Long-chain per-and polyfluoroalkyl substances (PFASs) are being replaced by short-chain PFASs and fluorinated alternatives. For ten legacy PFASs and seven recently discovered perfluoroalkyl ether carboxylic acids (PFECAs), we report (1) their occurrence in the Cape Fear River (CFR) watershed, (2) their fate in water treatment processes, and (3) their adsorbability on powdered activated carbon (PAC). In the headwater region of the CFR basin, PFECAs were not detected in raw water of a drinking water treatment plant (DWTP), but concentrations of legacy PFASs were high. The U.S. Environmental Protection Agency's lifetime health advisory level (70 ng/L) for perfluorooctanesulfonic acid and perfluorooctanoic acid (PFOA) was exceeded on 57 of 127 sampling days. In raw water of a DWTP downstream of a PFAS manufacturer, the mean concentration of perfluoro-2-propoxypropanoic acid (PFPrOPrA), a replacement for PFOA, was 631 ng/L (n = 37). Six other PFECAs were detected, with three exhibiting chromatographic peak areas up to 15 times that of PFPrOPrA. At this DWTP, PFECA removal by coagulation, ozonation, biofiltration, and disinfection was negligible. The adsorbability of PFASs on PAC increased with increasing chain length. Replacing one CF 2 group with an ether oxygen decreased the affinity of PFASs for PAC, while replacing additional CF 2 groups did not lead to further affinity changes.

We synthesize current understanding of the magnitudes and methods for assessing human and wildlife exposures to poly‐ and perfluoroalkyl substances (PFAS). Most human exposure assessments have focused on 2 to 5 legacy PFAS, and wildlife assessments are typically limited to targeted PFAS (up to ~30 substances). However, shifts in chemical production are occurring rapidly, and targeted methods for detecting PFAS have not kept pace with these changes. Total fluorine measurements complemented by suspect screening using high‐resolution mass spectrometry are thus emerging as essential tools for PFAS exposure assessment. Such methods enable researchers to better understand contributions from precursor compounds that degrade into terminal perfluoroalkyl acids. Available data suggest that diet is the major human exposure pathway for some PFAS, but there is large variability across populations and PFAS compounds. Additional data on total fluorine in exposure media and the fraction of unidentified organofluorine are needed. Drinking water has been established as the major exposure source in contaminated communities. As water supplies are remediated, for the general population, exposures from dust, personal care products, indoor environments, and other sources may be more important. A major challenge for exposure assessments is the lack of statistically representative population surveys. For wildlife, bioaccumulation processes differ substantially between PFAS and neutral lipophilic organic compounds, prompting a reevaluation of traditional bioaccumulation metrics. There is evidence that both phospholipids and proteins are important for the tissue partitioning and accumulation of PFAS. New mechanistic models for PFAS bioaccumulation are being developed that will assist in wildlife risk evaluations. Environ Toxicol Chem 2021;40:631–657. © 2020 SETAC

For several decades, a common processing aid in the production of fluoropolymers was the ammonium salt of perfluorooctanoic acid (PFOA). Because PFOA is persistent, bioaccumulative, and toxic, its production and use are being phased out in the United States. In 2009, the US Environmental Protection Agency stipulated conditions for the manufacture and commercial use of GenX, a PFOA replacement. While GenX is produced for commercial purposes, the acid form of GenX is also generated as a byproduct during the production of fluoromonomers. The discovery of high concentrations of GenX and related perfluoroalkyl ether acids (PFEAs) in the Cape Fear River and in finished drinking water of more than 200,000 North Carolina residents required quick action by researchers, regulators, public health officials, commercial laboratories, drinking water providers, and consulting engineers. Information about sources and toxicity of GenX as well as an analytical method for the detection of GenX and eight related PFEAs is presented. GenX/PFEA occurrence in water and GenX/PFEA removal by different drinking water treatment processes are also discussed.

