A Study of the Catalysis of MoS2 using Optical Photoluminescence
Monolayer molybdenum disulfide (MoS2) has many unique characteristics, one of which is a strong photoluminescence (PL) excitation due to its direct band gap property. Because of this characteristic, the surface morphologies can be inferred by studying the photoluminescence peak frequency and intensity. Regions where the surface is disrupted by changes in structural phase and defect density will be indicated by the PL fluctuations. We have investigated the hydro-desulfurization (HDS) catalysis using this MoS2 response by widefield PL imaging. This wide field PL imaging technique has the advantage of shorting each acquisition time of a large sample area to 1-2 minutes instead of hours required for mapping scans. Within this time frame, surface morphology changes from temperature under a hydrogen environment and dosing a sulfur containing organic compound, benzenethiol, studied in real time. We have also studied the reaction efficiency using gas chromatography (GC) with a mass spectrometer for the same condition as in the PL widefield imaging experiments. We have found PL image activities in pre-HDS temperatures around 200°C to 300°C. Although PL intensity gets small, there are some PL activities in HDS temperatures between 300°C to 400°C and little over this temperature. We have observed HDS conversion in this temperature regime as well as hydrogen sulfide (H2S) on our GC system. It was not only edges but also the basal region which had PL intensity fluctuation. This activity may imply the HDS in both the edges and the basal plane, unlike previous belief that edges are the sole active catalytic sites.