Highly efficient preconcentration using anodically generated shrinking gas bubbles for per- and polyfluoroalkyl substances (PFAS) detection.

Here we report a highly efficient PFAS preconcentration method that uses anodically generated shrinking gas bubbles to preconcentrate PFAS via aerosol formation, achieving ~ 1400-fold enrichment of PFOS and PFOA-the two most common PFAS-in 20 min. This new method improves the enrichment factor by 15 to 105% relative to the previous method that uses cathodically generated H2 bubbles. The shrinking gas bubbles are in situ electrogenerated by oxidizing water in an NH4HCO3 solution. H+ produced by water oxidation reacts with HCO3- to generate CO2 gas, forming gas bubbles containing a mixture of O2 and CO2. Due to the high solubility of CO2 in aqueous solutions, the CO2/O2 bubbles start shrinking when they leave the electrode surface region. A mechanistic study reveals two reasons for the improvement: (1) shrinking bubbles increase the enrichment rate, and (2) the attractive interactions between the positively charged anode and negatively charged PFAS provide high enrichment at zero bubble path length. Based on this preconcentration method, we demonstrate the detection of ≥ 70 ng/L PFOA and PFOS in water in ~ 20 min by coupling it with our bubble-nucleation-based detection method, fulfilling the need of the US Environmental Protection Agency.

Harnessing bubble behaviors for developing new analytical strategies.

Gas bubbles are easily accessible and offer many unique characteristic properties of a gas/liquid two-phase system for developing new analytical methods. In this minireview, we discuss the newly developed analytical strategies that harness the behaviors of bubbles. Recent advancements include the utilization of the gas/liquid interfacial activity of bubbles for detection and preconcentration of surface-active compounds; the employment of the gas phase properties of bubbles for acoustic imaging and detection, microfluidic analysis, electrochemical sensing, and emission spectroscopy; and the application of the mass transport behaviors at the gas/liquid interface in gas sensing, biosensing, and nanofluidics. These studies have demonstrated the versatility of gas bubbles as a platform for developing new analytical strategies.

Stabilizing Hard Magnetic SmCo5 Nanoparticles by N-Doped Graphitic Carbon Layer.

We report a chemical method to synthesize size-controllable SmCo5 nanoparticles (NPs) and to stabilize the NPs against air oxidation by coating a layer of N-doped graphitic carbon (NGC). First 10 nm CoO and 5 nm Sm2O3 NPs were synthesized and aggregated in reverse micelles of oleylamine to form SmCo-oxide NPs with a controlled size (110, 150, or 200 nm). The SmCo-O NPs were then coated with polydopamine and thermally annealed to form SmCo-O/NGC NPs, which were further embedded in CaO matrix and reduced with Ca at 850 °C to give SmCo5/NGC NPs of 80, 120, or 180 nm, respectively. The 10 nm NGC coating efficiently stabilized the SmCo5 NPs against air oxidation at room temperature or at 100 °C. The magnetization value of the 180 nm SmCo5/NGC NPs was stabilized at 86.1 emu/g 5 days after air exposure at room temperature and dropped only 1.7% 48 h after air exposure at 100 °C. The stable SmCo5/NGC NPs were aligned magnetically in an epoxy resin, showing a square-like hysteresis behavior with their Hc reaching 51.1 kOe at 150 K and 21.9 kOe at 330 K and their Mr stabilized at around 84.8 emu/g. Our study demonstrates a new strategy for synthesizing and stabilizing SmCo5 NPs for high-performance nanomagnet applications in a broad temperature range.

Design of the offline test electronics for the nozzle system of proton therapy.

A set of nozzle equipment for proton therapy is currently under development at China Institute of Atomic Energy (CIAE). To facilitate the off-line commissioning of the whole equipment, a set of ionization chamber signal generation system, known as the test electronics, was designed. The results showed that the system can simulate the beam position, beam fluence (which exhibits a positive correlation with the dose), and other related analog signals generated by the proton beam when it traverses the ionization chamber. Moreover, the accuracy of the simulated beam position is within ± 0.33 mm, and the accuracy of the simulated beam fluence signal is within ± 1%. The test electronics can output analog signals representing environmental parameters. The test electronics meets the design requirements, which can be used for the commissioning of the nozzle system as well as the treatment control system without the presence of the proton beam.

Experimental study for 15-20 mA dc H- multicusp source.

Recently, a new H- source and test stand was developed at CIAE. The design of this new source is based on the experience on our previous 10-15 mA H(-) ion source and the source at TRIUMF. Major efforts include the study of the virtual filter magnetic field, confining magnetic field, filament shape and location, the vacuum improvement on the extracting area, the extraction optics, new control and interlock system of the power supplies. More than 15 mA of H-beam was obtained for 36 h with stability of +/-0.5%. The normalized emittance of 0.48pi mm mrad (4 rms normalized emittance) were measured with approximately 8 mA dc beam. Further experimental studies are proceeding in an effort to reach 20 mA with reasonable emittance at this moment. More study plans are conducted, e.g., building a longer source body and using cesium injection to get better emittance, which will be presented as a separate paper at this conference.