The combined effects of sampling parameters on the sorbent tube sampling of phthalates in air

Zinc-doped titanium oxynitride as a high-performance adsorbent for formaldehyde in air

The potential utility of titanium oxynitride doped with 5% zinc (ZnTON) has been investigated as an adsorbent for the treatment of gaseous formaldehyde (FA) using a fixed-bed adsorption system. The adsorption capacity of ZnTON, when estimated at 10%/100% breakthrough (BT) levels from a dry feed gas consisting of 10 Pa FA, was far superior to two reference materials (i.e., commercial P25-TiO₂ and activated carbon (AC)) by factors of 1.7/1.3 and 10/2.5, respectively. The adsorption capacity of ZnTON increased with the increase in the initial feeding concentration of FA (5-12.5 Pa), while decreasing with the rising temperature (25-100 ^oC). An increase in moisture level (0-100% relative humidity) also led to 5.4- and 2.5-fold reductions in adsorption capacity of ZnTON at 10% and 100% BT levels, respectively. Thermodynamically, the adsorption of FA onto ZnTON is an exothermic (ΔH^o = - 9.69 kJ.mol^-1) to be feasible in nature based on physisorption mechanism. Further, the adsorption of FA onto ZnTON was governed by surface interactions and monolayer surface coverage (Van der Waal's force/electrostatic attraction), as it obeyed the Langmuir isotherm and pseudo-second-order kinetic models. Regeneration tests indicated a positive effect of moisture on FA desorption and durability of ZnTON (i.e., over three adsorption-desorption cycles). This study offers valuable mechanistic insights into the synthesis of an advanced adsorbent for the efficient removal of hazardous volatile organic compounds under near-ambient conditions.

Characterizing the external exposome using passive samplers-comparative assessment of chemical exposures using different wearable form factors

BACKGROUND

Organic contaminants are released into the air from building materials/furnishings, personal care, and household products. Wearable passive samplers have emerged as tools to characterize personal chemical exposures. The optimal placement of these samplers on an individual to best capture airborne exposures has yet to be evaluated.

OBJECTIVE

To compare personal exposure to airborne contaminants detected using wearable passive air samplers placed at different positions on the body.

METHODS

Participants (n = 32) simultaneously wore four passive Fresh Air samplers, on their head, chest, wrist, and foot for 24 hours. Exposure to 56 airborne organic contaminants was evaluated using thermal desorption gas chromatography high resolution mass spectrometry with a targeted data analysis approach.

RESULTS

Distinct exposure patterns were detected by samplers positioned on different parts of the body. Chest and wrist samplers were the most similar with correlations identified for 20% of chemical exposures (Spearman's Rho > 0.8, p < 0.05). In contrast, the greatest differences were found for head and foot samplers with the weakest correlations across evaluated exposures (8% compounds, Spearman's Rho > 0.8, p < 0.05).

SIGNIFICANCE

The placement of wearable passive air samplers influences the exposures captured and should be considered in future exposure and epidemiological studies.

IMPACT STATEMENT

Traditional approaches for assessing personal exposure to airborne contaminants with active samplers presents challenges due to their cost, size, and weight. Wearable passive samplers have recently emerged as a non-invasive, lower cost tool for measuring environmental exposures. While these samplers can be worn on different parts of the body, their position can influence the type of exposure that is captured. This study comprehensively evaluates the exposure to airborne chemical contaminants measured at different passive sampler positions worn on the head, chest, wrist, and foot. Findings provide guidance on sampler placement based on chemicals and emission sources of interest.

