Selection of Covalent Organic Framework Pore Functionalities for Differential Adsorption of Microcystin Toxin Analogues.

Microcystins (MCs), produced by Microcystis sp, are the most commonly detected cyanotoxins in freshwater, and due to their toxicity, worldwide distribution, and persistence in water, an improvement in the monitoring programs for their early detection and removal from water is necessary. To this end, we investigate the performance of three covalent organic frameworks (COFs), TpBD-(CF3)2, TpBD-(NO2)2, and TpBD-(NH2)2, for the adsorption of the most common and/or toxic MC derivatives, MC-LR, MC-RR, MC-LA, and MC-YR, from water. While MC-LR and MC-YR can be efficiently adsorbed using all three COF derivatives, high adsorption efficiencies were found for the most lipophilic toxin, MC-LA, with TpBD-(NH2)2, and the most hydrophilic one, MC-RR, with TpBD-(NO2). Theoretical calculations revealed that MC-LA and MC-RR have a tendency to be located mainly on the COF surface, interacting through hydrogen bonds with the amino and nitro functional groups of TpBD-(NH2)2 and TpBD-(NO2)2, respectively. TpBD-(NO2)2 outperforms the adsorbent materials reported for the capture of MC-RR, resulting in an increase in the maximum adsorption capacity by one order of magnitude. TpBD-(NH2)2 is reported as the first efficient adsorbent material for the capture of MC-LA. Large differences in desorption efficiencies were observed for the MCs with different COFs, highlighting the importance of COF-adsorbate interactions in the material recovery. Herein we show that efficient capture of these toxins from water can be achieved through the proper selection of the COF material. More importantly, this study demonstrates that by careful choice of COF functionalities, specific compounds can be targeted or excluded from a group of analogues, providing insight into the design of more efficient and selective adsorbent materials.

Extraction of Ibuprofen from Natural Waters Using a Covalent Organic Framework.

Ibuprofen is one of the most widely used pharmaceuticals, and due to its inefficient removal by conventional wastewater treatment, it can be found in natural surface waters at high concentrations. Recently, we demonstrated that the TpBD-(CF3)2 covalent organic framework (COF) can adsorb ibuprofen from ultrapure water with high efficiency. Here, we investigate the performance of the COF for the extraction of ibuprofen from natural water samples from a lake, river, and estuary. In general, the complexity of the natural water matrix induced a reduction in the adsorption efficiency of ibuprofen as compared to ultrapure water. The best performance, with over 70% adsorption efficiency, was found in lake water, the sample which featured the lowest pH. According to the theoretical calculations, ibuprofen more favorably interacts with the COF pores in the protonated form, which could partially account for the enhanced adsorption efficiency found in lake water. In addition, we explored the effect of the presence of competing pharmaceuticals, namely, acetaminophen and phenobarbital, on the ibuprofen adsorption as binary mixtures. Acetaminophen and phenobarbital were adsorbed by TpBD-(CF3)2 with low efficiency and their presence led to an increase in ibuprofen adsorption in the binary mixtures. Overall, this study demonstrates that TpBD-(CF3)2 is an efficient adsorbent for the extraction of ibuprofen from natural waters as well.

Influence of 1,2-alkanediols on the structure of their intercalates with strontium phenylphosphonate solved by molecular simulation and experimental methods.

Strontium phenylphosphonate intercalates with 1,2-diols (from 1,2-ethanediol to 1,2-hexanediol) were synthesized and characterized by X-ray diffraction, thermogravimetry, chemical analysis, and molecular simulation methods. Prepared samples exhibit a very good stability at ambient conditions. Structural arrangement calculated by simulation methods suggested formation of cavities surrounded by six benzene rings. Each cavity contained one molecule of diol and one molecule of water for the 1,2-ethanediol to 1,2-butanediol intercalates. In the case of 1,2-pentanediol two types of cavities alternated: one with diol molecules and another one with two water molecules. In the 1,2-hexanediol intercalate the benzene rings created two types of cavities containing one or two diol molecules, respectively, and this conformational variability led to a more disordered arrangement with respect to the models with shorter alkyl chains. Coordination of the oxygen atoms of the diols to the strontium atoms of the host follows the same pattern for all 1,2-diol intercalates except the 1,2-hexanediol intercalate, where these oxygen atoms can be mutually exchanged at their positions. The calculated basal spacings and structural models are in good agreement with experimental basal spacings obtained from X-ray powder diffraction and with other experimental results.