From ultrafine thiolate-capped copper nanoclusters toward copper sulfide nanodiscs: A thermally activated evolution route

This report shows that the size, shape, and composition of presynthesized copper nanoparticles can be nanoengineered through exploiting concurrent interparticle aggregative growth and interfacial carbon-sulfur cleavage in a thermally activated evolution route. This is demonstrated by thermally activated processing of ultrafine copper nanoclusters encapsulated with thiolate monolayer (Cu_n,(SR)_m) toward semiconducting copper sulfide (Cu²S) nanodiscs with controllable sizes and shapes. Under controlled temperatures (120-150 °C), the ultrafine Cu_n(SR) _m nanoclusters, with a size of ∼0.5 nm evidenced by TEM, SAXS-WAXS, DCP-AES, and MALDI-TOF measurements, were shown to evolve into thiolate-capped Cu₂S nanodiscs via thermally activated coalescence and copper-catalyzed interfacial C-S cleavage reactivities. The Cu₂S nanodiscs, as confirmed by XPS and HRTEM analyses, exhibited controllable and monodispersed sizes depending on the thermal processing parameters, ranging from 5 to 35 nm in the disk dimension and 3-6 nm in the thickness dimension. These nanodiscs are stable and display remarkable 1D/2D ordering upon self-assembly. This process is not a simple digestive ripening of smaller particles because it involves an aggregative nucleation and growth process distinctively different from traditional ripening and a reactive carbon-sulfur bond cleavage controlled by the catalytic effect of copper under the specified temperatures. The coupling of the thermally activated coalescence and C-S bond cleavage to convert the ultrafine Cu nanoclusters toward the formation of Cu₂S nanodiscs is highly effective for tuning nanoscale size, shape, and composition, and could find applications in nanoengineering a variety of semiconducting nanocrystals for applications in nanostructured electronic, sensing, and photochemical devices.