Structure-Function Relationship of Highly Reactive CuOx Clusters on Co3O4 for Selective Formaldehyde Sensing at Low Temperatures

Designing reactive surface clusters at the nanoscale on metal-oxide supports enables selective molecular interactions in low-temperature catalysis and chemical sensing. Yet, finding effective material combinations and identifying the reactive site remains challenging and an obstacle for rational catalyst/sensor design. Here, the low-temperature oxidation of formaldehyde with CuOx clusters on Co3 O4 nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame-aerosol technology, such CuOx clusters are finely dispersed, while some Cu ions are incorporated into the Co3 O4 lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X-ray absorption fine structure spectroscopy and temperature-programmed reduction in H2 identified Cu+ and Cu2+ species in these clusters as active sites. Remarkably, the Cu+ surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman's coefficient ρ = 0.89) and sensor response (0.96), rendering it a performance descriptor. At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts-per-billion (ppb) at 75°C, superior to state-of-the-art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to humidity and stable performance over 4 weeks are achieved, rendering such sensors promising as gas detectors in health monitoring, air and food quality control

Handheld Device for Selective Benzene Sensing over Toluene and Xylene

More than 1 million workers are exposed routinely to carcinogenic benzene, contained in various consumer products (e.g., gasoline, rubbers, and dyes) and released from combustion of organics (e.g., tobacco). Despite strict limits (e.g., 50 parts per billion (ppb) in the European Union), routine monitoring of benzene is rarely done since low-cost sensors lack accuracy. This work presents a compact, battery-driven device that detects benzene in gas mixtures with unprecedented selectivity (>200) over inorganics, ketones, aldehydes, alcohols, and even challenging toluene and xylene. This can be attributed to strong Lewis acid sites on a packed bed of catalytic WO3 nanoparticles that prescreen a chemoresistive Pd/SnO2 sensor. That way, benzene is detected down to 13 ppb with superior robustness to relative humidity (RH, 10–80%), fulfilling the strictest legal limits. As proof of concept, benzene is quantified in indoor air in good agreement (R2 ≥ 0.94) with mass spectrometry. This device is readily applicable for personal exposure assessment and can assist the implementation of low-emission zones for sustainable environments

Monitoring of selected skin- and breath-borne volatile organic compounds emitted from the human body using gas chromatography ion mobility spectrometry (GC-IMS)

ISSN:1873-376XISSN:1570-0232ISSN:1572-6495ISSN:1387-227

Metabolomic Plasticity in GM and Non-GM Potato Leaves in Response to Aphid Herbivory and Virus Infection

An important aspect of ecological safety of genetically modified (GM) plants is the evaluation of unintended effects on plant–insect interactions. These interactions are to a large extent influenced by the chemical composition of plants. This study uses NMR-based metabolomics to establish a baseline of chemical variation to which differences between a GM potato line and its parent cultivar are compared. The effects of leaf age, virus infection, and aphid herbivory on plant metabolomes were studied. The metabolome of the GM line differed from its parent only in young leaves of noninfected plants. This effect was small when compared to the baseline. Consistently, aphid performance on excised leaves was influenced by leaf age, while no difference in performance was found between GM and non-GM plants. The metabolomic baseline approach is concluded to be a useful tool in ecological safety assessment

Room-Temperature Catalyst Enables Selective Acetone Sensing

Catalytic packed bed filters ahead of gas sensors can drastically improve their selectivity, a key challenge in medical, food and environmental applications. Yet, such filters require high operation temperatures (usually some hundreds °C) impeding their integration into low-power (e.g., battery-driven) devices. Here, we reveal room-temperature catalytic filters that facilitate highly selective acetone sensing, a breath marker for body fat burn monitoring. Varying the Pt content between 0–10 mol% during flame spray pyrolysis resulted in Al2O3 nanoparticles decorated with Pt/PtOx clusters with predominantly 5–6 nm size, as revealed by X-ray diffraction and electron microscopy. Most importantly, Pt contents above 3 mol% removed up to 100 ppm methanol, isoprene and ethanol completely already at 40 °C and high relative humidity, while acetone was mostly preserved, as confirmed by mass spectrometry. When combined with an inexpensive, chemo-resistive sensor of flame-made Si/WO3, acetone was detected with high selectivity (≥225) over these interferants next to H2, CO, form-/acetaldehyde and 2-propanol. Such catalytic filters do not require additional heating anymore, and thus are attractive for integration into mobile health care devices to monitor, for instance, lifestyle changes in gyms, hospitals or at home

Zeolite membranes for highly selective formaldehyde sensors

ISSN:0925-400

Y-doped ZnO films for acetic acid sensing down to ppb at high humidity

Acetic acid is a potential breath marker for cystic fibrosis and gastroesophageal reflux. Also, it is a key tracer for aroma development in the food industry for chocolate and coffee processing. However, its selective detection down to relevant parts per billion (ppb) concentrations under realistic relative humidity (RH) is most challenging, especially with low-cost sensors. Here, highly porous Y-doped ZnO films for sensing acetic acid down to 10 ppb within 2 min at 90% RH are prepared by single-step flame-aerosol deposition with close control over their composition. X-ray diffraction and energy-dispersive X-ray spectroscopy reveal Y traces inside the ZnO wurtzite nanoparticles assuring small (below 25 nm) and thermally stable crystal sizes even upon annealing at 500 °C for 5 h in air. Separate Y2O3 nanoparticles are formed at elevated Y-contents. At an optimal Y-content of 2.5 mol% and sensing at 350 °C, remarkable selectivities of acetic acid over H2 (200), acetone (15), ethanol (5) and isoprene (3) are obtained. This is attributed to the high surface basicity of Y-doped ZnO featuring up to three orders of magnitude higher acetic acid selectivity than less basic SnO2 and WO3 sensors. Additionally, the influence of RH (10 - 90%) on acetic acid sensing is examined. This sensor is compact and inexpensive, thus promising for integration into hand-held and low-cost food processing or breath monitors.ISSN:0925-400

Structure‐Function Relationship of Highly Reactive CuOx Clusters on Co3O4 for Selective Formaldehyde Sensing at Low Temperatures

Abstract Designing reactive surface clusters at the nanoscale on metal‐oxide supports enables selective molecular interactions in low‐temperature catalysis and chemical sensing. Yet, finding effective material combinations and identifying the reactive site remains challenging and an obstacle for rational catalyst/sensor design. Here, the low‐temperature oxidation of formaldehyde with CuOx clusters on Co3O4 nanoparticles is demonstrated yielding an excellent sensor for this critical air pollutant. When fabricated by flame‐aerosol technology, such CuOx clusters are finely dispersed, while some Cu ions are incorporated into the Co3O4 lattice enhancing thermal stability. Importantly, infrared spectroscopy of adsorbed CO, near edge X‐ray absorption fine structure spectroscopy and temperature‐programmed reduction in H2 identified Cu+ and Cu2+ species in these clusters as active sites. Remarkably, the Cu+ surface concentration correlated with the apparent activation energy of formaldehyde oxidation (Spearman's coefficient ρ = 0.89) and sensor response (0.96), rendering it a performance descriptor. At optimal composition, such sensors detected even the lowest formaldehyde levels of 3 parts‐per‐billion (ppb) at 75°C, superior to state‐of‐the‐art sensors. Also, selectivity to other aldehydes, ketones, alcohols, and inorganic compounds, robustness to humidity and stable performance over 4 weeks are achieved, rendering such sensors promising as gas detectors in health monitoring, air and food quality control