Highlights
- Zinc oxide nanospheres, nanobushes, and pearl-chain nanowires were self-assembled from PVA/zinc acetate nanofibers via electrospinning, without added surfactants.
- PVA molecular weight and zinc-ion concentration controlled which nanostructure formed after calcination.
- The pearl-chain ZnO nanowire achieved a room-temperature ethanol response of 78 toward 100 ppm with 9 s/12 s response/recovery times.
- The sensor remained selective for ethanol over methanol, acetone, and acetaldehyde and stayed stable over 60 days.
Abstract
This study reports a template-free electrospinning route to self-assembled zinc oxide (ZnO) nanostructures for room-temperature ethanol sensing. Zinc acetate dihydrate was electrospun together with poly(vinyl alcohol) (PVA) of two different molecular weights, using the polymer itself as an inherent structural template rather than an added surfactant. After calcination, the resulting nanofibers transformed into nanospheres, nanobushes, or pearl-chain-like nanowires depending on the PVA molecular weight and metal-ion concentration used. The nanowire samples showed the highest carrier concentration, lowest activation energy, and the strongest ethanol response, reaching a sensing response of 78 toward 100 ppm ethanol with response and recovery times of 9 and 12 seconds at room temperature.
Research summary
Ethanol vapor is monitored for indoor air quality, breath analysis, and fuel/food safety, and there is ongoing interest in sensors that work at room temperature instead of requiring a heater. This study developed self-assembled zinc oxide (ZnO) nanostructures using an electrospinning method that relies on the structure of the precursor polymer itself, rather than an external template or surfactant, to control the shape of the resulting nanomaterial.
What the study examined
- ZnO nanofibers electrospun from zinc acetate dihydrate combined with poly(vinyl alcohol) (PVA) at two different molecular weights (14,000 and 140,000 g/mol)
- The effect of zinc-precursor concentration (1, 1.5, and 2 g) on the nanostructures formed after calcination
- Structural, morphological, and electrical properties of the resulting ZnO nanospheres, nanobushes, and pearl-chain-like nanowires
- Room-temperature sensing response, selectivity, humidity sensitivity, and long-term stability toward ethanol vapor
Main findings
After calcination, the composite nanofibers transformed into different ZnO nanostructures depending on the PVA molecular weight and precursor concentration used: nanospheres and nanobushes formed under some conditions, while longer polymer chains combined with higher zinc-ion concentrations favored the self-assembly of nanospheres into pearl-chain-like nanowires.
The nanowire samples had the highest carrier concentration and the lowest activation energy among the structures tested, and this correlated with their sensing performance. The best-performing nanowire sample reached a room-temperature ethanol response of 78 toward 100 ppm, with response and recovery times of 9 and 12 seconds, and remained selective for ethanol over methanol, acetone, and acetaldehyde. The response also stayed within about 5% across a range of humidity levels and remained stable over 60 days of repeated testing.
Why it matters
The results show that a polymer’s own molecular structure can be used as an internal template to steer the growth of metal-oxide nanomaterials, offering a simpler alternative to surfactant- or seed-layer-based synthesis routes. For gas sensing, the room-temperature ethanol response demonstrated here points toward sensor designs that would not need a heating element, which could simplify hardware for breath analyzers and environmental monitoring.
Citation
Prabakaran Shankar, J. B. B. Rayappan. Monomer: Design of ZnO Nanostructures (Nanobush and Nanowire) and Their Room-Temperature Ethanol Vapor Sensing Signatures. ACS Applied Materials & Interfaces 9 (2017) 38135-38145.
