PFAS: playing hard to get
Although governments worldwide try to eliminate exposure to PFAS, there are still no treatment techniques available that can remove these compounds from large water bodies in a cost- and energy-efficient way.
Techniques that have been explored so far are energy-devouring, require pretreatment steps and/or suffer from a drastic decline in PFAS adsorption capacity when used in real situations. In addition, most of these techniques are expensive and used materials are difficult to recover from aqueous streams and hard to regenerate.
Not your average zeolite
In a study, zeolites (microporous, aluminosilicate minerals) showed adsorptive capacity for PFOS, but the nature of the zeolite sorbent remained unclear. Since zeolites, as crystalline microporous materials, present a multitude of pore architectures and compositions, KU Leuven and VITO researchers initiated a detailed search into the best zeolite adsorbent for adsorptive PFAS removal.
Even though adsorption might be the best available technique for the low-cost and energy efficient removal of PFASs from water, many adsorbents simply lack the selectivity that is required to be used for “real” waters containing various organic competitors. Adsorption selectivity is therefore arguably the most important feature for adsorbent selection. In their article, the researchers demonstrate all-silica zeolite Beta to be a highly selective and high-capacity adsorbent for removing PFOA and PFOS from water, even in the presence of organic competitors.
More than PFOS and PFOA
Also is shown that the high selectivity of all-silica zeolite Beta is not limited to PFOA, but also applies to other PFASs. The adsorbate scope can thus be extended towards other types of perfluoro-compounds like non-functional perfluoroalkanes (for instance perfluorooctane and perfluorodecane).
Also the stability and reusability of all-silica zeolite Beta were assessed. This revealed that after complete saturation with PFOA, all adsorbed molecules can be removed at 350 °C without any damage to the zeolites framework and its crystallinity. The possibility of a thermal regeneration is a significant asset for all-silica zeolite Beta, because such a simple treatment cannot be applied for organic adsorbents like macrocyclic polymers or ion-exchange resins.
Summarizing, the KU Leuven researchers believe the exceptionally high affinity and selectivity of all-silica zeolite Beta for PFOA and similar perfluorinated compounds, makes it the lead candidate for combating PFAS pollution.
The study “Highly Selective Removal of Perfluorinated Contaminants by Adsorption on All‐Silica Zeolite Beta” by M. Van den Bergh, D. De Vos et al. was published in “Angewandte Chemie” .