Stability of Iodine Species Trapped in Titanium‐Based MOFs: MIL‐125 and MIL‐125_NH<sub>2</sub>
Pedro H. M. Andrade, Jérémy Dhainaut, Christophe Volkringer, Thierry Loiseau, Aurélien Moncomble, Matthieu Hureau, Alain Moissette
Abstract
Abstract Two titanium‐based MOFs MIL‐125 and MIL‐125_NH 2 are synthesized and characterized using high‐temperature powder X‐ray diffraction (PXRD), thermogravimetric analysis (TGA), N 2 sorption, Fourier transformed infrared spectroscopy (FTIR), Raman spectroscopy, ultraviolet‐visible spectroscopy (UV–Vis), and electron paramagnetic resonance (EPR). Stable up to 300 °C, both compounds exhibited similar specific surface areas (SSA) values (1207 and 1099 m 2 g −1 for MIL‐125 and MIL‐125_NH 2 , respectively). EPR signals of Ti 3+ are observed in both, whith MIL‐125_NH 2 also showing ─NH 2 ●+ signatures. Both MOFs efficiently adsorbed iodine in continuous gas flow over five days, with MIL‐125 trapping 1.9 g.g −1 and MIL‐125_NH 2 trapping 1.6 g.g −1 . MIL‐125_NH 2 exhibited faster adsorption kinetics due to its smaller band gap (2.5 against 3.6 eV). In situ Raman spectroscopy conducted during iodine adsorption revealed signal evolution from “free” I 2 to “perturbed” I 2 , and I 3 − . TGA and in situ Raman desorption experiments showed that ─NH 2 groups improved the stabilization of I 3 − due to an electrostatic interaction with NH 2 ●+ BDC radicals. The Albery model indicated longer lifetimes for iodine desorption in I 2 @MIL‐125_NH 2 , attributed to a rate‐limiting step due to stronger interaction between the anionic iodine species and the ─NH 2 ●+ radicals. This study underscores how MOFs with efficient charge separation and hole‐stabilizer functional groups enhance iodine stability at higher temperatures.