Per- and polyfluoroalkyl substances (PFAS) have been detected in groundwater, surface water, and operation- or investigation-derived wastewater at hundreds of sites. In particular, the use of PFAS-laden aqueous film-forming foam (AFFF) has been a major environmental liability. As the pertinent environmental regulations are rapidly evolving, there is an urgent need for “more cost-effective and efficient technologies” to treat PFAS at impacted sites. This project was conducted in two phases, with a proof-of-concept tested in the first phase and further optimization of the technology conducted in the second phase.

In Phase I, preliminarily testing of an innovative “Concentrate-&-Destroy” strategy was conducted. The technology is based on a new class of adsorptive photocatalysts that can effectively adsorb (or trap) and then photodegrade (zap) perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). Three of the most promising adsorptive photocatalysts were preliminarily synthesized, characterized and tested under controlled conditions. While bench-scale data unveiled great promise of these materials for both adsorption and photocatalytic destruction of pre-sorbed PFOA and PFOS, there was a need to further polish the material preparation and optimize the subsequent photocatalytic degradation conditions for treating more DoD-relevant PFAS under DoD field conditions.

The overall goal of Phase II of this project is to further polish and optimize the technology for destruction of aqueous PFAS under relevant field conditions. The specific objectives of this follow-on research are to:

1. tailor the two modes of adsorptive photocatalysts (i.e., activated carbon supported/modified photocatalysts and carbon-modified photocatalysts) towards DoD applications,
2. test the new materials for enhanced adsorption and photocatalytic mineralization of 11 different PFAS under relevant field conditions,
3. enhance the material performances through additional physico-chemical means,
4. preliminarily demonstrate the technical feasibility and cost effectiveness, and
5. initiate technology transfer to DoD end users.

The following key hypotheses will be tested: 1) the carbon-photocatalyst composite materials can be further tailored to more selectively adsorb PFAS under relevant field conditions by enhancing concurrent hydrophobic, Lewis acid-base, and anion-π interactions; 2) the selective adsorption will mitigate potential interfering effects of co-solutes and dissolved organic matter on the subsequent photodegradation; and 3) the photodegradation/mineralization rates of pre-concentrated PFAS can be further improved through low-cost engineered means.

The ‘Trap-&-Zap’ technology is based on a new class of adsorptive photocatalysts that are prepared by integrating low-cost carbonaceous materials and metal-doped titanate nanotubes (Me/TNTs) or other photocatalysts. The composite materials act as both an adsorbent and a photocatalyst. As an adsorbent, the materials offer not only rapid adsorption rate, but also high adsorption selectivity towards PFAS, thanks to the concurrent hydrophobic interactions (between carbons and PFAS tail groups) and Lewis acid-base interactions (between metals and PFAS head groups). As a photocatalyst, the materials provide superior photocatalytic activity over conventional photocatalysts (e.g., TiO₂) owing to the carbon-mediated side-on adsorption mode, carbon-mediated electron transfer, and enhanced generation of reactive species.

During Phase II of the study, treating PFAS in groundwater will be tested. As such, groundwater from the Naval Air Station Joint Reserve Base Willow Grove will be used as a representative PFAS-impacted groundwater. While PFOS will be used as a probe compound in the material screening tests, 10 other relevant priority PFAS also will be targeted in assessing the overall material performances. The research objectives will be achieved by carrying out the following tasks:

1. tailor the adsorptive photocatalysts by polishing the synthesis recipes and conditions,
2. measure the adsorption rates and capacities through batch and column experiments under relevant water matrix conditions,
3. determine the photocatalytic degradation rates under UV or solar light,
4. enhance the material performances by optimizing the reaction conditions and by mitigating water matrix effects through engineered physico-chemical means,
5. demonstrate the technical feasibility through treatment of the site groundwater using an integrated adsorption/photodegradation system, and
6. carry out a preliminary cost analysis and promote the technology through a series of outreach activities.

Phase I Results

The key findings from Phase I are summarized as follows and are available in the Phase I Final Report:

• Three reusable adsorptive photocatalysts were prepared based on low-cost and well-accepted commercial materials (AC and TiO₂).
• As an adsorbent, the materials can effectively adsorb/concentrate PFAS from water through commonly used reactor configurations (fixed-bed column or batch reactor); as a photocatalyst, the materials can degrade PFOA and PFOS under UV or solar light.
• The carbon and metal modifications of TNTs or iron oxide not only facilitate selective adsorption of PFAS, but greatly enhance the photocatalytic degradation.
• The in situ efficient photodegradation of PFAS also regenerates the materials, allowing for repeated uses of the photocatalysts, avoiding costly chemical regeneration and generation of waste residuals.
• Dilute Corexit EC9500A can serve as an effective, safe, and low-cost extractant for removing PFOS and PFOA from field soil, and the “Concentrate-&-Destroy” technique can be applied to treat the spent dispersant solution so as to reuse the solution and destroy the PFAS.

