Influences of Deprotonation and Modulation on Nucleation and Growth of UiO-66: Intergrowth and Orientation

Abstract

The most common products obtained in the synthesis of zirconium-based metal−organic frameworks (ZrMOFs) are fine powders. The particle size of a typical ZrMOF UiO-66 was first reported to be around 200 nm, so the original crystal structure was only solved by powder XRD coupled with Rietveld refinement due to the incapability of single crystal XRD to solve such small crystals with poor crystallinity. One may ask the reason why the particle size of UiO-66 is so small compared to that of other common MOFs and what the key factor terminating the growth of UiO-66 is. In this work, we try to answer this question by proposing a hypothesis that the partially deprotonated ligand caused by the accumulated protons in the reaction solution is the key factor preventing the continuous growth of the UiO-66 crystal. The hypothesis is verified by growth reactivation with the addition of a deprotonating agent in an in situ biphase solvothermal reaction. As long as the protons were sufficiently coordinated by the deprotonating agent, the continuous growth of UiO-66 is guaranteed. Moreover, the modulation effect can impact the coordination equilibrium and nucleation so that an oriented attachment growth of UiO-66 film was achieved in membrane structures.

Experimental evidence for a general model of modulated MOF nanoparticle growth

“…Although the seesaw model at present does not offer predictions of particle morphologies, we expect that its foundation in acid-base and metal-ligand chemistry can help explain the dependence of morphology on solution acidity and modulator composition. Although previous reports have used modulators in combination with manipulation of pH, 27,33 this report is the rst to systematically manipulate particle sizes with a buffer.…”

Ultimate Control over Hydrogen Bond Formation and Reaction Rates for Scalable Synthesis of Highly Crystalline vdW MOF Nanosheets with Large Aspect Ratio

“…To circumvent this problem, we added a deprotonating agent triethylamine (i.e., N(CH 2 CH 3 ) 3 ) in the upper hexane phase (Figure d, pink phase) which has been successfully shown to be effective in increasing the reaction speeds (Section S.1.3, Supporting Information). As TEA diffuses into the bottom phase, it governs the quantity of proton in a direction where TEA diffuses . Here, hexane also buffers the contact between formic acid and TEA, in that way we have the high crystallinity and yield all at the same time, and optimizing the hexane amount is of paramount importance in the growth process as shown in Section S.1.4 (Supporting Information).…”

Design of a Semi-Continuous Selective Layer Based on Deposition of UiO-66 Nanoparticles for Nanofiltration

“…The resultant membrane showed an excellent permeability by possessing a flux value of 265 L/m 2 h MPa with efficient rejection of methylene blue (MB). In spite of promising performance, a key issue is that the nucleation and growth of MOFs usually requires hours under thermal treatment and/or in the presence of a harsh solvent [25], and this severely limits the combination between an MOF and a polymeric support that can form a uniform selective layer before damaging the polymeric support. Moreover, as the nucleation of MOF crystals likely occurs in a solution rather than on a substrate surface, it is not easy to control the thickness of the selective layer in in situ processes unless a cyclic layer-by-layer technique is employed [24,26].…”