Conversion of a pharmaceutical tar waste into porous carbon for supercapacitors by rational combination of pyrolysis and microwave plasma treatment

Combination of pyrolysis and microwave plasma treatment was utilized to prepare porous carbon materials using an industrial tar waste as the precursor. The results show that the treatment with microwave plasma can significantly enhance the specific surface area and pore volume of carbon prepared through pyrolysis. The specific surface area increased by 14.8 % (2419.6 m 2  g −1 to 2778.8 m 2  g −1 ) and the pore volume increased by 23.5 % (1.15 cm 3  g −1 to 1.42 cm 3  g −1 ) through only 1.5 min treatment with 1060 W of microwave plasma. The waste-derived porous carbon could be used as the electrode material of the supercapacitor and the specific capacitance enhanced by 67.9 % (178.4 F g −1 to 299.6 F g −1 at 1 A g −1 ) by the plasma treatment. The specific capacitance of the plasma treated carbon remained nearly same after 12,000 cycles of charging and discharging. In addition, due to its unique structure, the plasma treated carbon could completely eliminate methylene blue within 6 h without the use of other chemical activators, indicating its capability of waste water treatment. The work illustrates the potential of microwave plasma for activating the surface of porous carbon and provides a way to convert industrial wastes to high value materials.