Transferable Two-Dimensional Hydrophobic Metal-Organic Framework Encapsulation of MoS₂-Based Humidity-Resistant NO₂...

Humidity deteriorates the performance and detection accuracy of gas sensors, especially for two-dimensional (2D) materials with large specific surface areas. Here, we proposed a hydrophobic encapsulation strategy for molybdenum disulfide (MoS₂) using a porous metal-organic framework (MOF), poly[Fe(benzimidazole)₂], denoted as Fe_n(bim)_2n, to effectively suppress the adsorption of H₂O molecules. By ammonia-assisted chemical vapor deposition, large Fe_n(bim)_2n flakes with lateral dimensions up to 72 × 72 μm were synthesized on mica. Owing to the hydrophilic nature of mica, the Fe_n(bim)_2n flakes could be easily peeled off from mica using polydimethylsiloxane (PDMS) soaked in water and subsequently transferred onto MoS₂ without contamination, forming a transferable hydrophobic encapsulation layer. The Fe_n(bim)_2n/MoS₂ heterojunction exhibited highly humidity-resistant NO₂ sensing performance with only a 4.28% relative response variation across 40-70% relative humidity (RH) at room temperature. Compared to bare MoS₂, the response of Fe_n(bim)_2n/MoS₂ to 500 ppb NO₂ increased from 0.53 to 2.03 at 70% RH, with a low practical limit of detection (LOD) of 20 ppb. This improvement not only arose from the hydrophobic Fe_n(bim)_2n layer that suppressed H₂O adsorption on the MoS₂ but also benefited from the charge transfer in Fe_n(bim)_2n/MoS₂, demonstrating the effectiveness of this encapsulation strategy in mitigating humidity-induced sensing performance fluctuation.