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.