Pt decorated CoFe₂O₄/Co₃O₄ nanosheets derived from 2D Fe–Co MOF for enhanced HCHO detection

Highly sensitive and selective detection of volatile organic compounds (VOCs) is highly important, and designing a suitable microstructure and constructing heterostructures are two main effective strategies for gas-sensing materials to achieve this goal. In this study, Pt nanoparticle-decorated CoFe₂O₄/Co₃O₄ nanosheets were prepared via a solution method for highly accurate detection of formaldehyde (HCHO), where the CoFe₂O₄/Co₃O₄ nanosheets were derived from a two-dimensional Fe‒Co metal-organic framework (MOF). The response (R_g/R_a, where R_g represents the electrical resistance of the gas sensor when exposed to a specific target gas under defined conditions; R_a denotes the baseline resistance of the gas sensor in clean air) of the ternary Pt₂/CoFe₂O₄/Co₃O₄ composite to 100 ppm HCHO at 280 °C can be calculated as 95.5, and it still exhibits a very high response to low concentrations of HCHO (1.26 to 50 ppb HCHO gas) and an ultralow limit of detection (LOD) of 6 ppb. The ternary composite also presented excellent reproducibility, selectivity, and long-term stability. The first-principles calculations demonstrated that the Pt/CoFe₂O₄/Co₃O₄ model presented the most stable structure and the strongest adsorption capacity for HCHO. The high sensitivity of Pt/CoFe₂O₄/Co₃O₄ to HCHO can be attributed mainly to the formation of multiple heterojunctions and the catalytic effect of the Pt nanoparticles. This work describes the facile preparation of MOF-derived multi-heterojunction materials and highlights the superior gas-sensing performance to that of VOCs.