Improving FAPbBr3 Perovskite Crystal Quality via Additive Engineering for High Voltage Solar Cell over 1.5 V.

Lead bromide-based perovskites are promising materials as the top cells of tandem solar cells and for application in various fields requiring high voltages owing to their wide band gaps and excellent environmental resistances. However, several factors, such as the formation of bulk and surface defects, impede the performances of corresponding devices, thereby limiting the efficiencies of these devices as single-junction devices. To reduce the number of defect sites, urea is added to the formamidinium lead bromide (FAPbBr3) perovskite material to increase its grain size. Nevertheless, urea undesirably reacts with lead(II) bromide (PbBr2) in the perovskite structure, creating unfavorable impurities in the device. To solve this problem, herein, in addition to urea, we introduced formamidinium chloride (FACl) into FAPbBr3. Owing to the synergistic effect of urea and FACl, the FAPbBr3 film quality effectively improved due to suppression of the generation of impurities and stabilization of film crystallinity. Consequently, the FAPbBr3 single-junction solar cell constructed using FACl and urea as additives demonstrated a power conversion efficiency of 9.6% and an open-circuit voltage of 1.516 V with negligible hysteresis. This study provides new insights into the use of additive engineering for overcoming the energy losses caused by defects in perovskite films.

Leaves are a Source of Biogenic Persistent Free Radicals.

Nonsenescent and senescent leaves of selected coniferous and broadleaf plants contained substantial levels of naturally occurring persistent free radicals (PFRs). These biogenic PFRs (BPFRs) were stable and persistent despite multiple wetting and drying cycles, implying that BPFRs can leach and sorb on soil particles. Results suggest that endogenous chemicals in plants and their transformation byproducts can stabilize unpaired electrons in leaves under ambient conditions. Thus, the vast amount and perpetual supply of leaf litter is an unaccounted natural source of BPFRs. If toxic, inhaling and accidentally ingesting fine soil dust and powder from degraded leaf litter may increase our environmental and health burdens to PFRs. We expect that this finding will generate more studies on natural sources of PFRs, establish their properties, and distinguish them from those formed from combustion and thermal processes.

A MEMS-enabled portable gas chromatography injection system for trace analysis.

Growing concerns about environmental conditions, public health, and disease diagnostics have led to the rapid development of portable sampling techniques to characterize trace-level volatile organic compounds (VOCs) from various sources. A MEMS-based micropreconcentrator (µPC) is one such approach that drastically reduces the size, weight, and power constraints offering greater sampling flexibility in many applications. However, the adoption of µPCs on a commercial scale is hindered by a lack of thermal desorption units (TDUs) that easily integrate µPCs with gas chromatography (GC) systems equipped with a flame ionization detector (FID) or a mass spectrometer (MS). Here, we report a highly versatile µPC-based, single-stage autosampler-injection unit for traditional, portable, and micro-GCs. The system uses µPCs packaged in 3D-printed swappable cartridges and is based on a highly modular interfacing architecture that allows easy-to-remove, gas-tight fluidic, and detachable electrical connections (FEMI). This study describes the FEMI architecture and demonstrates the FEMI-Autosampler (FEMI-AS) prototype (9.5 cm × 10 cm x 20 cm, ≈500 gms). The system was integrated with GC-FID, and the performance was investigated using synthetic gas samples and ambient air. The results were contrasted with the sorbent tube sampling technique using TD-GC-MS. FEMI-AS could generate sharp injection plugs (≈240 ms) and detect analytes with concentrations <15 ppb within 20 s and <100 ppt within 20 min of sampling time. With more than 30 detected trace-level compounds from ambient air, the demonstrated FEMI-AS, and the FEMI architecture significantly accelerate the adoption of µPCs on a broader scale.

Temperature dependence of the gas-particle partitioning of selected VOCs.

The gas-particle partitioning coefficients for volatile organic compounds (VOCs) are difficult to acquire because discriminating the small mass fraction of the VOCs in the aerosol particle relative to that in the gas phase is challenging. In this paper, we report the temperature dependence of the gas-particle partitioning coefficient (Kp) for n-butanol (n-BuOH) and trichloroethylene (TCE). Using the bench-scale system that we developed, we measured the Kp of surrogate VOCs, n-BuOH, and TCE onto inorganic (ammonium sulfate, Am Sulf) and organic (succinic acid, SA) aerosol particles at a fixed relative humidity (RH) of 35%. At this RH level and temperature range of 278.15-308.15 K, the ln Kp for TCE and n-BuOH partitioning on SA aerosol particles were -27.0 ± 0.70 to -27.9 ± 0.01 and -13.9 ± 0.03 to -17.4 ± 0.17. In contrast, the ln Kp for TCE and n-BuOH partitioning on Am Sulf aerosol particles ranged from -26.4 ± 0.70 to -27.4 ± 0.71 and -14.1 ± 0.03 to -17.1 ± 0.17, respectively. Results showed that TCE fitted well with the classic van't Hoff relationship. The enthalpy of desorption (ΔHdes) for TCE was constant over the temperature range of 278.15 K to 308.15 K, behaving similarly to 1,2-dichlorobenzene. At a similar temperature range, n-BuOH partitioning into both aerosol particles exhibited nonlinear temperature dependence. The minimum ratio of ΔHdes (Am Sulf:SA) for n-BuOH partitioning on each aerosol type was at ∼278.15 K. The magnitude of the entropy ΔSdes for all VOCs was <1 kJ mol-1.

