A Review on Functionalized Graphene Sensors for Detection of Ammonia

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.

Keywords: ammonia detection; chemical vapor deposition graphene; conducting polymers; field-effect transistor sensor; functionalized graphene; reduced graphene oxide.

Figure 1

Schematic diagram for band structure of single-layer graphene. The inset on the lower right highlights the linear dispersion at the Dirac point. Reproduced from (Ernie W. Hill, [31]), Copyright 2011, IEEE.

Figure 2

Schematic diagram of a graphene-based quartz crystal microbalance sensor.

Figure 3

Schematic diagram for a graphene-based surface acoustic wave sensor.

Figure 4

Schematic energy band diagram of the graphene/n-type Si interface for the pristine graphene state (middle), the graphene exposed to electron-donor gas (left) and the graphene exposed to electron-acceptor gas (right). E_VAC, E_C, Φ_G, E_F, and ψ_SBH indicate the vacuum energy, conduction band, graphene work function, Fermi level, and Schottky barrier height, respectively. Reproduced from (Hye-Young Kim, [55]), Copyright 2013, American Chemical Society.

Figure 5

Schematic illustration of the I–V characteristics for a graphene/n-type Si Schottky diode sensor in air, exposed to electron-donor gas and electron-acceptor gas.

Figure 6

Optical image of Au interdigitated electrode (IDEs) on SiO₂/Si substrate for a graphene chemiresistor sensor. The sensing area is of 200 × 200 µm². The finger width and finger space are consistent (2 µm).

Figure 7

(a) Energy band diagrams of graphene: pristine graphene (middle), n-type graphene (left), and p-type graphene (right). (b) Graphene resistance as a function of gate voltage. E_F and E_D indicate Fermi level and Dirac point, respectively.

Figure 8

Schematic cross-sections of a graphene FET sensor applied by: (a) positive gate voltage for NH₃ off; (b) negative gate voltage for NH₃ off; (c) positive gate voltage for NH₃ on; (d) negative gate voltage for NH₃ on.

Figure 9

Resistance responses of a pristine graphene sensor to 1 ppm ammonia (NH₃), carbon monoxide (CO), nitric oxide (NO), and water vapor (H₂O) in pure helium or nitrogen at atmospheric pressure, at 150 °C. Reproduced from (F. SCHEDIN, [23]), Copyright 2007, Nature Publishing Group.

Figure 10

Energy band diagrams (a) for Pt and p-type graphene and (b) for Pt-NH₃ phase and p-type graphene. E_VAC, Φ_Pt, E_FPt, Φ_G, E_FG, Φ_Pt-NH3 indicate the vacuum energy, Pt work function, Pt Fermi level, graphene work function, graphene Fermi level, and Pt-NH₃ work function, respectively.

Figure 11

Sensing behaviors of a typical PPy/reduced graphene oxide (rGO) sensor at relative humidity of 50% and at 20 °C: (a) The sensor resistance behavior to 1 ppm NH₃ for 10 cycles. (b) The sensor resistance response as a function of NH₃ concentration. Reproduced from (Xiaohui Tang, [135]), Copyright 2020, Elsevier.

Figure 12

Optical image of graphene oxide (GO), dispersions (in water) on interdigitated electrodes over SiO₂/Si substrate. The GO dispersions (deposited by ultrasonic spray pyrolysis) are agglomerated to form clusters. Reproduced from (Xiaohui Tang, [135]), Copyright 2020, Elsevier.