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A series of ordered mesoporous chromium oxides (CrO) were synthesized by first replicating bicontinuous cubic Ia3d mesoporous silica (KIT-6), then a controlled mesostructural transformation from Ia3d to I432 symmetry during the replication from KIT-6 to CrO 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 CrO replicas. The gas-sensing behavior of the CrO replicas toward formaldehyde (HCHO) was systematically investigated. Ordered mesoporous CrO with both large accessible pores (12 nm) and an ultrathin framework (5 nm) exhibits the best sensing performance, with a response (R/R = 119) toward 9 ppm of HCHO 4.4 times higher than that (R/R = 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, HS, and moisture. The significantly enhanced sensing performance of ordered large-pore mesoporous CrO with ultrathin framework suggests its great potential for the selective detection of HCHO.

Developing a membrane material with both high CO2 permeability and high CO2/N2 selectivity is always desired for CO2 capture, while improving the sustainability of the membrane preparation process is of equal importance. In the current work, a nanocellulose crystal (CNC) was blended with hydrophilic Pebax 1657 for CO2 separation application. The CO2/N2 separation performance of Pebax 1657/CNC hybrid membranes with up to 40 wt % CNC was evaluated by mixed-gas permeation tests under both dry and humid conditions. The humid test condition simultaneously increases CO2 permeability and CO2/N2 selectivity of all CNC/Pebax hybrid membranes compared to those under dry conditions. Introduction of only 5 wt % CNC into Pebax 1657 realizes 42 and 18% increments in CO2 permeability (305.7 Barrer) and CO2/N2 selectivity (41.6), respectively. However, further increasing the CNC loading increases the tortuosity of the membrane and results in the self-assembly of CNC in the Pebax matrix, which is observed by SEM, thus leading to both reduced gas permeability and CO2/N2 selectivity. The CO2/N2 separation results of 5 wt % CNC/Pebax locate close to Upper Bound 2008, showing its potential as a CO2/N2 separation membrane material.

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