Synthesis of phase-pure monolayer 1T-MoS₂ and 2H-MoS₂ colloidal nanomaterials with negative photoconductivity

MoS₂ is an important two-dimensional transition metal dichalcogenide (TMD), whose physical and chemical properties are closely related to its layer number, size, defects, and crystal structure. Therefore, the controllable synthesis of phase-pure monolayer MoS₂ represents a key challenge. Herein, we report a simple and efficient wet-chemical synthesis strategy for 1T-MoS₂ and 2H-MoS₂, with the crystal phase controlled by the reaction temperature. At 220 °C, ultra-small (1–2 nm) monolayer 1T-MoS₂ colloids are obtained; at 250 °C, monolayer 2H-MoS₂ nanosheets are produced. Both materials exhibit good dispersibility in nonpolar solvents and can be readily spin-coated into thin films. Interestingly, the 1T-MoS₂ and 2H-MoS₂ exhibit different exciton dynamics in transient absorption (TA) spectra, but similar trap state-induced negative photoconductivity (NPC) under near-infrared (825 nm) illumination. These findings provide new perspectives for the design of MoS₂-based optoelectronic devices.