Few-Layered WS2 Nanoplates Confined in Co, N-Doped Hollow Carbon Nanocages: Abundant WS2 Edges for Highly Sensitive Gas Sensors

Edges of 2D transition metal dichalcogenides (TMDs) are well known as highly reactive sites, thus researchers have attempted to maximize the edge site density of 2D TMDs. In this work, metal-organic framework (MOF) templates are introduced to synthesize few-layered WS2 nanoplates (a lateral dimension of approximate to 10 nm) confined in Co, N-doped hollow carbon nanocages (WS2_Co-N-HCNCs), for highly sensitive NO2 gas sensors. WS2 precursors are assembled in the surface cavity of Co-based zeolite imidazole framework (ZIF-67) and subsequent pyrolysis produced WS2_Co-N-HCNCs. During the pyrolysis, the carbonized ZIF-67 are doped by Co and N elements, and the growth of WS2 is effectively suppressed, creating few-layered WS2 nanoplates functionalized Co-N-HCNCs. The WS2_Co-N-HCNCs exhibit outstanding NO2 sensing characteristics at room temperature, in terms of response (48.2% to 5 ppm), selectivity, response and recovery speed, and detection limit (100 ppb). These results are attributed to the enhanced adsorption and desorption kinetics of NO2 on abundant WS2 edges, confined in the gas permeable HCNCs. This work opens up an efficient way for the facile synthesis of edge abundant few-layered TMDs combined with porous carbon matrix via MOF templating route, for applications relying on highly active sites.