Hansen solubility parameters (HSP) have found their greatest use in the evaluation of solvent-polymer chemical interactions. Given their great interest among the scientific community, host-guest interactions in metal-organic frameworks (MOFs), with organic and inorganic moieties, could benefit from a HSP approach. In this work we have initiated the application of HSP to the study of caffeine encapsulation in MOFs ZIF-8 and NH2-MIL-88B(Fe). However, the availability of HSP for MOFs is nearly zero. As a first step to evaluating the potential of HSP for rational design we have made the simplifying assumption that the HSP distance of the caffeine-ligand interaction (i.e. ignoring the metal and the MOF structure) dominates the ability to form a MOF host-guest system. Although much work remains to be done, the first indications are that this approach has much potential.
Besides the substitution or minimization
of the use of harmful
solvents, one essential goal of chemistry is to try to avoid their
use altogether whenever possible. In the case of the synthesis of
MOFs (metal–organic frameworks), this can only be achieved
by finding alternatives to conventional processes. An example is the
approach described here which involves working at high pressure (at
0.31 GPa) without using a solvent. This has evident advantages over
mechanochemical synthesis by grinding or milling (also a solventless
process) where the sample is submitted to attrition. The present paper
reports the simple high pressure synthesis of the ZIF (zeolitic imizadolate
framework) ZIF-8. This methodology enables fast synthesis of MOF materials
and offers new insights into their industrial implementation. In addition,
this technique could be applied to the synthesis of other MOFs and
even COFs (covalent organic frameworks).
The solvent‐free encapsulation of caffeine and kojic acid was carried out in different carboxylate‐based MOFs [MIL‐53(Al), UiO‐66 and Mg‐MOF‐74] by high pressure (0.32 GPa) contact. This methodology enables fast and ecofriendly encapsulation and gives rise to additive@MOFs with physical and features equivalent to those of materials obtained by common liquid phase encapsulation processes. It could be applied to other host–guest systems, simplifying the procedures, reducing the use and waste of harmful chemicals, and approaching the conditions of interest in the industry. The characterization carried out by thermogravimetry, X‐ray diffraction, N2 adsorption, and 13C NMR provided information about the presence and conformation of the additives in the MOFs. The highest encapsulation values for caffeine (37 %) and kojic acid (32 %) were obtained with MIL‐53(Al).
Correction for 'Using Hansen solubility parameters to study the encapsulation of caffeine in MOFs' by Lorena Paseta et al., Org. Biomol. Chem., 2015, DOI: 10.1039/c4ob01898b.
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