No abstract

organic compounds made of two or more aromatic rings, fused together in linear, angular, or cluster arrangements. They can be also referred as low-molecular weight PAHs (two or three rings) and high-molecular weight PAHs (four or more rings). [3] These ubiquitous compounds can be generated from both anthropogenic activities, such as industrial, residential, and vehicular emissions, and natural pheno mena, i.e., open burning, volcanic activities, and spills from coal deposits. [2,3,[5][6][7] The occurrence of PAHs has been assessed worldwide in different aquatic systems including influents and effluents from wastewater treatment plants, groundwater, surfaceand sea-water. [3] Currently, over 400 PAHs and derivatives have been identified and classified, but most regulations, analyses, and data are focused on only 14 to 20 PAH compounds. [2,3,7] PAHs are well-known toxic, mutagenic, either carcinogenic or suspected carcinogenic compounds, accumulating in human and animal tissues. [2,3] These compounds are characterized by high hydrophobicity and good lipid solubility due to their aromatic and delocalized structure: when their molecular weight increases, their aqueous solubility diminishes, whereas resistance to oxidation and reduction rises. [2][3][4] PAHs absorption and bioaccumulation in several tissues, as well as their ubiquitous occurrence in the environment, pushed US EPA (United States Environmental Protection Agency) and EEA (European Environment Agency) to identify 24 PAH compounds as priority contaminants, thus introducing strict regulations for their monitoring. [8][9][10][11] The 16 PAHs considered as priority pollutants by US EPA are: naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno[1,2,3-cd] pyrene, dibenz[a,h]anthracene, and benzo[ghi]perylene (Chart S1, Supporting Information). The European Union has set the maximum limit of 0.1 µg L −1 as sum of benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[ghi]perylene, and indeno [1,2,3-cd] pyrene in water for human consumption, with a particular attention to benzo[a]pyrene limited to 0.01 µg L −1 . [12] The removal of PAHs represents one of the current challenges in environmental chemistry. Methods are based on biodegradation, chemical, and physical removal processes, often combined in order to obtain the highest degree of PAHs removal. [2][3][4]6,7,13] Despite biological treatment methods have been proposed in municipal wastewaterThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.202104946.

Auxetics are materials characterized by a negative Poisson’s ratio (NPR), an uncommon mechanical behavior corresponding to a transversal deformation tendency opposite to the traditional materials. Here we present the first example of a 3D synthetic molecular auxetic polymer, obtained by embedding a conformationally expandable cavitand as crosslinker into a rigid polymer of intrinsic microporosity (PIM). The rigidity and microporosity of the polymeric matrix are pivotal to maximize the expansion effect of the cavitand that, under mechanical stress, can assume two different conformations: a compact vase one and an extended kite form. The auxetic behavior and the corresponding NPR of the proposed material is predicted by a specific micromechanical model that considers the cavitand volume expansion ratio, the fraction of the cavitand crosslinker in the polymer, and the mechanical characteristics of the polymer backbone. The reversible auxetic behavior of the material is experimentally verified via Digital Image Correlation technique (DIC) performed during the mechanical tests on films obtained by blending the auxetic crosslinked polymer with pristine PIM. Two specific control experiments prove that the mechanically driven conformational expansion of the cavitand crosslinker is the sole responsible of the observed NPR of the polymer.