No abstract

Environmental context. Per-and poly-fluoroalkyl substances (PFASs) are contaminants of emerging concern, creating a need to develop efficient multi-functional adsorbents for improved remediation performance. By exploiting the versatility of graphene technology, we demonstrate that combining mineral and carbonaceous phases greatly increases and strengthens PFAS-binding to the adsorbent. The study highlights the benefits and potential applications of mixed adsorbents in PFAS-remediation.Abstract. As the degradation of perfluorooctanoic acid (PFOA) and related per-and poly-fluoroalkyl substances (PFASs) is energy-intensive, there is a need to develop in situ remediation strategies to manage PFAS-contamination. The sorption of PFOA by graphene oxide (GO), an iron-oxide-modified reduced-GO composite (FeG) and an activated-carbon(C)/clay/ alumina-based adsorbent, RemBind TM (RemB), are evaluated. Sorption by FeG and RemB (.90 %) is much greater than GO (60 %). While an increase in pH hinders PFOA-sorption by GO, owing to the increased repulsion of anionic PFOA, variations in pH and ionic strength do not significantly influence PFOA-sorption by FeG and RemB, which indicates that binding is predominantly controlled by non-electrostatic forces. Hydrophobic interactions are assumed at the graphene or C-surface for all adsorbents, with added ligand-exchange mechanisms involving the associated Fe-and Al-minerals in FeG and RemB, respectively. Desorption of adsorbed PFOA is greatest in methanol, compared to water, toluene, or hexane, which provides estimates of the binding strength and reversibility from an environmental-partitioning perspective; i.e. risk of remobilisation of bound PFOA owing to rainfall events is low, but the presence of polar organic solvents may increase leaching risk. Iron-mineral-functionalisation of GO enhances the amount of PFOA adsorbed (by 30 %) as well as the binding strength, which highlights the advantage of combining mineral and C-phases. Successful sorption of a range of PFASs from a contaminated-site water sample highlights the potential of using 'mixed' adsorbents like FeG and RemB in situ for PFAS-remediation, as they provide avenues for enhanced sorption through multiple mechanisms.

The unique physical and chemical properties of graphene-based nanomaterials (GNMs) have inspired a diverse range of scientific and industrial applications. The market value of GNMs is predicted to reach $US 1.3 billion by 2023. Common to many nanomaterials, an important and unresolved question is the environmental consequences of the increases in GNMs use. The current deficiencies in studies reporting ecotoxicology data for GNMs include differences in analytical methodologies for quantification, no standardized test guidelines, differences in morphology of GNMs, the lack of Chemical Abstract Service numbers, and the quality of the reported data. The assessment of potential adverse effects on aquatic organisms typically relies on guideline values based on species sensitivity distributions (SSDs) of toxicity data. We present preliminary water quality guideline values for graphene oxide NMs in freshwaters. Data include 10 species from 7 phyla (bacteria and fungi were not included). The most sensitive organism was found to be the freshwater shrimp Palaemon pandaliformis. The derived guideline values for 99, 95, 90, and 80% species protection were 350, 600, 830, and 1300 μg/L, respectively. These results will contribute to the regulatory derivations of future water quality guideline values for graphene-based NMs. Environ Toxicol Chem 2018;37:1340-1348. © 2018 SETAC.

Cadmium (Cd) and arsenate (As) are notorious environmental contaminants, and co‐contamination usually requires opposing treatment strategies due to their differing physico‐chemical properties. Developing adsorbents that can bind both contrasting contaminants simultaneously is desirable. Two prepared graphene materials, graphene oxide (GO) and iron‐oxide‐modified reduced‐GO (FeG), are evaluated for Cd‐ and As‐sorption, and performance is compared to a mixed‐mode commercial adsorbent. Negatively charged GO shows affinity toward cationic Cd, and positively charged FeG shows affinity toward anionic As. Sorption is pH dependent: Increase in pH‐promotes Cd‐sorption and retards As‐sorption. GO displays excellent Cd‐sorption even in acidic conditions. The maximum amounts adsorbed by GO and FeG are 782 μmol Cd g−1 and 408 μmol As g−1, respectively. Competition by calcium strongly suppresses Cd‐sorption, whereas competition by phosphate does not hinder As‐sorption. A mixture of GO and FeG demonstrates successful simultaneous sorption of Cd and As from co‐contaminated solutions, including a natural water sample, displaying greater sorption than the commercial adsorbent. Data highlight the potential application of graphene materials in effective mixed‐mode remediation of multiple contaminants (cations and anions).