A comparison of temperature dependent photoluminescence and photo-catalytic properties of different MoS2 nanostructures

Abstract

Here, a comparison of optical absorption, photoluminescence (PL) emission and catalytic properties of hydrothermally synthesized MoS2 nanoplatelets (MNPs), a few-layer MoS2 nanosheets (MNSs), and MoS2 nanorods (MNRs) have been done, which is rarely available in the literature. The formation of MNSs has been confirmed by transmission electron microscopy, field emission scanning electron microscopy, and Raman spectra analyses. In UV–Vis absorption and PL emission spectra of colloidal aqueous dispersions of the samples, ‘A’ and ‘B’ excitonic peaks having energy separation of ∼219 meV are clearly observed. The ‘D’ excitonic band-gap at 0 K of MNSs has been calculated to be 3.21 eV from the temperature-dependent PL emission studies. A thermodynamic approach has been employed to understand the adsorption of methylene blue (MB) dye onto MNPs, MNRs, and MNSs at various temperatures and it is revealed that the adsorption process is spontaneous, endothermic, and physisorption in nature. The equilibrium adsorption capacities of the samples are found out to be 7.75, 7.67, and 10.17 mg/g, respectively of MNPs, MNRs, and MNSs at room temperature. It is found that MNSs, having large specific surface area and a large number of active sites, exhibit a relatively higher photo-catalytic activity than those of MNPs and MNRs. In case of MNSs, the obtained value of hydrogen evolution reaction (HER) onset overpotential of −49 mV (vs. reversible hydrogen electrode) which is much smaller than those of MNPs and MNRs. The relatively lower Tafel slope of 38 mV/dec of MNSs suggests that these can act as the best electrocatalyst amongst MNSs, MNPs, and MNRs. Thus, it has been revealed that a few layered 2D MoS2 nanosheets are the best candidate for degradation of hazardous organic dye and HER activity in compared to MoS2 nanoplatelets and nanorods.