Dual regulation of hierarchical porosity and heterogeneous interfaces in Cu-BTC/Bi2MoO6 for thermally-driven and UV-light-activated selective acetone sensing

Abstract

Hazards caused by noxious gases have urged the probing of applicable gas sensors for air quality monitoring. Functionalized porous material platforms with high permeability have attracted broad interest in fabricating efficient gas sensors. Metal–organic frameworks (MOFs) with structure diversity, high porosity, and adjustable functionality have been considered outstanding candidates for hazardous gas detection. However, most MOF sensors suffer from inherent defects of low conductivity and insufficient utilization efficiency of their micropores. Herein, a mesoporous Cu-BTC (BTC = tricarboxylic acid) MOF was successfully prepared through a top-down etching method using small inorganic oxoanions of MoO₄²⁻; then a hierarchical porous defective-Cu-BTC@Bi₂MoO₆ (d-CuM@BMO) heterostructure was fabricated by the in situ growth of Bi₂MoO₆ nanocrystallites over Cu-BTC. Structural characterization revealed that such an etching-and-growth strategy can significantly improve the conductivity of MOF while retaining its skeleton structure. Benefiting from the hierarchical porosity, efficient charge transfer, and photosensitivity, the d-CuM@BMO heterostructure showed selective and sensitive photoactivated acetone sensing properties with a response value of 14.8 towards 30 ppm acetone, which was 9 times higher than that of pristine Cu-BTC under UV irradiation. It also exhibited a rapid response/recovery time (8.9 s/11.7 s) and high stability, even over 70 days, at an operating temperature of 270 °C. The UV-light-activated acetone sensing mechanism was deduced in detail. This work provides a feasible etching-and-growth strategy towards the assembly of MOF-based heterostructures for high-performance gas sensing applications.