(173am) Enhancing Water Security and Defense: Exploring Graphene Nanoplatelet (GnPs) for Efficient Cyanotoxin Removal

The escalating frequency of Harmful Algal Blooms (HABs) poses a significant concern, not only impairing the operational capabilities of the United States Army, but also presenting serious health risks due to the release of toxins into water sources. These toxins can adversely affect both military personnel and the civilian populace, underscoring the critical need for state-of-the-art water purification technologies. These cyanotoxins are not effectively removed by traditional treatment methods, such filtration and UV disinfection. Graphene nanomaterials have recently emerged as a promising solution for efficient and sustainable removal of emerging contaminants from water due to their high surface area, cost effectiveness, and ability to adsorb many classes of contaminants. Addressing this challenge is crucial for ensuring the health and readiness of our forces as well as protecting the health and safety of communities and ecosystems impacted by these blooms.

In this study, we demonstrate the use of graphene nanoplatelets (GnPs) as an adsorptive nanomaterial for the enhanced removal of cyanotoxins, including microcystin-LR (MC-LR), Anatoxin-a (ATX), and saxitoxin (STX). Using batch adsorption experiments, we benchmarked GnPs against the commercially available granular activated carbon (GAC) to evaluate the efficiency of GnPs for adsorbing these contaminants from water.

Our updated experimental results have shown that the sp2 carbon network and pore characteristics (pore size and morphology) of graphene make GnPs a highly effective adsorbent for the removal of all three cyanotoxins from water. GnPs, characterized by their mesoporosity and robust π-π electron coupling with aromatic toxin substrates, exhibit unprecedented adsorption capacities—133, 8, and 15 times greater for MC-LR, ATX-a, and STX, respectively, compared to conventional GAC. Sorption kinetic studies proved graphene adsorbs 99% of MC-LR, ATA, and STX with pseudo-second-order kinetics in less than 30 minutes. We provided mechanistic insight on graphene’s enhanced ability to adsorb MC-LR by modeling the pore diffusion using intra-particle diffusion methods, calculating binding energies from DFT computations, and using NMR titrations to experimentally verify p-pi interactions between the aromatic ADDA chain of MC-LR and graphene’s sp2 carbon network.

To gain deeper insight into the adsorption mechanisms, we fit 12 isotherm models to our data, elucidating the π-π , electrostatic, and pore diffusion interactions. Furthermore, we validated our findings with real-world spiked samples, confirming that no unwanted effects on adsorption were observed. Additionally, we expanded our study to include the removal of emerging contaminants and micropollutants, such as acetaminophen, caffeine, DEET, and DEP, demonstrating the versatility and broad-spectrum efficacy of GnPs.

Our conclusions prove the potential of GnPs in transforming water purification strategies, offering robust, rapid, and high-capacity solutions essential for military applications where water quality is paramount. The application of GnPs not only enhances the safety and efficiency of military operations but also holds considerable promise for civilian use, addressing public health concerns and protecting ecosystems from the detrimental effects of cyanotoxins and micropollutants. This pioneering research aligns with the defense sector's aim to innovate for environmental protection, providing a scalable and effective approach to managing water quality in diverse and challenging environments.