Gas sensors play a crucial role in personal safety and environmental monitoring, yet traditional sensors often struggle with sensitivity and energy efficiency. To address these challenges, researchers from Japan have developed an improved gas-sensing technology by treating graphene sheets with plasma under different conditions.
Altering the structure of graphene via plasma treatment creates defects, such as carbon vacancies and oxidation sites. These modifications can make graphene more useful in gas sensors by favoring the adsorption of target gases, such as ammonia (NH3). Image Credit: Tomonori Ohba from Chiba University
This process introduces structural and chemical defects that enhance the detection of ammonia (NH3), a toxic gas. The functionalized graphene sheets demonstrated superior sensing capabilities compared to pristine graphene, potentially paving the way for wearable gas detection devices for everyday use.
Gas sensing technology is essential in modern life, from ensuring safety in homes and workplaces to monitoring environmental pollution and industrial processes. While traditional gas sensors are effective, they often face limitations in sensitivity, response time, and power consumption.
To overcome these limitations, researchers have increasingly turned to carbon nanomaterials, particularly graphene. This versatile and cost-effective material offers exceptional sensitivity at room temperature with minimal power consumption, making it a promising candidate for next-generation gas detection systems.
A team led by Associate Professor Tomonori Ohba from the Graduate School of Science at Chiba University, Japan, has explored a novel approach to further enhance graphene’s gas-sensing properties.
Their latest study, published in ACS Applied Materials & Interfaces, investigates how plasma treatment with different gases affects graphene’s sensitivity to ammonia.
The researchers produced graphene sheets and exposed them to plasma treatment in argon (Ar), hydrogen (H2), and oxygen (O2) environments. This process "functionalized" the graphene by introducing specific chemical groups and controlled defects that act as additional binding sites for gas molecules like NH3. Using advanced spectroscopic techniques and theoretical calculations, the team analyzed the precise chemical and structural changes in the graphene sheets.
Their findings revealed that different plasma treatments created distinct types of defects.
The O2 plasma treatment induced oxidation of the graphene, producing graphoxide, whereas the H2 plasma treatment induced hydrogenation, producing graphene. Spectroscopic analysis suggested that graphoxide had carbon vacancy-type defects, graphane had sp3-type defects, and Ar-treated graphene had both types of defects.
Tomonori Ohba, Associate Professor, Graduate School of Science, Chiba University
To clarify, an sp3-type defect is a structural change where a carbon atom in graphene shifts from having three bonds in a flat plane to forming four bonds in a tetrahedral arrangement, often due to hydrogen atoms attaching to the surface.
Surprisingly, inserting these defects into graphene sheets significantly improved their performance for sensing NH3. Since NH3 binds more easily to defects than to pure graphene, the electrical conductivity of functionalized sheets changed significantly when exposed to NH3.
This feature can be used in gas sensors to detect and quantify the presence of NH3. When exposed to NH3, graphite showed the highest changes in sheet resistance (the inverse of conductivity), with increases of up to 30 %.
Notably, the scientists investigated whether functionalized graphene sheets could endure repeated exposure to NH3 without losing their gas-sensing ability. Although certain irreversible changes in sheet resistance were identified, others were completely reversible and cyclable.
“The results showed that functionalizing graphene structures with plasma generated noble materials with a superior NH3 gas-sensing performance compared with pristine graphene,” concluded Ohba.
In general, this study is an essential step toward next-generation gas-sensing devices.
Ohba, excited by their findings, stated, “As graphene is among the thinnest possible sheets with gas permeability, the functionalized graphene sheets developed in this work could be used in daily wearable devices. Thus, in the future, anyone would be able to detect harmful gases in their surroundings.”
Hopefully, further work in this field will make this vision a reality and push graphene-based technology forward.
Journal Reference:
Iwakami, S. et. al. (2025) Graphene Functionalization by O2, H2, and Ar Plasma Treatments for Improved NH3 Gas Sensing. ACS Applied Materials & Interfaces. doi.org/10.1021/acsami.4c17257