Structural dependence of PFAS oxidation in a boron doped diamond-electrochemical system.

Driven by long-term persistence and adverse health impacts of legacy perfluorooctanoic acid (PFOA), production has shifted towards shorter chain analogs (C4, perfluorobutanoic acid (PFBA)) or fluorinated alternatives such as hexafluoropropylene oxide dimer acid (HFPO-DA, known as GenX) and 6:2 fluorotelomer carboxylic acid (6:2 FTCA). Yet, a thorough understanding of treatment processes for these alternatives is limited. Herein, we conducted a comprehensive study using an electrochemical approach with a boron doped diamond anode in Na2SO4 electrolyte for the remediation of PFOA common alternatives, i.e., PFBA, GenX, and 6:2 FTCA. The degradability, fluorine recovery, transformation pathway, and contributions from electro-synthesized radicals were investigated. The results indicated the significance of chain length and structure, with shorter chains being harder to break down (PFBA (65.6 ± 5.0%) < GenX (84.9 ± 3.3%) < PFOA (97.9 ± 0.1%) < 6:2 FTCA (99.4 ± 0.0%) within 120 min of electrolysis). The same by-products were observed during the oxidation of both low and high concentrations of parent PFAS (2 and 20 mg L-1), indicating that the fundamental mechanism of PFAS degradation remained consistent. Nevertheless, the ratio of these by-products to the parent PFAS concentration varied which primarily arises from the more rapid PFAS decomposition at lower dosages. For all experiments, the main mechanism of PFAS oxidation was initiated by direct electron transfer at the anode surface. Sulfate radical (SO4•-) also contributed to the oxidation of all PFAS, while hydroxyl radical (•OH) only played a role in the decomposition of 6:2 FTCA. Total fluorine recovery of PFBA, GenX, and 6:2 FTCA were 96.5%, 94.0%, and 76.4% within 240 min. The more complex transformation pathway of 6:2 FTCA could explain its lower fluorine recovery. Detailed decomposition pathways for each PFAS were also proposed through identifying the generated intermediates and fluorine recovery. The proposed pathways were also assessed using 19F Nuclear Magnetic Resonance (NMR) spectroscopy.

Particle Size Distributions for Cellulose Nanocrystals Measured by Transmission Electron Microscopy: An Interlaboratory Comparison.

Particle size is a key parameter that must be measured to ensure reproducible production of cellulose nanocrystals (CNCs) and to achieve reliable performance metrics for specific CNC applications. Nevertheless, size measurements for CNCs are challenging due to their broad size distribution, irregular rod-shaped particles, and propensity to aggregate and agglomerate. We report an interlaboratory comparison (ILC) that tests transmission electron microscopy (TEM) protocols for image acquisition and analysis. Samples of CNCs were prepared on TEM grids in a single laboratory, and detailed data acquisition and analysis protocols were provided to participants. CNCs were imaged and the size of individual particles was analyzed in 10 participating laboratories that represent a cross section of academic, industrial, and government laboratories with varying levels of experience with imaging CNCs. The data for each laboratory were fit to a skew normal distribution that accommodates the variability in central location and distribution width and asymmetries for the various datasets. Consensus values were obtained by modeling the variation between laboratories using a skew normal distribution. This approach gave consensus distributions with values for mean, standard deviation, and shape factor of 95.8, 38.2, and 6.3 nm for length and 7.7, 2.2, and 2.9 nm for width, respectively. Comparison of the degree of overlap between distributions for individual laboratories indicates that differences in imaging resolution contribute to the variation in measured widths. We conclude that the selection of individual CNCs for analysis and the variability in CNC agglomeration and staining are the main factors that lead to variations in measured length and width between laboratories.

Synthesis of a hexaalkoxybenzo[b]triphenylene mesogen.

The synthesis of the first mesogenic hexaalkoxybenzo[b]triphenylene derivative is reported; this compound exhibits a broad columnar liquid crystal phase at temperatures only slightly above room temperature.