Optical properties of the nanocomposite of molybdenum disulphide monolayers/cellulose nanofibrils

Abstract

Studies on nanocomposites of cellulose nanofibrils (CNFs) and transition-metal dichalchogenides (TMD) monolayers are still rare in the literature. Among the TMDs, the molybdenum disulphide (MoS2) monolayers have been employed in a great variety of applications, such as sensors, photovoltaic devices, and transistors. The synthesis of the MoS2/CNF nanocomposite was performed through a liquid exfoliation process and the optical and morphological properties of MoS2/CNF films were characterized by confocal microscopy and UV–Vis absorption and the nanocomposite morphology was characterized by atomic force microscopy (AFM) and by field emission scanning electron microscopy (FESEM) techniques. UV–Vis measurements showed that the CNF addition caused a narrowing in the MoS2 flakes absorption band at 1.89 eV and 2.0 eV energy values, similar to those present in a MoS2 monolayer. Morphological analyses of the MoS2/CNF composite by FESEM indicate that the CNF addition reduces the MoS2 flakes anisotropy and corroborates the absorption narrowing bands. Stationary Photoluminescence (PL) and Second Harmonic Generation (SHG) were carried out by Confocal Microscopy indicating the presence of few layers composing the MoS2 flakes. The PL and SHG arise due to the liquid exfoliation process, which produces heterogenic flakes with randomic numbers of MoS2 layers. Results showed that the addition of up to 10% w/w of CNFs gives rise to a high fluorescence gain. However, the amount of SH regions increases as a function of the addition of CNFs above 10% w/w.