Abstract
Since the first graphene gas sensor has been reported, functionalized graphene gas sensors have already attracted a lot of research interest due to their potential for high sensitivity, great selectivity, and fast detection of various gases. In this paper, we summarize the recent development and progression of functionalized graphene sensors for ammonia (NH3) detection at room temperature. We review graphene gas sensors functionalized by different materials, including metallic nanoparticles, metal oxides, organic molecules, and conducting polymers. The various sensing mechanism of functionalized graphene gas sensors are explained and compared. Meanwhile, some existing challenges that may hinder the sensor mass production are discussed and several related solutions are proposed. Possible opportunities and perspective applications of the graphene NH3 sensors are also presented.
Highlights
Ammonia (NH3 ) is a colorless gas with a pungent smell
We mainly review the graphene sensors functionalized by PPy and PANI, which are frequently used due to their excellent performance, i.e., inherent flexibility, low preparation cost, simple deposition process, environmental stability, operation at room temperature, and easy compatibility with other technologies [111,112,113,114,115]
Our results suggest that the unique application of the NH3 sensors does not absolutely need high-quality single-layer graphene, such as the chemical vapor deposition graphene (CVD-G)
Summary
Ammonia (NH3 ) is a colorless gas with a pungent smell. Most of NH3 in our life environment is emitted directly or indirectly by agricultural sector, waste handling, road transportation, industrial applications, and human activities. Metal oxides, such as SnO2 , V2 O2 , WO3 , ZnO, In2 O3 , TiO2 , and Cu2 O, are very popular compounds for NH3 sensing [10,11,12] Even though they possess a very low detection limit, they exhibit poor gas selectivity. Different authors proposed hybrid structures mixing conducting polymers with metal oxides or even carbon nanotubes [18,19,20] Though those sensors can work at room temperature, they are sensitive to humidity.
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