Bardiya Valizadeh
Metal-organic frameworks (MOFs) are a fascinating class of porous materials that have become the subject of research owing to their unique characteristics such as high surface areas, low densities, and structural tunability. Recently, the research has been directed towards large-scale synthesis of MOFs and their industrial applications. In terms of synthesis, MOFs are conventionally isolated as crystalline powders that are not industrially favorable due to their limitations in processing. Shaping MOFs into different forms while preserving or improving their properties offers several advantages as they can be easily processed, handled, and stored. Controlling the shape of MOFs in a systematic way can represent a major step forward to bringing them to the market, testing them at industrial scales and realizing their true potential.
In this thesis, a new shaping method in the form of MOF@polymer composite beads (M@PB) is presented in which the MOF crystals are dispersed in a porous matrix of polymeric beads. This shaping method, based on phase inversion technique, not only preserves the intrinsic properties of the MOF crystals such as crystallinity and porosity, but also improves their performance for targeted applications. Due to the versatility and flexibility of this method virtually any MOF can be incorporated into any polymer structure. In addition, the method allows for pre- and post-synthetic modification of both the MOF and polymer phases, hence, making the composite material of superior tunability toward targeted applications. Such tunable properties have been illustrated in the context of this thesis for liquid-phase separation and photocatalysis applications.
HKUST-1 was used with three different polymers to form M@PB that improve I2 capture and recovery in liquid phase, a process used for recovery of precious metals from waste of electrical and electronic equipment. M@PBs have shown superior mechanical and chemical robustness for advanced adsorption systems that paves the way for their industrial applications. UiO-66, was functionalized with double amino groups and was incorporated into M@PB using polyethersulfone (PES) that was chemically modified with carboxylic acid groups to capture toxic hexavalent chromium (Cr(VI)) from wastewater and reduce it to its non-toxic trivalent form (Cr(III)). The Cr(VI) capture and subsequent photoreduction was carried out, for the first time, in a single integrated adsorption-photoreduction system equipped with a visible light source, demonstrating that the Cr(VI) concentration is brought below drinkable levels and the Cr(VI) subsequently photoreduced to Cr(III) species using light irradiation during adsorbent regeneration. This illustrates the tunability of M@PBs through careful design of the MOF and polymer toward a targeted application.
EPFL2020
