Cost-effective liquid-phase exfoliation of molybdenum disulfide by prefreezing and thermal-shock

In this work, we present a facile method without hazardous material for improving the liquid-phase exfoliation of MoS₂ nanosheets by use of pre-freezing and thermal shock. The MoS₂ bulk is easily exfoliated and functionalized by prefreezing and thermal shock of MoS₂ powder in the ethanol solvent. Atomic force microscopy confirms that the approach can exfoliate MoS₂ powder to nanosheets. UV–visible spectroscopy of the prepared samples shows that fingerprint excitonic peaks appear in the spectrums and they become sharper by repeating the process. Optical band gap from Tauc plot of UV–visible spectrum shows an increase in the band gap of exfoliated MoS₂ up to 1.85 eV and the surface energy of the exfoliated MoS₂ is measured as 29.8 mJ/m². Annealing the prepared samples at temperatures up to 400 °C decreases the contact angle of water droplet from 130° down to 2°. X-ray diffraction patterns and Fourier transform infrared spectroscopy confirm that exfoliated MoS₂ is functionalized during the exfoliation process and molybdite is formed on the surface by crumpling and agglomerating nanosheets due to heating, which is mainly responsible for increasing the surface energy as well as superhydrophilicity of the samples at 400 °C.