Abstract
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.
Highlights
Increased acetic acid concentrations from 48 ppb to 85 [1] and 170 ppb [2] are in the breath of people suffering from gastro esophageal reflux and cystic fibrosis, respectively
Crystal phase composition was determined by X-ray diffraction (XRD) on collected powders with a Bruker AXS D8 Advance diffrac tometer operated at 40 kV and 30 mA
STEM combined with energydispersive X-ray spectroscopy (EDXS) was performed on a Talos F200X microscope (ThermoFisher) with a high brightness field emission gun operated at an acceleration potential of 200 kV
Summary
Increased acetic acid concentrations from 48 ppb (healthy) to 85 [1] and 170 ppb [2] are in the breath of people suffering from gastro esophageal reflux and cystic fibrosis, respectively. FSP-made ZnO particles can be deposited in a single step onto sensor substrates forming porous films with outstanding LODs at humid conditions, as shown with isoprene (e.g., 5 ppb at 90% RH) [30]. We prepare such highly porous and thermally-stable nano structured Y-doped ZnO sensing films for ppb-level acetic acid sensing at variable RH. The selective sensing of acetic acid down to ppb and the influence of RH (0 – 90%) were demonstrated and benchmarked against state-of-the-art chemoresistive sensors (including FSP-made SnO2 and WO3)
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