Key Takeaways & Executive Findings
- •• Pt-loaded nanoporous GaN enables room-temperature NO2 sensing with high sensitivity (200 ppm to 100 ppb) and fast response (22 s) and recovery (170 s). • The sensor exhibits excellent selectivity for NO2 over other gases, attributed to the spillover effect and electronic interaction of Pt. • The low detection limit of 100 ppb and stability over 70 days highlight its practical potential for environmental and health monitoring. • The gas-sensing mechanism is clarified, emphasizing the role of Pt in enhancing electron donation and oxygen dissociation.
Abstract
In this work, we realized a room-temperature nitrogen dioxide (NO2) gas sensor based on a platinum (Pt)-loaded nanoporous gallium nitride (NP-GaN) sensing material using the thermal reduction method and coreduction with the catalysis of polyols. The gas sensor gained excellent sensitivity to NO2 at a concentration range of 200 ppm to 100 ppb, benefiting from the loading of Pt nanoparticles, and exhibited a short response time (22 s) and recovery time (170 s) to 100 ppm of NO2 at room temperature with excellent selectivity to NO2 compared with other gases. This phenomenon was attributed to the spillover effect and the synergic electronic interaction with semiconductor materials of Pt, which not only provided more electrons for the adsorption of NO2 molecules but also occupied effective sites, causing poor sites for other gases. The low detection limit of Pt/NP-GaN was 100 ppb, and the gas sensor still had a fast response 70 d after fabrication. Besides, the gas-sensing mechanism of the gas sensor was further elaborated to determine the reason leading to its improved properties. The significant spillover impact and oxygen dissociation of Pt provided advantages to its synergic electronic interaction with semiconductor materials, leading to the improvement of the gas properties of gas sensors.
1. Introduction
Nitrogen dioxide (NO2) is one of the most critical gaseous pollutants affecting human health, global ecology, and climate change and is a typical atmospheric nitrogen gas marker [1]. Once the oxidation reaction of NO2 occurs, its reaction products (nitrite and nitrate) pollute the environment, causing a reduction in crop yield and eutrophication [2]. The particulate matter produced by the reaction between NO2 and volatile organic compounds is a severe pollutant [3]. Moreover, NO2 commonly induces human respiratory diseases and is one of the marker gases in human disease detection. Studies have shown that long-term exposure to NO2 can increase the risk of high blood pressure, and prolonged NO2 irritation can cause olfactory damage [4]. Therefore, the detection of NO2 in the environment and the human body is of great significance, and the development of a NO2 gas sensor with high selectivity, wide detection range, and high response is highly anticipated.
In recent years, semiconductor gas sensors have attracted increased attention because of their flexible operating temperature, high sensitivity, rapid response/recovery, and repeatability, such as in atmospheric monitoring [5], wearable devices for gas pollutant monitoring [6], and human disease monitoring [7]. Silicon (Si) field-effect transistors represent conventional gas sensors with their well-established techniques and properties [8]. However, because of the inadequate chemical stability and the narrow band gap (≈1.4 eV) of Si, the potential risk of sensor failure arises. In contrast, wide-band-gap semiconductors (>2 eV) show better chemical properties, such as Si carbide and gallium nitride (GaN). GaN has been widely used in new energy industries because of its wide band gap (0.7–6.1 eV) and excellent temperature stability.
Nowadays, the application of GaN to gas sensing is also anticipated. GaN grown on sapphire and Si through metal–organic chemical vapor deposition not only guarantees excellent gas-sensing characteristics but also demonstrates potential applications for integrated circuits. For example, our group successfully synthesized Au–GaN nanofilms with controllable morphology and gained a low theoretical limit of detection (72 ppb) of ammonia (NH3). Further, we designed an integration application for gas sensors [9]. Meanwhile, P-type GaN prepared through pulsed-laser ablation in a liquid was deposited onto a porous Si substrate for a NO2 gas sensor [10]. It showed a response time of 13.5 s with the limit of detection of 2 ppm at 250°C. Although the sensor exhibited a fast response, the theoretical limit was not enough to satisfy the current requirement. Thus, a NO2 gas sensor with a lower limit of detection is needed.
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Dan Han, Xiaoru Liu, Donghui Li, Jiexu Shi, Yu Wang, Yuxuan Wang, Hongtao Wang, Shengbo Sang (2025). NO2 gas sensor with high selectivity and fast response based on Pt-loaded nanoporous GaN. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-2959-8
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Frequently Asked Questions
What is the detection range of the Pt-loaded nanoporous GaN NO2 sensor?
The sensor detects NO2 concentrations from 200 ppm down to 100 ppb, with a low detection limit of 100 ppb.
How fast does the sensor respond to NO2?
The sensor exhibits a response time of 22 seconds and a recovery time of 170 seconds when exposed to 100 ppm NO2 at room temperature.
Why does the sensor show high selectivity to NO2?
The high selectivity is attributed to the spillover effect and synergic electronic interaction of Pt, which provides more electrons for NO2 adsorption and occupies effective sites, making them poor for other gases.
What is the operating temperature of the sensor?
The sensor operates at room temperature, making it energy-efficient and suitable for portable applications.
How stable is the sensor over time?
The sensor maintains a fast response even 70 days after fabrication, indicating good long-term stability.
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