Anthropogenic activity releases hazardous contaminants and pollutants that are not removed fully by water treatments. Among such pollutants, bisphenol-A (BPA) and bisphenol-S (BPS) are included in a series of Endocrine Disruptive Compounds, which may cause disruption due to hormone blockage or mimicking. Thus, even though those pollutants are not considered lethal, they are hazardous to health due to their similarity to 17β-estradiol, and they have been shown to cause developmental malformation in Zebrafish and breast and prostate tumors in rodents. Both BPA and BPS have been found in water sources at concentrations >30 μg L–1 and since water treatment plants are ineffective at removing them, their concentration is constantly increasing. The purpose of the present study, using a collection of experiments performed by B.Sc. and M.Sc. students, was to apply clay-based materials to the removal of such health hazards from water. Specifically adapted modified clays as neutral organoclays can optimize the interaction between pollutants and the matrix to achieve efficient adsorption. Such an approach is very effective for relatively insoluble pollutants such as BPA, but less so for the more soluble BPS. On the other hand, BPS can be photodegraded catalytically using raw clay or TiO2-impregnated clay. At low catalyst concentration, the modified clay was as effective as a commercial TiO2 catalyst, whereas combining it with H2O2 yielded considerably better results. In summary, clay minerals offer solutions for the removal of health-hazardous pollutants from water, based on different procedures and mechanisms. The versality of clay minerals allows 'tailoring' specifically adapted materials that might improve their efficiency based on such very specific pollutant-matrix interactions.

Abstract. Smectites, like other clay minerals, have been shown to promote ice nucleation in immersion freezing mode and likely contribute to the population of ice nucleating particles (INPs) in the atmosphere. Smectites are layered aluminosilicates, which form platelets that depending on composition might swell or even delaminate in water by intercalation of water molecules between their layers. They comprise among others montmorillonites, hectorites, beidellites, and nontronites. In this study, we investigate the ice nucleation (IN) activity of a variety of natural and synthetic smectite samples with different exchangeable cations. The montmorillonites STx-1b and SAz-1, the nontronite SWa-1, and the hectorite SHCa-1 are all rich in Ca2+ as the exchangeable cation, the bentonite MX-80 is rich in Na+ with a minor contribution of Ca2+, the synthetic Laponite is a pure Na+ smectite. The bentonite SAu-1 is rich in Mg2+ with a minor contribution of Na+, and the synthetic interstratified mica-montmorillonite Barasym carries NH4+ as the exchangeable cation. In emulsion freezing experiments, all samples except Laponite exhibited one or two heterogeneous freezing peaks with onsets between 239 K and 248 K and a quite large variation in IN activity, yet without clear correlation with the exchangeable cation, with the type of smectite, or with mineralogical impurities in the samples. To further investigate the role of the exchangeable cation, we performed ion exchange experiments. Replacing NH4+ with Ca2+ in Barasym reduced its IN activity to the one of other Ca-rich montmorillonites. In contrast, stepwise exchange of the native cations in STx-1b once with Y3+ and once with Cu2+ showed no influence on IN activity. However, aging of smectite suspensions in pure water up to several months revealed a decrease in IN activity with time, which we attribute to the delamination of smectites in aqueous suspensions, which may proceed over long timescales. The dependence of IN activity on platelet stacking and thickness can be explained if the hydroxylated chains forming at the edges are the location of ice nucleation in smectites, since the edges need to be thick enough to host a critical ice embryo. We hypothesize that at least three smectite layers need to be stacked together to host a critical ice embryo on clay mineral edges and that the larger the surface edge area is the higher the freezing temperature. Comparison with reported platelet thicknesses of the investigated smectite samples suggests that the observed freezing temperatures are indeed limited by the surface area provided by the mostly very thin platelets. Specifically, Laponite, which did not show any IN activity, is known to delaminate into single layers of about 1 nm thickness, which would be too thin to host a critical ice embryo.

Abstract. Smectites, like other clay minerals, have been shown to promote ice nucleation in the immersion freezing mode and likely contribute to the population of ice-nucleating particles (INPs) in the atmosphere. Smectites are layered aluminosilicates, which form platelets that depending on composition might swell or even delaminate in water by intercalation of water molecules between their layers. They comprise among others montmorillonites, hectorites, beidellites, and nontronites. In this study, we investigate the ice nucleation (IN) activity of a variety of natural and synthetic smectite samples with different exchangeable cations. The montmorillonites STx-1b and SAz-1, the nontronite SWa-1, and the hectorite SHCa-1 are all rich in Ca2+ as the exchangeable cation; the bentonite MX-80 is rich in Na+ with a minor contribution of Ca2+, and the synthetic Laponite is a pure Na+ smectite. The bentonite SAu-1 is rich in Mg2+ with a minor contribution of Na+, and the synthetic interstratified mica-montmorillonite Barasym carries NH4+ as the exchangeable cation. In emulsion freezing experiments, all samples except Laponite exhibited one or two heterogeneous freezing peaks with onsets between 239 and 248 K and a quite large variation in IN activity yet without clear correlation with the exchangeable cation, with the type of smectite, or with mineralogical impurities in the samples. To further investigate the role of the exchangeable cation, we performed ion exchange experiments. Replacing NH4+ with Ca2+ in Barasym reduced its IN activity to that of other Ca-rich montmorillonites. In contrast, stepwise exchange of the native cations in STx-1b once with Y3+ and once with Cu2+ showed no influence on IN activity. However, aging of smectite suspensions in pure water up to several months revealed a decrease in IN activity with time, which we attribute to the delamination of smectites in aqueous suspensions, which may proceed over long timescales. The dependence of IN activity on platelet stacking and thickness can be explained if the hydroxylated chains forming at the edges are the location of ice nucleation in smectites, since the edges need to be thick enough to host a critical ice embryo. We hypothesize that at least three smectite layers need to be stacked together to host a critical ice embryo on clay mineral edges and that the larger the surface edge area is, the higher the freezing temperature. Comparison with reported platelet thicknesses of the investigated smectite samples suggests that the observed freezing temperatures are indeed limited by the surface area provided by the mostly very thin platelets. Specifically, Laponite, which did not show any IN activity, is known to delaminate into single layers of about 1 nm thickness, which would be too thin to host a critical ice embryo.