Ultrathin ZIF-8 film containing polyoxometalate as an enhancer for selective formaldehyde sensing

Gas sensing performances in ZnO sensors are critically limited by their fast electron–hole recombination, low gas selectivity and elevated operation temperature. To alleviate these problems, new and high-performance sensor materials are desirable. Herein, we fabricate a core–shell composite material of POM@ZIF-8@ZnO with an ultrathin ZIF-8 film containing H5PMo10V2O40 polyoxometalate on the ZnO substrate surface. The device based on this composite exhibits an improved gas sensing ability toward formaldehyde (HCHO) at room temperature (25 °C) with a sensitivity of ∼0.4 ppm. Additionally, the POM@ZIF-8@ZnO material exhibits selective gas responses for reducible gases with small molecular sizes, in particular for a selectivity value of 15.0 for formaldehyde over ethanol. The specific roles of the ZIF-8 shell and POM are discussed in detail: ZIF-8 is responsible for concentrating and recognizing analyte molecules on the ZnO surface, and POM accounts for enhancing the sensing ability. The new material of POM@ZIF-8@ZnO with high performance holds great promise in sensor materials for selective formaldehyde sensing.