Controlled Growth of MoS₂ Flakes from in-Plane to Edge-Enriched 3D Network and Their Surface-Energy Studies

Controlled and tunable growth of chemically active edge sites over inert in-plane MoS2 flakes is the key requirement to realize their vast number of applications in catalytic activities. Thermodynamically, growth of inert in-plane MoS2 is preferred due to fewer active sites on its surface over the edge sites. Here, we demonstrate controlled and tunable growth from in-plane MoS2 flakes to dense and electrically connected edge-enriched three-dimensional (3D) network of MoS2 flakes by varying the gas flow rate using tube-in-tube chemical vapor deposition technique. Field emission scanning electron microscope results demonstrated that the density of edge-enriched MoS2 flakes increase with increase in the gas flow rate. Raman and transmission electron microscopy analyses clearly revealed that the as-synthesized in-plane and edge-enriched MoS2 flakes are few layers in nature. Atomic force microscopy measurement revealed that the growth of the edge-enriched MoS2 takes place from the in-plane MoS2 flakes. On the basis of the structural, morphological, and spectroscopic analysis, a detailed growth mechanism is proposed, where in-plane MoS2 was found to work as a seed layer for the initial growth of edge-enriched vertically aligned MoS2 flakes that finally leads to the growth of interconnected 3D network of edge-enriched MoS2 flakes. The surface energy of MoS2 flakes with different densities was evaluated by sessile contact angle measurement with deionized water (polar liquid) and diiodomethane (dispersive liquid). Both liquids show different nature with the increment in the density of the edge-enriched MoS2 flakes. The total surface free energy was observed to increase with increase in the density of edge-enriched MoS2 flakes. This work demonstrates the controlled growth of edge-enriched vertically aligned MoS2 flakes and their surface-energy studies, which may be used to enhance their catalytic activities for next-generation green fuel production.