Construction of Hierarchical Conductive Metal-Organic Frameworks via Template-Directed Synthesis Strategy for Ultratrace H2S Sensing.

Two-dimensional conductive metal-organic frameworks (2D c-MOFs) hold great promise for chemiresistive gas sensing due to their intrinsic porosity and charge transport properties. Nevertheless, to fully utilize the aforementioned features of 2D c-MOFs, it remains crucial yet highly challenging to achieve controllable synthesis of hierarchically nanostructured 2D c-MOFs with high crystallinity and tailored morphologies. Herein, we describe a template-directed synthesis strategy for constructing hierarchical c-MOF architectures that simultaneously enhance mass transfer and electrical conduction. ZIF-67 was selected as the precursor template because of its well-defined morphology and accessible Co2+ coordination sites that facilitate ligand-exchange-driven framework conversion. Under solvothermal conditions, insulating ZIF-67 is transformed into conductive Co-HHTP by introducing the conjugated ligand 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP), during which the template framework undergoes a dissolution-recrystallization process while partially inheriting the spatial architecture of the parent template. Using ZIF-67 nanoparticles (NP) as the template, this method successfully yielded hollow-structured Co-HHTP nanoparticles (NPs), whereas the ZIF-67 nanoflakes (NS) were transformed into Co-HHTP nanosheets (NSs) assembled from nanoparticles. The resulting Co-HHTP NPs exhibit not only enhanced electrical conductivity but also a significantly higher specific surface area (230.6 m2·g-1) compared to the directly synthesized Co-HHTP (173.3 m2·g-1), highlighting the advantage of its hollow architecture in gas adsorption and mass transfer. The conversion mechanism involves a continuous dissolution-recrystallization process, HHTP first coordinates on the ZIF-67 NP surfaces, and then the reaction moves inward to form a hollow structure. In terms of sensing performance, the Co-HHTP NP-coated sensors demonstrate highly sensitive and selective detection toward H2S at room temperature with a detection limit of 44 ppb for Co-HHTP NPs and 34 ppb for Co-HHTP NSs, outperforming most state-of-the-art H2S sensors. This work provides valuable insights into the preparation of hierarchical c-conductive MOFs with high conductivity and tunable morphology, underscoring their potential for applications in industrial safety monitoring and environmental pollution control.