An all-inorganic three-dimensional polyoxoniobate framework with ppb-level chemiresistive sensing for ammonia

Fabrication of gas sensors with high sensibility appears particularly important due to the urgent demand for toxic gases monitoring in public safety and atmosphere detection, especially for the detection requirement of ultra-low concentration gases. Here, we present a rare three-dimensional (3D) all-inorganic polyoxoniobate (PONb) framework based on {Cu₄@Nb₂₉} secondary building units linked with both tetranuclear {Cu₄(OH)₅} clusters and mononuclear [Cu(H₂O)]²⁺ units. Remarkably, this 3D PONb framework exhibits an ultrasensitive response to NH₃ with a lowest limit of detection of 1.64 ppt up to now. Furthermore, the NH₃ induced single-crystal-to-single-crystal transformation as well as density functional theory analysis reveal that the strong coordination affinity of [Cu(H₂O)]²⁺ linker for NH₃, along with more injection of charge into the framework, results in a ultrasensitivity chemiresistive responses to NH₃, at atomic-level insight.