Efficiently treating waste nylon-tire to prepare sulfur and nitrogen doped porous carbon material via pyrolysis and activation

Waste nylon-tires are greatly produced and would bring serious pollutions when they are inappropriately disposed. Herein, a typical waste nylon-tire was efficiently treated by pyrolysis, sulfur and nitrogen doped porous carbon material was then firstly prepared from the low-quality char. The activation experiments were systematically conducted at different KOH additive ratios (mass ratios of KOH/char were 2, 3, 4, and 5) and activation temperatures (700 °C, 800 °C, and 900 °C) respectively. The corresponding yields, specific capacitances, and physical/chemical structures of sulfur and nitrogen doped porous carbon materials were further studied. The specific capacitance was largest to 129.6 F/g when KOH additive ratio was 4 at 800 °C, which was responded to the amorphous carbon skeleton structure with some graphitic microcrystals, large specific surface area (301.03 m2/g), doped sulfur (1.47 wt%) and nitrogen (0.25 wt%). The key activation mechanisms were revealed: More KOH addition disordered the carbon matrix, decreased doped sulfur, promoted smaller pores formation and thus improved specific surface area with decreasing doped nitrogen only when KOH additive ratio was lower than 4. Higher activation temperature promoted the ordered arrangement of amorphous carbon, increased doped sulfur, enriched nitrogen and expanded the pores with decreasing specific surface area after 800 °C. Summarily, the relationship between specific capacitance and relevant structures was successfully built.