A kinetic study of facile fabrication of MIL-101(Cr) metal-organic framework: Effect of synthetic method

MIL-101(Cr) metal-organic framework samples were successfully synthesized through the conventional electrical heating (CE), ultrasound (US), and microwave (MW) synthetic methods at three different temperatures and various synthesis times. These were done with the aim of understudying the crystallization kinetics of these complex MIL's structures. The nucleation and crystal growth steps were thus, quantified through measuring the relative crystallinity of the prepared MIL-101(Cr) utilizing the PXRD and FESEM analysis under various synthesis conditions. In addition, the textural properties of the fully crystallized samples measured through the N-2 adsorption-desorption isotherms at 77 K. The rates of these steps estimated from crystallization curves revealing changes of relative crystallinity with synthesis time. The activation energies (E-a) and pre-exponential factors (A) of each step calculated from their corresponding Arrhenius plots. This demonstrated that the rate of crystallization steps (i.e., both nucleation and crystal growth) downgraded in the order of CE << MW< US. Moreover, it turned out that increasing of pre-exponential factors played more important role in accelerated crystallization under MW and US conditions in comparison to lowering of the activation energies. Hence, it was suggested that physical effects (i.e., hot spots) were playing more important role in comparison to the chemical ones (i.e., acidity of the reaction medium) in the accelerated synthesis of the MIL-101(Cr) utilizing US and MW techniques. (C) 2017 Elsevier B.V. All rights reserved.