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

A series of ordered mesoporous chromium oxides (Cr 2 O 3 ) were synthesized by first replicating bicontinuous cubic Ia 3 d mesoporous silica (KIT-6), then a controlled mesostructural transformation from Ia 3 d to I 4 1 32 symmetry during the replication from KIT-6 to Cr 2 O 3 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 Cr 2 O 3 replicas. The gas-sensing behavior of the Cr 2 O 3 replicas toward formaldehyde (HCHO) was systematically investigated. Ordered mesoporous Cr 2 O 3 with both large accessible pores (12 nm) and an ultrathin framework (5 nm) exhibits the best sensing performance, with a response ( R gas / R air = 119) toward 9 ppm of HCHO 4.4 times higher than that ( R gas / R air = 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, NH 3, H 2 S, and moisture. The significantly enhanced sensing performance of ordered large-pore mesoporous Cr 2 O 3 with ultrathin framework suggests its great potential for the selective detection of HCHO.