Preparation and characterization of high-surface-area activated carbon fibers from silkworm cocoon waste for congo red adsorption

• A new biomass fibroin precursor for activated carbon fibers (ACFs) was proposed.
• High specific surface area (2797 m2 g−1) and total pore volume (1.74 cm3 g−1) were obtained.
• The original fibrous structure of raw silkworm cocoons was retained in the ACF product.
• Congo red maximum monolayer adsorption capacity of our ACF product was up to 1100 g kg−1.

Herein, we report the preparation of activated carbon fibers from silkworm cocoon waste via the combination of (NH4)2HPO4-pretreatment and KOH activation. The morphology, phase structure and surface chemistry constitute of the obtained ACFs were characterized by X-ray diffraction, IR spectroscopy, Micro Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, thermal analysis and N2 adsorption–desorption isotherm. The effects of various factors such as the concentration of (NH4)2HPO4 and the activation time of KOH were also evaluated. These results demonstrated that the synthesized ACFs retained the fibrous morphology of silkworm cocoon waste, and exhibited highly defective graphite layer structure. A large amount of surface oxygen-containing functional groups were found on the ACFs surface. The obtained samples exhibited high BET surface areas ranging from 1153 to 2797 m2 g−1, total pore volumes of 0.64–1.74 cm3 g−1 with micropore volume fractions between 75.2 and 93.6%. In addition, we also evaluated the congo red (CR) adsorption performance of the obtained ACFs. The CR adsorption fitted well to the pseudo-second-order kinetic model. Adsorption isotherm data indicated that the adsorption of CR onto ACFs was monolayer adsorption which followed well the Langmuir isotherm model. The maximum adsorption capacity of CR was 512 g kg−1. The mechanism of the adsorption process was also described from the intraparticle diffusion model.

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