UiO-66 and UiO-66-NH2 based sensors: Dielectric and FTIR investigations on the effect of CO2 adsorption

Nano-scaled UiO-66 and UiO-66-NH2 crystals are synthesized via a solvothermal procedure and investigated regarding their applicability in CO2 sensing devices. The interaction between CO2 and UiO-66 as well as UiO-66-NH2 is studied via FTIR and dielectric measurements with a home-made sensing-cell contraption. The affinity towards low CO2 concentrations is proved by FTIR measurements with 20 ppm CO2. We show, that the co-existence of water leads to an even higher CO2 adsorption compared to the absence of water. Both UiO-MOFs show a good response towards low CO2 concentrations, but UiO-66-NH2 is far more sensitive than UiO-66. In dielectric studies, the affinity of UiO-66 and UiO-66-NH2 towards CO2 results in a strong decrease of the capacity at low frequencies. While UiO-66-NH2 seems to be suited for sensing devices within a CO2 concentration range from 1 up to 100%, UiO-66 seems not be suitable for capacitive CO2 sensing.