Stability of Iodine Species Trapped in Titanium-Based MOFs: MIL-125 and MIL-125_NH 2 .

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.