Multiscale, porous anion-exchangeable sponge for sustainable and convenient boron removal.

To address the limitations, such as complex treatment processes, reduced durability, and poor reusability, of typical micro- and nanoscale adsorbents for boron removal, a simple method for removing residual boron is introduced using a multiscale porous anion-exchangeable sponge (MP-AES) that electrostatically attracts boron in areas with locally high pH. Because commercially available anion-permselective materials are absent, custom nanoporous materials surrounded by microporous melamine foam are used to increase surface area and durability under repeated compression. The hydrophilic porous sponge facilitates liquid diffusion, enhancing adsorption in the user-friendly system. Our MP-AES exhibits remarkable boric-acid-adsorption efficiency, achieving up to 21 mg/g in a 100 mg/L solution within 20 min. Under low-solute conditions (2 mg/L), over 90 % of boron is removed within 10 min, which is a 120 % improvement relative to that of the commercial resin, IRA-743. Notably, the MP-AES sustains its adsorption capacity over at least 10 regeneration cycles with basic treatment and withstands multiple compressions (80 % strain) over 100 cycles without experiencing structural failure. When tested with a reverse osmosis permeate, the MP-AES meets the stringent drinking water standards (0.5-1 mg/L). This sustainable, efficient, and convenient adsorption system has the potential for widespread application in water treatment technologies.