Ordered Large-Pore Mesoporous Cr 2 O 3 with Ultrathin Framework for Formaldehyde Sensing.

A series of ordered mesoporous chromium oxides (Cr ₂ O ₃ ) were synthesized by first replicating bicontinuous cubic Ia3d mesoporous silica (KIT-6), then a controlled mesostructural transformation from Ia3d to I4 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.