Ultrasensitive Formaldehyde Sensor Based on SnO₂ with Rich Adsorbed Oxygen Derived from a Metal Organic Framework

SnO₂ has been a commonly researched gas-sensing material due to its low cost, good performance, and good stability. However, gas sensors based on pure SnO₂ usually show a low response or high working temperature. In this work, laminar SnO₂ was obtained by using a Sn-based metal organic framework(Sn-MOF)@SnO₂ as a precursor. Sn-MOF@SnO₂ is prepared at low temperatures using water and dimethylformamide as a solvent, which is simple, low cost, and easily reproducible. After sintering, Sn-MOF@SnO₂ is derived to SnO₂ with rich adsorbed oxygen, large specific surface area, and unique nanoparticle piled pores, thus showing excellent gas-sensing properties. The prepared SnO₂ has an ultrahigh response value of 10,000 to 10 ppm formaldehyde at an optimal working temperature of 120 °C, a fast response/recovery time of 33 s/142 s, and an actual detection limit of lower than 10 ppb as well as high selectivity and high stability. Density functional theory calculations show that the exposed (110) plane of oxygen-rich vacancies in laminar SnO₂ can effectively increase the coadsorption capacity of O₂ and formaldehyde molecules, thereby improving the formaldehyde gas-sensing performance of the material. The present original approach paves the way to design advanced materials with excellent gas-sensing properties as well as broad application prospects in formaldehyde monitoring.