**Thermal Post-Treatments to Enhance the Water Stability of NH 2-MIL-125(Ti)**

#### **Almudena Gómez-Avilés, Virginia Muelas-Ramos, Jorge Bedia \*, Juan Jose Rodriguez and Carolina Belver \***

Chemical Engineering Department, Universidad Autónoma de Madrid, Campus Cantoblanco, E-28049 Madrid, Spain; almudena.gomeza@uam.es (A.G.-A.); virginia.muelas@uam.es (V.M.-R.); juanjo.rodriguez@uam.es (J.J.R.)

**\*** Correspondence: jorge.bedia@uam.es (J.B.); carolina.belver@uam.es (C.B.); Tel.: +34-91-497-29-11 (J.B.);

+34-91-497-84-73 (C.B.)

Received: 20 April 2020; Accepted: 27 May 2020; Published: 29 May 2020

**Abstract:** NH2-MIL-125(Ti) is a metal organic framework (MOF) based on Ti-oxo-clusters widely investigated in water-related applications. Such applications require MOFs with an excellent stability in the aqueous phase, but, despite this, the extent of MOFs' degradation in water is still not ye<sup>t</sup> fully understood. In this study, we report a quantitative study of the water stability of NH2-MIL-125(Ti), analyzing the ligand release along the contact time in water. This study demonstrates that NH2-MIL-125(Ti) easily leached out over time while maintaining its structure. The e ffect of di fferent thermal treatments applied to NH2-MIL-125(Ti) was investigated to enhance its water stability. The structural and textural properties of those modified MOFs were studied in detail and those maintaining the NH2-MIL-125(Ti) properties were exposed to aqueous medium. The analysis of the released ligand concentration in the filtrate can provide information on the water stability of this material.

**Keywords:** metal organic frameworks; NH2-MIL-125(Ti); water stability; purification
