Formation of highly graphitic char derived from phenolic resin carbonization by Ni-Zn-B alloy

Waste Tire Heat Treatment to Prepare Sulfur Self-Doped Char: Operando Insight into Activation Mechanisms Based on the Char Structures Evolution

Waste tire (WT) can be heat-treated to be high-quality sulfur self-doped char via pyrolysis and K2FeO4-assisted activation processes. This work aimed at further studying the activation mechanisms based on the char structures evolution by operando experimental method. Activation treatment process (from 50 °C to 800 °C and then held for 3 h) was divided into six typical stages (S1–S6) and consisted of carbonization process (S1–S4) and effective activation process (S4–S6). During the carbonization process, the specific capacitance only increased from 0.2 F/g to 12.4 F/g, aromatic ring systems and alkyl-aryl C-C bonds generated, S 2p3/2 (sulphide bridge) was mainly gradually consumed. During the effective activation process, the specific capacitance hugely increased from 12.4 F/g to 112.5 F/g, aromatic ring systems and alkyl-aryl C-C bonds turned to ordered graphitic char. The pores massively generated from S4 to S5, while micropores partly formed to larger and mesopores+macropores fractionally converting to smaller from S5 to S6. Besides, both S 2p3/2 and S 2p5/2 (sulphone bridge) were enriched after S5. Furthermore, the key structural parameters for huge improvement of specific capacitance were found and it further revealed that mesopores+macropores possessed stronger promotion effect than micropores and S 2p3/2 was more beneficial than S 2p5/2.

Waste tire heat treatment to prepare sulfur self-doped char via pyrolysis and K2FeO4-assisted activation methods

Waste tire was heat-treated to prepare sulfur self-doped chars via pyrolysis and activation processes. Pyrolytic waste tire chars were activated at different temperatures (600 °C, 800 °C, 1000 °C, and 1200 °C) with K₂FeO₄ additive ratios (mass ratio of K₂FeO₄ to char) being 0.5, 1, 2, and 3, respectively. The effective activation occurred over 600 °C with K₂FeO₄ additive ratios over 0.5. The strongest activation occurred at 1000 °C with K₂FeO₄ additive ratio of 3, and the specific capacitance increased to 129.5 F/g at 1 A/g, which was six times higher than that without K₂FeO₄. The activation mechanism revealed that higher K₂FeO₄ additive ratio promoted the transformation of large aromatic ring systems (≥6 rings) to small ones and smaller pores formation. When K₂FeO₄ additive ratio was less than 2, high ratio not only promoted alkyl-aryl C-C bonds formation, but also inhibited sulfur enrichment with S 2p_3/2 (sulphide bridge) converting to S 2p_5/2 (sulphone bridge). But when the ratio was further increased, slight decomposition of alkyl-aryl C-C bonds with the promoted conversion of S 2p_5/2 to S 2p_3/2 was witnessed. Furthermore, higher activation temperature promoted the conversion of aromatic ring systems and alkyl-aryl C-C bonds to form ordered graphitic structures. S 2p_3/2 was enriched before 800 °C, but both S 2p_3/2 and S 2p_5/2 were released at higher temperature. Formation of smaller pores was promoted before 1000 °C, but the char structure was then destroyed to form larger pores when temperature was further increased.