Mesoporous activated carbon fibers synthesized from denim fabric waste: Efficient adsorbents for removal of textile dye from aqueous solutions

Denim fabric waste was used as a carbon precursor, and chemically activated with phosphoric acid in the ratio of 1:1 (v:m) under a slow pyrolysis process to obtain activated carbon fibers (ACFs). The chemical and physical properties of the ACFs were investigated from the thermogravimetric analysis (TGA), N₂ porosimetry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and Fourier transform infrared spectroscopy (FTIR), Boehm titration method, and point of zero charge (pH_PZC). The obtained ACFs showed high yield (53%), BET surface area of 1582 m² g⁻¹, mesoporous features (average pore diameter of 3.60 nm), and surface acidic properties (pH_PZC value of 2.13 and 1.13 mmol g⁻¹ of acidic groups). The ACFs were applied in the removal of textile dye, Remazol Brilliant Blue R (RBBR), from aqueous solution. The adsorption isotherm and kinetic studies showed that adsorption of RBBR on the ACFs were better described by the pseudo-second order kinetic model and the Freundlich equilibrium model. The maximum adsorption capacity of the ACFS for RBBR was determined to be 292 mg g⁻¹, which is higher than other adsorbent materials reported in the literature. The adsorption thermodynamic parameters indicated that adsorption process is spontaneous and exothermic.