Simultaneous capping and substitution of nitrogen ions of Cu3N nanocrystals with sulfur ions using DDT as a co-surfactant to form chalcocite and digenite nanocrystals

Autor: Makwena J. Moloto, Lerato F.E. Machogo, Tshwarela Kolokoto, Nosipho Moloto, Juanita L. van Wyk, Grace N. Ngubeni, Rudo K. Sithole
Rok vydání: 2020
Předmět:
Zdroj: Materials Chemistry and Physics. 251:123074
ISSN: 0254-0584
Popis: Uncapped nanocrystalline cuprous nitride (Cu3N) decomposes spontaneously to CuO at room temperature due to the presence of water and oxygen in the atmosphere. Long-chain capping molecules have been successfully used to cap and protect the core nanocrystals from complete oxidation. Moreover, the use of co-surfactants has been shown to alter the morphologies and properties of nanocrystals due to preferential binding. In an attempt to cap Cu3N nanocrystals and alter their morphology, hexadecylamine (HDA) and 1-dodecanethiol (DDT) were used as surfactant and co-surfactant respectively. Contrary to common belief, herein we show that DDT does not only act as a co-surfactant however it also results in the complete substitution of nitrogen ions in Cu3N with sulfur ions thereby resulting in the formation of a mixture of Cu3N and Cu2S after 2.5 min of DDT addition. Longer reaction times result in the formation of pure Cu2S (chalcocite) and ultimately Cu9S5 (digenite). The substitution is consistent with the HSAB theory. XRD, EDX, TEM, and XPS confirmed the transitioning of Cu3N nanocrystals to chalcocite and digenite nanocrystals. The resultant morphologies were spherical particles for Cu3N, hexagonal particles for Cu2S and small spherical particles for Cu9S5 nanocrystals. 1HNMR and FTIR spectroscopies elucidated the capping of the nanocrystals by HDA and DDT. The optical properties showed the transitioning of the band-gap. The photoluminescence spectra of both Cu2S and Cu9S5 showed blue-shifted emission energy from the band gap energy due to surface traps and defects.
Databáze: OpenAIRE
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