Collaborative Research: Transformation, Interaction and Toxicity of Emerging 2D Nanomaterials Free-standing and Embedded onto Nanocomposite Membranes for PFAS Degradation

The purpose of this research is to develop and validate environmentally safe 2D nanomaterial-based holistic approach aimed at development of nanocomposite catalytic membranes for degradation of persistent organic pollutants, such as per- and polyfluorinated substances (PFAS), in drinking water. Non-carbon-based novel 2D nanomaterials with different electronic and physicochemical properties, non-metallic phosphorene and metalloid hexagonal boron nitride (h-BN), have shown promising results for degradation of PFAS. However, there is a knowledge gap on how these properties affect transformation, stability, and toxicity of the 2D nanomaterials in free-standing form and after embedding them into nanocomposite membranes. For effective utilization of such nanocomposite membranes for PFAS degradation, it is critical to examine mechanisms of interaction with PFAS, identify PFAS breakdown products and verify that degradation products are less toxic than initial PFAS. The overarching goal of this project is to develop novel phosphorene- and h-BN-based nanocomposite membranes with high efficiency for removal and degradation of PFAS into compounds with minimal toxicity. Intellectual Merit In preliminary studies, we demonstrated the successful synthesis of nanocomposite membranes made of SPEEK and phosphorene. The investigation of leaching of phosphorene from these membranes showed minimal release in the neutral and acidic with some increase under basic conditions. The toxicity testing of phosphorene in free-standing and membrane forms in a powerful in-vivo toxicity model, Caenorhabditis elegans, identified toxicity threshold for phosphorene concentration, with permeates being non-toxic. However, we examined toxicity only on less sensitive standard endpoints (mortality and reproduction), while more sensitive endpoints can show adverse effects at much lower concentrations. For PFAS studies, the phosphorene membranes achieved nearly complete rejection of PFOA at 99%, and the flux recovery after reverse-flow filtration was 84%, indicating that PFOA did not significantly adsorb to the membranes. After filtration, the membranes were subjected to UV photolysis that removed and/or destroyed 98.4% of the adsorbed PFOA. However, catalysis mechanisms and PFOA breakdown products were not identified. The preliminary data on toxicity of the breakdown products showed significant decrease in toxicity. Broader Impacts Reactive removal of pollutants, for example through catalysis, is often the optimal treatment choice. The novel 2D nanocomposite membranes offer unique synergistic benefits by combining separation with reactions for catalytic degradation of PFAS. This proposed research will advance knowledge and understanding of differing phosphorene and h-Bn properties and their effect on degradation, behavior, toxicities and catalytic abilities of the nanomaterials in unbound form and after their immobilization into membrane structures. Furthermore, this study aims to investigate the ability of phosphorene and h-BN to breakdown PFAS into degradation products with lower toxicity. With regards to education and training, this project will strengthen the ongoing outreach activities of the PIs, who have tracks record of integrating research and education, mentoring undergraduate and graduate students, reaching out to community organizations, and engaging underrepresented students in STEM fields. Technology dissemination to end users will be accomplished through peer-reviewed manuscripts and abstracts/proceedings to relevant conferences. Underrepresented groups will be engaged and educated about water quality issues through the numerous activities.