3D-printed indium oxide monoliths for PFAS removal

More efficient removal methods for per- and polyfluoroalkyl substances (PFAS), anthropogenic compounds with high persistence in the environment, are urgently needed due to their significant adverse health effects. Current technologies for PFAS removal in water are limited by incomplete degradation or practical concerns about the use of slurry-based adsorbents. In this study, self-supported indium oxide (In2O3) monoliths were produced via extrusion-based 3D printing and used for the removal of perfluorooctanoic acid (PFOA) via adsorption in a recirculating flow system. A detailed study of the sintering temperature, monolith geometry, and flow rate allowed maximising PFOA adsorption due to the improvement of PFOA diffusion and the increased number of active sites on the monolith, resulting in 53 % of PFOA removal with fast adsorption kinetics in 3 h. Additionally, a low-temperature pyrolysis process at 500 °C effectively regenerated the In2O3 monoliths, allowing reusing the monoliths for three adsorption cycles, while also improving the PFOA removal to 75 % in 3 h. The regenerated In2O3 monoliths not only have a high adsorption capacity (0.16 mg g−1), but also required a much shorter time to reach the adsorption equilibrium compared with other adsorbents reported in the literature. The effectiveness, robustness and reusability of the 3D printed In2O3 monoliths highlight their potential as an efficient and sustainable adsorbent for PFAS removal. The approach presented here represents an effective strategy for the fabrication of complex adsorbents, which are reusable and can be easily handled, eliminating the expensive downstream removal required for slurries while offering a clear route for scale-up towards industrial use.