Sustainable activated carbon from industrial residue: Transforming sewage sludge, biomass, and polymers into high-performance adsorbents

The growing demand for sustainable residue management has encouraged the development of processes to convert industrial, agricultural, and polymeric wastes into high-value materials. This study reports the production of activated carbons (ACs) from lignocellulosic residue (LR), industrial sewage sludge (SSR), and a polymer-containing mixture (Mix) via chemical activation with phosphoric acid. The effects of precursor type and acid concentration on the physicochemical properties and adsorption performance of ACs were systematically evaluated. The produced ACs exhibited high surface areas (up to 960 m² g⁻¹), well-developed micro/mesoporous structures, and abundant oxygenated functional groups. Adsorption experiments with methylene blue (MB), rhodamine B (RhB), and methyl orange (MO) revealed outstanding capacities, particularly for AC_LR3 (384 mg g⁻¹ for MB) and AC_SSR3 (349 mg g⁻¹ for MB and 101 mg g⁻¹ for MO). The feasibility of reusing phosphoric acid in successive activation cycles was also demonstrated, with AC_SSR3 maintaining excellent surface properties and adsorption performance in the first reuse. These findings validate a circular strategy for activated carbon production that minimizes chemical consumption and waste generation while delivering effective wastewater treatment and environmental remediation materials.