Highly Efficient Adsorption of Emerging Freshwater Saxitoxins with Graphene

Abstract

The rapid proliferation of saxitoxin (STX)-producing cyanobacteria in freshwater ecosystems poses an emerging threat to global drinking water security. STXs (STX), produced by these harmful algal blooms, are a class of potent neurotoxic alkaloids that exhibit resistance to conventional water treatment processes like oxidation. Adsorption using carbon-based materials is recommended for STX removal, but current adsorbents have limited efficacy. Here, we demonstrate that mesoporous graphene nanoplatelets (GnPs) are a superior adsorbent for STX, outperforming granular activated carbon (GAC) and other benchmarks in both kinetics and capacity. GnPs achieved a 93.5-fold higher adsorption capacity and over 6-fold faster kinetics compared to GAC. The exceptional performance of GnPs is attributed to their high surface area, favorable surface chemistry, and optimized pore structure that facilitate rapid and extensive STX adsorption through π–π interactions, electrostatic attraction, and intraparticle diffusion. Mechanistic studies revealed a critical role of solution conditions, with higher pH and lower ionic strength enhancing STX removal by promoting electrostatic interactions. GnPs also demonstrated excellent performance in simulated field water, maintaining >90% removal within 1 h even in the presence of competitive organics. This study highlights the immense potential of GnPs as an advanced adsorbent for mitigating the rising threat of STX contamination in drinking water.

Novel graphene-based adsorbents demonstrate exceptional removal of freshwater saxitoxins, offering promising solutions for emerging water contaminant treatment.