Green Colloidal Synthesis of MoS2 Nanoflakes

Currently, two approaches dominate the large-scale production of MoS2: liquid-phase exfoliation, referred to as top-down approach, and bottom-up colloidal synthesis from molecular precursors. Known colloidal synthesis approaches utilize toxic precursors. Here, an alternative, green route for bottom-up synthesis of MoS2 nanoflakes (NFs) is described. The NFs were synthesized by colloidal synthesis using [Mo(CH3COO)2]2 and a series of sulfur (S-) precursors including Thioacetamide (TAA), 3-Mercaptopropionic acid (3-MPA), L-cysteine (L-CYS), Mercaptosuccinic acid (MSA), 11-Mer-captoundecanoic acid (MUA), 1-Dodecanethiol (DDTH) and Di-tert-butyl disulfide (DTBD). While TAA, a S-precursor most commonly used for MoS2 NF preparation, is a known carcino-gen, the other investigated S-precursors have low or no known toxicity. High-resolution Transmission Electron Microscopy (HR-TEM), Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) confirmed that in all cases the syntheses yielded sin-gle layer MoS2 NFs with lateral sizes smaller than 15 nm and well-defined crystal structure. Electronic absorption and Ra-man spectra show the characteristic features associated with the MoS2 monolayers. The evolution of the absorption spectra of the growth solution during the syntheses reveals how the ki-netics of the NF formation is affected by the S-precursor as well as the nature of the coordinating ligands.