Functions of 1-Dodecanethiol in the Synthesis and Post-Treatment of Copper Sulfide Nanoparticles Relevant to Their Photocatalytic Applications

Copper-deficient, nonstoichiometric copper sulfide (Cu2–xS, x > 0) nanoparticles (NPs) have been explored as an important hole-based plasmonic material because of their size, morphology, carrier density, and crystal-phase-dependent localized surface plasmon resonance (LSPR) properties. In synthesis of Cu2–xS NPs, alkyl thiols containing sulfur element such as 1-dodecanethiol, C12H25SH (1-DDT), are well-utilized sulfur sources. In addition to the sulfur element in 1-DDT molecules, soft base S2–, linear hydrocarbon chain CH3(CH2)11–, and the proton in the −SH group may provide unique functions in the synthesis and post-treatment of Cu2–xS NPs. Here, we systematically demonstrate the ability of 1-DDT molecules to act as sulfur source and capping ligand for low-chalcocite Cu2S nanodisks (NDs), and size controller for covellite CuS NDs in the process of synthesis. These CuS NDs can be applied as electron donor and hole acceptor to improve the efficiency of photocatalytic reactions. Furthermore, in the post-treatment process, 1-DDT molecules initiated face-to-face self-assembly of roxbyite Cu7S4 NDs under mild sonication. These assembled one-dimensional structures may provide a simple mode for investigations on exciton–exciton, plasmon–plasmon, and exciton–plasmon interactions between adjacent Cu2–xS NDs. Without sonication, 1-DDT molecules reduced the Cu7S4 NDs (filling of copper vacancies), and the reduced NDs hold potential applications of photocatalytic organic synthesis.