Facile Single-Step Pyrolysis and Activation of Waste Cotton Textiles for High-Throughput Synthesis of Nanoporous Carbon

To reduce the ecological impact of textile waste disposal, we propose a highly scalable one-step pyrolysis method to convert textiles into activated carbon in air with limited oxygen access. This is done by sealing textiles in a ceramic crucible and subjecting them to high-temperature treatment, which produces nanoporous hard carbon composed of graphitic nanocrystals (width < 10 nm; thickness < 3 nm) and disordered carbon. Openings in the crucible can expose the textiles to oxygen during pyrolysis, which increased ash content and decreased carbon yield. Simulations that track oxygen diffusion into the enclosure gave excellent predictions on the locations of carbon and ash formation. The availability of oxygen also allowed pores to nucleate and grow on the carbonized textiles, increasing their specific surface area (SBET) by up to 27%. SBET increased with peak temperature until 900 °C but fell thereafter due to excessive pore coalescence. On the other hand, the dominant pore size of ∼3.8 nm was not influenced by peak temperature, as expected from classic nucleation theory. The carbonized textiles were assembled as electrodes in electrical double-layer capacitors, which gave a serviceable gravimetric capacitance of 54.83 F/g at a current density of 1 A/g. In addition, carbonized textiles with SBET = 722.13 m2/g were shown to remove 5 mg/L methyl orange within 5 min, compared to 40 min for the previous waste-derived activated carbon, further illustrating the utility of activated carbon obtained through this single-step technique.