Breathable MOFs Layer on Atomically Grown 2D SnS₂ for Stable and Selective Surface Activation

Two-dimensional (2D) materials (MoS2, SnS2, MXene, black phosphorus (BP), and graphene oxide) with intriguing physicochemical properties such as abundant reactive edge-sites, tunable electrical properties, and mechanical flexibility, have been developed for broad applications in chemical sensing, electrocatalysis, filtration membrane, and energy storage system.[1] Among various 2D materials, SnS2 (IV-VI A group), which is a semiconducting layered structure with a large bandgap of ~2.2 eV and has many advantages (low-cost, nontoxic, and environmental friendly properties), can be catered well into the broad applications.[2] Based on these interesting material properties of SnS2, 2D SnS2 is widely used as active surface reactor with rapid, sensitive, and selective surface reactivity to various molecules including ions, gases, and biomolecules. Even though the outstanding and exceptional characteristics of SnS2 has been proved in many previous studies, its poor stability due to oxidation and degradation issues under the ambient operation conditions limits the practical usage of SnS2.<br/><br/>In this work, we newly developed ‘Sandwich’ like hybrid materials platform, 2D SnS2 layer covered by uniformly porous ZIF-8, employing in-situ growing methods. First of all, the 2D SnS2 layer (1st layer) was directly grown on the Si based sensor substrate through ALD method, and as such, strong bonds between active material (SnS2 in this case) and the sensor substrate are able to be formed. Then, the in-situ growing of ZIF-8 was followed on the heterogeneous SnS2 layers, so the defect free ZIF-8 covered the whole SnS2 layers. The top-side of ZIF-8 membrane and bottom-side SnS2 play critical role for molecular sieving and chemical detection, respectively. Due to the uniform pore distribution of ZIF-8 layer on the SnS2 sensing layer, H2O molecules can be reliably blocked by ZIF-8 breathable layer, while target NO2 molecules can selectively penetrate through the ZIF-8 layer. Therefore, our hybrid materials exceptionally showed high stability and selective surface activity from the chemical sensing case study and the underlying mechanisms were further investigated in the atomistic level using theoretical calculations.