Microwave Preparation of Porous Graphene from Wasted Tires and Its Pyrolysis Behavior

Abstract

Nowadays, most waste tires are disposed of by direct combustion or via landfill, which inevitably creates a large volume of waste. However, the soft carbon found in tires can be an excellent precursor in the preparation of graphene. In this study, waste tires were mixed with potassium hydroxide and heated in a microwave environment to be converted rapidly into porous graphene, a process having no complicated pre-processing. Moreover, the processes, tools, and chemical reagents are distinct and inexpensive. This research innovatively uses the characteristics of microwave rapid and selective heating to study the pyrolysis behavior of waste tires after adding alkali, and realizes the conversion of soft carbon in tires to graphene. At the same time, the time required for the preparation process is greatly reduced which compared with conventional heating methods. Thermogravimetric analysis and dielectric property testing of the tires and mixtures were conducted to study their pyrolysis behavior and catalytic reactions. It was found that when the temperature reached more than 750 °C, potassium ions and carbon underwent a reduction reaction to generate potassium vapor, which catalyzed the carbon in the tires into porous graphene, and that microwave heating could shorten the heating time. Simultaneously, the carbon in the tire could be sheared smaller and thinner during the rapid pyrolysis and volatilization of the gas, benefitting the graphene production. The products of the mixed materials were then characterized and analyzed at different holding temperatures and times. As the holding time increased, the degree of graphitization of the products increased, the number of layers increased slightly, and the impurity elements were completely removed from the products.Graphical Abstract