The on-site “Concentrate-&-Destroy” technique represents a significant advancement of current practices (adsorption, ion exchange, landfill and incineration) for treating PFAS in investigation-derived waste or PFAS-impacted water and soil at large. Upon further testing and polishing (especially under field conditions), the technology will provide DoD remedial project managers with a more cost-effective technology for handling and disposal of these PFAS-impacted materials. (Anticipated Phase II Completion - 2026)

Rather R. A., T. Xu, R. N. Leary III, and D. Zhao. 2024. Aqueous and Solid Phase Photocatalytic Degradation of Perfluorooctane Sulfonate by Carbon- and Fe-modified Bismuth Oxychloride. Chemosphere, 346:140585. doi.org/10.1016/j.chemosphere.2023.140585.

Zhang M., X. Zhao, D. Zhao, T-Y Soong, and S. Tian. 2023. Poly-and perfluoroalkyl Substances (PFAS) in Landfills: Occurrence, Transformation and Treatment Waste Management, 155(1):162-178. doi.org/10.1016/j.wasman.2022.10.028.

Zhu Y., T. Xu, and D. Zhao. 2022. Metal-Doped Carbon-Supported/Modified Titanate Nanotubes for Perfluorooctane Sulfonate Degradation in Water: Effects of Preparation Conditions, Mechanisms, and Parameter Optimization. Science of the Total Environment, 853:158573. doi.org/10.1016/j.scitotenv.2022.158573.

Zhu Y., H. Ji, K. He, L. Blaney, T. Xu, and D. Zhao. 2022. Photocatalytic Degradation of GenX in Water Using a New Adsorptive Photocatalyst. Water Research, 220:118650. doi.org/10.1016/j.watres.2022.118650.

Ji H., J. Ni, D. Zhao, and W. Liu. 2022. Application of Titanate Nanotubes for Photocatalytic Decontamination in Water: Challenges and Prospects. ACS ES&T Engineering 2:1015−1038. doi.org/10.1021/acsestengg.1c00451.

J-M. A. Juve, F. Li, Y. Zhu, W. Liu, L. D. M. Ottosen, D. Zhao*, Z. Wei. 2022. Concentrate and Degrade PFOA with a Photo-Regenerable Composite of In-Doped TNTs@AC. Chemosphere, 300:134495. doi.org/10.1016/j.chemosphere.2022.134495.

Duan, J., H. Ji, T. Xu, F. Pan, X. Liu, W. Liu, and D. Zhao. 2021. Simultaneous Adsorption of Uranium(VI) and 2-Chlorophenol by Activated Carbon Fiber Supported/Modified Titanate Nanotubes (TNTs@ACF): Effectiveness and Synergistic Effects. Chemical Engineering Journal, 406:126752.

Li, F., J. Duan, S. Tian, H. Ji, Y. Zhu, Z. Wei, and D. Zhao. 2020. Short-chain Per- and Polyfluoroalkyl Substances in Aquatic Systems:  Occurrence, Impacts and Treatment. Chemical Engineering Journal, 380(1):122506.

Li, F., W. Liu, X. Cheng, M. Boersma, Z. Wei, K. He, L. Blaney, and D. Zhao. 2020. A Concentrate-&-destroy Technique for Degradation of Perfluorooctanoic Acid in Water using a New Adsorptive Photocatalyst. Water Research, 185:116219.

Wei, Z., T. Xu, and D. Zhao. 2019. Treatment of Per- and Polyfluoroalkyl Substances in Landfill Leachate:  Status, Chemistry and Prospects. Environmental Science: Water Research & Technology, 5:1814–1835.

Xu, J., B. Xu, D. Zhao. 2019. Enhanced Adsorption of Perfluorooctanoic Acid (PFOA) from Water by Granular Activated Carbon Supported Magnetite Nanoparticles. Science of The Total Environment, 723:137757. (The journal’s 2019 Best Paper of the Year)

Xu, T., Y. Zhu, J. Duan, Y. Xia, T. Tong, L. Zhang, and D. Zhao. 2020. Enhanced Photocatalytic Degradation of Perfluorooctanoic Acid using Carbon-modified Bismuth Phosphate Composite:  Effectiveness, Material Synergy and Roles of Carbon. Chemical Engineering Journal, 395:124991.

Zu, T., H. Ji, Y. Gu, T. Tong, Y. Xia, L. Zhang, and D. Zhao. 2019. Enhanced Adsorption and Photo-degradation of Perfluorooctanoic Acid in Water using Iron Oxide/Carbon Sphere Composite. Chemical Engineering Journal, 388:124230.

Theses and Dissertations

Li, F. 2019. A New Class of Adsorptive Photocatalysts for Enhanced Adsorption and Destruction of 4-Chlorophenol and Perfluorooctanoic Acid (Ph.D. Dissertation). Auburn University.

Patents

Zhao, D. and W. Liu. 2017. Novel High-capacity and Photo-regenerable Materials for Efficient Removal of Polycyclic Aromatic Hydrocarbons and PFAS from Water. U.S. Patent 62/452,648.

D. Zhao and W. Liu. 2024. Photo-Regenerable Materials for Removing Contaminants from Water. U.S. Patent US12102980.