One-step polyol growth of crystalline MoS₂ quantum dots directly on carbon cloth in 30 minutes at 210 °C
Author: Kamran Akbar (Ph.D)
Published: 2026-07-25
Outcome: positive
Abstract
A single-step polyol route grows crystalline MoS₂ quantum dots (1–10 nm) directly onto carbon cloth in 30 minutes at 210 °C, with no autoclave, no exfoliation, and no binder. Ammonium tetrathiomolybdate serves as a single-source precursor in diethylene glycol, which acts as both solvent and growth medium. HRTEM, SAED, EDS and XPS confirm crystalline 2H-MoS₂ bonded to the substrate. Under identical conditions the same reaction yields only amorphous MoS₂ nanosheets in solution, indicating the carbon cloth surface — not the bulk solution — provides the nucleation sites.
Methodology
Substrate preparation. Plain carbon cloth (1071 HCB) was treated with piranha solution overnight to remove organics, then immersed in concentrated HNO₃ to strip deposited metals. After repeated washing with distilled water and ethanol it was dried at 45 °C overnight and cut into 4 cm² pieces. Growth. (NH₄)₂MoS₄ was dissolved in diethylene glycol (DEG, b.p. 245 °C) under continuous stirring to give a 2 mM solution. 100 mL was transferred to a two-neck round bottom flask with the cleaned carbon cloth immersed. The stirred solution was heated at 180 °C or 210 °C for 0.5, 1 or 2 h at ambient pressure. Workup. The cloth was washed with ethanol and distilled water to remove DEG and unreacted precursor, then dried at 45 °C overnight, giving a standalone binder-free material. Characterization. FESEM (JEOL JSM7500F); HRTEM + SAED + EDS (JEOL JEM 2100F with Oxford AZtec EDX); XPS (Thermo VG Scientific ESCA Sigma Probe).
Key findings
Crystalline QDs form in 30 min at 210 °C. HRTEM shows MoS₂ quantum dots of 1–10 nm distributed through the carbon matrix. Lattice fringes give a d-spacing of 0.25 nm, matching the (102) plane of MoS₂. The SAED inset shows an inner ring from carbon (006) with outer rings indexed to MoS₂ ((104), (205)). Composition is uniform. EDS mapping over the boxed HRTEM region shows Mo and S distributed uniformly across the carbon matrix. Phase is 2H, and it is chemically bonded to the substrate. Mo 3d peaks at 229.0 and 232.3 eV place Mo in the 4+ state; S 2p peaks at 161.7 and 162.8 eV (2p₃/₂, 2p₁/₂) correspond to S²⁻. Peak positions indicate the 2H phase rather than 1T. An additional peak at 236 eV indicates Mo–O–C bonding between the QDs and the carbon substrate. Growth is heterogeneous, driven by the substrate. Under the same conditions, only amorphous MoS₂ nanosheets of 30–60 nm precipitate in the DEG solution itself. Crystalline QDs appear only on the cloth, implicating surface C–O species (C 1s, 286.2 eV) as nucleation sites. Practical growth window (from FESEM across the condition matrix): Condition Result 0.5 h @ 180 °C Surface still smooth — nucleation only just beginning 1 h @ 180 °C Small, uniformly distributed dots 0.5 h @ 210 °C Small, uniformly distributed dots (used for Fig. 2) 1 h @ 210 °C Small, uniformly distributed dots 2 h @ 180 °C Agglomeration 2 h @ 210 °C Agglomeration, increased QD size At 210 °C the usable window is 0.5–1 h; at 180 °C at least 1 h is needed to reach sufficient QD density. Beyond 1 h the dots agglomerate at either temperature.
Full text
A single-step polyol route grows crystalline MoS₂ quantum dots (1–10 nm) directly onto carbon cloth in 30 minutes at 210 °C, with no autoclave, no exfoliation, and no binder. Ammonium tetrathiomolybdate serves as a single-source precursor in diethylene glycol, which acts as both solvent and growth medium. HRTEM, SAED, EDS and XPS confirm crystalline 2H-MoS₂ bonded to the substrate. Under identical conditions the same reaction yields only amorphous MoS₂ nanosheets in solution, indicating the carbon cloth surface — not the bulk solution — provides the nucleation sites.