Validation of two contrasting capturing mechanisms for gaseous formaldehyde between two different types of strong metal-organic framework adsorbents

In this research, the adsorption behavior of formaldehyde (FA) onto two types of metal-organic frameworks (MOFs: MOF-199 [M199] and UiO-66-NH₂ [U6N]) is investigated against changes in the key process variables (e.g., FA partial pressure (0.5-10 Pa), temperature (30-120 °C), and relative humidity (RH: 0%, 50%, and 100%)). The results revealed that the FA adsorption behavior onto both MOFs is exothermic in nature. Besides, their relative dominance for FA uptake varies interactively with the changes in RH and FA partial pressure levels. As the FA levels increase in dry conditions, their breakthrough volumes (BTV (100% BT)) exhibit contrasting trends: The values of U6N decreased noticeably from 5232 and 3792 L·atm·g^-1, while those of M199 increased from 4152 to 5772 L·atm·g^-1. The superiority of U6N over M199 in the lower FA level (at<5 Pa) is supported by the Lewis acid-base interactions with amine groups (U6N) in line with kinetic/isotherm studies. Such superiority is also persistent at higher (10 Pa) FA level under all humid conditions in line with its higher moisture stability. However, in dry conditions, the reversal of relative dominance in which M199 exhibits enhanced efficacy for 10 Pa FA uptake (relative to U6N) should reflect its breathing effects with the potent role of pore-diffusion mechanism. This study offers valuable insights into the construction of tunable adsorbents with enhanced adsorptivity toward key targets.

Adsorption properties of advanced functional materials against gaseous formaldehyde

Intense efforts have been made to eliminate toxic volatile organic compounds (VOCs) in indoor environments, especially formaldehyde (FA). In this study, the removal performances of gaseous FA using two metal-organic frameworks, MOF-5 and UiO-66-NH₂, and two covalent-organic polymers, CBAP-1 (EDA) and CBAP-1 (DETA), along with activated carbon as a conventional reference material, were evaluated. To assess the removal capacity of FA under near-ambient conditions, a series of adsorption experiments were conducted at its concentrations/partial pressures of both low (0.1-0.5 ppm/0.01-0.05 Pa) and high ranges (5-25 ppm/0.5-2.5 Pa). Among all tested materials at the high-pressure region ㅐ (e.g., at 2.5 ppm FA), a maximum adsorption capacity of 69.7 mg g^-1 was recorded by UiO-66-NH₂. Moreover, UiO-66-NH₂ also displayed the best 10% breakthrough volume (BTV10) of 534 L g^-1 (0.5 ppm FA) to 2963 L g^-1 (0.1 ppm FA). In contrast, at the high concentration test (at 5, 10, and 25 ppm FA), the maximum BTV10 values were observed as: 137 (UiO-66-NH₂), 144 (CBAP-1 (DETA)), and 36.8 L g^-1 (CBAP-1 (EDA)), respectively. The Langmuir isotherm model was observed to be a better fit of the adsorption data than the Freundlich model under most of the tested conditions. The superiority of UiO-66-NH₂ was attributed to the van der Waals interactions between the linkers (framework) and the hydrocarbon "tail" (FA) coupled with interactions between its open metal sites and the FA carbonyl groups. This study demonstrated the good potential of these advanced functional materials toward the practical removal of gaseous FA in indoor environments.

Characterization and flux assessment of airborne phthalates released from polyvinyl chloride consumer goods

The concentrations and fluxes of airborne phthalates were measured from five types of polyvinyl chloride (PVC) consumer products (vinyl flooring, wallcovering, child's toy, yoga mat, and edge protector) using a small chamber (impinger) system. Airborne phthalates released from each of those PVC samples were collected using sorbent (Tenax TA) tubes at three temperature control intervals (0, 3, and 6 h) under varying temperature conditions (25, 40, and 90 °C). A total of 11 phthalate compounds were quantified in the five PVC products examined in this study. To facilitate the comparison of phthalate emissions among PVC samples, their flux values were defined for total phthalates by summing the average fluxes of all 11 phthalates generated during the control period of 6 h. The highest flux values were seen in the edge protector sample at all temperatures (0.40 (25 °C), 9.65 (40 °C), and 75.7 μg m^-2 h^-1 (90 °C)) of which emission was dominated by dibutyl isophthalate. In contrast, the lowest fluxes were found in wallcovering (0.01 (25 °C) and 0.05 μg m^-2 h^-1 (40 °C)) and child's toy (0.23 μg m^-2 h^-1 (90 °C)) at each temperature level. The information regarding phthalate composition and emission patterns varied dynamically with type of PVC sample, controlled temperature, and duration of control.