Preparation of cerium-based UiO-66 metal-organic framework (MOF) without addition of solvent for developing its sustainable synthesis

Abstract

UiO-66(Ce) metal-organic framework (MOF) has been a promising material for broad applications, including gas adsorption, photocatalysis, water treatment and reaction catalysis. For its usual preparation, a large amount of solvent is required and added during its fabrication process. This solvent is harmful to the environment most of the time. It is neither recyclable nor reusable, indicating the difficulty in waste disposal after MOF fabrication and the challenges for its scaling-up production. Given this, a solvent-free way of synthesizing the UiO-66 MOF to develop its sustainable synthesis was reported here. The MOF can be obtained by mechanically grinding the cerium (IV) ammonium nitrate (CAN) and terephthalic acid (BDC) using mortar and pestle without the addition of any solvent. Then the mixture was transferred into an autoclave and heated at 100 °C for one day. In this work, UiO-66(Ce) MOF samples with varying Ce to BDC molar ratios were successfully fabricated using the solvent-free method, supported by the XRD, SEM, EDX and FT-IR analysis results. By looking at their XRD patterns, two characteristic peaks for UiO-66(Ce) MOF were observed at 8.4° and 9.1°. The SEM images revealed the spherical crystalline morphology of UiO-66 MOF. At the same time, the EDX analysis result found the elemental composition of UiO-66 MOF was coherent with the reactants used, suggesting the excellent purity of MOF product formed in this work. As verified by the thermal stability test, the UiO-66 MOF produced here is thermally stable up to 250 °C in the air atmosphere.