Alginate cryogel beads for effectively aggregating nanoplastics for water remediation.

Nanoplastic (NP) pollution, consisting of particles smaller than 1 µm, poses a significant threat to both global ecosystems and human health. However, effective removal remains challenging due to their sub-micron size and low environmental concentrations. In this research, we discovered that an alginate cryogel can rapidly aggregate NPs (50-200 nm) into micrometer-sized clusters, enabling efficient removal via conventional membrane filtration. This cryogel-enhanced filtration achieved over 99% NP removal within 2 minutes. We attribute the observed aggregation to the combined effects of weakly bound alginate leaching upon cryogel rehydration and localized Ca²⁺ release from cryogels on driving NP aggregation. This mechanism enables effective NP removal across a pH range of 4-8 for both spherical and irregularly shaped NPs. While surface adsorption plays a role in NP removal, aggregation predominantly resulted into the effective filtration of NPs, with minimal influence from cryogel's internal porosity. By leveraging NP aggregation into the microscale rather than relying on size-dependent direct filtration, this strategy presents a promising scalable solution for wastewater treatment and broader environmental applications.