Humidity-enhanced photodegradation mechanism of UiO-66-NH2 metal organic framework

The Zr-based metal-organic framework UiO-66-NH2 has been investigated to study the effects of ultraviolet and visible light exposure under dry air and humid environments. Significant impedance and color changes in the material due to ultraviolet and blue light have been observed. These changes happen more rapidly and grow larger in total cumulative magnitude as the atmospheric humidity increases. Samples placed in darkness or in the presence of light with lower energy than blue (450 nm) light showed no discoloration or degradation, regardless of humidity. Impedance data modeling suggests that humidity increases the ionic conductivity of the material and that the degradation occurs at grain boundaries, to a depth that increases with humidity. Nuclear magnetic resonance, X-ray diffraction, and Fourier transform infrared spectroscopy indicate that degradation in samples exposed to light are due to broken linkers between the benzenedicarboxylic acid and Zr clusters. Distribution Statement A. Approved for Public Release. Distribution Unlimited.