A method to measure the partitioning coefficient of volatile organic compounds in nanoparticles.

The partitioning behavior of volatile organic compounds (VOCs) into nanoparticles is less studied compared to those of semivolatile organic compounds (SVOCs) because of the lower concentration of the VOCs that is expected to partition into particles. One challenge in measuring the accurate partition coefficient of VOCs is quantifying their low mass fraction that sorbed on nanoparticles and differentiating them from the high VOC concentrations present in the gas-phase. Systematically characterizing the partitioning coefficient at a specific environmental condition is also difficult when sampling in the field. During field sampling, thermal and non-thermal issues such as sampling artifacts and non-equilibrium conditions because of a dynamic environment often result in considerable variability in the measured partition coefficients. In this study, we developed a bench-scale system that can achieve precise control of the experimental condition (e.g., relative humidity, temperature, and particle composition) and allow us to measure the low concentration of 1,2-dichlorobenzene in the particles. A similar set up can be used to study the low mass fraction of other VOCs partitioning in nanoparticles. The detailed but uncomplicated system setup may assist other researchers that investigate the global fate and transport and health effects of VOCs.•A bench-scale system was built in the laboratory to study the gas-to-particle partitioning•Experimental conditions can be controlled and easily varied•The system enables the systematic study of a single environmental factor on the partitioning process.

Characterization of hazardous and odorous volatiles emitted from scented candles before lighting and when lit.

Scented candles are known to release various volatile organic compounds (VOCs) including both pleasant aromas and toxic components both before lighting (off) and when lit (on). In this study, we explored the compositional changes of volatiles from scented candles under various settings to simulate indoor use. Carbonyl compounds and other VOCs emitted from six different candle types were analyzed under 'on/off' conditions. The six candle types investigated were: (1) Clean cotton (CT), (2) Floral (FL), (3) Kiwi melon (KW), (4) Strawberry (SB), (5) Vanilla (VN), and (6) Plain (PL). Although a large number of chemicals were released both before lighting and when lit, their profiles were noticeably distinguishable. Before lighting, various esters (n = 30) showed the most dominant emissions. When lit, formaldehyde was found to have the highest emission concentration of 2098 ppb (SB), 1022 ppb (CT), and 925 ppb (PL). In most lit scented candles, there was a general tendency to show increased concentrations of low boiling point compounds. For some scented candle products, the emission of volatiles occurred strongly both before lighting and when lit. For instance, in terms of TVOC (ppbC), the highest concentrations were observed from the KW product with their values of 12,742 (on) and 2766 ppbC (off). As such, the results suggest that certain scented candle products should act as potent sources of VOC emission in indoor environment, regardless of conditions--whether being lit or not.

Odor and VOC emissions from pan frying of mackerel at three stages: raw, well-done, and charred.

Many classes of odorants and volatile organic compounds that are deleterious to our wellbeing can be emitted from diverse cooking activities. Once emitted, they can persist in our living space for varying durations. In this study, various volatile organic compounds released prior to and during the pan frying of fish (mackerel) were analyzed at three different cooking stages (stage 1 = raw (R), stage 2 = well-done (W), and stage 3 = overcooked/charred (O)). Generally, most volatile organic compounds recorded their highest concentration levels at stage 3 (O), e.g., 465 (trimethylamine) and 106 ppb (acetic acid). In contrast, at stage 2 (W), the lowest volatile organic compounds emissions were observed. The overall results of this study confirm that trimethylamine is identified as the strongest odorous compound, especially prior to cooking (stage 1 (R)) and during overcooking leading to charring (stage 3 (O)). As there is a paucity of research effort to measure odor intensities from pan frying of mackerel, this study will provide valuable information regarding the management of indoor air quality.

The reproducibility of indoor air pollution (IAP) measurement: a test case for the measurement of key air pollutants from the pan frying of fish samples.

To assess the robustness of various indoor air quality (IAQ) indices, we explored the possible role of reproducibility-induced variability in the measurements of different pollutants under similar sampling and emissions conditions. Polluted indoor conditions were generated by pan frying fish samples in a closed room. A total of 11 experiments were carried out to measure a list of key variables commonly used to represent indoor air pollution (IAP) indicators such as particulate matter (PM: PM1, PM2.5, PM10, and TSP) and a set of individual volatile organic compounds (VOCs) with some odor markers. The cooking activity conducted as part of our experiments was successful to consistently generate significant pollution levels (mean PM10: 7110 µg m(-3) and mean total VOC (TVOC): 1400 µg m(-3), resp.). Then, relative standard error (RSE) was computed to assess the reproducibility between different IAP paramters measured across the repeated experiments. If the results were evaluated by an arbitrary criterion of 10%, the patterns were divided into two data groups (e.g., <10% for benzene and some aldehydes and >10% for the remainders). Most noticeably, TVOC had the most repeatable results with a reproducibility (RSE) value of 3.2% (n = 11).