2D Rhenium- and Niobium-Doped WSe2 Photoactive Cathodes in Photo-Enhanced Hybrid Zn-Ion Capacitors.

Designing a multifunctional device that combines solar energy conversion and energy storage is an appealing and promising approach for the next generation of green power and sustainable society. In this work, we fabricated a single-piece device incorporating undoped WSe2, Re- or Nb-doped WSe2 photocathode, and zinc foil anode system enabling a light-assisted rechargeable aqueous zinc metal cell. Comparison of structural, optical, and photoelectric characteristics of undoped and doped WSe2 has further confirmed that ionic insertion of donor metal (rhenium and niobium) plays an important role in enhancing photoelectrochemical energy storage properties. The electrochemical energy storage cell consisting of Re-doped WSe2 (as the photoactive cathode and zinc metal as anode) showed the best photodriven enhancement in the specific capacitance of around 45% due to efficient harvesting of visible light irradiation. The assembled device exhibited a loss of 20% of its initial specific capacitance after 1500 galvanostatic charge-discharge cycles at 50 mA g-1. The cell also provided a specific energy density of 574.21 mWh kg1- and a power density of 5906 mW kg1- at 15 mA g-1. Under otherwise similar conditions, the pristine WSe2 and Nb-doped WSe2 showed photoenhanced induced capacitance of 43% and 27% at 15 mA g-1 and supplied an energy density of 436.4 mWh kg1- and 202 mWh kg1-, respectively. As a result, a reasonable capacitance improvement obtained by the Re-WSe2 photoenhanced zinc-ion capacitor could provide a facile and constructive way to achieve a highly efficient and low-cost solar-electrochemical capacitor system.

Can ultrafast single-particle analysis using ICP-MS affect the detection limit? Case study: Silver nanoparticles.

Ultrafast measurement using dwell times below 100 µs down to 10 µs is a relatively new feature of single particle analysis using ICP-MS. In this study, we tested the effect of shorter dwell times on the particle size detection limit (Dd.l.). Decreasing dwell times below 100 µs did not lead to a statistically significant decrease in Dd.l. The particle size detection limit (quadrupole ICP-MS) of silver nanoparticles (NP) was estimated to be approx. 10-11 nm. Ag NPs close to Dd.l. were analysed. The 14-nm NPs showed low detection yield; only 5% of number of NPs estimated from transport efficiency was detected. The 20-nm NPs showed 44% detection yield; only in the case of 30-nm NPs did the number of detected NPs correspond to transport efficiency. It is obvious that near Dd.l. estimates of NP concentrations should be made with great caution.

Non-spectral interferences in single-particle ICP-MS analysis: An underestimated phenomenon.

This work demonstrates the effect of NaCl and carbon-related interferences on the analysis of arsenic and silver nanoparticles (NPs) by single-particle inductively coupled plasma mass spectrometry. Spectral interference caused by ArCl+ ions disturbing arsenic NPs analysis was eliminated using ammonia as reaction gas in a dynamic reaction cell of inductively coupled plasma mass spectrometer. In comparison to aqueous dispersions, non-spectral interferences caused by sodium lead to under-evaluation of arsenic and silver NPs diameter by about 7% and 15% at NaCl concentration of 450 mg L-1 and about 28% and 41% at NaCl concentration of 4500 mg L-1, respectively. As a consequence of lower transport efficiency, sodium non-spectral interferences also lead to about a 9% lower number of detected NPs for dispersions of both arsenic and silver NPs in 4500 mg L-1 NaCl. On the contrary, measurement of NPs in matrices containing methanol gives results where Ag and As NPs diameter is over-evaluated by about 3% and 15% at a methanol content of 1% (v/v) and about 6% and 20% at a methanol content of 2% (v/v), respectively, in comparison to aqueous dispersions. In addition, the organic carbon species behave as surfactants and increase the transport efficiency; this leads to an increase in the determined number concentration of NPs. In comparison to aqueous dispersions, this is over-evaluated by about 17% for Ag NPs and about 10% for As NPs at a methanol content of 5% (v/v).

Peak bordering for ultrafast single particle analysis using ICP-MS.

The characterisation of inorganic nanoparticles (NPs) by single particle inductively coupled plasma mass spectroscopy is possible only if the spectrometer is capable of measurement with high time-signal resolution. The latest generation of spectrometers allow for measurements with dwell times (dt) shorter than the 100 µs gold standard, i.e. as low as 10 µs. The statistical behaviours of signals obtained with dt values of 10, 20, 50, and 100 µs were tested for 40, 60, and 100 nm silver NPs. Very low measured signals (units of counts) led to the occurrence of zero signal values inside the peaks corresponding to individual NPs. The probability of the occurrence of a zero signal inside the peak increased with decreasing dt and decreasing NP size. The standard approach to the bordering of the beginning and end of the peak by one zero signal point failed here and lead to the false detection of a larger number of smaller peaks. For example, in the case of 40 nm NPs a quadruple number of peaks were detected for a dt value of 10 µs compared to the 100 µs dt value; the mean peak width at 10 µs dt was approximately 220 µs, while at 100 µs dt it was 550 µs. The results tended to be less distorted when dt was longer and the NP size was larger. Low dt values also led to a distortion of the peak area distribution. For 40 nm NPs and 10 µs, the most frequent peak area and the width of the peak area distribution were not evaluated due to a non-Gaussian course; 20 µs dt caused (compared to 100 µs) a decrease in the most frequent peak area by approximately 35% (33 counts for 100 µs dt vs. 22 counts for 20 µs dt) and an increase in the width of the peak area distribution by 70% (10 counts for 100 µs dt vs. 17 counts for 20 µs dt). Therefore, new approaches to bordering peaks were tested, which consisted of searching for an uninterrupted zero signal point sequence with a total length of 50 µs or 100 µs. Only the criterion of a 100 µs delay between the two adjacent peaks resulted in values of the number of detected peaks, the most frequent peak areas, and the width of peak area distribution virtually independent of dt.

Transfer of thallium from rape seed to rape oil is negligible and oil is fit for human consumption.

Rape and other Brassicaceae family plants can accumulate appreciable amounts of thallium from the soil. Because some species of this family are common crops utilised as food for direct consumption or raw materials for food production, thallium can enter the food chain. A useful method for thallium determination is inductively coupled plasma mass spectrometry. The limit of detection (0.2 pg ml(-1) Tl or 0.02 ng g(-1) Tl, taking in the account dilution during sample decomposition) found in the current study was very low, and the method can be used for ultra-trace analysis. Possible transfer of thallium from rape seed to the rape oil was investigated in two ways. The balance of thallium in rape seed meal (content 140-200 ng g(-1) Tl) and defatted rape seed meal indicated that thallium did not pass into the oil (p < 0.05). Moreover, the analyses of thallium in six kinds of edible rape seed oil and three kinds of margarines showed that the amount of thallium in rape seed oil is negligible.