu 2p 1/2 (954.5 eV), Cu 2p 3/2 (934.5 eV), and their satellite peaks, which are mainly attributed to Cu 2+ .…”

“…The composition of adsorbed oxygen on CuO NSs/ ACF (23.79%) is much lower than that of pristine ACF (38.30%), resulting from the increased composition of lattice oxygen from CuO nanosheets. 45 The Cu 2p spectra in Figure 4d exhibit two spin−orbit peaks of Cu 2p 1/2 (954.5 eV), Cu 2p 3/2 (934.5 eV), and their satellite peaks, which are mainly attributed to Cu 2+ . 46 The relative 0.6 eV positive shift of the peaks with higher binding energy as well as the concomitant broadening of Cu 2p suggests the tuning of electronic structure in CuO NSs after the formation of hybrid CuO NSs/ACF.…”

Highly Active Cu@NC Catalyst Derived from Porous Organic Polymer for Solvent‐Free Coupling of Acyl Chlorides with Alkynes

“…Additionally, a peak at 35.5 ° was identified as the (002) facet of the monoclinic phase of CuO (JCPDS No. 45–0937) [33,34] . Furthermore, a weak characteristic peak corresponding to Cu2O (JCPDS No.…”