Fabrication of PANI-ZnO Nanocomposite Thin Film for Room Temperature Methanol Sensor

Research summary

Methanol vapor is toxic even at low concentrations, so detecting leaks quickly and reliably matters for workplace and industrial safety. Metal oxide gas sensors like zinc oxide (ZnO) are attractive for this because they are fast, compact, and compatible with electronic monitoring systems, but on their own they often need elevated operating temperatures or show only modest response.

This study explores whether blending ZnO with polyaniline (PANI), a conducting polymer known for good sensitivity and room-temperature operation, can produce a better methanol sensor than either material alone. PANI was synthesized by chemical oxidative polymerization, ZnO nanoparticles were prepared separately, and the two were combined into composite thin films with different ZnO loadings.

What the study examined

• PANI-ZnO nanocomposite thin films fabricated with 10, 20, and 30 wt% ZnO content
• Crystal structure and chemical bonding of ZnO, PANI, and the composites, using X-ray diffraction and infrared spectroscopy
• Surface morphology of the films using electron microscopy
• Room-temperature gas/vapor sensing response and selectivity toward methanol compared with other vapors

Main findings

X-ray diffraction and infrared spectra confirmed that both pure ZnO and PANI formed correctly, and that the composite retained the signatures of both. Electron micrographs showed a leaf-like ZnO structure blended with a porous PANI matrix, and this blend became most uniform at the 20 wt% ZnO loading.

That uniformity translated into sensing performance: the 20 wt% PANI-ZnO composite film gave the strongest and most selective response among the vapors tested, favoring methanol over the alternatives. At room temperature, this film produced a response of 1318 toward 100 ppm of methanol, with a fast response time of 7 seconds and a recovery time of 20 seconds.

The lower- and higher-ZnO composites (10 and 30 wt%) did not match this performance, indicating that the ratio of polymer to metal oxide – not just their combination – is what drives sensor quality.

Why it matters

The results show that a specific, tunable ZnO loading in a PANI-ZnO composite can deliver fast, sensitive, room-temperature methanol detection without the elevated operating temperatures that limit many metal oxide sensors. This supports the use of polymer-metal oxide composites as a practical route toward safer, lower-power methanol leak detectors for domestic and industrial settings.