Hierarchical TiO2:Cu2O Nanostructures for Gas/Vapor Sensing and CO2 Sequestration

We investigate the effect of high-surface-area self-assembled TiO 2 :Cu 2 O nanostructures for CO 2 and relative humidity gravimetric detection using polyethylenimine (PEI), 1-ethyl-3-methylimidazolium (EMIM), and polyacrylamide (PAAm). Introduction of hierarchical TiO 2 :Cu 2 O nanostructures on the surface of quartz crystal microbalance sensors is found to significantly improve sensitivity to CO 2 and to H 2 O vapor. The response of EMIM to CO 2 increases fivefold for 100 nm-thick TiO 2 :Cu 2 O as compared to gold. At ambient CO 2 concentrations, the hierarchical assembly operates as a sensor with excellent reversibility, while at higher pressures, the CO 2 desorption rate decreases, suggesting possible application for CO 2 sequestration under these conditions. The gravimetric response of PEI to CO 2 increases by a factor of 3 upon introduction of a 50 nm TiO 2 :Cu 2 O layer. The PAAm gravimetric response to water vapor also increases by a factor of 3 and displays improved reversibility with the addition of 50 nm TiO 2 :Cu 2 O structures. We found that TiO 2 :Cu 2 O can be used to lower the detection limits for CO 2 sensing with EMIM and PEI and lower the detection limits for H 2 O sensing with PAAm by over a factor of 2. Coarse-grained and all-atom molecular dynamics simulations indicate the dissociative character of ionic liquid assembly on TiO 2 :Cu 2 O interfaces and different distributions of CO 2 and H 2 O molecules on bare and ionic liquid-coated surfaces, confirming experimental observations. Overall, our results show high potential of hierarchical assemblies of TiO 2 :Cu 2 O/room temperature ionic liquid and polymer films for sensors and CO 2 sequestration.