Size-selective adsorption and multi-cycle treatment performance of hierarchical pitch-derived activated carbon for real textile effluent

Abstract

Industrial dye wastewater poses persistent environmental concerns; designing adsorbents with tailored porosity and high surface area is critical for efficient treatment. This work presents hierarchical pitch-derived activated carbon (P-PAC) synthesized via KOH activation, achieving an ultrahigh BET surface area (2614 m²/g) and a dual meso/microporous structure as verified by BET, XRD, FTIR, SEM-EDS, and XPS analyses. P-PAC exhibited superior adsorption capacities for Methylene Blue (867 mg/g), Acid Red 18 (505 mg/g), and Reactive Yellow 2 (417 mg/g), exceeding commercial activated carbons by more than two-fold. The exceptional performance arises from synergistic mechanisms including electrostatic attraction, π–π stacking by graphitic domains, and hydrogen bonding via oxygen functionalities. Crucially, the optimized hierarchical pore network enabled pronounced molecular sieving in competitive multi-dye systems (e.g., MB/RY2 selectivity factor = 15.1), which dictates the size-selective adsorption. P-PAC demonstrated superior multi-cycle treatment performance, maintaining high color removal efficiencies of 80–99% over 30 non-regenerative cycles when treating real textile effluent, which strongly validates its potential for long-term applications. This work establishes a performance–structure relationship that will guide the future design of high-efficiency adsorbents for large-scale industrial wastewater applications.