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 coexistence 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.