Abstract
Five different copper-oxide nanocrystals were prepared by colloidal synthesis to form either cubic, octahedral, rhombic dodecahedral, truncated cubic, or fluffy sphere structures. These Cu-oxide nanocrystals were characterised using scanning electron microscopy, X-ray photoelectron spectroscopy, and UV-vis. The SEM images show that the Cu2O nanocrystals are relatively uniform and all the crystals have a particle mean diameter below 1000 nm. The smallest particle mean diameter is 411 nm for the rhombic dodecahedral crystals, while the octahedral crystal displays the largest particle mean diameter of 864 nm. The XPS results indicate that the copper is primarily CuI in Cu2O, but some as CuII are also present. The apparent optical band gap energies could be determined from the optical properties of the five Cu-oxide nanocrystals, using the classical Tauc equation. The apparent optical band gap energies ranged between 2.04 and 2.14 eV. The Ullmann C-O coupling reaction was used to investigate the catalytic performance of the Cu-oxide nanocrystals. The fluffy sphere gave the highest % conversion, while the rhombic dodecahedral showed the lowest conversion.
Highlights
Aryl ethers are an important structural component since it is present in many pharmaceutical, polymers, dyes, pesticides, and fertilisers [1]
Palladium is one of the possible metals used as a catalyst, but more commonly inexpensive copper(I) catalysts are used in the Ullmann coupling reaction
The hybrid morphological features of these Cu-oxide nanocrystals could be determined from the scanning electron microscopy (SEM) images
Summary
Aryl ethers are an important structural component since it is present in many pharmaceutical, polymers, dyes, pesticides, and fertilisers [1] These aryl ethers can be prepared by catalytic arylation of phenols with aryl halides. With the development of many new catalysts involving nanomaterials, the Ullmann coupling reactions have proven to be successful with supported and unsupported copper(I) nanoparticles [3,4,5,6,7]. Cu2O/graphene has been used to catalyse the Ullmann C-O crosscoupling of aryl halides and phenols under mild conditions [9] Another stable Cu-containing catalyst successfully used for a variety of different crosscoupling reactions with broad functional group compatibility is chitosan@Cu2O [10], as well as CuCu2O/C and CuO-Cu2O/C [11], prepared from the carbonisation of Cu-BTC-MOF under an N2 atmosphere. There have been some interesting reports on the environmentally friendly preparation of Cu-oxide nanoparticles for catalytic purposes, using Euphorbia maculata [12], Convolvulus persicus L. [13], and Gum Arabic [14]
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