The specific synthesis method is as follows: take 30 mL graphene oxide solution of 1 mg/mL, disperse it evenly by ultrasound, add excessive thiourea, stir it vigorously for 12 h at room temperature, then wash and centrifuge the mixed solution, finally get the muddy substance, and carry out the next gas sensitivity test. Thus, we choose to add the sulfur source into graphene oxide solution at room temperature and stir it for a long time to make the sulfur element adhere to the surface of graphene oxide to obtain S-GO as S-1. At the same time, the conditions at high temperature and high pressure will lead to the agglomeration of graphene, which will reduce its specific surface area. Owing to the reducibility of the sulfur source, the hydrothermal method at high temperature and high pressure will lead to the reduction reaction of graphene oxide and the number of oxygen-containing groups on the surface will be greatly reduced, resulting in the decrease in gas adsorption capacity. prepared N- and S-doped carbons via the pyrolysis of cysteine however, the applicability of these approaches is significantly limited by the issues of high cost and inability to scale up. reported S-doped GNs, derived from annealing of graphene-oxide (GO) and benzyl disulfide, as a highly efficient metal-free catalyst for alkaline medium. Few studies exist on sulfur-doped graphene oxide nanosheets. Because of the above excellent properties, graphene has been widely used in basic research, various sensors, micro transistors, new energy batteries, aerospace materials, and other fields. On the other hand, it can be used as a sensitive material for gas sensor to adsorb and detect gas molecules. On the one hand, its characteristics can be changed by modification and doping. At the same time, it can adsorb and desorb many atoms and molecules. Graphene is composed of carbon atoms, so its chemical properties are relatively stable. In terms of thermal properties, graphene has high thermal conductivity, which is the highest among known carbon materials. Graphene has good electrical conductivity, high electron mobility at room temperature (RT), high mechanical strength, and high strength and toughness in the discovered materials. Since its discovery in 2004, graphene has attracted a lot of attention owing to its excellent physical and chemical properties, and has been further applied to many industries and research fields. Graphene is a two-dimensional planar material formed by the close arrangement of carbon atoms. The gas sensitive sensor can effectively overcome the problems of these traditional methods and is a promising method for ammonia detection. These methods require special instruments and equipment, which are costly, bulky, inconvenient, cannot be monitored in real time, and difficult to apply widely. These methods require special instruments and equipment, and problems exist such as high cost, large size, inconvenience in use, inability to monitor in real time, and difficulty in widespread. Currently, the common ammonia detection methods are optical, calorimetric, gasphase chromatography, and acoustic methods. Therefore, it is necessary to detect low concentrations of ammonia. Research shows that the concentration of ammonia must be lower than 20 ppm in the environment wherein humans work, so that it will not affect human health. On the other hand, ammonia will do harm to human health. In recent years, with the further development of the chemical industry and agriculture, people’s awareness of environmental protection has also been increasing, thus the demand for monitoring ammonia concentration is also increasing. According to the report of the European Union, the quality of ammonia emitted to the environment is about 20 to 30 million tons every year. At present, the increase in ammonia content in the environment is mainly due to direct or indirect human activities. Ammonia, as a harmful gas, not only damages the environment and endangers human health, but is also one of the contributors to PM2.5.
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