Short-term storability of volatile organic compounds in bag sampling systems under ambient conditions.

Although bag sampling is a common quantification tool for volatile organic compounds (VOCs), it can serve as a major source of experimental bias, when storing even over a short duration (<24 h). To learn more about the reliability of the bag sampling method, the temporal stability of 27 VOCs (classified into five groups (i.e., aldehydes, nonpolar aromatic hydrocarbons, aliphatic carboxylic acids, phenol and methylphenols, and miscellaneous odorants) is assessed using poly-ester aluminum (PEA) bags at five intervals over a day (0.17, 1, 2, 6, and 24 h). In terms of reproducibility (e.g., relative standard error [RSEt, %]), nonpolar aromatic hydrocarbons (BTXS) exhibit the highest consistency (e.g., average RSE <1.55%). Considerable loss of VOCs is observed in the preparation of gaseous standards from a liquid phase standard when assessed by gas/liquid (G/L) ratio. Further, VOCs with lower molecular weights (e.g., propionaldehyde: 77%-94.4%) and branched molecular structures (e.g., isovaleraldehyde: 67.2%-78.9%) tend to have high G/L ratio (e.g., relative to valeraldehyde: 55.1%-66%). The overall relative recovery (RR; %) values of VOCs indicate an exponential decrease over 24 h. BTXS maintain fairly good RR values (above 94.3% at all intervals), possibly due to the nonpolar structure with uniform distribution of π electrons. In contrast, indole and skatole show the least preservation after 24 h (e.g., RR4 values of 10.9% and 24.6%, respectively) due to their highly reactive characteristics. The storability of VOCs appears to be affected by a number of variables (e.g., molecular weight, presence of ethyl branch, and time: e.g., R2 > 0.9). The results of this study offer valuable guidelines for the accurate quantification of VOC levels in air.

Fabrication of Ternary Titanium Dioxide/Polypyrrole/Phosphorene Nanocomposite for Supercapacitor Electrode Applications.

In this paper, we report a titanium dioxide/polypyrrole/phosphorene (TiO2/PPy/phosphorene) nanocomposite as an active material for supercapacitor electrodes. Black phosphorus (BP) was fabricated by ball milling to induce a phase transition from red phosphorus, and urea-functionalized phosphorene (urea-FP) was obtained by urea-assisted ball milling of BP, followed by sonication. TiO2/PPy/phosphorene nanocomposites can be prepared via chemical oxidative polymerization, which has the advantage of mass production for a one-pot synthesis. The specific capacitance of the ternary nanocomposite was 502.6 F g-1, which was higher than those of the phosphorene/PPy (286.25 F g-1) and TiO2/PPy (150 F g-1) nanocomposites. The PPy fully wrapped around the urea-FP substrate provides an electron transport pathway, resulting in the enhanced electrical conductivity of phosphorene. Furthermore, the assistance of anatase TiO2 nanoparticles enhanced the structural stability and also improved the specific capacitance of the phosphorene. To the best of our knowledge, this is the first report on the potential of phosphorene hybridized with conducting polymers and metal oxides for practical supercapacitor applications.

Highly Conductive and Long-Term Stable Phosphorene-Based Nanocomposite for Radio-Frequency Antenna Application.

In this study, an omnidirectional and high-performance free-standing monopole patch radio-frequency antenna was fabricated using a urea-functionalized phosphorene/TiO2/polypyrrole (UTP) nanocomposite. The UTP nanocomposite antenna was fabricated via ball milling of urea-functionalized phosphorene, chemical oxidative polymerization of the UTP nanocomposite, and mechanical pelletizing of the composite. Based on experiments, the proposed UTP nanocomposite-based antenna exhibited long-term stability in terms of electrical conductivity. After 12 weeks, a slight change in surface resistance was observed. The proposed antenna exhibited high radiation efficiency (78.2%) and low return loss (-36.6 dB). The results of this study suggest the potential of UTP nanocomposite antennas for applications in 5G technology.

Influence of Polypyrrole on Phosphorus- and TiO2-Based Anode Nanomaterials for Li-Ion Batteries.

Phosphorus (P) and TiO2 have been extensively studied as anode materials for lithium-ion batteries (LIBs) due to their high specific capacities. However, P is limited by low electrical conductivity and significant volume changes during charge and discharge cycles, while TiO2 is hindered by low electrical conductivity and slow Li-ion diffusion. To address these issues, we synthesized organic-inorganic hybrid anode materials of P-polypyrrole (PPy) and TiO2-PPy, through in situ polymerization of pyrrole monomer in the presence of the nanoscale inorganic materials. These hybrid anode materials showed higher cycling stability and capacity compared to pure P and TiO2. The enhancements are attributed to the electrical conductivity and flexibility of PPy polymers, which improve the conductivity of the anode materials and effectively buffer volume changes to sustain structural integrity during the charge and discharge processes. Additionally, PPy can undergo polymerization to form multi-component composites for anode materials. In this study, we successfully synthesized a ternary composite anode material, P-TiO2-PPy, achieving a capacity of up to 1763 mAh/g over 1000 cycles.

The feasibility and temporal storability of gas phase standards of volatile organic compounds prepared through liquid phase vaporization in polyester aluminum bags at room temperature.

Currently, the presence of many classes of volatile organic compounds (VOCs) in indoor air is well recognized. There is an impetus to accurately quantify airborne VOCs for the proper assessment of their human health risks. VOC standards prepared in a solvent are often vaporized in N2 gas-filled sampling bags for external calibration as the use of grab sampling bags is a common practice for the collection of real ambient air samples. Such practices can nontheless be subject to many sources of biases in their calibration (e.g., VOC chemical reaction with the solvent, adsorption on the bag interior surface, or leakage). The main goal of this work is to measure the temporal stability of 11 VOC targets (benzene, toluene, o-xylene, styrene, propionaldehyde, n-butyraldehyde, isovaleraldehyde, valeraldehyde, acrylonitrile, isoprene, and methyl ethyl ketone) selected in this research over 24 h which started 10 min after the injection and vaporization of liquid-phase standards (all prepared in methanol solvent) into polyester aluminum (PEA) bags containing 1 atm N2. Although all tested VOCs showed gradual decreases of their concentrations (e.g., >17% in 24 h), the aromatic hydrocarbon VOCs (namely BTXS) yielded the best relative recoveries (e.g., decreases of 11%-30% in 24 h) and relative errors (e.g., relative standard error (RSE) = 2.14-3.59%) in 5 replicate tests. A good linear relationship was established between the 24 h VOC relative recovery and molecular weight (R2 > 0.81). The results of this study offers valuable clues to properly reduce the bias in the calibration of gas-phase VOC standards when calibrating the system through the vaporization of liquid-phase VOC standards prepared in a solvent.