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In situ X-ray Diffraction Investigation of the Crystallisation of Perfluorinated Ce(IV)-based Metal-Organic Frameworks with UiO-66 and MIL-140 architectures

preprint
submitted on 18.11.2020, 16:25 and posted on 19.11.2020, 12:30 by Stephen Shearan, Jannick Jacobsen, Ferdinando Costantino, Roberto D’Amato, Dmitri Novikov, Norbert Stock, Enrico Andreoli, Marco Taddei
We report on the results of a thorough in situ synchrotron powder X-ray diffraction study of the crystallisation in aqueous medium of two recently discovered perfluorinated Ce(IV)-based metal-organic frameworks (MOFs), analogues of the already well investigated Zr(IV)-based UiO-66 and MIL-140A, namely, F4_UiO-66(Ce) and F4_MIL-140A(Ce). The two MOFs were originally obtained in pure form in similar conditions, using ammonium cerium nitrate and tetrafluoroterephthalic acid as building blocks, and small variations of the reaction parameters were found to yield mixed phases. Here, we investigate the crystallisation of these compounds in situ in a wide range of conditions, varying parameters such as temperature, amount of the protonation modulator nitric acid (HNO3) and amount of the coordination modulator acetic acid (AcOH). When only HNO3 is present in the reaction environment, F4_MIL-140A(Ce) is obtained as a pure phase. Heating preferentially accelerates nucleation, which becomes rate determining below 57 °C, whereas the modulator influences nucleation and crystal growth to a similar extent. Upon addition of AcOH to the system, alongside HNO3, mixed-phased products, consisting of F4_MIL-140A(Ce) and F4_UiO-66(Ce), are obtained. In these conditions, F4_UiO-66(Ce) is always formed faster and no interconversion between the two phases occurs. In the case of F4_UiO-66(Ce), crystal growth is always the rate determining step. An increase in the amount of HNO3 slows down both nucleation and growth rates for F4_MIL-140A(Ce), whereas nucleation is mainly affected for F4_UiO-66(Ce). In addition, a higher amount HNO3 favours the formation of F4_MIL-140A(Ce). Similarly, increasing the amount of AcOH leads to slowing down of the nucleation and growth rate, but favours the formation of F4_UiO-66(Ce). The pure F4_UiO-66(Ce) phase could also be obtained when using larger amounts of AcOH in the presence of minimal HNO3. Based on these in situ results, a new optimised route to achieving a pure, high quality F4_MIL-140A(Ce) phase in mild conditions (60 °C, 1 h) is also identified.

Funding

Project CALIPSOplus - Grant Agreement 730872 - HORIZON2020

Marie Skłodowska-Curie Actions - Grant Agreement 663830 - HORIZON2020

FLEXIS - European Regional Development Fund

RICE - European Regional Development Fund

EPSRC EP/M028267/1

ERDF through the Welsh Government grant 80708

Sêr Solar project via the Welsh Government

History

Email Address of Submitting Author

marco.taddei@unipi.it

Institution

University of Pisa

Country

Italy

ORCID For Submitting Author

0000-0003-2805-6375

Declaration of Conflict of Interest

There is no conflict to declare.

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