As a result, reliable, real-time monitoring of ozone is essential in any process where the gas is generated or used.
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Current Limitations of Room-Temperature Sensing
Metal oxide semiconductor (MOS) sensors are often used for gas detection due to their low cost, compact size, and fast response.
In practice, however, most ozone sensors based on MOS materials require elevated operating temperatures to achieve adequate sensitivity. This increases energy consumption and raises safety concerns, limiting their suitability for continuous or portable monitoring.
Previous studies have shown that decorating metal oxides with noble metals, such as gold, can improve sensitivity and reduce operating temperature. But, the impact of gold modification on ozone sensing, particularly at room temperature, remains largely unexplored.
Gold-Doping the Nanosensor
In the new study, researchers created cauliflower-like indium oxide (In2O3) nanostructures via hydrothermal synthesis, followed by wet-chemical reduction to deposit gold nanoparticles on their surface. The gold acts as a catalytic sensitizer, modifying surface chemistry and electronic structure.
To understand how gold loading influences performance, the team prepared sensors containing 0.5, 1.0, 1.5, and 2.0 wt% gold.
Structural and surface analyses, conducted using X-ray diffraction, X-ray photoelectron spectroscopy, and electron microscopy, confirmed that gold nanoparticles were uniformly dispersed across the indium oxide surface at lower loadings.
A Clear Performance Optimum
Gas-sensing tests revealed a pronounced dependence on gold content. The sensor containing 1.0 wt% gold delivered the strongest performance, achieving a response of 1398.4 toward 1 ppm ozone at room temperature - approximately ten times higher than that of unmodified indium oxide.
At higher gold loadings, performance declined. The researchers attribute this to nanoparticle aggregation, which reduces the number of active surface sites available for gas interaction. This result indicates that noble-metal modification must be carefully controlled, rather than maximized.
Beyond high response, the optimized sensor demonstrated a detection limit as low as 100 ppb and showed strong selectivity for ozone over common interfering gases, including nitrogen dioxide, sulfur dioxide, and volatile organic compounds.
Long-term testing further indicated stable performance over extended periods, highlighting its potential for continuous monitoring applications.
Why Adding Gold Works
The improved sensing behavior arises from several reinforcing mechanisms.
The cauliflower-like architecture provides a porous, high-surface-area framework that facilitates gas diffusion. At the electronic level, charge transport is governed by grain boundary potential barriers within the polycrystalline indium oxide structure.
Gold nanoparticles introduce an additional effect: the formation of Schottky junctions at the gold–indium oxide interface. These junctions, combined with gold’s catalytic spillover effect, enhance oxygen activation and amplify resistance changes when ozone is adsorbed.
Together, these effects convert subtle surface reactions into large, measurable electrical signals at room temperature.
Implications for Gas Sensor Design
The findings demonstrate that tailoring grain boundary behavior and metal-semiconductor interfaces is an effective strategy for achieving high-performance ozone sensing without external heating.
While further work is needed to translate the technology into commercial devices, the study provides an initial design roadmap to low-power, high-sensitivity gas sensors.
Journal Reference
Xu, X. et al. (2026). In2O3 Cauliflower Modified with Au Nanoparticles for O3 Gas Detection at Room Temperature. Nanomaterials, 16(1), 50. DOI: 10.3390/nano16010050
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