Metal–Organic Framework-Derived LaFeO₃@SnO₂/Ag p–n Heterojunction Nanostructures for Formaldehyde Detection

Using n-type and p-type semiconductor materials to construct p–n heterostructures has proven effective for improving gas-sensing properties. In this study, we synthesized the nanocomposites of SnO2 derived from a metal–organic framework (MOF) and LaFeO3 by loading atomic silver on its surface. The response value (Ra/Rg) of the nanocomposites to 10 ppm formaldehyde reached 498 at 140 °C, but they showed almost no response to 50 ppm interference volatile organic compounds (VOCs), and the response–recovery time was 105 and 27 s, respectively. The crystal structure, heterojunction structure, chemical elements, and sensitive mechanism were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), Brunauer–Emmett–Teller (BET) analysis, and energy-dispersive spectrometry (EDS) elemental mapping. The characterizations revealed that the improvement of gas sensitivity was mainly due to the MOF-driven strategy, p–n heterojunction, and electron sensitization effect of Ag. This work provides a method and idea for preparing composites and shows the potential application value of LaFeO3@SnO2/Ag nanomaterials in formaldehyde gas detection.