Exploring the effect of hydrothermal precursor pH on the photosensitivity of 1T/2H–MoS2 nanosheets

Abstract

In this investigation, MoS2 nanosheets were synthesized via the hydrothermal method. The effects of precursor pH on the properties of as-synthesized MoS2 nanostructures have been investigated. Different techniques were employed to determine the structural, optical, and morphological characteristics of the synthesized nanopowders. X-ray diffraction (XRD) pattern analysis confirmed the formation of a polycrystalline hexagonal MoS2 structure. Raman spectra revealed the coexistence of trigonal (1T) and hexagonal (2H) polytypes of MoS2. Images of scanning electron microscopy (SEM) revealed that the obtained flower-like MoS2 powders have composed of nanosheets, where the sheet's thickness varies from 7 to 25 nm, depending on the pH value of the hydrothermal precursor solution. Increasing the pH prevents the aggregation of active points and causes the formation of thinner nanosheets. Optical spectroscopy showed the absorption of the incident radiation in the visible region. The energy bandgap of samples was estimated to be in the range of 1.46–1.82 eV by increasing the precursor pH value from 5.5 to 9.5, respectively. The photosensitivity measurements verified that the as-grown MoS2 nanopowders respond rapidly toward the incident light with a wavelength of 450 nm and show good response stability. The sample prepared in the basic environment of precursor (pH value of 9.5) showed the most stable response transient with the photo-response value of 16.72%.