26 Feb 2025

Demonstration of Photocatalytic Degradation of Per- and Polyfluoroalkyl Substances (PFAS) in Landfill Leachate Using 3D Printed TiO2 Composite Tiles

Abstract: Per- and polyfluoroalkyl substances (PFAS) are recalcitrant substances present globally in many landfill wastewater leachates and have potential ecological and human health risks. Conventional treatment technologies have shown limited efficacy for many PFAS due to the stable C–F bonds. Therefore, there is growing interest in applying advanced oxidation processes to decrease the aqueous concentrations in contaminated wastewater and mitigate risks. The goal of this study was to evaluate the photocatalytic performance of treating PFAS in landfill leachate using a novel photocatalyst composite. Treatment structures were fabricated using polylactic acid and compounded with TiO2, and 3D printed into tiles. A pilot-scale treatment system was designed to promote photocatalysis using 3D composite structures and UV irradiance intensity of 1.0 mW cm−2 following 24- and 36-h hydraulic retention times. Photocatalytic degradation was achieved for seven of the 11 PFAS evaluated in this study. Greater than 80% removal of PFOS, PFNA, PFDA, and PFOSAm was observed after 24 h of photocatalysis. These results indicate photocatalysis using TiO2 polymer composites can achieve beneficial levels of PFAS degradation. This study provides a proof-of-principle approach to inform the application of additive manufacturing of photocatalytic composites for use in the treatment of PFAS-contaminated wastewater.

28 Sep 2021

CuO Enhances the Photocatalytic Activity of Fe₂O₃ through Synergistic Reactive Oxygen Species Interactions

Abstract: Iron oxide (α-Fe2O3, hematite) colloids were synthesized under hydrothermal conditions and investigated as catalysts for the photodegradation of an organic dye under broad-spectrum illumination. To enhance photocatalytic performance, Fe2O3 was combined with other transition-metal oxide (TMO) colloids (e.g., CuO and ZnO), which are sensitive to different regions of the solar spectrum (far visible and ultraviolet, respectively), using a ternary blending approach for compositional mixtures. For a variety of ZnO/Fe2O3/CuO mole ratios, the pseudo-first-order rate constant for methyl orange degradation was at least double the sum of the individual Fe2O3 and CuO rate constants, indicating there is an underlying synergy governing the photocatalysis reaction with these combinations of TMOs. A full compositional study was carried out to map the interactions between the three TMOs. Additional experiments probed the identity and role of reactive oxygen species and elucidated the mechanism by which CuO enhanced Fe2O3 photodegradation while ZnO did not. The increased photocatalytic performance of Fe2O3 in the presence of CuO was associated with hydroxyl radical ROS, consistent with heterogeneous photo-Fenton mechanisms, which are not accessible by ZnO. These results imply that low-cost photocatalytic materials can be engineered for high performance under solar illumination by selective pairing of TMOs with compatible ROS.

24 Sep 2021

Leveraging Chemical Actinometry and Optical Radiometry to Reduce Uncertainty in Photochemical Research

Abstract: Subtle aspects of illumination sources and their characterization methods can introduce significant uncertainty into the data gathered from light-activated experiments, limiting their reproducibility and technology transition. Degradation kinetics of methyl orange (MO) and carbamazepine (CM) under illumination with TiO2 were used as a case study for investigating the role of incident photon flux on photocatalytic degradation rates. Valerophenone and ferrioxalate actinometry were paired with optical radiometry in three different illumination systems: xenon arc (XE), tungsten halogen (W-H), and UV fluorescent (UV-F). Degradation rate constants for MO and CM varied similarly among the three light systems as k W-H < kiv-F < kXE, implying the same relative photon flux emission by each light. However, the apparent relative photon flux emitted by the different lights varied depending on the light characterization method. This discrepancy is shown to be caused by the spectral distribution present in light emission profiles, as well as absorption behavior of chemical actinometers and optical sensors. Data and calculations for the determination of photon flux from chemical and calibrated optical light characterization is presented, allowing us to interpret photo-degradation rate constants as a function of incident photon flux. This approach enabled the derivation of a calibrated ‘rate-flux’ metric for evaluating and translating data from photocatalysis studies.