ZnO Nanorods Grown on WS₂Nanosheets for Chemiresistive H₂S Sensing

A scalable and CMOS-compatible fabrication of a transition-metal dichalcogenide-oxide heterostructure based chemiresistive sensor for the selective detection of hydrogen sulfide (H₂S) gas is detailed here. WS₂nanosheets, obtained by a liquid exfoliation technique, were used as the seed 2D material for fabricating the nano heterostructures. Using a microwave-irradiation-assisted solvothermal (MAS) process, ZnO nanorods (1D) were grown in situ on these 2D nanosheets, resulting in a 2D/1D heterostructure. The processing in an alcohol-rich solution medium also enabled the formation of a thin 2D-like layer of metal sulfate and/or metal oxide on the surface of these 2D nanosheets, thus forming the 2D/2D heterojunction. In presence of both 2D/1D and 2D/2D heterostructures, termed together as co-HS, the active sites are augmented for H₂S sensing. Furthermore, the formation of neat 1D/2D interfaces provides additional electron conduction paths while creating active sites at the basal plane of WS₂, which is otherwise inert. Therefore, this unique structure aided in achieving a 5-fold selectivity (5:1) to H₂S among other interfering gases such as NH₃, SO₂, NO₂, etc. with a reasonably good response magnitude (140% to 5 ppm) in the range of 100 ppb to 5 ppm. Notably, the sensor showed a speedy response of less than 1 min and a recovery of less than 50 s at concentrations of 1 ppm and lower, with a remarkable achievement of 14 s recovery at 500 ppb. The long-term stability of the sensor for at least 6 months is also demonstrated to be promising. The sub-ppm detection enables the sensor to be employed in breath-based diagnostics.