# Research Progress of Gas Sensor Based on Graphene and Its Derivatives: A Review
## 4 Graphene Gas Sensor
### Gas Sensors Based on Defective and Functionalized Graphene Materials  
In 2007, [PERSON] et al. from Lanzhou University simulated the adsorption effect of graphene, boron-doped graphene, nitrogen-doped graphene and defective graphene on different gas molecules, including CO, NO, NO\({}_{2}\) and NH\({}_{3}\), by first principle calculation [67]. The results showed that graphene had weak adsorption capacity for CO and NH\({}_{3}\), and better adsorption effect for NO and NO\({}_{2}\). Boron doping seemed to enhance the interaction between graphene and NO, NO\({}_{2}\) or NH\({}_{3}\). Defective graphene had strong interactions with CO, NO and NO\({}_{2}\), but weak interacts with NH\({}_{3}\). In summary, the introduction of appropriate doping elements and defects can improve the response of graphene materials to gas molecules. In 2009, the adsorption capacity and response of gas molecules to aluminum and sulfur doped graphene were further investigated by [PERSON] et al. from National University of Defense Technology [68]. Al-doped graphene was not suitable for the preparation of sensor materials due to its strong reaction to NO and NO\({}_{2}\). N-doped graphene was possibly not reactive enough, while B-doped and S-doped graphene were able to chemically bind NO\({}_{2}\) and possibly NO as well. In 2012, [PERSON] et al. grown polycrystalline graphene on the surface of polycrystalline copper foil and researched the influence of graphene line defect on the sensitivity of organic gas [69]. Figure 10 compares the response of the original graphene, graphene microstrip, and defective graphene to a 100 ms pulse of 300 ppb toluene (electron donor) and 1,2-dichlorobenzene (electron acceptor). The original graphene basically did not respond, but the graphene microspheres and defective graphene response is obvious. The linear defects of graphene can improve the gas sensing properties. Figure 9: Schematic view of connection with microheater and power wave generator: (**a**) 0% duty cycle means non-heating; (**b**) 60% duty cycle of oscillation with 2 V shows 1.05 mW of energy consumption; and (**c**) full duty cycle (continuous heating) generates 1.76 mW of energy consumption [66]. In 2012, [PERSON] et al. proposed a method for preparing graphene gas sensors by printing CVD graphene on a silicon wafer to form a regular-shaped graphene silicon wafer and modifying palladium particles on the surface. The sensor produced by this method has good sensing performance [70]. [PERSON] et al. (2014) proposed a patent about the preparation method of CO gas sensor based on nitrogen-doped graphene. This method was used to heat the mixture of urea and graphene powder under vacuum conditions, and the Gr-N/Pt electrode with electrocatalytic activity could be prepared at one time. The prepared sensor had significant electrochemical catalytic effect, short response time and good repeatability [71]. Sulfur hexafluoride (SF\({}_{6}\)) is widely used in gas-insulated electrical equipment due to its excellent insulating and arc extinguishing properties. However, partial discharge (PD), which is a common phenomenon during the equipment running processes, causes SF\({}_{6}\) to decompose into various products (e.g., H\({}_{2}\)S, SO\({}_{2}\), SOF\({}_{2}\) and SO\({}_{2}\)F\({}_{2}\)). These products may cause equipment failure. Researchers from the University of Texas at Austin investigated the decomposed gaseous components of SF\({}_{6}\), namely, H\({}_{2}\)S, SO\({}_{2}\), SOF\({}_{2}\), and SO\({}_{2}\)F\({}_{2}\), adsorbed on pristine and Au-embedded graphene based on first-principles calculations [72]. Au-graphene showed a more obvious adsorption effect on gas molecules than pristine graphene. The doping of Au increased the gas sensitivity of graphene because the metal properties of new structure were altered from the zero-gap semiconductor. A large-area monolayer fluorinated graphene (FG) was synthesized using a controllable SF\({}_{6}\) plasma treatment by [PERSON] et al. from Soochow University.