Volatile Organic Compound Gas-Sensing Properties of Bimodal Porous α-Fe2O3 with Ultrahigh Sensitivity and Fast Response.

Porous solid with multimodal pore size distribution provides plenty of advantages including large specific surface area and superior mass transportation to achieve high gas-sensing performances. In this study, α-Fe2O3 nanoparticles with bimodal porous structures were prepared successfully through a nanocasting pathway, adopting the bicontinuous 3D cubic symmetry mesoporous silica KIT-6 as the hard template. Its structure and morphology were characterized by X-ray diffraction, nitrogen adsorption-desorption, transmission electron microscopy, and so on. Furthermore, the gas sensor fabricated from this material exhibited excellent gas-sensing performance to several volatile organic compounds (acetone, ethyl acetate, isopropyl alcohol, n-butanol, ethanol, and methanol), such as ultrahigh sensitivity, rapid response speed (less than 10 s) and recovery time, good reproducibility, as well as stability. These would be associated with the desirable pore structure of the material, facilitating the molecules diffusion toward the entire sensing surface, and providing more active sensing sites for analytical gas.

Ordered Large-Pore Mesoporous Cr2O3 with Ultrathin Framework for Formaldehyde Sensing.

A series of ordered mesoporous chromium oxides (Cr2O3) were synthesized by first replicating bicontinuous cubic Ia3d mesoporous silica (KIT-6), then a controlled mesostructural transformation from Ia3d to I4132 symmetry during the replication from KIT-6 to Cr2O3 was achieved by reducing the pore size and interconnectivities of KIT-6, accompanied with an increase in pore size from 3 to 12 nm and a decrease in framework thickness from 8.6 to 5 nm of the resultant Cr2O3 replicas. The gas-sensing behavior of the Cr2O3 replicas toward formaldehyde (HCHO) was systematically investigated. Ordered mesoporous Cr2O3 with both large accessible pores (12 nm) and an ultrathin framework (5 nm) exhibits the best sensing performance, with a response (Rgas/Rair = 119) toward 9 ppm of HCHO 4.4 times higher than that (Rgas/Rair = 27) of its counterpart with small pores and a thick framework. Moreover, it possesses excellent selectivity for detecting HCHO over other interference gases such as CO, benzene, toluene, p-xylene, NH3, H2S, and moisture. The significantly enhanced sensing performance of ordered large-pore mesoporous Cr2O3 with ultrathin framework suggests its great potential for the selective detection of HCHO.