Bimetallic gold-ruthenium microrods are propelled in opposite directions in water by ultrasound and by catalytic decomposition of hydrogen peroxide. This property was used to effect reversible swarming, to stall and reverse autonomous axial propulsion, and to study the chemically powered movement of acoustically levitated microrods.

The UV-sulfite reductive treatment using hydrated electrons (e aq − ) is a promising technology for destroying perfluorocarboxylates (PFCAs, C n F 2n+1 COO − ) in any chain length. However, the C−H bonds formed in the transformation products strengthen the residual C−F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, C n F 2n+1 −CH 2 CH 2 −COO − ) and sulfonates (FTSAs, C n F 2n+1 − CH 2 CH 2 −SO 3 − ) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidation (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixture of PFCAs. This process also cleaved 35−95% of C−F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent reduction (Red) with UV-sulfite achieved deep defluorination of the PFCA mixture for up to 90%. The following use of HO• to oxidize the H-rich residues led to the cleavage of the remaining C−F bonds. We examined the efficacy of integrated oxidative and reductive treatment of n = 1−8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, C n F 2n+1 −SO 3 − ), n = 1−8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quantitative overall defluorination (97−103%), except for n = 7,8 fluorotelomers (85−89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technology design and water sample analysis.

Metal particle size plays essential roles in metal-catalyzed heterogeneous reactions. Reducing the particle size from a few nanometers down to atomically dispersed single atoms alters both the morphology and electronic property of the metal enormously, thus greatly modulating its catalytic performance. Detailed investigation of the particle size effect as well as taking account of a metal single-atom catalyst (SAC), the frontier in heterogeneous catalysis, can provide a deeper insight into structure–activity relations and facilitate the rational design of advanced metal catalysts. However, such studies have been rarely reported. Herein, Cu single atoms and nanoparticles with different sizes of about 3.4, 7.3, and 9.3 nm were synthesized on an alumina support using atomic layer deposition. Comprehensive microscopic and spectroscopic characterization shows that the Cu single atoms remain very stable and have 1+ valence state after reduction at 300 °C in hydrogen. In semihydrogenation of acetylene in excess of ethylene, we show that a decrease in the Cu particle size reduces the activity considerably but gradually improves both the ethylene selectivity and durability. In particular, the Cu SAC exhibits the highest ethylene selectivity of 91% at the complete conversion along with excellent long-term stability for at least 40 h, in sharp contrast with the rapid deactivation on Cu nanoparticle catalysts. In situ thermogravimetry measurements further reveal that coke formation on Cu1 SAC is significantly suppressed by up to ∼89% compared to that on the 9.3 nm Cu nanoparticle catalysts. In brief, our findings demonstrate that SACs can be promising candidates for selective hydrogenation reactions in terms of high selectivity and high coking resistance.

We report room temperature broad range (ultraviolet to short-wavelength infrared) photodetectors made from few-layer α-In2Se3 nanosheets.

Two‐dimensional (2D) materials have been demonstrated as promising building blocks in future electronic and their mechanical properties are quite important for various applications. Due to their atomic thickness and planar nature, the investigation of the mechanical properties and related atomic mechanism are quite challenging. This review focuses on the recently developed in situ techniques based on scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) in characterization of the mechanical properties of 2D materials. In situ methods used for studying their elastic properties, fracture behavior, and surface/interface energy are introduced in detail. Specifically, the AFM indentation test and microelectromechanical systems (MEMS) device are generally used to investigate the elastic properties; the manipulator based methods show their flexibility in studying the fracture, adhesion, cleavage, and friction properties; atomic level fracture mechanism can be revealed with in situ high resolution TEM (HRTEM); the pressurized blister test and the buckle/wrinkle based methods are widely used to measure the surface/interface properties. Moreover, the influence of sample preparation process, defects and layer numbers to their mechanical properties are also discussed. Finally, the extensions of above methods to investigate the strain‐modulated physical properties of 2D materials are introduced.