Rationally Designed Polypyrrole-Encapsulated MoO₃ Hollow Nanostructures for Enhanced Formaldehyde Detection at Room Temperature

Formaldehyde, a volatile organic compound (VOC) and ubiquitous indoor pollutant, is a known probable carcinogen that poses significant health risks even at low concentrations. Consequently, the development of selective detection methods for formaldehyde is imperative. This study focuses on a surface diffusion strategy to develop hollow nanostructured molybdenum trioxide (MoO3 HNs) encapsulated with polypyrrole (PPy) shell which can selectively detect sub-ppm formaldehyde at room temperature (25 °C) under elevated humidity conditions (65% RH). A self-template strategy was utilized, wherein Fe3+ cations played a dual role as oxidizing agents to initiate pyrrole polymerization and as catalysts to facilitate the formation of hollow nanostructures through the nanoscale Kirkendall effect. MoP75 sensor has exhibited stable response-recovery up to 85% relative humidity (RH), with a significant sensitivity 6.5-fold (Ra/Rg) to 100 ppm of HCHO, along with rapid response (Γres = 13.34 s) and recovery (Γrec = 46.37 s). The enhanced sensing performance of MoP75 can be attributed to its high surface area (71.433 m2/g) and efficient charge transfer at the heterojunction interface. These results highlight the promising potential of MoP75 as a highly efficient material for selective formaldehyde detection at room temperature, rendering it suitable for practical applications.