Insights into Paraben Adsorption by Metal-Organic Frameworks for Analytical Applications.

Metal-organic frameworks (MOFs) are attractive materials used as sorbents in analytical microextraction applications for contaminants of emerging concern (CECs) from environmental liquid matrices. The demanding specs for a sorbent in the analytical application can be comprehensively studied by considering the interactions of the target analytes with the frameworks by the use of single-crystal X-ray diffraction, computational analysis, and adsorption studies, including the kinetic ones. The current study intends a better understanding of the interactions of target CECs (particularly, propylparaben (PPB) as a model) and three Zn-based layered pillared MOFs: [Zn(tz)(bdc)] (Htz = 1,2,4-triazole and Hbdc = 1,4-benzenedicarboxylic acid) and their amino derivatives [Zn(NH-tz)(bdc)] and [Zn(tz)(NH-bdc)] (NH-Htz = 3-amino-1,2,4-triazole and NH-Hbdc = 2-amino-1,4-benzenedicarboxylic acid). The crystal structures of the two solvate compounds ( (dma = dimethylacetamide) and ) were solved by single-crystal X-ray diffraction to determine the points of interaction between the framework and the guest molecules. They also served as a starting point for the computational modeling of the compound, showing that up to two PPB molecules can be hosted in one of the pores, while only one can be trapped in the second pore type, leading to a maximum theoretical capacity of 291.9 mg g. This value is close to the value obtained by the adsorption isotherm experiment for (283 mg g). This value is, by far, higher than those previously reported for other materials for the removal of PPB from water, and also higher than the experimental values obtained for (54 mg g) and (153 mg g). The kinetics of adsorption is not very fast, with uptake of about 40% in 3 h, although a 70% release in methanol is achieved in 1 h. In addition, a further comparison of performance in analytical microextraction (requiring only 10 mg of ) was carried out together with chromatographic analysis to support all insights attained, with the method being able to monitor CECs as low as μg L levels in complex environmental water samples, thus performing successfully for water monitoring even in multicomponent scenarios.